Chapter 23 - Aspiration pneumonitis and pneumonia

Question 1

What are the 2 phases in aspiration pneumonia?

Answer 1

1. Direct chemical injury
2. Inflammatory mediator cascades producing neutrophil chemotaxis, sequestration, and subsequent increased permeability edema

Question 2

Define aspiration pneumonia

Answer 2

Acute lung injury caused by inhalation of chemical irritants

Question 3

What are the most common risk factors for aspiration pneumonia?

Answer 3

• Gastrointestinal disorders (60%) including oegaesophagus (26%)
• Neurologic disorders (18%)
• Laryngeal diseases (13%)

Question 4

What does the magnitude of ALI after gastric aspiration depend on?

Answer 4

• pH (<1.5 is associated with the most severe damage)
• Volume
• Osmolality
• Presence of particulate matter in the aspirate

Question 5

What are the neurons stimulated by acid aspirate and in control of bronchial smooth muscle tone and vascular permeability?

Answer 5

Tracheobronchial substance P-immunoreactive neurons

Question 6

What happens after stimulation of tracheobronchial substance P-immunoreactive neurons by acid aspirate (1st phase)?

Answer 6

Tachykinin neuropeptidase release

–> neurogenic inflammation, bronchoconstriction, vasodilation, increased vascular permeability

Question 7

What are the mechanisms involved in the second phase of acid-induced ALI?

Answer 7

• Larger increase in pulmonary capillary permeability and protein extravasation
• -> Edema formation compromising gas exchange / ventilation-perfusion mismatch / decreased lung compliance
• Chemotactic mediators released by alveolar macrophages (particularly IL8, TNFα, macrophage
  inflammatory protein 2)
  –> Sequestration of activated neutrophils
  –> Increased concentrations of reactive oxygen species, proteinases and complement proteins
  –> Pro-inflammatory state

Question 8

How may the presence of particulate matter in the aspirate worsen the pneumonia?

Answer 8

• Small airway obstruction
• Inflammatory response prolongation
• Nidus for bacterial contamination

Question 9

Where do the bacteria involved in aspiration pneumonia most commonly come from?

Answer 9

Oropharyngeal environment > GI content

Question 10

What are the common bacteria involved in aspiration pneumonia?

Answer 10

• Enteric bacteria: Escherichia coli, Klebsiella spp, and
  Enterococcus spp
• Oropharyngeal: Mycoplasma spp
• Primary respiratory pathogens: Pasteurella spp, Pseudomonas spp, and Streptococcus spp
• Commensals: Staphylococcus spp

Question 11

True/False: Transtracheal wash is less sensitive than lung aspirate and BAL to diagnose bacterial pneumonia

Answer 11

False: may be as sensitive, but is less specific

Question 12

What are the typical changes seen on arterial blood gas with pneumonia?

Answer 12

Hypoxemia, hypocapnia, increased alveolar-arterial gradient

Question 13

What are the consequences of prolonged high inspired oxygen concentration in lungs? (prolonged time on 100% O2)

Answer 13

Increased lung permeability
Protein extravasation
Impaired compliance

Question 14

Why are bronchodilators NOT recommended in dogs with pneumonia?

Answer 14

The inotropic and vasodilator properties of these agents can increase perfusion of poorly ventilated lung units, thus worsening hypoxemia

Question 15

True/False: the use of proton-pump inhibitors decreases the risk of acid-induced ALI, but increases the risk of community- and hospital-acquired pneumonia

Answer 15

True

pH >2.5 but gastric bacterial colonization