U3 O2 - Respiratory Emergencies Flashcards

Question

What is the main stimulus for the rate and depth of breathing?

Answer 1

In dogs and cats, the main stimulus for increased rate and depth of breathing is increased carbon dioxide levels in the blood stream (hypercapnia) rather than decreased arterial oxygen (hypoxemia). Arterial oxygen levels must fall very low (< 50 mmHg) before hypoxaemia stimulates breathing Decreased blood carbon dioxide (hypocapnia) is the main stimulus for decreasing ventilation. Respiratory distress is caused by decreased arterial oxygen levels (hypoxaemia) and/or increased arterial carbon dioxide levels (hypercapnia)

Answer 2

The respiratory system should be assessed in all patients that present as an emergency, particularly if they have been involved in an RTA. It should be remembered that a patient who has recently sustained thoracic trauma, and presents with mild to no respiratory distress, may deteriorate and require supportive measures e.g. the signs of pneumothorax will develop as more air builds up in the thorax. A patient with pulmonary contusions may deteriorate over 6-12hrs despite having normal rate and effort on presentation. Animals with any respiratory compromise at presentation will require respiratory support and should be monitored for response to therapy. It is absolutely vital that a RVN carrying out triage can recognise a patient with even mild respiratory distress, as the risks of decompensation during the stabilisation period are significant. Special consideration must be given to handling and housing to minimise stress whilst allowing the patient to receive intensive monitoring.

Answer 3

Signs of respiratory distress can include postural changes such as neck extension and elbow abduction ‘air hunger’; paradoxical abdominal breathing; restlessness; deep or shallow breaths; and increased or decreased respiratory rate.

Answer 4

It is important to remember that a patient demonstrating these signs is at their limit of physiologic reserves with a significantly decreased lung functional residual capacity. It is essential to minimise patient stress to avoid respiratory arrest and/or cardiac arrest; it is also essential that handling or positioning of the patient does not prevent them adopting its preferred position. Ideally a patient would be observed from a distance initially to obtain a true assessment of the its respiratory rate, effort and pattern with minimal stress

Answer 5

The normal respiratory rate is ~ 10-30/ minute in dogs

Answer 6

The normal respiratory rate is ~ 20- 30/ minute in cats (range 24 - 48 breaths per minute)

Answer 7

Increased respiratory rate (tachypnoea) in dogs | and cats is generally considered to be above 50 breaths per minute.

Answer 8

However, it is important to assess it in context - the respiratory rate may be increased in a patient who is anxious or painful. “White coat” effect is common in patients presenting to veterinary practice – it is important to appreciate the patient’s respiratory rate may be elevated purely in response to being in the clinic. Other causes of tachypnoea should be considered in trauma patients since an increase in respiratory rate does not always indicate respiratory compromise. Pain, fever, hyperthermia, stress/fear, and compensation for metabolic acidosis will all cause an increase in respiratory rate.

Answer 9

Normal respiratory effort involves only slight outward movement of the thorax during inspiration with minimal movement of the abdominal musculature – if there is abdominal muscle involvement in breathing, the walls of the thorax and the abdominal wall move outwards at the same time during normal inspiration. Increased respiratory effort (respiratory distress) is characterised by increased thorax and abdominal musculature motions; and is perceived as laboured or difficulty in breathing. In some patients there may only be increased thoracic excursion. Signs of increased respiratory effort include extension of the head and neck and abduction of the elbows. Nostril flare may be observed. Open-mouthed breathing may be a sign of severe respiratory distress in cats, especially

Answer 10

It should be noted that in a patient with a tension pneumothorax, there is actually reduced movement of the thorax as the pressure in the intra-thoracic space increases and minimises the ability to ventilate at all. This is a respiratory emergency and needs rapid intervention.

Answer 11

An increase in respiratory effort can be seen with pleural space disease (e.g. pneumothorax, haemothorax or diaphragmatic hernia), pulmonary parenchymal disease (e.g. pulmonary contusions, pulmonary oedema and pneumonia) and upper airway disease.

Answer 12

Upper airway problems such as brachycephalic obstruction syndrome, laryngeal paralysis or airway obstruction are associated with laboured inspiration.

Answer 13

Lower airway problems are associated with laboured expiration.

Answer 14

Parenchymal (lung tissue) conditions are associated with laboured inspiration and expiration.

Answer 15

Pleural space disease is associated with rapid and shallow inspiration and expiration.

Answer 16

Decreased respiratory effort is less commonly seen and is characterised by decreased thorax and abdominal muscle movement. Disease processes associated with decreased respiratory effort include brain and spinal injury, and end stage respiratory fatigue. It may also be seen with some intoxications that cause severe respiratory depression such as baclofen ingestion.

Answer 17

Paradoxical respiration is an indicator of severe inspiratory effort where the thorax moves outwards with inspiration; and the abdominal muscles are pulled inwards. Causes of paradoxical respiration include upper airway obstruction, diaphragmatic injury (rupture; or paralysis secondary to injury to the cervical spinal cord or the phrenic nerve) and severe decreases in pulmonary compliance (as may occur with severe pulmonary contusion).

Answer 18

A flail chest is a type of segmental fracture where fractures of two or more adjacent ribs, in two or more locations, results in a ‘flail segment’. This may be caused by a crush injury e.g. small dog/cat grasped by large dog; fall or kick.

Answer 19

The fractured section of the chest wall moves in the opposite direction to the rest of the thorax during breathing. It is drawn inward on inspiration due to negative pressure generated within the thorax and the free-floating nature of the fractured segment. Similarly, the segment will move outward on expiration.

Answer 20

This is a very painful condition and provision of analgesia is essential. A local anaesthetic ring block either side of the flail segment, in addition to systemic opioid, is commonly required.

Answer 21

Additionally, the flail segments are often splinted to reduce the movement and discomfort associated with the fractured ribs grating against each other and to decrease the risk of the fractured ribs causing lung damage.

Answer 22

A patient with a flail chest will often prefer to lie on the affected side as this minimises movement of the flail segment. However a significant nursing consideration/ concern for this patient is the need to re-position to avoid atelectasis and further compromise of ventilation.

Answer 23

The partial pressure of oxygen in arterial blood (PaO2) should normally be > 90-100 mmHg

Answer 24

Cyanotic mucous membranes are seen | with severe hypoxaemia (PaO2 < 80 mmHg)

Answer 25

By the time cyanosis is apparent, it means the haemoglobin is very poorly oxygenated i.e. a profound disturbance in the oxygenation of haemoglobin. At this point there is at least 50 g/L of deoxygenated haemoglobin in the bloodstream meaning that significant hypoxaemia must therefore occur before a patient’s mucous membranes are cyanotic. Thus, it is essential to be aware that the absence of cyanosis does not rule out significant respiratory compromise.

Answer 26

even if PaO2 has declined significantly/ dangerously from 100-80 mmHg, the pulse oximeter reading SpO2 remains relatively high (> 90 %). It is only when the PaO2 declines even lower (< 60 mmHg) that the pulse oximeter reading starts to decline significantly. Most sources state that if the SpO2 is less than 94%, for a patient breathing room air, then supplemental oxygen should be supplied because this patient is likely to be seriously hypoxaemic (PaO2 < 80 mmHg.) See 3.2.8 for a description of assessment of pulmonary function in relation to PaO2, SaO2 and SpO2 etc.

Answer 27

There are toxins that can cause respiratory difficulty/ distress and can alter the colour of blood. Examples are carbon monoxide (which can turn the blood/ mucous membranes cherry red)

Answer 28

There are toxins that can cause respiratory difficulty/ distress and can alter the colour of blood. Examples paracetamol (which turns the blood/ mucous membranes a muddy brown colour).

Answer 29

In addition to causing liver damage, metabolites of paracetamol cause damage to red blood cells. This oxidative damage leads to alteration of the iron in haemoglobin leading to formation of methaemoglobin. Unlike haemoglobin, methaemoglobin does not release oxygen molecules to tissues which results in hypoxia. Methaemoglobinaemia causes the blood and mucous membranes to appear brown therefore pulse oximeter readings will not be accurate. Brashear (2013) discusses acetaminophen (paracetamol) toxicity and includes an image of an effected patient

Answer 30

Carbon monoxide has a much stronger affinity for binding with haemoglobin than oxygen – resulting in oxygen being displaced from the haemoglobin molecule. This results in decreased oxygen delivery to cells and progressive hypoxia. The patient may have cherry red mucous membranes but this is not a consistent finding. Pulse oximetry readings will also not be accurate in this condition demonstrating the importance for all patients of assessing the patient clinically rather than relying on monitoring devices.

Answer 31

Air under the skin If a patient has subcutaneous emphysema, it feels as if there is crackling under the skin when palpating the skin around the neck and thorax.

Answer 32

Any abnormal noises should be noted e.g. hissing. This might indicate air leakage from e.g. a tracheal rupture. Subcutaneous emphysema is another clinical sign that might be present in a patient with rupture or penetrating wound of the larynx, trachea or the bronchial tree

Answer 33

Crackles are produced by a gas/fluid interface (e.g. oedema, pneumonia, contusion, haemorrhage);

Answer 34

wheezes typically from the movement of air through a narrowed airway (e.g. feline lower airway disease). Wheezes may have a musical quality

Answer 35

Auscultation of the thorax of patients with pleural space disease will reveal quiet lung sounds

Answer 36

if the patient has diaphragmatic rupture, gut sounds/ borborygmi may be auscultated.

Answer 37

If there is pulmonary parenchymal disease, and the animal is dyspnoeic then louder lung sounds than normal will usually be heard

Answer 38

Quiet lung sounds dorsally are consistent with a pneumothorax

Answer 39

quiet lung sounds ventrally are consistent with a pleural effusion

Answer 40

Where possible a patient should be left to rest and supplied with oxygen before it is examined e.g. a cat placed in an oxygen cage. However, as mentioned above with pleural space disease emergency thoracocentesis may be required as soon as possible to facilitate improved ventilation. In this scenario, it is sensible to provide supplemental oxygen to the patient whilst the equipment is prepared for thoracocentesis. The veterinary surgeon may decide that mild sedation, alongside oxygen therapy, should be administered if the patient does not appear to be in pain. In this situation, butorphanol is often used as it has a predictable onset and duration of action, with minimal cardiovascular and respiratory depression. If the patient is in respiratory distress following a painful, traumatic incident, then a stronger analgesic will be more appropriate.

Answer 41

Flow-by oxygen, 2-3 l/min, may produce an inspired oxygen content that is ~ 25%- 40% (x2 concentration of oxygen in normal room air) i.e. a FiO2 of 0.25-0.4; at a flow rate of 5-6 l/min, a loose-fitting mask will provide ~35-55 % (x 2-4 concentration of oxygen in normal room air) i.e. a FiO2 of ~ 0.35- 0.55

Answer 42

A tight-fitting mask in a collapsed individual can provide an oxygen level of 70-90% (> x 4 room air) i.e. FiO2 of 0.7-0.9 but promotes rebreathing of CO2 and may cause hyperthermia

Answer 43

Flow by is only effective if it is very close to the patient’s mouth and nose - having the end of the oxygen line more than a cm or so away from the patient probably has minimal benefit. It can be useful, if the patient tolerates it, to hook the line through the patient’s collar, if wearing one, and then position it in such a way it is close to the mouth and nose. If using a tight-fitting mask for oxygen delivery, it should be removed intermittently to clear away condensation that will build up and build-up of CO2. Patients receiving oxygen via mask should have their eyes lubricated often as oxygen is a cold dry gas which can dry the corneas and lead to ulcers.

Answer 44

Oxygen collar tent - ‘Crowe Collar’ Other techniques can be employed. These include applying an Elizabethan collar to the patient: making sure it extends beyond the patient’s nose. The front of the collar is then covered with cling-film; the tubing from the oxygen supply is then fed in from the animal’s collar/neck. It is important to leave a 2.5-5cm opening at the top of the cling-film to ensure carbon dioxide and moisture can escape - as oxygen is heavier than air it will remain within the ‘tent’. Despite this, the temperature and humidity within the mask can still rapidly increase and some patients do not tolerate this technique of oxygenation

Answer 45

At 1-8 l/minute (depending on the patient size), inspired oxygen levels should be ~30- 60 % i.e. FiO2 0.3-0.6

Answer 46

Disadvantages of oxygen cages include patient isolation (Waddell and King, 2018), the prolonged period it can take for the, often, large space to reach significant oxygen enriched levels (meaning that it is only ~ 50% oxygen being delivered i.e. FiO2 of 0.5 ; and the cost of oxygenating so much free space. Large patients are unlikely to be able to fit into them. The oxygen levels decrease rapidly each time the cage is opened. Improvised oxygen cages can develop high humidity and temperature levels; and can make it difficult for the nurse and clinician to monitor the patient. Oxygen cages can either be improvised within the practice or specifically designed for the purpose e.g. a Snyder oxygen cage. In theory an oxygen cage should be able to provide a FiO2 of 1.0 e.g. 100% oxygen

Answer 47

They may be beneficial where other techniques are not being tolerated by the patient; and, in the case of cats, where confinement away from other animals and humans can allow them to calm down and so reduce their oxygen demand. Placing cooling devices e.g. icepack on top of the oxygen cage, can help with cooling

Answer 48

Incubator Paediatric, thermostatically controlled, human incubators can be used for small patients and are very efficient- reaching oxygen levels of ~ 80-90% i.e. FiO2 of 0.8- 0.9. They also have the benefit of humidifying the gases. Small doors allow for patient monitoring without significant oxygen loss.

Answer 49

Two main types of nasal catheter can be used - the single nasal catheter that may, either, be an adapted pliable feeding tube, a red rubber urinary catheter or a dedicated nasal catheter; or nasal prongs, as used in human medicine, which sit as a looped tube around the nose, with a small prong from the tube inserted into each nostril.

Answer 50

Using nasal catheters bilaterally will increase the FiO2 by up to 60% if used in both nostrils

Answer 51

Nasal oxygen catheters are not effective at increasing FiO2 in patients that are panting or open mouth breathing. Some animals do not tolerate nasal prongs and they are easily dislodged. Brachycephalic breeds may have stenotic nares (abnormal narrowing or constricted) that may not allow insertion of a catheter – however in many brachycephalic patients nasal prongs are well-tolerated and remain in place. A tape bridge over the nasal prongs can be helpful. On occasion, if a patient requires long term supplementation e.g. aspiration pneumonia, a clinician may suture nasal prongs to the lateral edge of the alar fold.

Answer 52

Trans-tracheal oxygen provision is a temporary rescue procedure until a patent airway can be provided e.g. a tracheostomy tube. As oxygen is delivered via a catheter or needle placed between tracheal rings, the pressure and flow rate can be compromised due to the narrow bore.

Answer 53

For all methods of oxygen delivery, if prolonged supplementation is required, the oxygen should be humidified; if supplementary oxygen is supplied at an FiO2 > 0.6 for long time (>12 hours), the lungs are at risk of damage- ‘oxygen toxicity’

Answer 54

Endotracheal (ET) intubation In the unconscious, emergency patient without an upper airway obstruction, placing an ET tube ensures a patent airway and is the most efficient means of oxygen delivery. It also allows intermittent positive pressure ventilation (IPPV) to be performed as well as the provision of 100% oxygen.

Answer 55

Where complete upper airway obstruction has occurred, e.g. a pharyngeal foreign body, laryngeal or tracheal trauma (especially dog bites), pharyngeal or laryngeal foreign bodies, or laryngeal paralysis an emergency tracheostomy may be required

Answer 56

If there is any chance that a patient might require a tracheostomy, the procedure should ideally be performed before the patient becomes apnoeic secondary to the airway obstruction. Therefore, very careful patient monitoring is essential with the veterinary surgeon being alerted immediately if the patient worsens. Any patient deterioration e.g. worsening of stertor/ stridor, increased respiratory rate and effort and signs of air hunger is an indication for tracheostomy in this situation . It is far safer to place a tracheostomy tube in a controlled manner than as an emergency once the patient arrests.

Answer 57

Effective cooling techniques include electric fans, spraying with tepid (not cold water), cool intravenous fluids (but avoiding over infusion) and cool packs in the axillae and inguinal region N.B. ice should not be applied directly to the skin as it can cause burns. If ice or cold water is applied to the skin, it may cause peripheral vasoconstriction thus limiting heat loss and shunting the hot blood back to the main organs so risking further damage occurring. Placing towels soaked in cool water over the patient will insulate the patient and prevent further heat loss- therefore this is not an effective means of promoting heat loss

Answer 58

Point of care ultrasound examination (POCUS) can be an especially useful technique in trying to determine the cause of respiratory distress in an emergency patient. It can be performed kennel-side with minimal to no patient restraint being required. As with all POCUS/FAST techniques, the aim is to answer specific questions i.e. is there evidence of pleural effusion, pneumothorax or pericardial effusion? It may also identify soft tissue within the thorax (Waddell and King, 2018). Ultrasound can also be used when emergency procedures are being performed e.g. thoracocentesis

Answer 59

Radiography of the thorax may provide useful information e.g. identify rib fractures, cardiomegaly, pulmonary contusions etc. However, its use is limited in the patient in respiratory distress as any manipulation for X-ray positioning could cause the patient to deteriorate further. The only position a patient with respiratory distress could possibly be placed in is sternal recumbency for a dorso-ventral (DV) view- however this should not be attempted if it causes any further distress to the patient. A DV view of small patients can sometimes be obtained by X-raying them in an oxygen cage. If radiography is performed, it may be possible to angle the beam by 90˚ to obtain a lateral view with horizontal beam radiography. Although great care must be taken when performing this view to avoid accidental exposure of personnel to ionising radiation.

Answer 60

The commonest form of laryngeal disease is laryngeal paralysis.

Answer 61

This is generally caused by compromised nerve supply to the muscles of the larynx which are responsible for moving vocal folds and so altering the size of the glottis during inspiration.

Answer 62

This can be congenital or acquired.

Answer 63

Idiopathic, acquired, laryngeal paralysis is the commonest form, generally seen in older, large-breed dogs such as Labrador Retrievers and Golden Retrievers. It can occur in cats occasionally. Other acquired forms can occur due to neck or thoracic trauma

Answer 64

The recurrent laryngeal nerve originates from the cervical spinal cord but travels down into the thorax, before then returning to the neck to innervate the larynx.

Answer 65

The patient often presents in respiratory distress with marked inspiratory effort and stridor due to the narrowing of the larynx. The stridor commonly sounds like a whistle which becomes higher in pitch as the obstruction worsens . The patient may be collapsed and cyanotic, with/ without a cough. The owner may report a recent change in phonation, exercise tolerance, noisy breathing and/ or dysphagia. The patient may also be hyperthermic which further increases the oxygen demand, hypoxia and patient distress

Answer 66

The history, presentation and physical examination are usually highly suggestive of laryngeal paralysis. Once the patient is stable, the diagnosis can be confirmed under general anaesthetic by visualising movement of the vocal folds of the larynx, using a laryngoscope (or endoscope). Both unilateral and bilateral paralysis may occur.

Answer 67

Initial management involves placing in a low stress environment with minimal handling and provision of oxygen therapy (see above). Cooling of the patient, as described in 3.2.3.2 will be required if the patient is hyperthermic. Sedation, on veterinary direction, will often have an anxiolytic effect and help to improve the patient’s breathing, hopefully preventing the need for further emergency intervention, until medical treatment and active cooling starts to be effective. Corticosteroids (e.g. dexamethasone) are likely to be administered for their anti-inflammatory effect. Whilst anti-tussive medication may also be considered in some patients, care must be taken not to suppress coughing if there is any risk of aspiration pneumonia. As there will often be large amounts of mucous and saliva in the pharynx/ oral cavity, suction may be required. This should be readily available for any patient who requires rapid anaesthetic induction and intubation. In severe cases the patient may need to be anaesthetised and intubated for a period until the swelling and oedema has reduced. Occasionally a patient may need to undergo an emergency tracheostomy if they cannot be managed by other means.

Answer 68

Initial management involves placing in a low stress environment with minimal handling and provision of oxygen therapy (see above). Cooling of the patient, as described in 3.2.3.2 will be required if the patient is hyperthermic. Sedation, on veterinary direction, will often have an anxiolytic effect and help to improve the patient’s breathing, hopefully preventing the need for further emergency intervention, until medical treatment and active cooling starts to be effective. Corticosteroids (e.g. dexamethasone) are likely to be administered for their anti-inflammatory effect. Whilst anti-tussive medication may also be considered in some patients, care must be taken not to suppress coughing if there is any risk of aspiration pneumonia. As there will often be large amounts of mucous and saliva in the pharynx/ oral cavity, suction may be required. This should be readily available for any patient who requires rapid anaesthetic induction and intubation. In severe cases the patient may need to be anaesthetised and intubated for a period until the swelling and oedema has reduced. Occasionally a patient may need to undergo an emergency tracheostomy if they cannot be managed by other means.

Answer 69

Ongoing monitoring and nursing care requires assessment of respiratory rate and pattern, mucous membrane colour, body temperature (hypothermia should be avoided; pyrexia may be present if aspiration pneumonia) and perfusion parameters (care must be taken not to over-infuse IV fluids and cause greater breathing difficulties). Arterial blood gas measurement (PaO2 and PaCO2) is the best indicator of effective ventilation. If arterial sampling is not possible venous blood gas measurement can be performed. The patient should be cage-rested and exercise restricted. Great care should be taken when feeding if the patient has dysphagia. In this situation, food is normally fed ‘balled up’ and from a height to encourage appropriate swallowing. If placed careful monitoring and maintenance of the tracheostomy tube and the tracheostomy site (see section 3.2.7.3) is required. Longer term a weight loss programme may be required; surgical solutions to laryngeal paralysis include laryngeal tie-back (arytenoid lateralisation). In the period between initial presentation and surgical intervention, acupuncture may provide some relief for a patient with laryngeal paralysis

Answer 70

A patient with laryngeal paralysis is often middle to older aged and often a larger breed. Additional concerns and co-morbidities may be present e.g. osteoarthritis. Padded bedding in the kennel and protection of pressure points may be needed. Stress must be kept to a minimum and ongoing sedation may be indicated to manage this in some patients. Recumbency management, including adjustments in position to avoid further compromise of lung function, is indicated. If the patient is mobile and the veterinary surgeon approves, short periods of slow calm exercise will help maintain mobility and, in the case of patients with pneumonia/aspiration pneumonia will loosen lung secretions. Coupage may also be indicated for these patients. Alongside assessment of the respiratory system function, ongoing monitoring must also focus on the patient’s ability to carry out day to day activities. If there is any disparity between this and the patient’s ability, then nursing care must be provided to bridge the gaps until the patient recovers.

Answer 71

Foreign bodies (FB) may lodge in the trachea. The most serious foreign body, however, is likely to be found in the caudal pharynx, just in front of the epiglottis. This may cause a complete obstruction of the airway. It occurs relatively commonly in dogs with ‘the swallowed ball syndrome’, causing rapid asphyxiation, respiratory arrest and death. It is very important not to try to remove a pharyngeal foreign body from the conscious patient (and to advise the owner of this). It is very unlikely to be successful; will distress the patient further; possibly cause injury to the handler and run the risk of dislodging the foreign body further into the trachea. N.B. It is much harder, in a sedated patient, to retrieve a tracheal foreign body, than a pharyngeal foreign body.

Answer 72

Tracheal collapse is commonly seen in smaller breeds, particularly the Yorkshire Terrier.

Answer 73

The condition is due to a weakness of the cartilage that maintains the luminal shape of the trachea. In affected dogs, the unsupported section of the trachea (dorsal tracheal membrane) dips into the lumen causing partial to complete occlusion during respiration

Answer 74

This results in chronic cough and exercise intolerance. A patient with tracheal collapse often has a distinctive cough, which is usually harsh and dry cough - sounding like a goose ‘honk With tracheal collapse and tracheal stenosis, the patient will usually have a history of persistent cough and exercise intolerance. Palpation of the distal cervical trachea is likely to induce a harsh cough. The patient may present in acute respiratory distress with tachypnoea and marked inspiratory effort, if there is complete collapse of the trachea

Answer 75

With a foreign body, causing a partial obstruction, there may be harsh, coughing and a foul-smelling odour. The odour originates from the airways, particularly if the FB has been there for a few days. In the case of a complete airway obstruction, as can occur with a ball caught in the caudal pharynx, the dog will often impersonate a goldfish-opening and shutting its mouth but unable to breathe or make a sound. This is naturally a hyperacute emergency, as after a minute or so of a complete obstruction, the patient will be comatose

Answer 76

History, and palpation of the neck and pharyngeal region (if appropriate) will often detect a pharyngeal foreign body; or stimulate a cough reflex in tracheal collapse cases. An examination of the oral cavity will determine if a pharyngeal foreign body exists, although this is unlikely to be appropriate in distressed patient; anaesthesia may be required to confirm the presence, and remove, many foreign bodies. If a pharyngeal foreign body e.g. grass blade in a cat or tracheal foreign body, of several days’ duration, exists then there is often a foul odour to the breath. Further diagnostic testing for tracheal conditions, may include endoscopy under general anaesthesia. The tracheal lumen can be assessed; and tracheal foreign bodies may be identified and removed. Radiodense tracheal foreign bodies can be detected radiographically. Because the gas-filled tracheal lumen appears radiolucent radiographically, even slightly radiopaque foreign bodies may be apparent. Radiography can be used to assess the trachea for e.g. stenosis or collapse but dynamic real-time fluoroscopic imaging is of greater diagnostic value.

Answer 77

The initial management of the emergency presentation, with a partial or complete tracheal obstruction, is to try to minimise respiratory distress whilst anticipating that further veterinary interventions will be required. Patient handling should be limited, flow-by oxygen should be provided and preparation for the general anaesthetic, that will probably be required, should be performed. Sedation may be indicated to reduce the patient’s level of distress. However, it is vital that everything is prepared for a rapid induction of anaesthesia as the patient y can decompensate very quickly. In a patient with complete airway obstruction, the veterinary surgeon must be summonsed immediately. However, the RVN can and should place an endo-tracheal tube, if appropriate i.e. not a foreign body obstruction and provide oxygen until the veterinary surgeon arrives. Rapid intravenous anaesthetic induction will be required, followed by manual removal either through the mouth, in the case of a pharyngeal foreign body; or via endoscopy/ tracheotomy for a tracheal foreign body. An emergency tracheostomy or trans-tracheal catheterisation may be required, prior to pharyngeal foreign body removal, to provide emergency oxygen to help stabilise/calm the patient - see section 3.2.7.3 for further information on these techniques. Additional, initial management of other tracheal conditions is aimed at counteracting the hyperthermia that occurs following upper airway obstruction and calming the patient. The animal may be cooled as previously discussed; the veterinary surgeon may prescribe an anxiolytic (mild tranquilliser), e.g. acepromazine to reduce excitation and aid treatment of hyperthermia. However, these drugs should be used with caution in brachycephalic breeds and patients with cardiovascular disease. Any patient who has received acepromazine, needs constant monitoring for evidence of hypotension, especially if brachycephalic or with pre-existing cardiovascular disease. The head and neck should always be kept extended in sedated patients, with the mouth opened and the tongue pulled forward if possible. In a patient with tracheal collapse, anti-inflammatory medication, to decrease tissue inflammation/oedema, and anti-tussive medication may be administered. Opioids e.g. codeine or butorphanol, at doses lower than used for sedation, have a moderate anti-tussive effect. Tracheostomy is not likely to help a patient with tracheal collapse as large sections of the cervical and thoracic trachea can be affected (Waddell and King, 2018). If medical management is not successful, surgical treatment may be indicated e.g. tracheal stenting or placement of extraluminal tracheal ring prostheses.

Answer 78

In addition to monitoring the respiratory system, perfusion parameters should be constantly monitored. SPO2 monitoring provides valuable information about the ability to deliver oxygen during the recovery period. Blood pressure should be monitored regularly- many sedatives and anaesthetic agents cause vasodilation and hypotension. This may need to be managed during sedation, anaesthesia or recovery. Close, careful monitoring is indicated in a patient that has had treatment for tracheal obstruction. It is possible the obstruction will re-occur in a patient with tracheal collapse. Also, a patient which has had a solid foreign body removed may have increasing swelling due to ongoing inflammation and/or infection. If a patient recovering from upper airway obstruction, develops increasingly noisy breathing the veterinary surgeon should be immediately alerted and the cause investigated as soon as possible.

Answer 79

Inflammatory naso-pharyngeal polyps in cats, upper airway masses, feline viral upper respiratory tract disease, infection laryngotracheitis ‘kennel cough’ in dogs and smoke inhalation are other possible causes of a patient presenting as an emergency with upper respiratory tract signs.

Answer 80

There are various reasons for emergency presentations due to nasal disease/ injury including brachycephalic obstructive airway syndrome (BOAS), nasal foreign bodies, trauma, neoplasia and nasal/nasopharyngeal polyps. Stenotic nares and narrow nasal passages associated with brachycephalic obstructive airway syndrome; and trauma of the nasal passages can lead to upper airway obstruction

Answer 81

brachycephalic obstructive airway syndrome

Answer 82

BOAS is typically seen in brachycephalic breeds such as English and French Bulldogs, Boston Terriers and Pugs, especially if they are obese

Answer 83

The conformational problems associated with BOAS include- stenotic nares, excessive pharyngeal soft tissue, elongated soft palate and hypoplastic trachea

Answer 84

Affected dogs must increase their inspiratory effort to help overcome the resistance created by the various upper airway obstructions. This high negative pressure leads to the soft tissues of the upper respiratory tract being sucked into the air passages so causing further obstruction (University of Cambridge, 2019). The soft tissues become oedematous, swollen and hyperplastic and the negative pressure causes the laryngeal saccules to collapse so compounding the problem. The combination of swollen, oedematous, hyperplastic tissues (pharynx, soft palate and larynx) plus laryngeal saccule eversion and laryngeal collapse can lead to asphyxiation.

Answer 85

Brachycephalic obstructive airway syndrome (BOAS) can also lead to rapid onset hyperthermia, especially in hot weather, due to the muscular effort required to breathe

Answer 86

Patients may also present with epistaxis secondary to trauma, coagulopathy, nasal aspergillosis or neoplasia Epistaxis is usually unilateral but could be bilateral secondary to coagulopathy or erosion of vomer bone by tumour. There may be evidence of head trauma and it is important to assess the patient carefully for neurological signs in this case; or hypovolaemia if coagulopathy is a possibility. Epistaxis can be associated with other trauma e.g. knock on the nose with a heavy ball etc. The nose, especially in dogs, has a well-developed supply of arteries and veins and so bleeding can be significant.

Answer 87

Foreign bodies of the nasal cavity are often associated with grass blades or grass seeds but can also be sticks etc. Grass blades may be swallowed, coughed or regurgitated and can lodge in the caudal nasal passages or nasopharynx. Grass seeds can also be inhaled into the nasal cavity and travel to the lungs where they can cause further damage Nasal foreign bodies are usually unilateral- clinical signs are variable. There may be sneezing and/or a unilateral nasal discharge; or gagging and dysphagia. There may be an odour from the affected nostril. Sometimes affected cats are anorexic, lethargic and depressed but with no obvious nasal signs.

Answer 88

Nasopharyngeal polyps are common in cats and may be found in the nasal passages, the pharynx or the middle ear cavity with the clinical signs being dependant on the location. Those in the nasopharynx can be a cause of inspiratory stridor often in young cats.

Answer 89

In a patient with BOAS, the clinical signs will depend on the degree of obstruction and secondary complications at presentation. The patient may only have stertorous (snoring, sonorous respiration) breathing; or it may be making marked inspiratory effort, with mouth breathing and respiratory distress, as well as being hyperthermic. It could be collapsed and cyanotic. It should be noted when carrying out triage of brachycephalic breeds, that many clients consider the stertor or stridor associated with their pet’s breathing to be completely normal. It is important, therefore, not to be judgemental - it is often more beneficial to ask the owner if the breathing noises have worsened over time.

Answer 90

Nasopharyngeal polyps may cause a marked inspiratory stertor, often in young cats, which may result in mouth breathing. They may also cause sneezing, nasal discharge, gagging, dysphagia and altered voice. Whilst the naso-pharyngeal polyp, may have been present for some time, signs may appear to develop suddenly. Nasal tumours will have similar respiratory signs as nasopharyngeal polyps although there may be other signs e.g. epistaxis, pain, deformity. The signs are usually unilateral initially.

Answer 91

Brachycephalic obstructive airway syndrome may be suspected from the breed, clinical history and presenting signs. Following emergency stabilisation, endoscopic or laryngoscopic examination of the caudal pharynx and larynx, under anaesthesia, will show evidence of soft tissue oedema and inflammation, elongated soft palate, eversion of the laryngeal saccules and possibly laryngeal collapse.

Answer 92

Nasal foreign bodies may be visualised using fine needle or rigid endoscopes. Alternatively, a bronchoscope may be passed through the mouth, in the anaesthetised patient, and reflexed rostrally to look behind the soft palate as many blades of grass are only visible caudally. Nasal foreign bodies may be manually removed, using endoscopic equipment, under anaesthesia. Antibiotics may be required if there is secondary infection.

Answer 93

Nasopharyngeal polyps may be seen at the nares rostrally; or may require a needle or rigid endoscope to visualise them.

Answer 94

Lateral and dorso-ventral radiographs of the skull may show nasopharyngeal polyps- within the pharynx or tympanic bulla. They might also demonstrate fractures secondary to trauma. Nasal cavity radiographs (e.g. dorso-ventral intra-oral in the dog) may demonstrate features associated with nasal tumours, foreign body or destructive mycosis.

Answer 95

For a patient with BOAS, oxygen supplementation is required- a nasal catheter may not be feasible due to stenotic nares, but nasal prongs may be well-tolerated. As outlined previously, an oxygen cage, flow-by oxygen etc. may be preferable but avoidance of hyperthermia is important. However, in severe cases, transtracheal catheterisation, an emergency tracheostomy or general anaesthesia, followed by endotracheal intubation and ventilation, may be required. Cooling the patient to reduce hyperthermia is essential as previously discussed using fans, cool water, clipping etc. Ice, gastric lavage and enemas are not recommended for management of hyperthermia/ heatstroke. Tabor (2014) discusses heatstroke and its management in veterinary patients. The veterinary surgeon may prescribe corticosteroids to reduce the laryngeal and pharyngeal swelling and oedema. Long term treatment involves corrective surgery e.g. shortening the soft palate, stenotic nares, weight control and exercise management.

Answer 96

A patient with signs of nasal disease/ injury should not be muzzled as it may require to mouth breathe; it is important that any nursing/treatment interventions do not further increase oxygen requirements. If the patient is aggressive, placing a large buster collar can be helpful to facilitate intra venous catheter placement and examination. Sedation is also a consideration as any increased patient activity, including struggling against restraint, will increase oxygen demand.

Answer 97

Nasopharyngeal polyp disease can be usually be managed acutely with oxygen supplementation if indicated; if soft tissue oedema/swelling is present, due to excessive inspiratory effort, short acting corticosteroids may be administered to provide temporary relief. Nasopharyngeal polyps are often removed, surgically, by traction, although they can recur following this. They may also be removed surgically (ventral bulla osteotomy or total-ear canal ablation with a lateral bulla osteotomy), and if removed in their entirety this approach can result in a cure.

Answer 98

A patient with epistaxis, secondary to suspected head trauma should have minimal handling; it should be positioned with its head and neck elevated, ideally, and no pressure should be put on the jugular vein to avoid increasing intracranial pressure (ICP). It should be monitored closely for any change in mental status etc.

Answer 99

A patient with epistaxis of unknown cause may be managed by instilling adrenaline +/- lidocaine into the affected nostril. These will both cause vasoconstriction and should decrease the haemorrhage. Additional methods of trying to manage epistaxis include placing something into the nasal cavity through the external nares such as a cotton ball or a cellulose dressing designed to stop haemorrhage e.g. Traumastem. Transaxemic acid may also be administered. Rarely a blood transfusion may be needed.

Answer 100

If epistaxis could be secondary to a coagulopathy, an assessment of the patient’s primary and secondary haemostatic mechanisms will be required. Ongoing monitoring and management of hypovolaemia may be necessary. One of the main patient concerns, apart from blood loss and potential hypovolaemia, is the risk of inhaling large volumes of blood which can lead to aspiration pneumonia. Therefore, ongoing nursing care must reflect this and the patient’s respiratory system and function must be monitored particularly carefully.

Answer 101

Clinical signs of lower airway (bronchial) disease will depend on the underlying cause but can include cough (often harsh), exercise intolerance/ lethargy, tachypnoea → dyspnoea, increased lung sounds and wheezes on auscultation +/- pyrexia if infectious cause

Answer 102

Noting the respiratory pattern is important e.g. in cats with ‘asthma’ (bronchitis) there is often a marked expiratory effort due to air trapping.

Answer 103

Bronchitis can be secondary to infection (viral, bacterial and parasitic), allergies, irritation, foreign body and smoke inhalation. Some breeds have an inherited tendency. Whilst it is generally a chronic condition, cases will often present acutely.

Answer 104

Feline asthma’/’allergic airway disease’/ ‘allergic bronchitis’

Answer 105

‘Feline asthma’/’allergic airway disease’/ ‘allergic bronchitis’ has a complex aetiology that is not clearly understood, as is the case with human asthma (International Cat Care, 2017). Asthma in people is thought to have an allergic basis and it is considered that this may be the case in cats

Answer 106

The clinical signs are caused by bronchial inflammation, of a cellular nature; resultant increased mucous secretion, mucosal oedema and increased bronchiolar smooth muscle development. This latter condition results in bronchoconstriction leading to air trapping within the alveoli. This makes it hard to expel air, so the animal must make a marked expiratory effort. A cat with feline asthma may present as an emergency, with no previous history, or as a flare-up of a controlled condition. It can occasionally be fatal.

Answer 107

Canine chronic bronchitis is classified as persistent coughing for a consecutive period of 2 months or more (Rozanski, 2014), without any other signs of specific lung disease. Pathology associated with the condition is like feline asthma with increased mucous secretions and mucous glands and a cellular infiltrate around the bronchi causing narrowing of the airways.

Answer 108

A cat may present with asthma at any age but it is most common in young cats- median 4-5 years of age. It is unlikely for an older cat to suddenly develop asthma

Answer 109

The cat often presents with a cough or the owners report history of an intermittent cough. Asthma is the likeliest cause of coughing in a cat, although it may be confused with vomiting or ‘fur balls’ by owners. Other signs include wheezing and varying degrees of respiratory difficulty - tachypnoea and increased expiratory effort. Severe cases will present with breathing, cyanosis, abdominal respiration, expiratory effort and wheezing, particularly on expiration - ‘status asthmaticus’ dyspnoea, open mouth. An affected cat will often have a cough on tracheal palpation and an expiratory wheeze will usually be audible. The cat may hypersalivate and appear less responsive due to the increased respiratory effort. Occasionally areas of the lungs will appear to produce no sound due to complete airway obstruction.

Answer 110

Canine bronchitis is often chronic (> two months) but may have acute flare-ups. It may develop secondary to various conditions e.g. infectious laryngotracheitis ‘kennel cough’; tracheal stenosis, tracheal collapse, environmental irritants etc Other less common causes include lower airways masses and foreign bodies. Obstruction of a bronchus leading into a lung lobe will cause collapse of the affected lobe

Answer 111

There is often a persistent, dry ‘honking’ coughing and evidence of increased expiratory effort. Cases may present with mild signs or with severe respiratory distress - constant coughing, dyspnoea, hyperthermia and cyanosis. Wheezes and coarse crackles are often heard all over the chest on auscultation.

Answer 112

Caution should be taken when deciding where to place a patient to be hospitalised with clinical signs of bronchitis/ lower airway disease. As some of these conditions are infectious in origin and airborne, the patient would need to be isolated, in a different air space, and barrier nursed to protect the other patients in the practice.

Answer 113

Radiography is useful when the patient can be safely positioned. In some cases of feline asthma, there may be no abnormal radiographic findings, but other causes of respiratory distress can be excluded. There may be a bronchiolar pattern; evidence of pulmonary hyperinflation with flattening of the diaphragm; collapse of the right middle lung lobe and occasionally evidence of rib fractures secondary to expiratory effort. Pneumothorax may also occur with feline asthma. Haematology will often demonstrate eosinophilia if there is an underlying allergic or parasitic cause. Definitive diagnosis requires bronchoscopy or bronchoalveolar lavage (BAL).

Answer 114

Canine chronic bronchitis shows a similar bronchiolar pattern on radiographs, however the severity of changes seen radiographically do not always correlate with the severity of the clinical disease (Waddell and King, 2018). Bronchiectasis may be apparent. Evidence of tracheal stenosis or collapse may be seen on plain radiographs or with fluoroscopy. A history of coughing for longer than two months with no other evidence of specific pulmonary disease aids the diagnosis. Haematology, BAL and bronchoscopy can be used for definitive diagnosis.

Answer 115

``` Initial stabilisation with oxygen therapy is essential in both cases. As cats with asthma often present in a severely compromised state, they should ideally be placed into an oxygen cage initially, be observed closely but have minimal handling. A hands-off approach initially is essential. Once the cat is more stable, an Iv catheter should ideally be placed on veterinary direction. If this causes the cat to become stressed/ deteriorate then placement should be postponed until the patient is more stable. A corticosteroid (e.g. dexamethasone) may be administered intravenously to a cat with asthma for its anti-inflammatory effects. Due to the powerful bronchoconstriction that occurs in feline asthma, bronchodilators (e.g. terbutaline, salbutamol) are likely to be used in the management. They may be administered intravenously in the emergency patient- but ongoing administration for disease control could be by nebulisation or metered inhaler (International Cat Care, 2015). Occasionally, in a severe, collapsed/ terminal patient with status asthmaticus, that have failed to respond to other treatments, epinephrine/ adrenaline may be administered as a constant rate infusion. This causes profound bronchodilation, peripheral vasoconstriction and cardiac inotropic effects (Waddell and King, 2018). If the response to emergency treatment is poor, then general anaesthesia, placement of an ET tube and intermittent positive pressure ventilation may be necessary. Caution must be exercised when performing IPPV in this case as the patient’s lung compliance will be poor initially. Managing airway pressures and avoiding barotrauma is vital. ```

Answer 116

Initial stabilisation with oxygen therapy is essential Canine chronic bronchitis is managed in a similar manner although dogs with chronic bronchitis are less likely to present with severe respiratory difficulty/ in a collapsed state than cats Cooling may, however, be required in a dog with acute signs of respiratory distress. It may also be helpful to nebulise the patient with warmed saline, to moisten airway mucous and help clear this from the airways. Bronchodilators may also be used (theophylline or salbutamol). Steroids may be administered for their anti-inflammatory effect e.g. dexamethasone. Cough suppressants may be used- codeine or butorphanol. Sedation may also be required - careful monitoring of cardiovascular parameters will be required in such cases patients. Once the patient is stable, consideration will have to be made of chronic management of the condition. This usually involves environmental control (avoidance of airway irritants), medical management and weight loss (often for dogs).

Answer 117

Pulmonary Parenchymal Disease | This includes pneumonia, pulmonary oedema, haemorrhage, pulmonary thrombo-embolism and neoplasia.

Answer 118

Pneumonia is inflammation of the lung parenchyma itself.

Answer 119

Pneumonia is inflammation of the lung parenchyma itself. It is more common in dogs than cats and is, generally, infectious, often bacterial, in origin.

Answer 120

Pneumonia may be caused by bacteria, mycoplasma, viruses, fungi or parasites. These may be community acquired infectious agents contracted from other dogs or cats e.g. the bacteria Bordetella bronchiseptica or the virus, canine distemper.

Answer 121

It may be secondary to aspiration of food material, fluid or vomitus in animals with e.g. neurological disease, following induction of emesis for poisoning, laryngeal disease, cleft palate, myasthenia gravis or megaoesophagus. The acidic nature of gastric contents means that they can cause serious damage to the lower airways if inhaled so aspiration pneumonia can be very severe.

Answer 122

acute respiratory distress syndrome (ARDS)

Answer 123

Pneumonia may develop after a period of hospitalisation in patients who have had recent surgery or another medical condition- hospital acquired rather than community acquired pneumonia Patients at risk of aspiration include brachycephalic breeds, patients with GDV, and patients with foreign bodies amongst others. Pneumonia may also arise in association with conformational defects in brachycephalic dogs with BOAS. Steps can be taken to reduce the risk and to limit the amount of damage that might occur if this is considered prior to performing interventions e.g. ensuring suction is available, controlling vomiting and administering medication to alter gastric pH.

Answer 124

The signs are usually acute onset. There are several similarities in the clinical signs of patients with pulmonary parenchymal (lung) disease of various causes (e.g. oedema, pneumonia etc.). The signs are mainly caused by material (usually) fluid within the alveoli which limits gas (O2/CO2) exchange and decreases lung compliance, thus making breathing difficult. Patients usually have increased inspiratory effort/ respiratory distress, tachypnoea, orthopnoea and a soft, moist cough, especially evident with changes in position or exercise. They are often dull, lethargic and pyrexic although a patient can have pneumonia and not be pyrexic depending on the cause. They may have pale mucous membranes, or in severe cases, cyanosis. There are often harsh crackles and fluid sounds on auscultation especially in the ventral lung fields. Occasionally they may additionally have signs of sepsis or SIRS

Answer 125

The history and clinical signs, especially pyrexia, with compatible respiratory signs, may be suggestive. Radiography/ computed tomography of the thorax usually shows areas of lung consolidation with an alveolar pattern (fluffy, white radiodense areas) and air bronchograms. The changes may be widespread or caudally distributed with viral and some bacterial pneumonias. In the case of aspiration pneumonia, the radiographic changes are often confined to the right middle lung lobe. An underlying cause may be obvious e.g. megaoesophagus. Haematology and blood gas analysis will aid diagnosis. Haematological changes often suggest infection- increased white blood cell count with neutrophilia. If haematology is not available, a blood smear can be performed quickly for a differential white cell count. Arterial blood gas analysis is likely to demonstrate hypoxaemia and hypercapnia and pulse oximetry (SpO2) readings may be < 94%. Confirmation of pneumonia can be made using samples obtained from bronchoalveolar lavage (blind or preferably bronchoscopic) or via transtracheal sampling. Transtracheal sampling can be performed in a patient that is not stable enough for anaesthesia (Eggleston, 2018). Samples can be obtained for cytology, culture and sensitivity. In-house cytology will demonstrate many neutrophils and macrophages in bacterial or fungal pneumonias. If it is a bacterial pneumonia, rods or cocci will also be present. The presence of bacteria within neutrophils and magrophages demonstrate an active inflammatory response. Bacterial and/or fungal culture and sensitivity would be required to confirm the actual cause and the most appropriate treatment. Cytology of parasitic pneumonia may also show macrophages and often eosinophils. Cytology of viral pneumonia may show neutrophils and lymphocytes

Answer 126

Depending on the underlying cause of the pneumonia, the patient may be in isolation and require barrier nursing especially if any suggestion SIRS/ sepsis. The initial priority should be to stabilise the patient using oxygen therapy, where necessary. In severe cases, the patient will need to be anaesthetised and mechanically ventilated using positive end expiratory pressure (PEEP) ventilation to recruit alveoli (Hopper and Powell, 2013). There are significant risks with anaesthesia in these cases and associated complications with prolonged ventilation using IPPV or PEEP. If acute bacterial pneumonia is suspected, first-line, broad-spectrum intravenous antibiotics, such as potentiated amoxicillin, will often be started. Ongoing antimicrobial use should be based on culture and sensitivity results. Intravenous fluid therapy may be required. It is important to avoid over infusion which could result in pulmonary oedema and cause a worsening of the respiratory signs. Nutrition is very important to promote recovery - assisted feeding may be required. The method chosen will depend on the patient’s condition and other considerations e.g. is it dysphagic. If a nasal catheter is used for oxygen delivery and a feeding tube is also placed, these must be VERY clearly marked to avoid accidental infusion of food into the airways. Regular nebulisation may help to dislodge exudate from alveoli, although this may cause bronchoconstriction which could be counterproductive (Waddell and King, 2018). There is no evidence to support coupage, but it may, additionally, help to promote effective circulation (Eggleston, 2018). The most effective and simple method for the prevention of atelectasis (consolidated lungs secondary to the patient lying down for a prolonged period) support the patient in sternal recumbency and encourage standing and walking as soon as possible. If a patient is recumbent, it should be turned regularly (every 2-4 hours) and supported in sternal for as long as possible. Changing the patient’s position and having it in sternal, promotes increased tidal volume. With respiratory patients supported standing outside their cage for a few minutes, ~ every four hours, can help. Oxygen dependent patients that are ambulatory (if even for a few steps), can be taken for very short walks with a mobile oxygen source. As previously stated, these patients will be very debilitated -it is important for the nursing team to assess what the patient is able to do for themselves and what they need assistance with. The nursing plan should then be developed and reviewed on a regular basis to ensure appropriate goals are being met for the patient. As with all patients appropriate consideration must be given to recumbency care, mobility, bladder management, nutritional support, grooming, pain management and tender loving care.

Answer 127

Pulmonary oedema | This is when fluid builds up in alveoli and the interstitial tissue of the lungs

Answer 128

There are two main forms of pulmonary oedema - cardiogenic and non-cardiogenic.

Answer 129

Cardiogenic associated pulmonary oedema is more common and is associated with left sided congestive heart failure leading to backing-up of blood into the pulmonary blood vessels and leakage of fluid from capillaries into the surrounding parenchyma.

Answer 130

Neurogenic pulmonary oedema is a non-cardiogenic form which can occur secondary to seizuring, electrocution, head trauma or airway obstruction. Pulmonary oedema may also develop secondary to smoke inhalation or drowning episodes

Answer 131

it is essential to monitor any patient, especially a cat, receiving IVFT to ensure it does not develop iatrogenic pulmonary oedema due to excessive fluid administration. In a cat, over administration of IV fluids will often lead to pleural effusion.

Answer 132

Cardiac origin - with small volume (mild) pulmonary oedema, there may be exercise intolerance and a cough (more likely to be caused by tracheal compression from the associated cardiomegaly than the alveolar fluid). As the oedema worsens the animal will become increasingly dyspnoeic. Occasionally the animal will present as an emergency, with fulminant, life-threatening pulmonary oedema. On auscultation, there may be a heart murmur or arrhythmia; and harsh crackles may be heard. Mucous membranes may be pale or cyanotic and may be excessively moist.

Answer 133

The clinical signs of a patient with non-cardiogenic oedema can vary from being mild to collapse with severe respiratory distress and cyanosis. Cardiac changes are less likely on auscultation. If electrocution is suspected to be the underlying cause, examination of the lip fissures/ oral cavity will often reveal burns in addition.

Answer 134

A patient with smoke inhalation may also have upper airway swelling/ laryngospasm with inspiratory stridor. Smoke causes direct tissue damage with secondary swelling and oedema; as well as stimulating marked bronchoconstriction. The patient may also have signs of carbon monoxide poisoning with cherry red mucous membranes.

Answer 135

With pulmonary oedema a fluffy interstitial to alveolar pattern is seen. With cardiogenic associated oedema, in dogs, it is usually perihilar in distribution, above the heart base. There may also be signs of left-sided cardiomegaly e.g. left atrial enlargement. In cats, the distribution of pulmonary oedema is often patchier and diffuse, rather than perihilar, but cardiomegaly, +/- pleural effusion, may also be evident. Arterial blood gas analysis may demonstrate hypoxaemia and hypercapnia with the degree dependant on how severe/ widespread the pulmonary oedema is

Answer 136

With pulmonary oedema a fluffy interstitial to alveolar pattern is seen. In cases of neurogenic pulmonary oedema, the caudo-dorsal lung lobes are more likely to be affected. In both cases dilation of the pulmonary vasculature will be seen. Arterial blood gas analysis may demonstrate hypoxaemia and hypercapnia with the degree dependant on how severe/ widespread the pulmonary oedema is

Answer 137

The radiographs of patients with smoke or fluid inhalation will generally show patchy, widespread changes. With pulmonary oedema a fluffy interstitial to alveolar pattern is seen. Arterial blood gas analysis may demonstrate hypoxaemia and hypercapnia with the degree dependant on how severe/ widespread the pulmonary oedema is

Answer 138

The initial management involves the provision of oxygen therapy in the manner most tolerated by the patient. Handling should be kept to a minimum in any patient with respiratory distress. If a patient is severely affected, IPPV may be required but this is usually associated with a poor prognosis. In mild cases, supportive therapy +/- specific medication and rest will often result in clinical improvement within 1-2 days. Medical management will usually be required, depending on the underlying cause. As discussed in Unit 3, outcome 1, congestive cardiac disease will be managed with various medications including diuretics and ACEi. Neurogenic pulmonary oedema however, does not respond well to the use of diuretics and they would not normally be indicated in this situation. Corticosteroids and intravenous fluids are not required in cases of pulmonary oedema

Answer 139

Patients with neurogenic and smoke inhalation pulmonary oedema require supportive care and their clinical signs should hopefully resolve with time (2-3 days). A patient who is suspected of having smoke inhalation should be placed into an oxygen enriched environment even if the breathing on presentation is normal. A period of 12-24hrs is normally recommended. There are various presentations of a patients with neurogenic pulmonary oedema- however it is likely that oxygen support will be part of the management also (Lang and Glaus, 2010). Bacterial infection may be a complication of tissue damage secondary to smoke inhalation.

Answer 140

Pulmonary haemorrhage is usually associated with trauma, coagulopathy or rodenticide poisoning, although occasionally it could be secondary to neoplasia.

Answer 141

Pulmonary thromboembolic disease is due to a hypercoagulable state of the blood, which may be brought about by several unrelated conditions e.g. protein losing nephropathy, post-surgery, hyperadrenocorticism, pancreatitis, Angiostrongylus vasorum infection and immune-mediated haemolytic anaemia

Answer 142

With pulmonary haemorrhage, a patient may present with respiratory distress and coughing blood (haemoptysis). If a clotting deficit is present, the patient may have other related signs e.g. swollen joints and spontaneous bleeding from other sites. In the case of Angiostrongylus, for example, it is common to find scleral bleeding in addition to epistaxis. There may be signs of pleural space disease following bleeding into the thoracic cavity. In addition to respiratory signs, the patient is likely to have signs related to blood loss, anaemia and hypovolaemia. With a traumatic cause, there may be associated thoracic discomfort/ pain, even if there are no obvious rib fractures.

Answer 143

coughing blood (haemoptysis).

Answer 144

With pulmonary thrombo-embolism there is sudden onset serious pulmonary signs - tachypnoea, increased inspiratory effort, cyanosis, chest pain, frothy pink blood stained mucous from the mouth and harsh lung sounds.

Answer 145

Clotting times will be prolonged in patients with rodenticide poisoning or coagulopathy. With pulmonary haemorrhage, radiographs often demonstrate a patchy alveolar pattern. In some cases, there may be a pleural effusion as well.

Answer 146

Pulmonary thrombo-embolism may not be detectable on radiographs although computed tomography can be diagnostic . Radiographically, there may be a mild alveolar or interstitial pattern and occasionally dilated pulmonary arteries. Clinically, there is often a mild to moderate thrombocytopaenia. Definitive diagnosis requires CT-angiography, under general anaesthetic, although Waddell and King (2018) describe the use of fast CT scanning techniques in conscious patients.

Answer 147

Oxygen, Vitamin K1 therapy is required for rodenticide poisoning. Fresh frozen plasma may be required to manage the coagulopathy. In some cases, a whole blood transfusion, may be required depending on the clinical signs and PCV.

Answer 148

If a diagnosis of pulmonary thromboembolism has been confirmed with CT angiography, tissue plasminogen activator (tPA) may be used to treat (Johnson, 2014). However, this drug is expensive and not widely available. Thromboprophylaxis (e.g. heparin, clopidogrel or aspirin) is more likely to be used in animals at risk of pulmonary thromboembolism however outcomes are usually poor.

Answer 149

Gentle handling, restricted exercise and appropriate nursing care is essential. If a coagulopathy is suspected, blood samples should be obtained only from peripheral veins and appropriate haemostasis must be supported e.g. pressure for five minutes following venipuncture. Caution should be exercised with the volume of injections given by the subcutaneous route if this must be used. Intravenous catheterisation must be carried out with caution if the patient is dyspnoeic but also if they have a coagulopathy- there is a significant risk of excessive bleeding The patient’s kennel should be well padded and ,ideally, smooth fronted to prevent the patient harming themselves further. It is good practice to monitor the urine for evidence of haematuria in a patient with coagulopathy. Whilst coagulopathy is not itself a painful condition, pain assessment and management is indicated as for all patients. The patient may be painful secondary to intraarticular bleeding or may have coexisting problems

Answer 150

There is normally a very small amount of fluid in the pleural space (the space between the pulmonary/visceral and parietal pleura)

Answer 151

The presence of air, fluid or soft tissue in the pleural space prevents the lungs expanding fully during inspiration, thus limiting the amount of air the patient can inhale in each breath.

Answer 152

The signs associated with pleural space disease are due to the space occupying effect of whatever is abnormally present in the pleural space. The larger the volume of abnormal material in the pleural space, the greater the patient’s respiratory distress.

Answer 153

Pleural effusion This is the presence of free fluid within the pleural space. The clinical signs are mainly due to the volume of fluid in the pleural space rather than the actual fluid type.

Answer 154

Based on composition, an effusion may be classified as a pure transudate, a modified transudate, an exudate, a haemorrhagic effusion, or a neoplastic effusion.

Answer 155

Analysis of an effusion, by checking total protein, cell counts, and cytologic appearance, will confirm the type of effusion however effusions are often dynamic, and their characteristics can change. Analysis of an effusion can be performed in-house and will aid with developing a treatment plan for the patient by identifying the origin and type of fluid.

Answer 156

An exudate is associated with an inflammatory reaction and has a relatively high protein level and cell count.

Answer 157

A modified transudate is intermediate between an exudate and a transudate – the mesothelial cells lining the abdominal/ thoracic cavity can be irritated by a chronic transudate and an inflammatory response may start to develop. It can also be caused by increased hydrostatic pressure in blood vessels with fluid being forced out at capillaries e.g. patient with congestive cardiac failure. This effusion has higher protein and more cells than a transudate but less protein and less cells than an exudate. It could also be caused by some types of neoplasia

Answer 158

Causes of pleural effusions include - • rupture of the thoracic duct resulting in chylothorax • haemorrhage into the pleural space due to clotting defects, trauma or neoplasia (haemothorax) • a pleural infection resulting in pus formation (pyothorax) • a pleural infection resulting in a non-purulent effusion e.g. feline infectious peritonitis (FIP) • neoplasia • transudates associated with a low plasma oncotic pressure such as protein losing nephropathies and enteropathies and congestive heart disease.

Answer 159

A pure transudate usually develops due to decreased plasma oncotic pressure in a patient with hypoalbuminaemia or it can be caused by increased hydrostatic pressure as above - this effusion is low protein and low cellularity. Transudates are aqueous, clear to yellow coloured, with a low cellularity and low protein content. They are often associated with right sided heart failure in dogs or left-sided cardiac failure in cats.

Answer 160

Pyothorax, unilateral or bilateral purulent exudate, is a relatively common condition in cats but less common in dogs. It can be caused by a penetrating foreign body, local spread of infection e.g. pulmonary abscess, haematogenous spread, ruptured oesophagus or the cause may be unknown - idiopathic. It is often caused by anaerobic bacteria or is a mixed infection.

Answer 161

Animals with pleural space disease, usually present with a restrictive breathing pattern- increased inspiratory effort with rapid, shallow respirations. The patient may show signs of respiratory distress with cyanosis, mouth breathing, extended head and neck, abducted elbows and orthopnoea. If the cause is traumatic, there may be additional signs of trauma e.g. rib fractures. Additional signs may include weight loss, pyrexia and anorexia, depending on the underlying cause and time course. On auscultation there is frequently muffled lung and heart sounds, particularly ventrally when the patient is in an orthograde stance i.e. upright or standing. There may be a heart murmur or arrhythmia if cardiac disease is the cause. There may be goitre in a cat with hyperthyroidism and congestive cardiac failure secondary to hypertrophic cardiomyopathy. The mucous membranes may be pale or cyanotic depending on how compromised the patient is. If the patient tolerates it, thoracic wall percussion will show increased dullness ventrally.

Answer 162

POCUS scans can be performed kennel side and confirm the presence of free fluid in the thorax. Thoracocentesis is important in the diagnosis and emergency management of most cases of pleural effusion (see section 3.2.6.1.4) N.B. if a patient has a coagulopathy, thoracocentesis would not be appropriate; if a patient has haemothorax because of trauma but there is only a small volume of blood, conservative management, i.e. no thoracocentesis, is generally indicated. As thoracocentesis involves entry into a body cavity, this procedure must be performed by a veterinary surgeon (VS). To provide appropriate support to the patient and the VS, it is essential that the RVN is fully aware of the equipment required, patient preparation and technique involved. Durham (2017) discusses thoracocentesis. Samples obtained by thoracocentesis should be placed into appropriate sample tubes (plain, EDTA) for cell counts, cytology +/- biochemistry as appropriate to the case. Aerobic and anaerobic culture and sensitivity may also be performed especially if pyothorax is suspected . Samples should be examined microscopically in-house too. With pyothorax, there is likely to be many

Answer 163

With pyothorax, there is likely to be many neutrophils, macrophages and bacteria (Moriello, 2013). Toxic changes in neutrophils are likely to be apparent – these changes suggest an inflammatory response in a patient. Toxic changes include cytoplasmic basophilia, vacuoles and presence of Döhle bodies (Sharkey and Heinrich,2019). Strict asepsis should be maintained when handling samples because of the zoonotic potential of Pasteurella associated pyothorax

Answer 164

A Feline Infectious Peritonitis exudate is usually viscous and straw coloured, with a high protein level but low cellularity – this exudate is non-septic i.e. no bacteria. There may also be ascites as well.

Answer 165

Chylothorax effusions appear milk-like, sometimes with a pink tinge, due to their high triglyceride content - the triglyceride level is higher than that found in a, concurrently taken, plasma sample. Chylous effusions have been associated with feline cardiomyopathy, trauma and lymphoma- they may also be idiopathic.

Answer 166

A sanguineous effusion appears like watery blood. It contains blood cells but the PCV is significantly less than whole blood

Answer 167

The PCV/ cell counts (RBC, WBC) may be like whole blood with a haemothorax depending on how recent the haemorrhage was; but can be significantly less with a sanguinous effusion

Answer 168

Haemothorax is generally associated with trauma, clotting deficits e.g. rodenticide coagulopathy or neoplasia e.g. haemangiosarcoma. A patient with rodenticide coagulopathy may have additional signs due to bleeding elsewhere e.g. signs associated with pulmonary haemorrhage +/- swollen joints.

Answer 169

With pyothorax, haematology findings will be suggestive of infection with leucocytosis due to neutrophilia and a left shift. Leucopaenia (neutropaenia) is a poor prognostic sign as this can be associated with an increased mortality rate. Patients with pyothorax are at risk of developing sepsis and septic shock and therefore must be monitored very diligently. The patient may have increased PCV due to dehydration or the PCV may be decreased in a patient with haemorrhage

Answer 170

Radiography, following thoracocentesis, can be useful to determine the cause of the effusion. However, it is less likely to be of benefit prior to thoracocentesis due to the risk to the patient of positioning; and the poor radiographic contrast when there is free thoracic fluid. Evidence of cardiac enlargement may suggest a cardiogenic source. Physical examination of the chest wall may determine if there has been any puncture of the chest cavity leading to pyothorax (although this is often not the case). Pyothorax can occur secondary to penetrating wounds of the thorax but also due to lung infections.

Answer 171

Initial management of a patient with a suspected pleural effusion, involves the provision of oxygen, minimal handling and avoidance of stress. If the patient can be supported in sternal recumbency, without compromising it further, this may help to improve ventilation. If pleural effusion is suspected, thoracocentesis should ideally be performed as soon as the patient’s condition will permit if it is indicated- both for diagnostic purposes and emergency treatment. It should relieve the patient’s signs by removing fluid from the pleural space thus allowing better lung inflation. Thoracocentesis should be performed before radiography when pleural effusion is present. Generally, removal of 10-20ml/kg of air or fluid from the thorax should result in a marked improvement in the patient’s ability to ventilate. Restraint for radiography could lead to rapid deterioration of the patient’s condition, without yielding much diagnostic information. See section 3.2.7.4 for a description of thoracocentesis. Vascular access should be achieved as soon as possible to allow administration of emergency medications for cardiovascular support or IV antibiotics etc. This should be performed on veterinary direction but not if it causes additional stress to the patient. It is often sensible to carry out placement of an IV catheter in a step by step manner with patients that are dyspnoeic. This allows the patient a period of recovery before the next step.

Answer 172

A suggested protocol is outlined below - ➢ Pre-oxygenate the patient for 15 minutes ➢ Clip over the site of venepuncture and apply EMLA before returning to oxygen enriched environment. ➢ Perform an aseptic scrub of the clipped area, while also delivering oxygen. Then return the patient to an oxygen enriched environment ➢ Place the IV cannula and tape in place – return to oxygen enriched environment. ➢ Apply protective dressing over the top return to oxygen enriched environment.

Answer 173

If pyothorax is confirmed following thoracocentesis, first-line IV antibiotics will be required. Further antibiotic selection will depend on the results of culture and sensitivity. Bacterial populations can be mixed and include both aerobes and anaerobes- it is important that the samples are collected and stored appropriately. Thoracic chest drain(s) are likely to be required in a patient with pyothorax but placement, usually under general anaesthetic, is often delayed (1-2 days) until the patient is more stable (see section 3.2.7.5). Once placed, frequent, intermittent aspiration of the chest drain will be required, several times daily, to ensure clearance of the effusion; or an active suction device, that provides continuous, gentle, negative pressure, can be used. Flushing of the pleural cavity, with sterile warmed 0.9% saline, aids in the removal of very viscous secretions and dilution of the infectious material. Drainage should continue until the nature of the effusion has changed to a sero-sanguineous one that does not contain any toxic neutrophils (those showing degenerative changes). Thoracoscopic evaluation of the lungs and pleural surface; or thoracotomy may be performed to allow removal of abscessed and diseased material.

Answer 174

Treatment of chylothorax is difficult unless there is an underlying cause that can be treated e.g. cardiomyopathy. It is unlikely that the thoracic duct can be repaired surgically; it may instead be ligated, and the pericardium removed in an attempt to prevent recurrence

Answer 175

Management of haemothorax due to rodenticide poisoning, may involve fresh frozen plasma/whole blood transfusions and vitamin K1 treatment. It is also possible to consider auto-transfusion which is discussed in Unit 3 Outcome 3. In the case of sanguineous exudate due to lung lobe torsion, a thoracotomy and lobectomy may be performed.

Answer 176

Transudates are often associated with underlying disease e.g. cardiac disease. Identification and treatment of the underlying condition is required.

Answer 177

Pneumothorax is a type of pleural space disease where air accumulates in the pleural space. As with pleural effusion, this inhibits inflation of the lungs and can cause varying degrees of respiratory distress depending on the volume of air and rate at which it builds up.

Answer 178

Pneumothorax can be open or closed. An open pneumothorax will be caused by a penetrating wound to the thorax and secondary infection may be a complication

Answer 179

Closed pneumothorax: blunt trauma to the thorax, without any puncture of the thorax e.g. RTA, fall, air leakage from damaged lung (e.g. neoplasia, ruptured bulla, feline asthma, excessive lung inflation during IPPV etc.). This can sometimes arise spontaneously due to rupture of lung bullae secondary to emphysema, pneumonia, foreign bodies, abscesses or asthma in cats.

Answer 180

Open pneumothorax: penetrating traumatic wound to the thorax (e.g. bite wound, knife wound, shotgun); or, rarely, iatrogenic following thoracocentesis. In each case air enters the pleural space, inhibiting lung inflation and leading to progressive lung collapse- atelectasis.

Answer 181

Tension pneumothorax is a very serious form of pneumothorax which will rapidly become life threatening. It can arise if there is a large escape of air from damaged lungs into the thorax during inspiration but due to a one-way valve effect, there is no air movement out during expiration. If the patient has a penetrating thoracic wound, a flap of tissue can act as a one-way valve, sucking air into the pleural cavity during inspiration but blocking its exit during expiration. This rapid accumulation of a large volume of free air, causes the patient severe respiratory distress with the lungs rapidly collapsing. It also causes progressive obstructive cardiac shock because the increased intrathoracic pressure compresses the heart, lungs and main veins thus decreasing cardiac filling (Waddell and King, 2018). Tension pneumothorax can very quickly be life-threatening due to pressure on the lungs and decreased cardiac filling.

Answer 182

As with any form of pleural space disease e.g. pleural effusion, a patient with pneumothorax, usually presents with a restrictive breathing pattern - increased inspiratory effort with rapid, shallow respirations. There will be varying degrees of respiratory distress depending on the volume of free air present in the thorax and how rapidly it accumulates. The patient may be cyanotic, mouth breathing and showing signs of air-hunger. As pneumothorax often develops following blunt trauma, it is important to closely monitor animals following injury. Damage to the lungs may occur at the time of the injury but clinical signs will not be apparent until free air starts to collect in the pleural space. As more air gathers in the pleural space, the patient may start to show increasing signs of respiratory distress.

Answer 183

A patient with severe pneumothorax, often due to tension pneumothorax, may also show signs of obstructive/ hypovolaemic shock e.g. tachycardia, weak/ absent peripheral pulses, prolonged CRT etc. Thoracic auscultation reveals a lack of breath sounds dorsally. There may be less chest wall movement on the side of the pneumothorax if it is unilateral. Chest percussion, if appropriate, shows increased resonance dorsally. Careful assessment for penetrating wounds should be performed.

Answer 184

POCUS examination can confirm the presence of pneumothorax. Thoracocentesis will reveal the presence of free air. Thoracocentesis is both diagnostic and therapeutic. Radiography should only be performed after thoracocentesis. It may still show some evidence of air in the pleural space.

Answer 185

Initial management involves oxygen therapy until the patient is suitably stable for thoracocentesis. As pneumothorax is commonly associated with trauma, the patient should be assessed frequently for pain and appropriate analgesia must be provided on veterinary direction. An IV cannula should be placed as soon as the patient can tolerate this. Thoracocentesis provides rapid improvement in the condition. However, it may be temporary if air continues to enter the pleural cavity. The condition may be self-limiting and respond to symptomatic treatment and cage rest. In large or recurring accumulations, chest drain (s) are likely to be required. Placement of a thoracic drain is indicated in a patient who has required thoracocentesis performed > three times in a 24hr period or where there is evidence of an ongoing air leakage. Ongoing monitoring of the patient’s ventilation and cardiovascular parameters is necessary. Arterial blood gases should be monitored ideally. If there is a chest drain in place, it requires careful, appropriate aseptic management e.g. regular checking to ensure it is not blocked or displaced. As previously outlined, these patients will often be very debilitated, and it is important for the nursing team to assess what the patient is able to do for themselves and what they need assistance with. The nursing plan should then be developed and reviewed on a regular basis to ensure appropriate goals for this patient are being met. As with all patients consideration must be given to recumbency care, mobility, bladder management, nutritional support, grooming, pain management and tender loving care.

Answer 186

Diaphragmatic rupture is a relatively common sequel to a road traffic accident or a fall, especially in cats. The ruptured diaphragm allows varying amounts of abdominal contents to enter the thoracic cavity; restricting the lungs’ ability to inflate. N.B. the abdominal contents often do not move through the tear at the time of the trauma occurring- therefore the onset of clinical signs may be delayed. A history of any (relatively) recent trauma is significant in a patient presenting with respiratory distress. It is generally cranial abdominal structures, i.e. spleen, liver (lobe), small intestine and occasionally stomach which move into the thorax. If a lobe of liver becomes entrapped, a secondary pleural, transudate, effusion may develop due to increased hydrostatic pressure. It is possible for the stomach or intestine to become incarcerated and strangulated within the diaphragmatic tear, necessitating emergency surgery as soon as possible. Gastric dilation may occur secondary to stomach entrapment which causes profound respiratory distress. Patients with a diaphragmatic rupture are often considered to require be emergency surgery. However, they will usually benefit from a significant period of stabilisation prior to surgical intervention. As discussed above, the only exception to this is if there is a gas filled organ (stomach or loop of intestine) within the thoracic cavity.

Answer 187

Such injuries can be asymptomatic. Signs may not arise at the time of the trauma as, although there may be a tear in the diaphragm, abdominal contents do not necessarily become displaced immediately. Clinically affected animals will present with varying level of respiratory distress – depending on the volume of abdominal contents in the chest and the severity of any co-existing conditions, such as pulmonary contusion. In some patients the abdomen may feel ‘empty’ on palpation. In severe cases where blood supply to abdominal organs is compromised by their cranial movement, the patient will show signs of hypovolaemic shock as well as the respiratory signs. However this can also be attributed to the traumatic incident. Lung and heart sounds may appear muffled on auscultation, often unilaterally. It may be possible to hear gut sounds (borborygmi) during thoracic auscultation. . There may be gastro-intestinal signs e.g. vomiting or jaundice in some cases.

Answer 188

Radiography will aid the diagnosis as presence of small intestine and other abdominal organs may be seen in the thorax. The patient must be handled with care and radiography only performed when the patient can tolerate it- a dorso-ventral view should be obtained with care. If the patient is small, a satisfactory, diagnostic radiograph may be obtained by X-raying it whilst it is in the oxygen cage. Radiographic diagnosis may be challenging especially if abdominal contents enter the mediastinum where they may be obscured by the heart and pericardial fat padshence the importance of producing diagnostic radiographs. Careful administration of a small volume of positive contrast agent (barium sulphate) into the gastrointestinal tract, prior to X-raying, may confirm displacement of the GIT. Ultrasonography can aid identification of abdominal contents in the thorax or a pleural effusion. Final diagnosis may, on occasion, only be made during an exploratory laparotomy.

Answer 189

Initial management involves supportive therapy and oxygen supplementation. Opioid analgesia may be required if the injury has occurred recently. If the patient has been in a traumatic incident, other injuries may require management e.g. fractured ribs/limbs and skin wounds. Once the patient is cardiovascularly stable, corrective surgery will be required (see Unit 2 Outcome 1). In some cases, it may, however, be that surgery is required to make the patient stable e.g. decreased cardiac filling due to compression by soft tissue. In this case the anaesthetic will be challenging and the patient will require very careful monitoring. Ideally if this patient needs an urgent anaesthetic and intervention to repair a life-threatening rupture, it is important to ensure sufficient nursing staff are available. There are multiple concerns for these patients and ideally one person would be ventilating the patient (IPPV), one monitoring the patient and another assisting the veterinary surgeon. Post-operative intensive care nursing and monitoring is vital for these patients to improve their survival.

Answer 190

Surgical repair involves performing a ventral exploratory laparotomy. The abdominal contents are returned to the abdomen from the thorax, followed by repair of the diaphragm. Intermittent positive pressure ventilation is required for this procedure as a large volume pneumothorax is created as soon as the abdomen is entered. Ideally a a thoracic drain is placed at the end of surgery to manage ongoing air and fluid accumulation. However, some advocate carrying out thoracocentesis when the procedure is complete and then as needed in the following hours.

Answer 191

A flail chest is a type of segmental fracture where fractures of two or more adjacent ribs, in two or more locations, results in a ‘flail segment’. It is usually the result of severe trauma, often a crush injury e.g. small dog/cat grasped by large dog; fall or kick. This results in a section of the chest wall that is not connected by ribs to either the vertebral column or the sternum. This ‘flail ’section then acts independently of the rest of the chest wall, as a free-floating section. The fractured section of the chest wall moves in the opposite direction to the rest of the thorax during breathing. It is drawn inward on inspiration due to negative pressure generated within the thorax and the free-floating nature of the fractured segment. Similarly, the segment will move outward on expiration – this is called paradoxical respiration. This can cause the patient marked discomfort as the fractured ribs grate against each other and may cause pulmonary damage.

Answer 192

The patient is often in immense pain with severe respiratory distress – the respiratory signs are often compounded by pulmonary contusions. An open wound may be present, leading to a rapidly developing pneumothorax. In the absence of an open wound, crepitus may be felt due to air building up beneath the skin surface from the thorax (subcutaneous emphysema- an accompanying closed pneumothorax is common. There may be ballooning of the skin at the site of the flail segment as the patient breathes. The patient is likely to be hypoxaemic due to decreased lung inflation and underlying pulmonary contusion.

Answer 193

The history and the physical appearance of the thoracic wall may suggest a flail chest. The affected section of thorax is often depressed inwards and moves in a different way to the rest of the thorax during breathing. It tends to move inwards on inspiration and move outwards on expiration. Radiography, when appropriate, confirms the presence of a section of rib cage with multiple rib fractures.

Answer 194

Initial management is aimed at minimising the patient’s distress, controlling pain and providing oxygen. If the patient will tolerate it, lying it on the affected side will minimise movement of the flail (fracture) segment which may decrease pain. Otherwise the patient should be allowed to adopt the position it finds most comfortable and be supported there if necessary. If there is a large open wound, it may require to be covered/sealed to prevent deterioration due to a pneumothorax and to limit infection.

Answer 195

Subsequent treatment depends on the severity of the condition but surgery may be required to stabilise the affected section of chest wall. Treatment of any associated pneumothorax may be required in addition. Pain management is vital for these patients to maintain appropriate ventilation and oxygenation. A validated pain scoring scale should be used. If the thorax is splinted to stabilise the flail segment the splints must be checked daily to ensure no friction rubs or pressure sores are developing. As with all our patients a nursing care plan should be developed with focus on the animal’s ability and the areas they will need help with. Oxygen supplementation is likely to be required longer term for these patients so placing a nasal catheter can be beneficial. However, if pain is managed using appropriate techniques, ventilation should not be impaired and oxygen may not be required.

Answer 196

These have several advantages - readily available, easily placed and can achieve a moderate to high FiO2 (~ 0.4 if unilateral and up to 0.8 if bilateral) (Boyle, 2012). However, they are not suitable for brachycephalic breeds, may not be well tolerated and are moderately invasive.

Answer 197

1. Topical lidocaine (no more than 1mg/kg in cats and 2mg/kg in dogs) 2. Lubrication 3. Soft 21-23-gauge IV catheter without needle 4. 3-12 French gauge (depending on the patient size) red soft urinary catheter or naso-oesophageal feeding tube 5. Tape e.g. zinc oxide 6. Luer connector/ tubing adaptor to connect the catheter to oxygen supply 7. Elizabethan collar

Answer 198

Instil local anaesthetic around the nares and into the nasal passages. Allow it time to work. The oxygen catheter is pre-measured to the medial canthus of the eye; lubrication or local anaesthetic gel should be applied to the tip of the catheter.

Answer 199

Elevate the patient’s head and insert the nasal catheter, carefully, to the premeasured depth, aiming ventrally and medially. The catheter can be secured, using a Roman sandal (Chinese finger trap) suture, to the side of the muzzle close to the planum nasale or through the alar fold. Alternatively, it can be secured by applying zinc oxide tape to the lateral alar fold and the forehead. An Elizabethan collar should be applied. On average, one nasal catheter increases the FiO2 to 0.4. A flow rate of 150ml – 200ml/kg/minute of oxygen can be administered this way. Correct placement can be confirmed radiographically. Nasal prongs are easier to place but they will often not stay in position. They are introduced into the nasal cavity and secured behind the ears. The prongs may be taped or sutured in place. A higher flow rate is required. For both, the oxygen should be humidified if longer term use is required.

Answer 200

This technique can be used as a means of providing oxygen in the following situations: 1. Complete pharyngeal or laryngeal airway obstruction e.g. foreign body such as a ball 2. Partial laryngeal obstruction e.g. laryngeal paralysis 3. Severe trauma to the nose and oral cavity when nasal catheterisation would be contra-indicated e.g. post RTA This technique involves percutaneous placement of a sterile catheter into the trachea

Answer 201

Equipment 1. Surgical skin preparation material 2. Clippers 3. Lidocaine in a syringe with 23g needle attached 4. Large bore (14-16 gauge) over the needle catheter 5. Connecting tubing and adaptor 6. Adhesive tape/suturing material

Answer 202

Patient preparation This can be performed in the conscious patient. A 5 cm area in the tracheal region, from the larynx to the mid-trachea, is clipped and surgically prepared. A small amount of local anaesthetic is introduced, subcutaneously, and allowed to take effect.

Answer 203

Method The trachea is secured between fore-finger and thumb and the catheter is inserted in between tracheal rings, in the ventral midline. Once the needle is removed, the catheter should be secured to the skin. Butterfly tape strips, attached to the catheter hub, can be sutured to the skin. A dressing should be placed around the neck; and oxygen supplied at 50 - 100ml/kg/minute or 1-2l/ min. A higher rate should be used if an airway obstruction is present. An FiO2 of ~ 0.6-0.8 is delivered. Incoming air should be humidified.

Answer 204

This may be required to bypass an upper airway obstruction and requires general anaesthesia, unless the patient is unconscious (Boyle, 2012). 1. Complete pharyngeal or laryngeal airway obstruction e.g. foreign body such as a ball 2. Partial laryngeal obstruction e.g. laryngeal paralysis; everted laryngeal saccules (BOAS) 3. Severe trauma to the nose and oral cavity e.g. post RTA

Answer 205

Equipment 1. Surgical preparation material 2. Clippers 3. Surgical kit containing: a. Scalpel handle b. Assorted curved round bodied needles c. Scalpel blade No. 11 d. Retractors e. Curved mosquito haemostats f. Rat-toothed forceps g. Needle holders 4. Non-absorbable monofilament suture material e.g. Prolene® 5. Commercial tracheostomy tube (lumen ~ 50% of the trachea diameter; length ~ 6-7 tracheal rings); or endotracheal tube 6. Piece of old clean drip tubing

Answer 206

Patient preparation The patient is placed in dorsal recumbency. The neck is extended and a foam wedge or sandbag placed underneath the neck to raise the surgical site. The ventral neck just caudal to the larynx is clipped, in the midline, and surgically prepared, rapidly.

Answer 207

Method A ventral midline skin incision is made from the caudal border of the larynx to the 6th tracheal ring and the underlying sternohyoid muscles are split down the midline and retracted laterally to expose the tracheal rings. An incision is made between the third and fourth tracheal rings to enter the tracheal lumen. The trachea is incised by 50-60% of its circumference to allow the tracheostomy tube to be inserted in a cranial to caudal direction. This is aided by placing monofilament non-absorbable stay sutures around the third and fourth rings to allow them to be elevated and abducted. The skin incision is then closed cranially and caudally leaving the area around the tracheostomy tube open. The old drip tubing is then threaded through the flanges on the tracheostomy tube and tied on the dorsal neck.

Answer 208

A patient with a tracheostomy tube requires intensive nursing and continual monitoring especially as an Elizabethan collar will not be appropriate, as it sits at the tube insertion point. Ongoing management of the tracheostomy tube is essential. It needs regular cleaning and sterility should always be maintained. Nebulisation of the tube site aids respiration as it prevents drying out of the mucous airway secretions reducing the likelihood of tube and airway blockage N.B. suction is not recommended (Waddell and King, 2018). 24-hour monitoring is required to check for tube obstruction. It is important to remember that placement of a tracheostomy tube means that incoming gas bypasses the filtering and additional protective functions of the nasal cavity which reduce the chance of infectious microorganisms e.g. bacteria getting into the lower airways. Because of this a patient with a tracheostomy tube is more susceptible to infectious pneumonias

Answer 209

Complications of a tracheostomy tube include haemorrhage after placement, obstruction e.g. mucous, bedding, food; dislodgement; irritation and damage of tissues around the trachea. Additional complications include aspiration pneumonia; drowning; tracheal infection, necrosis, stenosis; pneumomediastinum, subcutaneous emphysema and pneumothorax . An aseptic technique is essential when cleaning the tube and the surrounding area (2-4 times daily depending on the patient). Sterile gloves should always be worn.

Answer 210

Used in patients with pleural space disease caused by fluid or air. It is used both as a diagnostic aid and to relieve respiratory distress. It is contraindicated if a patient has a coagulopathy. Thoracocentesis should be performed before radiography to improve patient safety.

Answer 211

Equipment The following equipment is required for thoracocentesis 1. Surgical skin preparation material 2. Clippers 3. Sterile gloves 4. Intravenous catheter, hypodermic needle or butterfly needle a. Dogs >15kg require catheter/needle 1-1.5 inch; 19-21 gauge (consider the patient’s body condition when selecting- a large amount of subcutaneous fat will necessitate choosing a longer catheter). b. Dogs <10kg and cats require ¾ inch to 1 inch; 21-23 gauge catheter 5. Extension tubing to connect catheter/ needle to three-way tap 6. Three way tap or needle free connector 7. Syringe (preferably 20-50ml) 8. Kidney dish/ jug to measure 9. Selected sterile tubes for sample collection (plain and EDTA), and glass slides for smear

Answer 212

Patient preparation The patient should be oxygenated before starting the procedure. It should be positioned in sternal recumbency or standing, whichever position it appears to tolerate best and without compromising its breathing further. Many patients will tolerate this procedure with minimal if any restraint required. Cardiovascular sparing sedation may be required if it cannot be restrained without causing stress. The appropriate area of the thorax should be clipped - about 5 cm around the intended insertion point. It is likely that thoracocentesis will be performed bilaterally unless the condition is known to be unilateral. • if fluid is anticipated, the needle insertion point is the 7 th or 8th intercostal space at the costo-chondral junction i.e. ventral thorax • if air is anticipated, the needle insertion point is the 8th or 9th intercostal space about two thirds of the height of the thorax (midway between the vertebral bodies and the costochondral junction) i.e. dorsal thorax.

Answer 213

if fluid is anticipated, the needle insertion point is the 7 | th or 8th intercostal space at the costo-chondral junction i.e. ventral thorax

Answer 214

if air is anticipated, the needle insertion point is the 8th or 9th intercostal space about two thirds of the height of the thorax (midway between the vertebral bodies and the costochondral junction) i.e. dorsal thorax.

Answer 215

Method As this technique involves entry into a body cavity, by law it must be performed by a veterinary surgeon. It is, however, very important for the RVN to be fully aware of the procedure to support the patient and VS appropriately. Asepsis must be maintained, so appropriate hand hygiene should be performed and sterile gloves worn. The needle (already attached to the connection tubing, three way tap and syringe) is inserted through the intercostal space, whilst gentle negative pressure is applied to the syringe plunger. For a pleural effusion, the needle is usually inserted level with the costo-chondral junction between the 7th and 8th ribs (7th intercostal space). If a pneumothorax is suspected, the needle is inserted one third of the way down the chest, from the dorsal surface, between the 8th and 9th ribs (8th intercostal space). The needle is introduced cranial to the rib margin to avoid the intercostal nerves. It is important to keep the patient still as the needle is being inserted to avoid the intercostal blood vessels and nerves. Touching the intercostal nerves may cause pain to the patient. The needle is directed in a dorsal or ventral direction parallel to the ribcage, depending on whether fluid or air is anticipated. If the VS can feel the lungs rubbing backwards and forwards against the end of the needle, the needle will be withdrawn slightly. If a large amount of frank blood appears, 1-2 ml should be put into a plain tube to check for clotting. Any other fluid should be aspirated until it is completely removed and then the needle is removed from the thorax. Once a sample has been collected a sample of this should be placed into a sterile tube for culture and sensitivity; some placed into a potassium EDTA tube for cytological analysis and a fresh smear made. The patient should be returned to its kennel and observed closely after the procedure. There should be a dramatic improvement in the patient’s respiratory rate and effort over a relatively short period of time – it is however important to consider that the effusion or air can re-accumulate rapidly.

Answer 216

Rationale A chest drain/tube (thoracostomy) may be placed in the following situations 1. Pyothorax 2. Tension pneumothorax 3. Recurrent pneumothorax 4. Rapidly forming/recurring pleural effusion 5. Post-operative management following thoracotomy (e.g. diaphragmatic hernia repair)

Answer 217

This allows for continuous or intermittent aspiration of fluid or air from the thorax to improve the patient’s breathing. A patient with a chest drain requires continuous, intensive 24-hour monitoring.

Answer 218

Thoracostomy is contraindicated in a patient with severe coagulopathy

Answer 219

There are three techniques for tube placement – closed/tunnelling; closed/ skin pulled cranially and Seldinger technique. The choice of technique will depend on the size of the patient, its suitability for general anaesthesia, the nature of the effusion and equipment availability

Answer 220

Equipment This should include the following equipment: 1. Surgical skin preparation material 2. Clippers 3. Sterile gloves 4. Chest drain and connectors-there are various commercially available tubes 5. Local anaesthetic (lidocaine) 6. Scalpel blade and handle 7. Three-way tap or needle free connector 8. Suture material and/or SULL connector 9. Haemostats 10. Rat toothed forceps 11. +/- pleural drain system (water seal drain or Heimlich valve: although the latter should not be used in patients less than 15kg)

Answer 221

The patient usually requires a general anaesthetic which has the advantage of securing the airway; although in compromised patients, and depending on the type of chest drain used, sedation and local anaesthetic may be enough, especially in dogs. A narrow bore, wire-guided chest drain can be placed in a conscious patient using the Seldinger technique but is less suitable for a viscous effusion. Careful decision making is indicated when considering sedation versus anaesthesia. General anaesthesia means an endotracheal tube can be placed which means the patient has a patent airway and its ventilation can be supported in a safe manner. Whilst the anaesthetic agents can have harmful side-effects e.g. hypotension, the risks can usually be mitigated somewhat by multi modal techniques. The patient is placed in lateral recumbency and the lateral thoracic wall from the scapula to the last rib is clipped and surgically prepared. Drains may be required bilaterally. The area is draped and the technique is performed aseptically

Answer 222

There are many commercially available chest drains- newer drains are made of silicone or polyvinyl (Lombardi et al, 2012) which are more flexible and less irritant. Some have stylets to aid introduction and some use a trocar although there is a risk of iatrogenic damage especially in a cat. The type of drain and size used will depend on the patient size and what is being aspirated. Narrow bore tubes are less traumatic to place, may be better tolerated but are more likely to obstruct. Wider bore tubes are required for fluid, especially pus which is quite thick. Local anaesthetic may be injected locally or an intercostal nerve block may be performed. The tube should be premeasured prior to placement in the thorax. For placement three techniques may be used: 1. A stab incision is made in the skin, dorsally at the 9th or 10th intercostal space. The chest tube is then tunnelled in the subcutaneous space from the incision site to the level of the 7th or 8th intercostal space. It is then introduced into the pleural space, through the intercostal muscles. Many chest drains have trocars to aid placement- great care is required if a trocar is used in a cat. If a trocar is not used, the drain must be tunnelled and introduced into the thorax using a haemostat. If the patient is being manually ventilated, this may be temporarily halted, whilst the tube is inserted, to avoid lung damage. 2. An assistant pulls the thoracic skin cranially; the surgeon creates a stab skin incision at the 7th or 8th intercostal space and then introduces the drain into the pleural space by blunt dissection. Again, IPPV should be temporarily halted at this stage to ensure the lungs are deflated. When the assistant lets the skin go, it will return to the normal position meaning there will not be a skin wound directly over the entry point into the thorax, thus reducing the risk of pneumothorax. 3. Wire-guided/ Seldinger technique. A commercial kit is available for this. The technique is like placement of a central venous catheter. The patient may not need to be anaesthetised for this technique but will probably require to be sedated (Waddell and King, 2018). A catheter is introduced through the skin ~ 9-10th intercostal space and tunnelled cranially before being introduced into the thorax ~ 8th intercostal space. A wire is then placed through the catheter Once placed, the tube should then be connected to a three-way tap/ needle free connector and appropriate connection tubing, or a pleural drainage system. Any effusion should be aspirated at this stage- a sample may be kept for analysis. The volume of effusion should be recorded. There should always be at least two points of closure on the tube e.g. gate clamp. This should be closed before the tube is secured to the skin, using a Roman Sandal suture (Chinese finger-snare suture), or SULL connector. A purse string suture may be placed in the skin wound. Two orthogonal radiographs must be taken to ensure the tube is correctly placed. The tube should be bandaged in place or a body stocking used; and an Elizabethan collar applied to the patient to prevent removal. The patient should be assessed carefully for pain- adequate analgesia is essential for recovery. Opioids +/- NSAIDs (if cardiovascularly stable) can be administered parenterally and local anaesthetic (bupivacaine) administered via intercostal/ intrapleural nerve blocks etc

Answer 223

A stab incision is made in the skin, dorsally at the 9th or 10th intercostal space. The chest tube is then tunnelled in the subcutaneous space from the incision site to the level of the 7th or 8th intercostal space. It is then introduced into the pleural space, through the intercostal muscles. Many chest drains have trocars to aid placement- great care is required if a trocar is used in a cat. If a trocar is not used, the drain must be tunnelled and introduced into the thorax using a haemostat. If the patient is being manually ventilated, this may be temporarily halted, whilst the tube is inserted, to avoid lung damage.

Answer 224

An assistant pulls the thoracic skin cranially; the surgeon creates a stab skin incision at the 7th or 8th intercostal space and then introduces the drain into the pleural space by blunt dissection. Again, IPPV should be temporarily halted at this stage to ensure the lungs are deflated. When the assistant lets the skin go, it will return to the normal position meaning there will not be a skin wound directly over the entry point into the thorax, thus reducing the risk of pneumothorax.

Answer 225

Wire-guided/ Seldinger technique. A commercial kit is available for this. The technique is like placement of a central venous catheter. The patient may not need to be anaesthetised for this technique but will probably require to be sedated (Waddell and King, 2018). A catheter is introduced through the skin ~ 9-10th intercostal space and tunnelled cranially before being introduced into the thorax ~ 8th intercostal space. A wire is then placed through the catheter into the thorax and the catheter is then removed. The chest drain is then fed over the wire into the thorax. The wire is removed

Answer 226

The thorax may either be drained manually (intermittently) with a gated/ three-way tap arrangement or a continuously using a drainage system (active or passive). A Heimlich valve is a one-way valve which drains into a collection device. Because it is a one-way system, fluid and air cannot return to the thorax. To function correctly the Heimlich valve must be the correct size for the patient (>15 kg) – it is not suitable for small dogs or cats (Murgia, 2015) – if it is too large the patient’s respiratory effort will not be enough to open the unidirectional valve (ECPD, 2013). Strict asepsis must be maintained when handling the tube and surrounding tissues. For manual drainage, the frequency of drainage is case dependent but will usually be every 1-4 hours. If using a three-way tap, once there is negative pressure drainage should be stopped to minimise the risk of damage to the pleura. The volume and nature of the effusion should be recorded

Answer 227

A Heimlich valve is a one-way valve which drains into a collection device. Because it is a one-way system, fluid and air cannot return to the thorax. To function correctly the Heimlich valve must be the correct size for the patient (>15 kg) – it is not suitable for small dogs or cats (Murgia, 2015) – if it is too large the patient’s respiratory effort will not be enough to open the unidirectional valve

Answer 228

The tube needs to be monitored 24 hours a day to ensure it does not become blocked or kinked; or more seriously, disconnected which would cause a pneumothorax to develop. The thoracostomy site should be assessed and cleaned at least daily to identify any wound issues or signs of infection- redness, discharge, pain, heat etc. The sutures and position of the tube should be checked regularly to ensure there is no sign of dislodgement. The dressing/ bandage should be changed daily. If subcutaneous emphysema develops, the VS should be informed (Lombardi et al, 2012). Horner’s syndrome is a potential complication of a chest drain in a cat. Hospital acquired/ nosocomial infection is a risk so the patient should be monitored closely for any sign of infection and sepsis.

Answer 229

Drainage can stop when the output is < 2-4 ml/kg/day- the veterinary surgeon should be alerted so removal of the tube can be planned.

Answer 230

. In a normal patient, each haemoglobin molecule will carry 4 molecules of oxygen.

Answer 231

Pulse oximeters use light to measure the saturation of haemoglobin with oxygen i.e. how much oxygen is attached to the haemoglobin molecules

Answer 232

Whilst pulse oximetry is not as accurate as arterial blood gas analysis, it is non-invasive and is a relatively effective way of monitoring oxygenation especially in less critical patients. As discussed previously, the relationship between the PaO2 (the amount of oxygen in arterial blood) and the amount of oxygen attached to haemoglobin (SaO2), however, is not a linear one; instead it follows a sigmoid curve- the PaO2 may decline significantly before SaO2 starts to drop. This makes interpretation of pulse oximeter results slightly complicated.

Answer 233

Normally, the SpO2 of arterial blood should be ~ 95% or more. SpO2 is the SaO2 when measured with a pulse oximeter

Answer 234

Full haemoglobin saturation (>90%) occurs with a PaO2 of around 70 mmHg

Answer 235

SpO2 readings of >95% are acceptable in normal animals breathing room air. Once SpO2 levels drop below 94% though, supplemental oxygen should be provided; and once levels drop below 90%, the oxygenation levels start to become critical.

Answer 236

This is the partial pressure of oxygen dissolved in arterial blood and is generally around 90 – 100 mmHg for a normal animal breathing room air. As mentioned previously, the binding of oxygen to haemoglobin follows a sigmoid curve.

Answer 237

The PaO2 level is generally is around 5 times the inspired oxygen concentration, therefore an animal on 100% inspired oxygen should have a PaO2 of around 500. Most of the oxygen, however, is bound to haemoglobin and relatively little is present as dissolved oxygen in the plasma. Therefore, once the haemoglobin is saturated with oxygen, little if any increase in arterial oxygen can occur

Answer 238

The normal PaO2 level is 90-100 mmHg. A patient with a PaO2 < 80 mmHg is considered hypoxaemic and less than 50mmHg is life-threatening. Patients with PaO2 below 70 mmHg require immediate oxygenation.

Answer 239

Decreased PaO2 can occur due to: • lowered inspired oxygen level • hypoventilation • mixing of arterial blood with venous blood. This can occur with shunting of blood that by-passes the gaseous exchange areas of the lungs e.g. blood going to consolidated or atelectic areas of the lungs. • a ventilation-perfusion mismatch - where the normal supply of blood to the functional alveoli is altered e.g. pulmonary thrombo-embolism. This fails to maximise oxygen uptake into the bloodstream. • decreased diffusion of oxygen from alveoli into pulmonary capillaries e.g. fluid in alveoli (oedema/pneumonia etc.).

Answer 240

for various reasons, the level of oxygen (PaO2) in pulmonary capillaries/arterioles is normally slightly lower than the oxygen level in alveoli (PAO2). This creates an alveolar-arterial oxygen gradient (PAaO2).

Answer 241

The alveolar–arterial gradient (PA-aO2), is the difference between the alveolar concentration (A) of oxygen and the arterial (a) concentration of oxygen. The normal alveolar-arterial oxygen gradient is around 15 mmHg. Calculating the alveolar–arterial gradient can help to establish the reason for hypoxaemia.

Answer 242

Calculation of the alveolar-arterial oxygen gradient (PA-aO2) allows an estimate of the success of gas transfer across the alveolar-arterial surface, without considering the rate of ventilation. It is therefore possible to surmise that as respiratory dysfunction worsens, the PA-aO2 gradient will increase i.e. the amount of oxygen in the alveoli will be much greater than that in the pulmonary capillaries.

Answer 243

To calculate the alveolar-arterial oxygen gradient (PA-aO2) it is first necessary to estimate the partial pressure of oxygen in the alveoli (PAO2). The following equation is used: PAO2 = FiO2 (Pb-PH20) - PaCO2/RQ ➢ FiO2 is the fractional inspired oxygen concentration ➢ Pb is the barometric pressure ➢ PH2O is the saturated water pressure at body temperature ➢ PaCO2 is the arterial level of CO2 ➢ RQ is the respiratory quotient. At sea level, with normal room air, the equation is simplified to calculate alveolar oxygen partial pressure (PAO2) as: PAO2 = 150 – (PaCO2) x 1.1 The RQ for a dog is assumed to be 0.9. From this, the alveolar-arterial oxygen gradient (PA-aO2) is then calculated as PA-aO2 = PAO2 - PaO2 The alveolar-arterial oxygen gradient is generally around 15mmHg.

Answer 244

An increased PA-aO2 gradient will be seen with parenchymal lung disease due to decreased gas diffusion.

Answer 245

alveolar-arterial oxygen gradient

Answer 246

The alveolar-arterial oxygen gradient is, however, likely to be normal if the patient is hypoxic secondary to hypoventilation. If there is no parenchymal lung disease, the hypoxia is due to ineffective breathing rather than ineffective transfer of oxygen.

Answer 247

The ratio PaO2:FiO2 is useful to compare serial samples that are obtained at different concentrations of inspired air. Normal ratios are >400; values less than 200 suggest severe lung disease.

Answer 248

``` Hypoventilation may be due to: • damage to the midbrain or hindbrain (pons and medulla) or deep anaesthesia interfering with function • upper cervical spinal cord injury • a thoracic wall injury or restriction • respiratory muscle damage • airway obstruction • certain medications ```

Answer 249

Removal of carbon dioxide from the blood stream alters the arterial CO2 levels and so affects PaCO2. Carbon dioxide diffuses from the pulmonary capillaries, into the alveoli and is exhaled. The amount of CO2 in the bloodstream is largely dictated by tissue production. As this CO2 is transported away from cells in veins, the venous level of CO2 (PvCO2) is directly influenced by cellular production. The arterial level of CO2, PaCO2, however, is almost totally influenced by lung ventilation and gas exchange at the alveoli - blood interface e.g. pulmonary capillaries.

Answer 250

Hypoventilation leads to elevated PaCO2 as less CO2 is exhaled.

Answer 251

Hyperventilation, such as can occur in stress and panic situations, results in a lowered PaCO2 as more CO2 is exhaled.

Answer 252

Normal PaCO2 levels are ~ 37 mmHg (32-45 mmHg).

Answer 253

PaCO2 levels above 50mmHg are significant, indicating hypoventilation, and requiring treatment; levels above 70mmHg are imminently life-threatening as the patient will be profoundly hypoxic with a respiratory acidosis.

Answer 254

PaCO2 levels below 20mmHg, due to hyperventilation, can result in excessive cerebral vasoconstriction. This can cause cerebral hypoxia and can also be lifethreatening.

Answer 255

End-tidal capnography is an indirect method of monitoring respiration. The capnograph is either a side-flow or direct stream sensor device that measures the CO2 in expired air. This end-tidal CO2 level equates almost exactly with the CO2 present in the alveoli, during the mid to end part of expiration (in normal lungs only).

Answer 256

‘Capnography provides a non-invasive method that permits the assessment of the adequacy of patient ventilation, systemic metabolism, cardiac output and pulmonary perfusion in a variety of clinical situations

Answer 257

This end-tidal CO2 level equates almost exactly with the CO2 present in the alveoli, during the mid to end part of expiration (in normal lungs only).

Answer 258

During the initial phase of expiration, the CO2 levels measured are quite low, as this is air coming from the anatomic dead space where no gas exchange has occurred (e.g. the trachea and bronchi etc.). The CO2 levels increase as expiration proceeds and plateau before decreasing again during the expiratory pause:

Answer 259

Normal values of the plateau of expired CO2 should be in the 35-45 mmHg range and approximate the venous partial pressure of CO2.

Answer 260

If levels exceed 50mmHg, this equates to hypoventilation.

Answer 261

Trans-tracheal sampling This can be used in larger breeds of dog and may be performed without sedation. The ventral neck is clipped and surgically prepared over the trachea, caudal to the larynx. Local anaesthetic is infiltrated over the insertion site. An 18 gauge, through the needle, catheter is then introduced through the skin, between two cartilage rings into the lumen of the trachea – the precise choice of rings is not important. The catheter is then fed through the needle down into the lumen of the trachea and extended to a depth of around 20cm in dogs of 10-20kg; and 30cm in dogs of 20- 35kg. 5-10ml of sterile 0.9% saline is flushed through the catheter and coupage is performed to aid mixing. The sample is then aspirated and samples taken for culture and sensitivity and cytological analysis For dogs, smaller than 10kg, and cats, a direct endotracheal sample or bronchoalveolar lavage (BAL) is preferred- this requires general anaesthesia. A sterile endotracheal tube is required and it is important to avoid oral contamination when introducing the catheter.

Answer 262

The correct answer is: Yorkshire Terrier

Answer 263

The correct answer is: .......hyperthermic and tachypnoeic

Answer 264

The correct answer is: French Bulldog

Answer 265

The correct answer is: Bronchodilation

Answer 266

The correct answer is: The patient is unlikely to cough

Answer 267

The correct answer is: Glaucoma

Answer 268

The correct answer is: Arterial blood gas analysis

Answer 269

``` Congestive cardiac failure Haemorrhage Pyothorax/ infection e.g. bacterial or fungal Diaphragmatic rupture Feline infectious peritonitis Neoplasia Trauma e.g. ruptured oesophagus or chest wound Lung lobe torsion ```