Aspiration Pneumonitis During Anaesthesia

Aspiration pneumonitis is chemical lung injury from inhaled gastric contents during anaesthesia. Aspiration pneumonia is a later bacterial infection of the injured lung.

Epidemiology. It occurs in about 1 in 3,000 to 1 in 7,000 anaesthetics, up to 1 in 900 in emergency surgery. Mortality of clinically significant aspiration is about 5% overall and over 30% when it causes acute respiratory distress syndrome.

Risk factors. Emergency surgery, full stomach, bowel obstruction, pregnancy, obesity, diabetic gastroparesis, reflux, opioid use, light anaesthesia, difficult airway, head injury, and neurological or bulbar disease.

Pathophysiology.

Acid (gastric pH under 2.5, volume over 0.4 mL/kg) causes immediate epithelial burn and surfactant loss, followed 4 to 6 hours later by neutrophil driven inflammation. Particulate matter obstructs small airways. Bacterial infection can follow in 48 to 72 hours.

Visible gastric contents in the pharynx, sudden cough, wheeze, hypoxaemia, tachypnoea, tachycardia, bronchospasm, crackles and infiltrates. Silent aspiration may appear later as unexplained hypoxia.

Red flags.

• Saturation under 92% with 50% oxygen.
• Bilateral infiltrates (acute respiratory distress syndrome).
• Hypotension or shock.
• Particulate obstruction.

Clinical. Chest radiograph within 1 to 2 hours shows infiltrates in dependent segments (right lower and posterior upper lobes when supine). Blood gas, inflammatory markers and bronchoscopy for particulate matter. Fever and purulent sputum beyond 48 hours suggest infection.

Differential diagnosis.

• Anaphylaxis.
• Pulmonary oedema.
• Pulmonary embolism.
• Pneumothorax.
• Bronchospasm.
• Pneumonia from other cause.

Lower the head, suction the pharynx under vision before the next breath, turn the patient to the side, intubate if needed, and suction the trachea. Give 100% oxygen. Avoid saline lavage. Bronchoscopy removes particles.

Support: oxygen to saturation 94% to 98%, continuous positive airway pressure or lung protective ventilation (6 mL/kg ideal weight, plateau pressure under 30 cmH2O).

Antibiotics are not given for pneumonitis alone. Start them if a clinical infection develops (fever beyond 48 hours, purulent secretions, new infiltrate) or in bowel obstruction with faeculent aspirate.

• Amoxicillin-clavulanate: 1.2 g IV every 8 hours, then 625 mg orally every 8 hours; total 5 to 7 days; maximum 3.6 g IV daily; monitor liver function and rash; adjust for creatinine clearance under 30 mL/min (1.2 g then 600 mg every 12 hours).
• Piperacillin-tazobactam (hospital acquired or severe): 4.5 g IV every 6 hours for 5 to 7 days; maximum 18 g daily; monitor renal function and counts; reduce for creatinine clearance under 40 mL/min.

Corticosteroids are not advised.

Prevention. Fast before elective surgery, use rapid sequence induction with cricoid pressure in high risk patients, proton pump inhibitor or sodium citrate, a second generation airway device, and extubate awake.

• Sodium citrate 0.3 molar: 30 mL orally before induction, single dose; maximum 30 mL; monitor for nausea.
• Omeprazole: 40 mg orally or IV the night before and morning of surgery; maximum 80 mg daily; reduce in severe hepatic impairment.

Monitoring. Saturation, respiratory rate, temperature, chest radiograph at 4 to 6 hours and again if worsening.

Referral and escalation. Critical care for ventilation or acute respiratory distress syndrome. Bronchoscopy for obstruction.

Special groups. In pregnancy, give an antacid and use rapid sequence induction.