Overview

• Inflammation of the lungs caused by inhalation of oral ingesta, regurgitated material, and vomitus with subsequent pulmonary dysfunction; develops when laryngeal reflexes function improperly or are overwhelmed.
• Pulmonary dysfunction-caused by (1) direct obstruction of small airways and indirect obstruction from bronchospasm and production of mucus and exudate; (2) aspiration of gastric acid-damages respiratory epithelium; can cause bronchospasm and ALI/ARDS; (3) bacterial pneumonia-bacteria in aspirated material can initiate an immediate infection; or later infections occur secondary to lung damage.

Signalment

Dogs; less commonly cats

Signs

• Peracute, acute, or chronic.
• Cough, tachypnea, nasal discharge, or exercise intolerance.
• Respiratory distress or cyanosis when severe.
• Depending on underlying cause-regurgitation; vomiting; dysphagia; altered consciousness; stertor or stridor.

Causes & Risk Factors

• Pharyngeal abnormalities-local paralysis; generalized neuromuscular disease; cricopharyngeal motor dysfunction; anatomic malformations.
• Esophageal abnormalities-megaesophagus; reflux esophagitis; esophageal dysmotility; esophageal obstruction; bronchoesophageal fistula.
• Laryngeal paralysis, webbing, or obstruction; post-laryngeal surgery.
• Altered consciousness-sedation, anesthesia; post-ictus; forebrain disease; metabolic disturbance.
• Iatrogenic-force feeding; tube feeding, mineral oil administration.

Differential Diagnosis

• Bacterial pneumonia
• Lung abscess

CBC/Biochemistry/Urinalysis

Neutrophilic leukocytosis, left-shift, although WBCs may be normal.

Other Laboratory Tests

• Arterial blood gas analysis-hypoxemia; PaCO₂ generally low.
• Consider tests for predisposing problems-acetylcholine receptor antibodies, resting cortisol or ACTH stimulation, creatine kinase.

Imaging

• Thoracic radiography-bronchoalveolar pattern usually most severe in the gravity-dependent lobes (right cranial and middle, left cranial); can take up to 24 hours for pattern to develop after aspiration; scrutinize for evidence of esophageal or mediastinal disease.
• Videofluoroscopic swallowing study-provides evidence of swallowing or esophageal dysfunction that can predispose to aspiration. Caution: could result in aspiration of contrast medium.

Diagnostic Procedures

• Tracheal wash-for bacterial culture and sensitivity testing before administering antibiotics; infection often caused by multiple organisms with unpredictable susceptibility.
• Bronchoscopy-rarely indicated.
• Laryngeal function examination-always perform if patient anesthetized for other purposes; otherwise, after resolution of pneumonia if supportive clinical signs.

Drug(s)

• Antibiotic therapy-if signs of sepsis or severe compromise, ampicillin with sulbactam (20 mg/kg IV q8h) plus a fluoroquinolone IV. Adjust antibiotic selection based on results of airway cytology, C/S, and clinical response; continue for 10 days after resolution of clinical and radiographic signs.
• Beta agonist bronchodilators-sometimes cause dramatic improvement but have the potential to worsen ventilation:perfusion mismatch; most often helpful in acute aspiration or with auscultable wheezes.
• Short-acting corticosteroids-consider for up to 48 hours to combat inflammation associated with life-threatening aspiration.

Contraindications/Possible Interactions

• Diuretics-generally contraindicated; drying of airways reduces mucociliary clearance.
• Corticosteroids-contraindicated beyond initial stabilization; predispose patient to infection.
• Fluoroquinolones and chloramphenicol-can prolong clearance of theophylline-derivative bronchodilators; decrease theophylline dosage by 30–50% or prolong dosing interval.

Patient Monitoring

• Radiographs-evaluate every 2–7 days initially to determine appropriateness of treatment; then every 1–2 weeks.
• If signs do not resolve or suddenly worsen-possible recurrence of aspiration or a secondary infection; repeat diagnostic evaluation, including tracheal wash or bronchoscopy.

Prevention/Avoidance

• Predisposed patients undergoing anesthesia-cisapride (slow infusion, 1 mL/kg over 30 min) 1–2 hours pre-induction may decrease esophageal reflux.
• Suction esophagus prior to extubation.
• Antacids could decrease acid related lung injury in predisposed patients; may also increase risk of infection.

Possible Complications

• Secondary infection common.
• ALI/ARDS.
• Abscessation or granuloma formation rare.

Expected Course and Prognosis

• Prognosis-depends on severity of signs and ability to correct underlying disease.
• Severe aspiration-can be fatal.
• Recurrence-likely if underlying cause not addressed.

See Also

• Acute Respiratory Distress Syndrome
• Megaesophagus
• Pneumonia, Bacterial

Abbreviations

• ALI/ARDS = acute lung injury/acute respiratory distress syndrome
• C/S = culture and sensitivity
• WBC = white blood cell