Retrospective Study of Aspiration Pneumonia

Aspiration pneumonia occurs after caustic gastric contents are inhaled into the airways. Lung injury, called pneumonitis, reduces airway defense mechanisms and predisposes the lung to secondary infection via bacterial colonization. This retrospective case series investigated the diagnostics and treatments associated with survival in 125 dogs with aspiration pneumonia. Animals were included if radiographic findings consistent with pneumonia were observed and 2 of 3 criteria were met: 1) lethargy, fever, tachypnea, coughing, vomiting; 2) airway culture results, leukocytosis, presence of band neutrophils, or leukopenia; or 3) a history compatible with increased risk factors, including vomiting, regurgitating, laryngeal/esophageal disorders, recent anesthesia or sedation, recumbency, and seizures. Treatment modalities were examined and oxygen status or oxygenation ratio was calculated.

The number of lung lobes affected in a patient had a direct correlation with survival. Patients with 2 or more lung lobes involved had a worse outcome than those with single lobe involvement, but dogs with involvement of 3 or more lung lobes did not fare worse than patients with 2 lobes involved. Another important finding was that 77% of airway samples yielded positive growth from cultures and almost half of the samples had 2 or more species of bacteria isolated. Forty-three percent had mixed growth of both gram-positive and gram-negative bacteria, with Escherichia coli most frequently isolated. The presence of E coli was not associated with increased mortality. Overall, the prognosis associated with aspiration pneumonia in this study was found to be good as long as proper supportive care and broad-spectrum antibiotic therapy were provided.

Commentary: The retrospective nature of this study limited the authors’ ability to understand fully the severity of each individual case's progression of clinical signs. However, some interesting points were that only half of the dogs presented with lethargy, tachypnea, or a fever and that fewer than half presented with a cough. Severity of clinical signs was not correlated with survival, and the correlation between the number of lung lobes affected and survival had not been shown in previous reports. Although many practitioners are less likely to do a transtracheal wash and culture in patients with aspiration pneumonia, this study showed that the yield of this test in these cases makes it worthwhile.

Potential risks, prognostic indicators, and diagnostic and treatment modalities affecting survival of dogs with presumptive aspiration pneumonia: 125 cases (2005–2008). Tart KM, Babski DM, Lee JA. J VET EMERG CRIT CARE 20:319-329, 2010.