Aspiration Pneumonitis (Mendelson Syndrome)

Who is at risk - Emergency surgery, inadequate anesthetic depth, GI pathology, obesity, opioids on board, impaired consciousness, lithotomy positioning, reflux, hiatal hernia, and a difficult airway. Aspiration occurs about 3 in every 10,000 anesthetics, more often in emergency cases and at higher ASA status.

Fasting rules are moving - NPO intervals are an unreliable predictor of gastric volume in diabetics, patients after gastric bypass, and patients on GLP-1 receptor agonists, and in trauma or emergency cesarean they may be moot. Check your institution's current fasting policy rather than working from memory.

When the history doesn't settle it, image the stomach - Point-of-care ultrasound of the gastric antrum shows whether the stomach is actually empty.

Every parturient is a full stomach - Progesterone relaxes the lower esophageal sphincter, gastric emptying is prolonged, and the gravid uterus raises intra-abdominal pressure. Almost all parturients have a gastric pH under 2.5 and more than 60% have gastric volumes over 25 mL. RSI with cricoid pressure, and expect a harder airway: roughly 1 in 150 obstetric patients is a difficult intubation and 1 in 280 a failed one, against 1 in 2,230 in the general population.

Pharmacologic prophylaxis - Nonparticulate antacid (sodium citrate 15 to 30 mL orally, repeated every 3 hours) keeps gastric pH above 2.5, and giving it immediately before induction is a safe, effective way to blunt acid injury if aspiration happens. An H2 antagonist added to sodium citrate raises pH at intubation more than placebo. Metoclopramide reduces gastric volume, increases LES tone, and cuts peripartum nausea.

If it happens on your table - Suction the oropharynx, put the patient head-down with the head turned to the side, and intubate if airway reflexes are blunted or hypoxia develops. Pass a soft suction catheter down the ETT before positive pressure drives material deeper.

Bronchoscopy is for particles - Flexible bronchoscopy and lavage are indicated when food or particulate matter has been aspirated, to clear obstruction and to retrieve samples for culture. It does nothing for acid already neutralized by the mucosa.

Don't reflex to antibiotics - Most aspiration events never become bacterial pneumonia. Hold prophylactic antibiotics, even with a new infiltrate, unless the patient is hemodynamically unstable, symptoms last beyond 48 hours, or there is another plausible source of infection.

Skip the steroids - Routine glucocorticoids for aspiration pneumonitis are not recommended.

Expect the course - Most cases settle within 24 to 48 hours on supportive care: supplemental oxygen or noninvasive positive pressure, with intubation and invasive ventilation in severe cases. Because chemical pneumonitis can move fast to ARDS, follow the A-a gradient and PaO2/FiO2 and get critical care involved early if either is worsening.

Emergence is a second exposure - Aspiration after extubation is real: among patients over 65 having cardiovascular surgery, 9.8% developed aspiration pneumonia, and in one series 12 of 123 events occurred after extubation.

Aspiration pneumonitis is acute chemical lung injury from inhaling sterile gastric contents. It is a different animal from aspiration pneumonia, which is an infectious process seeded by bacteria-laden oropharyngeal material, and the two are managed differently. Injury is most likely when the aspirate pH is below 2.5 and the volume is at least 0.3 mL/kg.

Acid injures type I pneumocytes, so protein-rich interstitial fluid leaks into the alveolus, and injures type II pneumocytes, so surfactant is lost and alveoli collapse. The result within the first one to two hours is atelectasis, pulmonary edema, shunt, and hypoxemia. A second, neutrophil-driven inflammatory phase arrives about four to six hours later. The right lower lobe is the classic target because the right mainstem is wider and more vertical, but whichever segment is dependent at the time decides. Severe cases progress to ARDS.