Oxygenation and Ventilation

Question 1

compare and contrast oxygenation and ventilation

Answer 1

oxygenation: oxygen (PaO2)
-FiO2
-transfer across alveolus
-ventilation dependent

ventilation: carbon dioxide (PaCO2)
-rate and depth of breath

Question 2

what regulates the patients breathing rate and effort?

Answer 2

1. CO2 is produced, converted to H2CO3, split into HCO3- and H+
2. increased H+ is CSF stimulates chemoreceptors and triggers ventilation
   -as PaCO2 increases, minute ventilation increases in a normal patient

Question 3

what are 4 causes of hyperventilation?

Answer 3

1. pain, anxiety, excitement
2. hyperthermia
3. acidosis
4. hypoxemia

Question 4

what are 3 causes of hypoventilation?

Answer 4

1. central neurologic:
   -brain: medulla, pons, cerebrum
   -cervical spinal disease: IVDD, wobblers, AA subluxation
   -drugs: opioids, propofol, anesthesia
2. peripheral neurologic:
   -lower motor neuron disease: botulism, myasthenia gravis, polyradiculoneuritis, tick paralysis
3. respiratory system disease:
   -airway obstruction
   -parenchymal disease
   -pleural space disease
   -disorders of thoracic cage/diaphragm

Question 5

what determines ventilation when hypoxemia is severe?

Answer 5

oxygen/PaO2 <60mmHg (normal is 80-100mmHg) becomes stimulus for breathing, body stops paying attention to PaCO2

1. low PaO2 is sensed by aortic and carotid body chemoreceptors
   -also activated by anemia, high CO2, low SpO2, acidosis
2. increases minute ventilation
   -but the atmosphere only has so much oxygen to breathe so increasing minute ventilation will plateau in how much can increase PaO2 unless also increase FiO2

-but if have adapted to lower PaO2 (COPD, etc.) then suddenly increase FiO2, can trigger hypoventilation (body feels happy that job is finally done) and PaCO2 begins to rise but body has lost sensitivity to PaCO2 so will stay hypoventilating = tricky to treat

Question 6

describe the 5 causes of hypoxemia

Answer 6

1. decreased FiO2
   -under anesthesia or at altitude
   -altitude = same amount of O2 but less atmosphere false decreases PaO2
2. hypoventilation:
   -as minute ventilation decreases, we see a rise in PaCO2
   -hypoventilation due to: central neurologic, peripheral neurologic, or respiratory disease
3. diffusion impairment:
   -thickened alveolar membrane inhibits gas transfer
   -uncommon cause of hypoxemia in vet med because in a normal patient, oxygen exchange is completed in the first 1.3 of the alveolar capillary
   -commonly due to chronic obstructive pulmonary disease (COPD) or smoke inhalation
4. R to L shunt:
   -abnormal circulation allows deoxygenated blood to enter systemic circulation
   -due to: tetralogy of fallot, transposition of great vessels, persistent truncus arteriosis, tricuspid atresia, or R to L PDA
5. venous admixture (V/Q mismatch)
   -imbalance between blood flow and alveolar ventilation
   - V should = Q
   -if high V/Q, also called physiologic deadspace when Q = 0, due to pulmonary thromboembolism or pulmonary arterial hypertension

-if low V/Q, also called physiological shunt when V = 0, due to cardiogenic and non-cardiogenic pulmonary edema, pneumonia, inflammation, atalectasis, ARDS, airway obstruction
-the NUMBER ONE CAUSE OF HYPOXEMIA IN ANIMALS

Question 7

how does the body compensate for venous admixture?

Answer 7

1. high V/Q causes local hypocapnia which increases pH and causes local bronchoconstriction
   -high ventilation, low flow
2. low V/Q: the MOST COMMON CAUSE OF HYPOXEMIA IN ANIMALS
   -causes increased CO2 which stimulates increased ventilation that improves CO2 and O2, but improves CO2 more than O2
   -also causes hypoxic pulmonary vasoconstriction which diverts bloodflow to better ventilated areas (good if regional lung disease, not so great if you live at altitude, can cause more global pulmonary hypertension)

Question 8

what are the 6 locations of dyspnea?

Answer 8

1. extrathoracic airway: above thoracic inlet
2. intrathoracic airway
3. pulmonary parenchyma
4. vascular
5. thoracic cage and diaphragm
6. pleural space

Question 9

describe normal respiration (4)

Answer 9

1. barely noticeable at rest
2. ribs move cranially and outward
3. diaphragm moves caudally
   -abdomen moves passively outward
4. thorax and abdomen move together

Question 10

how do you recognize respiratory distress?

Answer 10

1. increased respiratory rate and effort
2. open mouth, FLARED nostrils
   -species differences: cats and birds should NEVER open mouth breathe
3. birds: tail bobbing (equivalent of abdominal motion), hyperinflated airsacs
4. anxiety, restlessness
5. orthopnea*
6. cyanosis*
7. noise*
8. irregular pattern or rhythm*

Question 11

describe orthopnea

Answer 11

1. a position the animal adopts to make airflow easier/more laminar
2. standing or seated with abducted elbows to expand chest, extended head and neck
3. other weird positions exist: bulldogs drape themselves over things to stretch out redundant tissue at back of throat and keep airway as open as possible
   -could also see downward dog while sleeping, also in bulldogs
4. cats don’t stand, they are sternal and tuck their feet in with elbows out, head and neck stretched out when orthopnic

Question 12

describe cyanosis

Answer 12

1. insensitive (long period of time between hypoxemic and cyanotic), but usually denotes a SEVERE oxygen deficiency if present!
   -PaO2 approx 40mmHg
   -SpO2 approx 75%
   -5 g/dl of deoxy Hb

-an anemic patient cannot be cyanotic!!
-cyanosis assumes that a patient has enough RBCs because cyanosis requires 5g/dl of deoxygenated Hb for our eyes to detect the color purple (PCV 15%) so by definition an anemic patient can not be cyanotic because then every RBC would be without hemoglobin an the patient would be dead

Question 13

describe respiratory noises: stridor and stertor

Answer 13

1. stridor: high pitched like a whistle by forcing air through a very narrow opening, the higher the pitch, the narrower the opening and vice versa
2. stertor: snoring noise, classic bulldog sound due to redundant tissue vibrating back and forth with airflow
   -abnormal but normalish for bulldogs to do this due to brachycephalic

these tell us that there is an upper airway problem, typically extrathoracic

Question 14

describe irregular breathing patterns

Answer 14

3 changes:

1. paradoxical respiration:
   -chest and abdomen move in opposite directions; oscillating
   -ribs/intercostals move inward during respiration; due to increased negative pressure and weakness of intercostal muscles due to fatigue
   -outward movement of abdomen during inspiration; inward on expiration; abdominal musculature assists chest movement
   -not specific for any location of a problem, just a sign of dyspnea, but can help differentiate panting for panting’s sake
2. irregular rhythm:
   -regardless of how dyspneic the patient is, should have a regular in out rhythm
   -breath holding or a pause in between breaths is irregular and usually a sign of impending arrest
   -can be in combo with paradoxical respiration
   -NOT in reptiles! non-ventilatory periods are NORMAL for them, but duration between breaths gets shorter in reptiles with respiratory disease, so if breathing more consistently like a mammal = abnormal
3. irregular pattern

Question 15

describe signs of impending respiratory arrest

Answer 15

1. prey species will hide clinical signs until really really sick, so be more suspicious of dyspneic birds, small mammals, etc. because could be more severe than appears
2. decreased mentation: hypoxemia and hypercapnea contribute
3. restlessness, changing body position
   -cats can start running around cage
4. vocalization
5. cats: lateral recumbency, mydriasis, puffed tail
6. irregular breathing pattern: paradoxical, or non-ventilatory periods

Question 16

what do you do in cases of impending respiratory arrest?

Answer 16

1. discuss with the client
   -esp for all dyspneic birds and small mammals
2. intubate and ventilate/act before animal dies
   -definitely do prior to arrest!
   -use low doses of drugs

Question 17

what are the 3 main abnormal respiratory patterns in mammalian species? how is this different in birds?

Answer 17

in birds: have unidirectional airflow so hard to tell source unless loss of voice (syrinx)/stridor, which indicates upper airway; need hx, PE, and rads!

reptiles:
-increased respiratory rate and effort, shorter nonventilatory periods, can visualize glottis (only place can see to localize), limited auscultation, so also need hx, PE, rads

Question 18

what are the 3 main abnormal respiratory patterns?

Answer 18

1. obstructive
2. restrictive
3. hypoventilation

Question 19

describe obstructive respiratory pattern

Answer 19

1. due to narrowing of airways
2. pattern: slower than normal deep breaths, lungs are still able to fully expand so large chest wall movement
3. dynamic obstructive: obstruction moves and only impedes breathing during one phase of respiration
4. fixed: obstruction does not change
5. dynamic extrathoracic airway obstruction has increased INSPIRATORY effort
6. intrathoracic airway obstruction has increased EXPIRATORY effort
7. fixed or dynamic intra AND extrathoracic obstruction has increased inspiratory AND expiratory efforts
8. extrathoracic airway differentials:
   -nasal obstruction: bigger issue for rabbits and horses (obligate nasal breathers)
   -nasopharynx/oropharynx obstruction: STRANGLES IN HORSES!!!
   -extrathoracic trachea obstruction
9. intrathoracic airway differentials:
   -asthma: cats and horses
   -tracheal stenosis/stricture
   -traumatic (rupture)
   -neoplasia
   -parasites
   -foreign body
   -bronchial disease
10. other systemic effects:
    -can’t move air and panic, both of which cause panic/anxiety
    -can’t breathe = hypoxemia, which also worsens the breathing harder and the panic
    -this can result in hyperthermia, which also causes them to breathe harder, more panic, etc
    -results in inflammation, which worsens everything else
    -SEVERE and life threatening!

Question 20

describe initial airway treatment

Answer 20

1. ensure patent airway!
   -verify airflow
2. intubate small animals if:
   -not passing air
   -cyanotic
   -depressed/panic
   -fatigued
3. treacheostomy:
   -rarely in SA, more common in LA
4. oxygen!!!
5. sedation or anxiolytic
   -butorphenol or acepromazine in SA
6. cooling as needed
7. +/- anti-inflammatory corticosteroids: prednisoe or dexamethasone
8. +/- bronchodilator (feline asthma): aminophylline or terbutaline

Question 21

describe the restrictive pattern

Answer 21

1. prevents lungs from fully expanding
   -shallow chest wall excursions
   -chest wall does NOT fully expand
   -large abdominal effort
2. indicates parenchymal disease or pleural space disease
   -differentiated by auscultation:
   –parenchymal: loud, crackly, wheezy lung sounds
   –pleural space: something between you and the lungs so dulled sounds
3. differentials:
   -pneumothorax
   -pleural effusion: blood, pus, chyle, pure or modified transudates, pleural pneumonia in the horse, thymoma related in goats
   -neoplasia
   -diaphragmatic hernia

Question 22

describe pleural space disease stabilization

Answer 22

1. oxygen supplementation
2. then tap out whatever is in there: air, fluid, etc.

Question 23

describe pulmonary parenchymal restrictive disease stabilization

Answer 23

1. oxygen
2. +/- sedation: butorphenol
3. the rest is disease specific
   -diagnostics usually necessary
   -may try empiric tx based on hx and PE

Question 24

describe hypoventilation pattern

Answer 24

1. easy to overlook because they don’t look dyspneic!! but could find them dead in the cage if not careful
2. reduced/absent chest wall movements
   -usually shallow movements, none or minimal signs of distress
   -barely any chest mvmt, some abdominal mvmt
3. central neurologic, peripheral neurologic, respiratory system disease
4. treatment:
   -oxygen
   -treat underlying cause
   -intubate and ventilate
   -monitor

Question 25

what 7 things can look like dyspnea?

Answer 25

1. hyperthermia
2. pain/fear/excitement
3. anemia/hemoglobinopathy
4. metabolic acidosis
5. hypoglycemia (esp neonates)
6. purring
7. display/threat behavior