U2 O1 - Monitoring the critical patient Flashcards
Why are the three major body systems the most important at assessing in an emergency when failure of other body systems can also lead to death?
The three body systems that should be assessed initially in the critically ill/ trauma
patient are the neurological, cardiovascular and respiratory systems. Some sources
will add in the renal system which is, of course, also important. However, with
emergency and critical care cases, the major body systems that are assessed are
those that that can lead to death within minutes and not hours if not functioning.
Why is it important to monitor trends?
Monitoring of trends, especially, is highly effective at identifying the stable versus the unstable patient; and the improving versus the deteriorating
patient. Monitoring trends involves comparing variables over a timescale e.g. respiratory rate, pulse rate, pulse strength, serum lactate etc. (Bradbrook, 2013). If a patient admitted for observation following a road traffic accident, became increasingly dull, with an increasing heart rate, increasing respiratory rate and
weakening/ absent peripheral pulses, the trends would be of concern. This patient does not have stable cardiovascular, respiratory and neurological parameters- there could be an undetected problem e.g. internal haemorrhage. It should be noted that
following a traumatic incident some abnormalities are not always apparent on admission of the patient to the hospital. For example, a patient could develop pulmonary contusions over a period of hours following blunt trauma to the chest.
Ongoing diligent monitoring is vital for the emergency presentation and will often be the task of the registered veterinary nurse.
What are the key principles to guide the care of the small animal ICU patient?
Key principles to guide the care of the small animal
ICU patient.
• Treat the most life‐threatening problem first
• Treat the patient, not the numbers
• Anticipate the worst and be ready for it
• Provide the right treatment, at the right time, in the right amount
• Examine the cause of the problem and the effect on the patient
• Weigh the pros and cons of every drug and procedure
• There is not a drug for every problem – less is best
• If it has not been written down, it has not been done
• Never ignore your gut feeling
• Things are done in the order of importance
What is the aim of Kirbys rule of 20?
Problems within the major organ systems should be anticipated in advance, with appropriate diagnostic, therapeutic, and monitoring efforts employed early, rather than waiting for a problem to surface and reacting to it. The Rule of 20 was developed to assist the critical care team in thoughtfully and carefully assessing these patients.
What are kirbys rule of 20 parameters?
Fluid balance Blood pressure Albumin, COP Glucose Electrolytes Acid – base Oxygenation/ventilation Coagulation Red blood cell status Heart rate, rhythm, contractility Neurological status Urinary tract status WBC, Immune status GI tract status Nutritional status Drug dosing, metabolism Body temperature Pain control Wound and bandage care Nursing care, TLC
The Rule of 20. Each parameter should be assessed regularly in any critically ill dog or cat. The order of importance will vary between individual patients. COP, colloidal osmotic pressure; GI, gastrointestinal,
TLC, tender loving care; WBC, white blood cell.
What history should be ascertained from the owner of a critically ill patient?
Signalment Alert for age, breed and intact reproductive
tract related disorders
Presenting complaint Noted by staff at time of presentation and recorded. Best not to start history with this inquiry in order to control the historical
sequence of the problem
Last normal Inquire when patient was last absolutely
normal, may be abnormal prior to presenting
complaint. Differentiates peracute, acute,
chronic, and acute‐on‐chronic problems
Progression Outline of sequence of changes occurring in the patient from the time of “Last normal”
until the present day
Characterization of problems
Identified problems are characterized (such as volume, rate, consistency, color, sound, intensity, duration). Individual problems in the Rule of 20 are discussed in individual chapters
Systems review Report on problems or systems not discussed related to the current problems and
progression. Examples include: vomiting, diarrhea, coughing, sneezing, nasal or ocular discharge, seizures, fainting, weakness, water
intake, urination frequency and effort, urine color, stool consistency
Past medical history Vaccination, heartworm, and parasite control are listed. Any blood transfusions, problems with anesthesia or sedation are reported. Past medical problems and laboratory results of
concern
Medications List prescribed, over the counter and
supplements given to the animal. Medications
taken by the owner may be important if patient exposure is possible Exposure to toxins or infectious disease Inquire about the patient environment
including outdoor habits, ill animals or people,
groups of animals, new products or people
and other lifestyle habits
Nutrition Inquire about type, quantity, and brand of
food, feeding routine, appetite, access to
water, weight gain or loss
What should be determined when assessing the cardiovascular system?
When examining the cardiovascular system, the focus should be upon determining if there is adequate tissue perfusion.
What should be assessed when checking the cardiovascular system?
The patient’s mentation should be judged as
appropriate or not - decreased cerebral perfusion will result in behaviour changes
e.g. the patient is obtunded or stuporous etc. Mucous membranes should be assessed regularly to ensure that they are a normal, pink colour and the capillary
refill time (CRT) is normal (1-2 seconds). Both an abnormally slow and an abnormally rapid CRT would be a significant finding.
Central and peripheral pulses should be regularly palpated to ensure that they are
strong and synchronous. Any change from normal should prompt further investigation of the cardiovascular system e.g. in a dog a palpable femoral pulse but absent dorsal pedal pulse would be a significant finding that should prompt thorough
re-evaluation of the cardiovascular system, including arterial blood pressure monitoring
Auscultation of the heart is important to detect the heart rate and rhythm. Additional
finding such as muffled or abnormal heart sounds e.g. murmurs should be recorded.
What does an ECG monitor?
ECG uses the electrical impulses generated by the cardiac conduction system to create a tracing which can be used for monitoring both the heart rate and rhythm.The ECG monitors and transmits electrical activity at the body surface to create the ECG trace.
What does an ECG not assess?
It does not, however, give any indication of heart function i.e. the ability of the
myocardium to contract nor if the patient is in heart failure.
What common ECG disturbances can be seen in critically ill patients?
Common ECG disturbances, in critically ill patients, include sinus tachycardia, sinus bradycardia, accelerated idioventricular (pertaining to the cardiac ventricle alone) rhythm, premature ventricular complexes and ventricular tachycardia. ECG
manifestations of hyperkalaemia (spiked T waves, prolonged PR interval, loss of P waves and widening of the QRS) may occur in patients with urinary tract dysfunction resulting in decreased urine output e.g. bladder rupture or urethral obstruction
Why is it important to perform an ECG on an animal with hyperkalemia?
Hyperkalaemia can cause a fatal cardiac arrythmia so prompt recognition of ECG
changes suggestive of it are crucial.
What factors depend on whether cardiac dysrhythmias require treatment?
The need to treat and choice of treatment for cardiac dysrhythmias is dependent on various factors- heart rate, clinical signs, evidence of perfusion abnormalities, underlying cause and presence of specific ECG changes e.g. multiform complexes or the ‘R on T’ phenomenon.
How do you determine if a patient has an accelerated idioventricular rhythm on an ECG?
It is likely that a dog has an accelerated idioventricular rhythm if there are four or more consecutive ventricular ectopic beats/ ventricular premature contraction (VPCs) but the heart rate is ≤ ~ 140 beats per minute.
Does an accelerated idioventricular rhythm on an ECG require treatment?
In the absence of perfusion abnormalities attributed to this rhythm, definitive treatment with an antidysrhythmic is not warranted as the treatment may lead to serious side-effects. Maintenance of
euvolaemia (normal blood volume), adequate oxygenation, and normal acid-base and electrolyte status is indicated.
Dysrhythmias resulting in decreased perfusion, as evidenced by clinical signs (e.g. depression, syncope, poor pulse quality, pale mucous membranes, cool extremities, prolonged CRT) or objective means (hypotension, hyperlactataemia) will required
additional treatment following correction of hypovolaemia and hypoxaemia.
What is blood pressure a marker for?
Blood pressure can be used as a surrogate marker of blood flow to tissues e.g. low blood pressure would indicate decreased perfusion.
Why might a patient with decreased perfusion have a normal blood pressure reading?
Blood pressure can be used as a surrogate marker of blood flow to tissues e.g. low blood pressure would indicate decreased perfusion. However, in some patients, intense peripheral vasoconstriction because of compensatory mechanisms in response to e.g. blood loss may result in an ‘adequate’ blood pressure reading (Thomovsky, 2013). This patient would, however, have minimal perfusion/ blood flow to the periphery despite a normal blood pressure reading- thus it is important to record blood pressure alongside other observations for it to be meaningful. Different vascular beds in the body may have differing blood flow (perfusion) at the same blood pressure.
What is the normal systolic blood pressure for a dog?
Systolic pressures of ~110-160 mmHg
What is the normal diastolic blood pressure for a dog?
Diastolic pressures of~ 55-110 mmHg
What is the normal mean blood pressure for a dog?
Mean pressure of ~100 mmHg
What is the normal systolic blood pressure for a cat?
Systolic pressures of ~120-170 mmHg
What is the normal diastolic blood pressure for a cat?
Diastolic pressure of ~70-120mmHg
What is the normal mean blood pressure for a cat?
Mean pressure of ~ 135 mmHg
When does hypertension become a concern?
Hypertension becomes a concern when systolic pressure increases above 170 mmHg, or diastolic pressure is greater than 110 mmHg.
Following trauma what would be a concern with blood pressure and heart rate which could indicate intracranial pressure?
Following head trauma, a systolic blood pressure recording of greater than 140 mmHg (with a heart rate of less than 100 beats per minute) could be an
indication of increased intracranial pressure (ICP).
What detrimental effects could hypertension cause in the body?
Hypertension can cause end-organ injury including retinal detachment and
glomerular damage.
What could elevations in arterial blood pressure be a result of?
Elevations in arterial blood pressure result from pain, fear, raised intracranial pressure, metabolic and endocrine diseases, renal and cardiac disease, and
various medications
At what low level blood pressure should be addressed?
Systolic blood pressure of less than 100 mmHg or mean arterial pressure of less than 65 mmHg should be addressed. The lower the value the more
serious the condition.
In the trauma patient what can low blood pressure be a result of?
In the trauma patient, low blood pressure can result from reduced cardiac output secondary to hypovolaemia, myocardial failure and dysrhythmias
What two categories can arterial be measured by?
Options include direct arterial blood pressure monitoring, which requires the insertion
of a catheter into an artery; or more commonly, indirect blood pressure monitoring.
What does indirect blood pressure monitoring involve?
It relies on the inflation of a cuff to occlude an artery and therefore temporarily prevent blood flow in it; followed by measurement of the pressure at which blood flow returns when the cuff is gradually deflated. The inflatable cuff is attached to a sphygmomanometer or, directly, to an oscillometric blood pressure monitoring
system.
What position should the patient be in to get the most accurate reading for direct blood pressure monitoring?
The patient should be kept still, in lateral recumbency, to get the most accurate readings with the cuff level with the right atrium
What are the benefits of indirect blood pressure monitoring?
Non-invasive blood pressure monitoring is readily available, relatively cheap and
easy to use
How do you select the correct cuff size for patient for indirect blood pressure monitoring?
Appropriate cuff size selection is important; the cuff should be 40% of the circumference of the limb for dogs; the cuff width should be 30- 40% of the width of
the limb in cats
How might results be inaccurate if the cuff size for indirect blood pressure monitoring is too large?
Cuffs that are too large will give falsely low pressure readings.
How might results be inaccurate if the cuff size for indirect blood pressure monitoring is too small?
Cuffs that are too small will generate falsely high pressure readings.
How does a doppler measure blood pressure?
This uses ultrasound waves to detect arterial blood flow and turns it into an audible signal. Earphones should be used to avoid the noise of the ultrasound causing increased patient stress
A 10-MHz ultrasound probe is placed over an artery distal to the cuff. The Doppler
sounds become audible when pressure in the cuff is less than pressure in the artery.
What type of blood pressure does a doppler measure?
Doppler ultrasonographic determination of blood pressure is thought to provide a systolic blood pressure measurement and can be used in all small animals. In cats it is thought to be closer to the mean arterial blood pressure.
What common arteries are used for doppler blood pressure?
Common arteries used for Doppler blood pressure measurement include the dorsal metatarsal, the plantar metatarsal, the palmar metacarpal, the ulnar and the coccygeal arteries.
How does oscillometric blood pressure measurement work?
These monitors utilise vibrations, conducted to adjacent tissues by the return of
blood flow to the occluded artery, to measure mean arterial blood pressure. The
machine uses algorithms to calculate systolic and diastolic blood pressure from the
mean arterial blood pressure. Oscillometry is often incorporated into multi-parameter
patient monitors where the blood pressure is recorded and the pulse is shown on the
screen. The cuff must fit snugly so that the
oscillometric blood pressure monitor is able to detect tissue vibrations.
What is the main advantage to using oscillometric blood pressure monitoring?
One advantage of oscillometry is that is automated – this means there is less
reliance on user technique being correct and it can be less stressful for the patient.
What areas can oscillometric cuffs be placed?
The oscillometry cuff can be placed on the forelimb, hindlimb or the tail - midantebrachium and the metatarsus. Bradbrook (2013) reports that using the
metatarsus is more reliable than the metacarpus.
What could cause oscillometric readings to be unreliable?
The accuracy of the readings is limited in patients
with peripheral vasoconstriction, patients who are moving/ shivering or patients with dysrhythmias. The cuff may also not fit snugly enough in very hairy patients to obtain accurate readings.
What is considered to be gold standard for the determination of blood pressure in veterinary patients?
Direct arterial blood pressure (invasive) measurement is considered the gold standard for the determination of blood pressure in human and veterinary patients
What information does direct arterial blood pressure invasive give you?
It enables continuous reading of systolic, diastolic and
mean arterial blood pressure, giving beat by beat information and enabling rapid
response to changes. This technique is mainly used for ECC patients requiring
intensive care
When is invasive direct arterial blood pressure indicated?
it is mainly ‘indicated in patients with severe haemodynamic abnormalities to assess the response to therapy and to monitor for any deterioration’
When is the placement of invasive arterial blood pressure contraindicated?
It is invasive and there are several potential
complications to be aware of. Direct arterial blood pressure monitoring is not indicated in healthy patients that are ambulatory due to the associated risks of the
procedure. There is a greater likelihood that a mobile patient could disconnect the line or remove the catheter, causing arterial haemorrhage
Arterial catheter placement is absolutely contraindicated in a patient with a
coagulopathy, or an injury/ wound on the limb of the proposed placement site; it is relatively contraindicated in a patient that is ambulatory or a patient that will not be monitored continually on a 1:1 basis due to the risk of serious blood loss.
Where is the catheter placed for direct arterial blood pressure measurement?
Direct arterial blood pressure measurement involves catheterisation of a peripheral artery. Whilst possible in cats, it is more technically demanding
If necessary, a cut down to the
dorsal metatarsal or femoral artery can be performed.
Describe the technique for placement of an arterial catheter for direct blood pressure measurement?
The arterial catheter is connected to a pressure transducer via a fluid-filled tubing system. Non-compliant tubing must be used to avoid dampening of the pressure signal
• The pressure transducer converts the mechanical signals induced by pulsatile
arterial pressure to electrical signals that are then recorded, quantitated and
displayed graphically.
• Most commercially available arterial blood pressure recording systems
provide a continuous delivery of a heparinised, isotonic solution, at 1-3mL/hr,
to prevent catheter occlusion.
• A catheter is most often placed in the dorsal metatarsal artery - although the
femoral, auricular, plantar metatarsal and plantar metacarpal arteries may
also be used. Some anaesthetists use the coccygeal artery in cats
(Bradbrook, 2013).
• Local anaesthetic cream (EMLA™) should be used in the conscious patient
as this can be a painful procedure
• The site should be aseptically prepared and the patient adequately restrained.
• After palpation of the metatarsal pulse, the catheter should be advanced through the skin and directed towards the artery. The angle is steeper than
when placing a peripheral venous catheter- insertion into the artery is normally achieved at an angle up to 45 degrees. Once the artery is punctured
with the catheter stylet, a flash of arterial blood will be seen in the hub of the stylet and it should fill readily due to arterial blood pressure. The entire
catheter and stylet should be advanced forward 1-2 mm to allow the distal tip of the catheter to penetrate the vessel lumen. At this point, the angle of the catheter to the artery is decreased and the catheter advanced off the stylet into the artery.
• Once the catheter is in the artery, it should be connected to the pressure monitoring system or a length of low compliance IV extension tubing, flushed
with saline, and occluded with an injection cap. The arterial catheter is then taped very securely and labelled as “arterial” so that it is not mistakenly used
for the administration of fluids or medications.
What type of blood pressure monitoring is the most reliable in hypoperfused patient and patients with peripheral vasoconstriction?
Direct arterial blood pressure measurement is reliable in hypoperfused patients and
patients with peripheral vasoconstriction, though placing an arterial catheter during
these situations is more technically challenging.
What are some do’s and don’t’s for using an arterial blood pressure catheter?
Direct arterial blood pressure measurement is reliable in hypoperfused patients and
patients with peripheral vasoconstriction, though placing an arterial catheter during
these situations is more technically challenging.
An arterial catheter may be used to obtain blood for arterial blood gas determination
- a strict aseptic technique must be performed.
What does central venous pressure represent?
CVP represents the hydrostatic pressure in the intrathoracic vena cava and provides
an assessment of right-sided preload. The CVP is equal to the pressure in the right atrium which, in turn, is equal to the pressure in the right ventricle as the tricuspid valve opens (e.g. end-diastolic pressure). CVP is therefore, an indirect reflection of intravascular volume- the pressure decreases as the blood volume decreases and vice versus
What is central venous pressure most useful for monitoring?
CVP measurement is most useful in for monitoring the acute resuscitation of patients with hypovolaemia. It is also useful in ensuring optimal blood volume in patients with oliguric/anuric renal failure; and to rule out heart disease. Additionally, it can be especially useful for monitoring patients with cardiac failure that need fluid therapy -it allows for careful titration of intravenous fluids to avoid volume overload.
Where is a central venous line usually placed?
CVP is usually recorded following placement of a jugular catheter. In the absence of
significant intra-abdominal disease, CVP can also be measured via placement of a catheter into the caudal vena cava, via the femoral vein. Most commonly, however, a peripherally inserted central line (PICC line) is used. The insertion sites are the lateral saphenous vein in dogs and the medial saphenous vein in cats
What are the contraindications for placing a jugular catheter?
Contraindications to jugular catheter placement include coagulopathy, skin infection,
increased intracranial pressure and increased risk of thromboembolism.
Describe the technique for placement of an central venous catheter for direct blood pressure measurement?
CVP monitoring requires the percutaneous or surgical placement of a catheter. The tip of the catheter should be positioned just outside the right atrium in the cranial vena cava.
• Appropriate catheter length is determined by measuring from the point of
insertion to the third rib (between intercostal spaces 2 and 3).
• If the central venous catheter is a double or triple lumen catheter, other ports
may be used for blood sampling and total parenteral nutrition administration as needed. The distal port should be used for monitoring of CVP.
• The central venous catheter can be connected to a commercially available pressure transducer system (as described above for arterial blood pressure
monitoring). The CVP measurements relate to right-heart preload and are affected by intravascular volume, tone and the function of the right heart.
Values obtained will typically be displayed using mmHg units.
• A standard water manometer may be used for intermittent CVP measurements. Values obtained will be in cmH2O.
• The transducer or manometer should be at the level of the right heart, and all measurements taken with the patient in the same position.
• The manometer should be filled with normal (0.9%) saline and connected to the patient’s central venous catheter. A three way stop-cock can be used between the manometer and patient’s catheter to facilitate filling the manometer and measuring CVP.
• The manometer should be perpendicular to the patient with the bottom of the manometer level with the right heart.
• Saline will move from the manometer to the patient’s vein until the pressures are equilibrated. The measurement is made when the meniscus of saline stops falling and instead fluctuates slightly around a given number with each respiration.
• The CVP should be read at end expiration to minimise the influence of changing intrapleural pressures (due to breathing).
• Williams and Linklater (2015) describe and demonstrate the modified Seldinger Technique that is often used for placement of a central/ jugular
catheter.
What units can central venous pressure be measured in?
CVP can be measured in millimetres of mercury (mm Hg) or in centimetres of water (cm H2O).
What is a normal venous pressure?
• Normal central venous pressure is 0-5 cm H2O or 0-4mmHg.
How do you convert readings for central venous pressure from mmHg to cm H2O
It is possible to convert readings from mm Hg to cm H2O using the followingcalculation - (mm Hg x 1.36) = cm H2O.
• 1 mmHg = 1.36 cmH2O; 1 cm H2O is equal to 0.74 mm Hg
What trauma associated pathologic processes can elevate central venous pressure?
There are several trauma associated pathologic processes that can elevate CVP including pleural space disease (e.g. pleural effusion and pneumothorax), cardiac tamponade and pulmonary hypertension. These conditions affect pressures on, in or around the heart muscle
What is a low central venous pressure consistent with?
A low CVP (less than 0 cm H2O) is consistent with hypovolaemia due to fluid
loss or vasodilation secondary to peripheral vasodilation e.g. sepsis
What is a high central venous pressure associated with?
A high CVP (greater than 10 cm H2O) may indicate volume overload (or volume expansion if fluid resuscitation has occurred), right-sided heart failure
or severe pleural space disease (pleural effusion or pneumothorax).
What can be done to test if a patient is hypovolaemic but still has a normal central venous pressure?
If CVP is normal, but there is still suspicion of underlying hypovolaemia, a small test bolus of 10 to 15 ml/kg of an isotonic crystalloid solution; (or, if
used, a 3-4 ml/kg bolus of a synthetic colloid administered over 5 minutes).
• If the patient has a low CVP due to hypovolaemia, the CVP will show no change or will have a transient rise toward normal, then rapidly decrease again.
What is a normal TP in dogs and cats?
Normal TS for dogs is ~ 55-77 g/l and 69 -79 g/l for cats.
What can serum lactate be used to assess?
Serum lactate provides an assessment of perfusion and should be regularly measured in the cardiovascularly unstable patient - it can be used to assess tissue oxygenation and response to therapy.
What does an elevated lactate suggest?
An elevated lactate suggests inadequate tissue perfusion and may indicate that further resuscitation is necessary. It is typically measured in patients in shock when they present but is most useful in determining whether resuscitation has been adequate or not. As such, it may need to be measured multiple times within a sixhour period. Elevations in lactate that do not respond to resuscitation should prompt further investigation into the patient’s primary problem. Whilst there can be mild lactate elevation in patients that are panting, have increased muscle activity e.g.
tremors or seizuring, ongoing elevated lactate after resuscitation suggests the patient may have a more serious underlying problem.
What is a normal serum lactate concentration in dogs?
Normal serum lactate concentrations in dogs have been reported to range from 0.3 –
2.5 mmol/L
If a patients lactate remains increased after resuscitation what does this signify?
Whilst there can be mild lactate elevation in patients that are panting, have increased muscle activity e.g.
tremors or seizuring, ongoing elevated lactate after resuscitation suggests the patient may have a more serious underlying problem
What is the most reliable prognostic indicator for serum lactate?
which compared preand post-surgery lactate levels in dogs with gastric dilation volvulus, the most reliable
prognostic indicator was how much the lactate reduced by rather than what the initial reading was. Therefore, this confirms that in dogs it is the lactate trend rather than a single reading that should be considered.
What would indicate hypoxaemia on a blood gas analysis?
Hypoxaemia is present if the arterial partial pressure of oxygen (PaO2) is < 80 mmHg.
What would an arterial partial pressure of oxygen be below if a patient was cyanotic?
If the patient is cyanotic, this indicates severe hypoxaemia ~
PaO2 < 60 mmHg.
What arterial partial pressure of oxygen is 90% on a pulse oximeter equivalent to ?
A pulse oximeter reading of 90% is equivalent
to a PaO2 of ~ 60 mmHg.
What does pulse oximetry rely on?
While pulse oximetry is a useful monitoring tool, it has several practical issues. Pulse
oximetry relies on pulsatile blood flow -
What can pulse oximetry be affected by?
Pulse oximeter readings will be affected by
hypoperfusion and compression of tissues. Certain forms of light and pigmented
mucous membranes may also reduce the accuracy of readings obtained
What does pulse oximetry measure?
Pulse oximetry provides a measure of the oxygenation of blood- more specifically, measures the percentage of haemoglobin in arterial blood that is saturated with
oxygen.
What is the only accurate way to determine oxygen saturation levels in the blood?
only completely accurate method of determining the PaO2 is with arterial blood gases.
What are the usual sites that a pulse oximeter can be used?
The probe of the pulse oximeter can be placed on any area of non-pigmented, non-haired skin. Typical sites include the lip, tongue, toe, ear margin, ventral abdomen and vulva. Rectal probes are also available. It is important to avoid patient stress and discomfort when attaching; and important to ensure the area is well-perfused
How does a pulse oximeter work?
A light signal, using two different wavelengths, is emitted from a phototransmitter and conducted through the tissues.
• A detector measures the difference in light absorbance of oxygenated and deoxygenated haemoglobin during pulsatile flow. From this the % saturation of haemoglobin with oxygen can be calculated
Pulse plethysmography describes the change in light absorption due to the pulsatile variation in volume of arteries and the transformation into a pulse waveform’ (Rigotti and DeVries, 2011). This allows an assessment of the accuracy of the reading- if the tracing resembles an arterial pressure waveform and the pulse rate displayed equates to the patient’s actual pulse rate, then the pulse oximeter reading is likely to
be accurate
What are the common causes of error on a pulse oximeter?
Common causes of error include heavily pigmented skin, motion and excessive peripheral vasoconstriction that prevents the generation of a detectable pulse
How can anaemia affect pulse oximetry?
Another limitation of pulse oximetry is a patient with anaemia. If the red blood cells (RBCs) that are present are saturated with oxygen, the SpO2 reading
will be normal. However, as the patient has fewer RBCs than normal to transport oxygen, there will be decreased overall oxygen carrying capacity.
How can you check the reliability of a pulse oximeter?
For the pulse oximetry reading to be considered reliable, the pulse rate generated must match that of the patient; and a consistent waveform must be produced (if available). If the probe is placed on an area of pulsatile blood flow, then the
auscultated heart rate should be the same as the one showing on the pulse oximeter. If there is significant variation in the auscultated heart rate and the pulse
oximetry rate, the accuracy of the pulse oximeter readings needs to be considered. A full review of the patient’s status and parameters would be indicated in this situation
Is it common to get a false low reading or high reading on a pulse oximeter?
While it is common for pulse oximetry to generate a falsely low reading, it is
uncommon for it to generate a falsely high reading. Therefore, the highest value
generated by the pulse oximeter, with a strong waveform and heart/pulse rate
matching that of the patient, should be considered the actual percentage of
haemoglobin saturated with oxygen.
What pulse oximetry reading should a patient on oxygen have?
Patients who are receiving 100% oxygen should have a pulse oximetry reading > 95%
What pulse oximetry reading requires supplemental oxygen?
Patients with readings less than 92% should receive supplemental oxygen
What is capnography?
Monitoring carbon-dioxide levels in the respiratory gases of an animal is called
capnography
What is end tidal capnography?
End-tidal capnography (ETCO2) measures carbon dioxide in expired gas and provides a non-invasive assessment of the partial pressure of CO2 in arterial
blood (PaCO2)
How do you acquire a non invasive assessment of partial pressure of CO2 in arterial blood?
End-tidal capnography (ETCO2) measures carbon dioxide in expired
gas and provides a non-invasive assessment of the partial pressure of CO2 in arterial
blood (PaCO2)
What will a patients ETCO2 be if they have had a cardiopulmonary arrest?
A patient in cardiopulmonary arrest (CPA) will have an ETCO2 reading of zero.
What information does ETCO2 provide?
• ETCO2 provides a continuous, non-invasive estimate of dissolved carbon
dioxide in arterial blood (PaCO2).
What is the normal ETCO2?
Normal ventilation results in ETCO2 of 35 to 45 mmHg
What is the usual difference in ETCO2 and PaCO2?
ETCO2 is usually 1-4mmHg lower than PaCO2
What would hypoventilation be defined on ETCO2?
Hypoventilation is defined as ETCO2 greater than 45 mmHg.
What ETCO2 reading would require breathing assistance?
An ETCO2 value above 50mmHg indicates inadequate ventilation meaning breathing assistance, manual or mechanical, may be required
What ETCO2 would require continuous ventilation?
An ETCO2 > 60 mmHg indicates severely compromised ventilation, where there will be corresponding respiratory acidosis, and the patient should be ventilated. N.B. The intervention ETCO2 reading would be 45 mmHg if the
patient has a traumatic brain injury.
What can hypoventilation be secondary to?
Hypoventilation (inadequate breathing) may occur secondary to
i. Head and spinal trauma
ii. Drugs that influence respiratory drive (e.g. opioids, propofol etc.)
iii. Severe pulmonary parenchymal/pleural space disease
respiratory fatigue from paralysis
What points should be considered if the ETCO2 is low during CPR?
Points to consider in this situation could include
I. Is the quality of the compressions adequate? Is the thorax being compressed by 30-50%? Is the compressor position correct? Is the compressor fatigued?
II. Is the rate of compressions adequate? Increasing the rate from 100 to
120 per minute may improve the situation.
III. Has the correct location been used to correspond with the
conformation of the patient’s thorax i.e. thoracic pump technique for
round-chested dogs? N.B. If the correct technique is being performed
but the ETCO2 is still low, sometimes moving from direct cardiac
compressions to thoracic pump technique can be effective.
IV. It should be considered if there are other factors affecting compliance
such as major thoracic trauma.
What test provides the best standard assessment of oxygenation and ventilation?
Arterial blood gas analysis (ABG) provides the best standard assessment of both oxygenation AND ventilation.
Explain how oxygenation and ventilation are seperate physiological processes?
Ventilation and oxygenation are separate
physiological processes. As previously stated, ventilation is the process of inhaling
and exhaling i.e. breathing. Oxygenation is the process of getting oxygen into the
circulatory system for delivery to cells i.e. transfer from the alveoli into the pulmonary
capillaries.
What is the difference between hypoxia and hypoxaemia?
If oxygenation is impaired for any reason, the patient will be hypoxaemic – low blood oxygen levels.
If the blood oxygen levels are low, delivery of oxygen to cells will be decreased – hypoxia.
Where should a blood gas analysis sample be collected from and which sites can be used?
The blood sample for ABG should, by definition, be obtained from an artery. Usually
the dorsal pedal or the femoral artery is used, however others can be used
depending on the patient e.g. the lateral (dog) or medial (cat) saphenous arteries.
What is FiO2?
Fraction of inspired oxygen
What relationship should PaO2 and FiO2 have?
Examine the PaO2-
o Should be 5 x the fraction of inspired oxygen (FiO2) value.
▪ E.g. If a healthy patient is breathing room air the FiO2 is ~ 21%
O2), therefore the PaO2 would be expected to be around
100mmHg
What is a normal PaO2?
A PaO2 >90 mmHg is considered normal
What PaO2 would be considered mild hypoxaemia?
If PaO2 = 75-90mmHg- the patient has mild hypoxaemia
What PaO2 would indicate severe hypoxaemia?
o If PaO2 < 75mmHg- the patient has severe hypoxaemia
What would a patients PaO2 be if the SPO2 was 91%?
A patient with a SpO2 of 91% will have a PaO2 < 60 mmHg e.g. it is severely
hypoxaemic
What is the alveolar arterial oxygen gradient?
The alveolar arterial oxygen gradient gives an estimate of the effectiveness of gas transfer from the alveoli into the circulation – it compares the amount of oxygen in the alveoli (PAO2) to the amount of oxygen in arteries (PaO2).
What is the PAO2 of oxygen in the alveoli and how does compare to arterial PaO2?
PAO2 is the partial pressure of oxygen in the alveoli. It is considered to
be ~ 150mmHg in a patient breathing room air at sea level. In a healthy patient,
in theory, there should be little difference between the alveolar oxygen levels and the
arterial oxygen levels. However, for various reasons the alveolar oxygen level will
always be higher than the arterial oxygen levels.
What are the different abbreviations for partial pressure of oxygen in the alveoli and partial pressure of oxygen for the arterial?
PAO2 is the partial pressure of oxygen in the alveoli.
PaO2 is the measured arterial oxygen concentration
How can the A (alveoli) gradient be calculated?
o The A – a gradient is the difference between alveolar oxygen levels
(PAO2) and arterial oxygen levels (PaO2) i.e. PAO2 - PaO2.
o The A-a gradient can be calculated using these formulae -
1. A-a = (150 * – [PaCO2/0.8 or 0.9]) - PaO2
2. A-a = (150* - [PaCO2 x 1.1]) - PaO2
What is the normal reference range for the A-a gradient for a patient breathing room air?
The normal reference range for the A – a gradient for a patient breathing room air is <20mmHg
If the A-a gradient is greater than 20 mmHg what does this indicate?
If the A-a gradient is greater than 20mmHg for a patient breathing room air, then the hypoxaemia is secondary to pulmonary dysfunction (i.e. decreased oxygenation) rather than hypoventilation. Possible causes of decreased oxygenation are pulmonary oedema, pulmonary contusions and pneumonia)
When might a patient with neurological signs require constant monitoring?
Neurological
monitoring may have to be continuous for patients with severe signs especially
where there is concern about the potential for increased intracranial pressure (ICP).
What quick initial neurological assessment can be made about a patients mentation by hands off observation?
An initial quick neurological assessment can be made of the patient’s mentation by hands-off observation e.g. conscious, ambulatory, ataxic and alert, stuporous, obtunded, unconscious or seizuring.
Most simply, the neurological monitoring will consist of assessment of mentation.
This can be rapidly determined (e.g. the dog is standing at the front of the kennel
wagging his/her tail) and may negate more intensive evaluation.
What is the modified Glasgow coma scale useful at evaluating? What benefits are there to it?
The modified Glasgow Coma Scale (MGCS) (Beal, 2010) has been evaluated in dogs, and is an extremely useful tool for serial monitoring of neurological patients. It is particularly useful when animals are in for a prolonged period and they will be assessed by multiple people within the team. It lends a degree of objectivity in an otherwise subjective assessment of neurological status. Using the MGCS can help to
inform when interventions may be required to support the patient e.g. early in the management of a patient with a traumatic brain injury. Using the MGCS may identify, for example, the patient that would benefit from intubation and ventilation. If the
patient is not breathing effectively, the high levels of carbon dioxide in the blood stream could cause vasodilation which would increase the risk of increased intracranial pressure and further brain damage.
What might a neurological assessment for a spinal injury involve?
A neurological assessment for spinal injury may also be indicated e.g. paralysis,
paresis, ataxia, hemiplegia etc. Assessment of spinal cord reflexes, bladder function
and, in certain situations, deep pain may be part of the ongoing monitoring plan
discussed with the veterinary surgeon. Assessment of these particular parameters
will commonly be the remit of the veterinary surgeon (especially deep pain
assessment). However clear communication is needed to ensure the best possible
care possible for the patient. For example, if the patient is paralysed, can the RVN
place a urinary catheter?
How often should body weight be measured?
Body weight should be measured at least once a day. In some patients e.g. those
undergoing peritoneal dialysis, it should be performed at least twice daily.
Is there any variability in a patients resting energy requirement?
Whilst the resting energy requirement (RER) is often used to calculate a patient’s nutritional requirements, it is important to consider that this calculated figure could be up to 50% more or less than the individual patient’s actual requirements
What is the most likely cause of a rapid change in body weight from a hospitalised patient?
Fluid balance is a very important factor in body weight- it is most likely to be responsible for a rapid change in a patient’s weight. Tissue breakdown will affect
weight but is likely to take place at a slower rate. Fluid loss and fluid overload can lead to weight loss and weight gain respectively. This fluid flux may be into/from the interstitial space and/or body cavity. For example, an animal can increase in body
weight whilst losing muscle mass- this could be due to fluid building up in the abdomen due to hypoproteinaemia (third space loss). Animals that are oliguric or anuric can quickly become volume overloaded (and hence quickly gain weight) if
they are on intravenous fluids. Serial monitoring of body weight can provide an estimate of how much excess fluid the animal has. For example, the optimum
bodyweight of an anuric dog with acute kidney injury is 30 kg. If following intravenous fluid therapy, the weight increases to 32 kg, it shows that the patient now has an excess of 2 litres of fluid that will need to be managed.
How often should body temperature be monitored in a hospitalised patient?
Body temperature should be monitored every 8-12 hours, in most patients - although
in critically ill animals it will need to be monitored more frequently e.g. patients with
SIRS/sepsis or hyperthermia.
What is responsible for maintaining an animals body temperature?
The thermoregulatory centre in the hypothalamus is responsible for maintaining an
animal’s body temperature within a narrow range (set-point) – like a thermostat for a
central heating system.
What is the difference between hyperthermia and pyrexia?
In a patient with pyrexia (fever) secondary to an
inflammatory/ infectious cause, there is a resetting of the hypothalamic set point which results in an increased body temperature.
Hyperthermia is when the patient’s body temperature is elevated because of ‘external’ causes e.g. being trapped in a car on a hot day, seizure activity or
increased respiratory effort e.g. brachycephalic dog. A patient with hyperthermia requires to be actively cooled
What is the normal urine output for a patient that is well hydrated and adequately volume resuscitated?
In a well hydrated and adequately volume resuscitated patient adequate urine
production is ~2 ml/kg/hr.
What urine output would be considered as oliguric?
Oliguria is generally considered to be urine production less than 1 ml/kg/hr.
What urine output would be considered as anuric?
In veterinary patients, anuria is present when urine production is less than 0.5
ml/kg/hr. N.B. The actual volume of urine output that is considered oliguric/anuric depends on individual patient factors as well as the source
consulted
What different ways are there of measuring urine output?
Objective measurements of urine output monitoring include
➢ placing an indwelling urinary catheter attached to a closed collection
system
➢ weighing disposable, plastic-backed, absorbent pads e.g. incontinence
pads. Each 1g equates to 1 ml of urine
➢ free catching urine (e.g. kidney dish) and measuring the volume in an
ambulatory dog
➢ using a litter tray with non-absorbent litter e.g. Katkor Urine Sampling
Kit ®
What is the most accurate way to measure urine output?
The most accurate way to measure urine output is by placement of an indwelling urinary catheter, attached to a closed collection system, as it allows quantification of ALL urine produced.
What are the risk associated with urinary catheter placement?
There are risks associated with catheter placement, however, including nosocomial infections. Female dogs are at particular risk of infection, especially if they have diarrhoea.
• Bladder and urethral trauma are rare but possible complications that may
occur during urinary catheter placement.
What should be monitored when a patient has a urinary catheter?
If a urinary catheter is placed, then daily evaluation of a fresh urine sample can be performed to identify the presence of bacteria. The results of this urinalysis will provide guidance as to whether the catheter requires to be removed and antibiotics administered.
Urine output
patient intereference
• As well as assessing the volume of urine produced, the specific gravity should
be measured
Additional monitoring may be performed depending on the specific situation
e.g. urine protein to creatinine ratio, culture and sensitivity, urine glucose etc.
How often should electrolytes be monitored in a patient with severe electrolyte derangements?
If a patient has significant electrolyte
derangements at the start of treatment (e.g. severe hypernatraemia or hyperkalaemia) then they should be monitored frequently - potentially every 1-4
hours.
How often should electrolytes be monitored in a patient at the start of treatment including fluid therapy?
if they are relatively normal at the start of treatment then repeat
measurement every 12-24 hours will generally be sufficient.
