Aspiration pneumonia occurs when oropharyngeal, gastric, or foreign material is inhaled into the lower airways. The inhaled substance can compromise normal pulmonary function by causing mechanical obstruction of the airways, inducing bronchoconstriction, chemically damaging the airway walls, and introducing bacteria into the lower airways. If the damage is severe enough, the animal will be presented for evaluation.
Aspiration pneumonia is most often a complication of vomiting and therefore secondary to another disease. It is a risk for dogs with megaesophagus and is of concern for patients who are undergoing or recovering from general anesthesia or sedation. Patients who are being force fed are also at risk for aspirating.
The diagnosis of aspiration pneumonia is formulated from the patient’s clinical history, signs, lab results and radiographic findings. The history may include such details as excessive vomiting, chronic regurgitation, generalized musculoskeletal weakness, or a recent episode of anesthesia. Most patients present with acute dyspnea, fever, coughing and lethargy. Lab tests may or may not reveal a leukocytosis. Patients typically demonstrate low oxygen saturation levels on pulse oximetry as well.
Thoracic radiographs are the most important diagnostic tool for diagnosing aspiration pneumonia. Two-view thoracic radiographs commonly demonstrate patchy alveolar consolidation and air bronchograms involving the ventral aspect of the left cranial and right middle lung lobes. The bronchus leading to the right middle lung lobe branches off of the trachea ahead of and ventral to the other bronchi, making it the most likely site for aspiration pneumonia. Pulmonary disease involving the caudal and dorsal lung fields are much less likely to be associated with aspiration and should prompt the clinician to search for another disease process. Radiographic evidence of aspiration pneumonia may not be evident for up to 24 hours after the aspiration has occurred. Therefore, the lack of radiographic evidence does not initially exclude aspiration in a respiratory patient.
Aspiration pneumonia is a life-threatening disease that requires immediate medical attention. Initial treatment should include basic balanced IV fluid therapy and oxygen support. Placement of single or double nasal oxygen catheters are the most efficient means of raising blood oxygen concentrations. Additional treatments include antibiotic administration, pulmonary coupage and nebulization. Antibiotics are best chosen based on bacterial culture results procured from a transtracheal wash, bronchoalveolar lavage, or fine needle aspiration of the lungs. However, these procedures are frequently bypassed because of the patient’s severe respiratory compromise. It can take several days for the pneumonia to respond to therapy. Respiratory rate, respiratory pattern, pulse oximetry and radiographs are all used to document clinical improvement or worsening in aspiration patients.
Aspiration pneumonia can lead to sepsis, acute respiratory distress syndrome, and even multiple organ failure. Those patients that have aspiration pneumonia are often at risk of getting it again if the underlying condition has not resolved. Therefore, the underlying condition which contributed to the patient’s aspiration must also be diagnosed and treated. The prognosis for a patient with aspiration pneumonia is guarded. Milder cases in which the underlying cause can be identified and treated carry a more favorable prognosis.