Pulmonary aspiration

What it is

Pulmonary aspiration is the passage of gastric contents (acid, bile, food particles) past the vocal cords into the lungs. Anaesthesia removes the protective reflexes of coughing and swallowing and relaxes the lower oesophageal sphincter, so regurgitated material can run into the airway, most often at induction, during airway manipulation and at emergence. The lung injury has three overlapping forms: chemical pneumonitis from acid (classically called Mendelson syndrome), mechanical obstruction of airways by solid particles, and, later, bacterial aspiration pneumonia. Risk is highest with a full stomach (emergency surgery, recent food, bowel obstruction, pregnancy, delayed gastric emptying from diabetes, opioids or newer weight-loss drugs), with gastro-oesophageal reflux, obesity, a difficult airway, light anaesthesia and head-down positions. Prevention rests on fasting, aspiration prophylaxis and rapid-sequence induction; when it happens, the response is to stop more material entering the lungs, clear what is there, secure the airway and support oxygenation. Many patients who aspirate stay well; those who develop symptoms within a few hours can progress to severe hypoxaemia and acute respiratory distress syndrome.

How to recognise it

• Gastric fluid or food seen in the mouth, pharynx, around a supraglottic airway or inside the tracheal tube.
• Falling oxygen saturation that does not respond as expected to more oxygen.
• Wheeze, bronchospasm, coughing or laryngospasm, and a rise in airway pressure under ventilation.
• Crackles on auscultation and, later, infiltrates on the chest radiograph in the dependent lung segments.
• Tachypnoea, tachycardia and fever in the hours after the event if the patient was awake or extubated.

Why it happens

• Anaesthetic drugs abolish the cough and swallow reflexes that normally protect the larynx.
• Lower oesophageal sphincter tone falls, while a full stomach, raised intra-abdominal pressure or a head-down position raises the pressure pushing contents up.
• Acid burns the airway lining and alveoli, causing leaky capillaries, oedema and loss of surfactant: a chemical pneumonitis.
• Solid particles block small airways and cause collapse beyond them; bacteria carried in later cause pneumonia.
• The right lower lobe is often affected because the right main bronchus is wider and more vertical; supine patients soil the posterior segments.

What to do at once

1. Call for help and tell the surgeon — aspiration is a team problem and surgery may need to pause.
2. If not intubated, tilt head-down and turn the patient to the side — gravity drains material out of the mouth instead of into the trachea.
3. Suction the mouth and pharynx with a wide-bore sucker — clearing the upper airway limits further soiling.
4. Release cricoid pressure if there is active vomiting — pressure against a forceful vomit risks oesophageal injury.
5. Give the highest oxygen concentration available — hypoxaemia follows quickly from airway soiling and bronchospasm.
6. Secure the airway with a cuffed tracheal tube, usually by rapid sequence — the cuff seals the trachea against further aspiration.
7. Suction down the tube before ventilating where possible — this removes fluid before positive pressure drives it to the periphery.
8. Treat bronchospasm with inhaled bronchodilators and add positive end-expiratory pressure as needed — this reopens airways and collapsed alveoli.
9. Consider bronchoscopy if solid material was aspirated or lobar collapse appears — particles must be removed physically.
10. Pass an orogastric tube to empty the stomach — this lowers the risk of a second episode.

Costly mistakes

• Lavaging the lungs with saline: it spreads the acid and worsens oxygenation.
• Giving corticosteroids or prophylactic antibiotics by reflex; neither prevents the pneumonitis.
• Ventilating hard by mask before suctioning, which blows the aspirate deeper into the lungs.
• Extubating or sending the patient home too early after a witnessed aspiration, before the observation period has shown they are well.
• Forgetting the cause: an unrecognised full stomach, bowel obstruction or delayed gastric emptying will recur at the next anaesthetic.

Next step

• Observe for at least about two hours with saturation, respiratory rate and a chest examination; a patient who stays well can follow the usual pathway.
• Obtain a chest radiograph and an arterial blood gas if there are symptoms, an oxygen need or a fall in saturation.
• Call a senior and arrange high-dependency or intensive care for persistent hypoxaemia; ventilate with a lung-protective strategy if acute respiratory distress develops.
• Start antibiotics only for signs of pneumonia that appear later, or at once if the aspirate came from an obstructed bowel.
• Decide with the surgeon whether to continue the operation, then tell the patient, document the event and plan aspiration precautions for future anaesthetics.

Test yourself

Think of the answer, then tap the question to see it.

Add to my cards (4)

Elsewhere in DurgiPedia

• The causes of hypoxemia
• Ventilation–perfusion matching and West zones
• Airway suctioning: oral, nasal and artificial airways
• Dysphagia and aspiration precautions

Connections

← All of anaesthesia

Educational content; it does not replace supervised training, your institution's protocols or the anaesthetist's or intensivist's decision. It contains no doses and no ventilator or infusion settings.

Sources: Aspiration Pneumonia (StatPearls (NCBI Bookshelf), 2024).

Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake

Send

Representative model, for educational purposes only.