November 2009 SA Benchmark Vignettes

Question 1

What are some of the more common bacterial pathogens associated with aspiration pneumonia?

Answer 1

Aerobic bacterial organisms isolated on culture included Escherichia coli, Klebsiella pneumonia, Pasteurella multocida, Streptococcus canis, Klebsiella oxytoca, Acinetobacter spp., Neisseria weaver, and Frederikenia canicola.

The only organism recovered on capnophilic culture was Pasteurella dagmatis.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/jvim.16310

Question 2

Name four different non‐surgical methods to obtain a sample from the airways/lung for culture.
List the pros and cons to each method.

Answer 2

Sputum sample
Pros: Minimally invasive, cheap, no procedure required
Cons: High risk of oral contamination

Transtracheal wash
Pros: Minimally invasive, easy to perform in large dogs
Cons: Difficult to perform in cats and small dogs, risk of haemorrhage, risk of hypoxaemia, need good
restraint, risk of inaccurate sampling (i.e. tracheal rather than alveolar), poor sensitivity (45‐57%).

Endotracheal wash
Pros: More sensitive technique than TTW, easy to perform in dogs and cats
Cons: Requires anaesthesia, risk of causing hypoxaemia,

Bronchoscopy and bronchoalveolar lavage
Pros: Higher sensitivity than other methods‐ directed sampling possible, superior diagnostic yield than
other methods
Cons: Experience, more invasive, higher risk of causing hypoxaemia and decreasing lung function

Fine needle aspiration of the lung
Pros: May be more beneficial than other sampling methods when interstitial disease or focal lesions are
present, less invasive than surgical biopsy, fewer complications than tru‐cut biopsy
Cons: risk of pneumothorax, poor cellular recovery due to small sample size, limited utility in diffuse
disease

Question 3

What are some factors that predispose to development of chemical pneumonitis/aspiration pneumonia?

Answer 3

Esophageal disease
Laryngeal disease
General anesthesia
Vomiting
Neurological conditions e.g. myasthenia gravis, seizures, spinal cord disease, lower motor neuron

Question 4

What are the five main causes of hypoxemia?

Answer 4

Decreased Fi02
Hypoventilation
Diffusion impairment
R to L shunt
Venous admixture (V/Q
mismatch)

Question 5

What are the three independent variables in the Stewart approach to acid-base assessment?

Answer 5

PCO2
SID
Atot

Question 6

What are the dependent variables (4)?

Answer 6

HCO3-
H+
OH-
CO3^2-

Question 7

Using the strong ion difference (SID), what factors affect the base excess?

Answer 7

Free water effect, chloride effect, contribution from unidentified strong anions, and changes in weak acids (albumin/phosphorous)

Question 8

A decrease in the strong ion difference (SID) suggests what type of acid-base disturbance?

Answer 8

Non respiratory acidosis / metabolic acidosis as a result of decreased sodium ion concentration,
increased chloride concentration or an increase in concentration of other strong ions.

Question 9

If a liter of water contains 140 mEq/L of Na+ and 110 mEq/L of Cl-, then the SID is 30mEq; if we were to add another liter of water without adding any more electrolytes, then the solution would
contain 70 mEq/L Na+ and 55 mEq/L Cl‐ and the new SID is 15 mEq. This represents what concept in Stewarts approach to acid base?

Answer 9

Dilutional acidosis

Question 10

What is the normal PaCO2 – ETCO2 difference?

Answer 10

PaCO2 to ETCO2 difference should be less than 5 mmHg. ETCO2 is slightly lower due to intrapulmonary
dead space ventilation.

Question 11

What does an increase in the PaCO2 – ETCO2 difference typically indicate?

Answer 11

An increase between these two indicates an increase in dead space. It can occur with increases in
anatomic dead space (such as open ventilator circuit, hypoventilation, excess ET tube length) or increases
in physiologic dead space (such as obstructive pulmonary disease, low cardiac output/pulmonary
hypoperfusion, pulmonary thromboembolism, excessive lung inflation).