Aspiration of gastric contents

Why examiners ask this

Aspiration is the complication that justifies most of what I do at induction and extubation, so the examiner uses it to test two things: whether I could have predicted and prevented it, and whether I treat the patient who has aspirated by physiology rather than by reflex. It stresses judgment, because the hardest question is "do you proceed with surgery?", and adaptability, because the inject arrives as a desaturation under drapes with no obvious cause.

The 60-second answer

Decision points and the "why"

• Suction before ventilation — positive pressure drives acid and particulate matter distally; thirty seconds of tracheal suction through the tube is worth the delay, provided the saturation allows it.
• No bronchial lavage — saline spreads the acid and adds no benefit; I use bronchoscopy only to remove visible particulate matter, because solid obstruction causes atelectasis and later abscess.
• No empiric antibiotics — early aspiration is a chemical pneumonitis, while bacterial aspiration pneumonia usually declares itself at 48 hours or later;¹ antibiotics select resistant organisms and I reserve them for a patient who develops fever, purulent sputum and a persistent infiltrate, is severely unwell, or aspirated particulate or bowel content.
• No steroids — they have no proven benefit in either pneumonitis or pneumonia.¹
• Proceed or stop — I weigh the surgical urgency against the trajectory: a patient with stable oxygenation on an FiO2 of 0.4 can have an urgent appendectomy; a patient with rising pressures and a saturation of 90% on 100% oxygen has nowhere to go, and the surgery stops.
• Extubation decision — a patient who aspirated a small volume, is oxygenating well on minimal support and has a clear radiograph at two hours can be extubated and observed; everyone else stays intubated, because the pneumonitis peaks at 24–48 hours.
• Prevention in the next patient — fasting by ASA guidelines, including clear liquids, with or without carbohydrate, up to 2 hours before,³ prokinetics and antacids where indicated, rapid sequence for the full stomach, gastric ultrasound when uncertain, and an awake extubation in the lateral position for the patient at risk.

The complication they will inject

Two hours after an uneventful appendectomy the PACU nurse reports a saturation of 86% on 6 L/min nasal cannula, tachypnea and a cough productive of frothy sputum, with bilateral crackles. I recognize a chemical pneumonitis declaring itself, and my differential includes negative-pressure pulmonary edema, atelectasis, and transfusion or fluid overload. I give high-flow oxygen or non-invasive ventilation with PEEP, sit the patient up, send a gas and a radiograph, and look for the bilateral or right-lower-lobe infiltrate. I call the ICU early, because if the work of breathing rises or the PaO2/FiO2 ratio falls below 150 I intubate before the patient tires, using lung-protective ventilation at 6 mL/kg ideal body weight. I speak to the patient and family, document the event, and report it through the quality system.

Pitfalls that cost points

• Reaching for antibiotics and steroids as the "treatment" of aspiration.
• Lavaging the bronchial tree.
• Proceeding with elective surgery after a witnessed aspiration.
• Extubating a patient who aspirated because the saturation is fine at 20 minutes.
• Attributing the PACU desaturation to opioids and giving naloxone without examining the chest.

Rapid-why

Q: Why does right-sided aspiration predominate? A: The right main bronchus is wider and more vertical; supine patients aspirate into the posterior segments of the upper lobes and the superior segments of the lower lobes.

Q: What makes an aspirate dangerous? A: Classic teaching is pH below 2.5 and volume above 25 mL (about 0.4 mL/kg), thresholds arbitrarily extrapolated from 1970s animal data,⁴ and particulate matter and bacterial load matter as much; the numbers are a guide, not a threshold for action.

Q: Why is the laryngeal mask a risk factor? A: It does not seal the esophagus, it abolishes the swallow and lowers the tone of the upper esophageal sphincter, and positive-pressure ventilation above 20 cmH2O can insufflate the stomach.

Q: Why does a patient who aspirates at induction often look fine for an hour? A: The acid injury takes hours to produce alveolar flooding and the inflammatory response peaks at 24–48 hours; early reassurance is the trap.

Numbers to know

Links

• Rapid sequence induction and full stomach, ARDS and lung-protective ventilation (coming), laryngospasm, Intraoperative bronchospasm, Postoperative mechanical ventilation and weaning
• Atlas: Lung ultrasound: pleura, A/B-lines, effusion, pneumothorax; Monitor atlas: perioperative respiratory events
• ASA Practice Guidelines for Preoperative Fasting (2023 update)