Postoperative nausea and vomiting

What it is

Postoperative nausea and vomiting (PONV) is nausea, retching or vomiting in the first 24 hours after anaesthesia and surgery. It affects roughly one patient in three overall and most high-risk patients without prophylaxis, and patients often rate it as worse than pain. Besides distress it can cause dehydration, electrolyte loss, wound strain, bleeding, aspiration in a drowsy patient and delayed discharge. Vomiting is coordinated in the brainstem; it receives input from the chemoreceptor trigger zone (which senses drugs such as opioids and volatile agents), the gut through the vagus nerve, the vestibular system and higher centres, and these pathways use serotonin, dopamine, histamine, acetylcholine and substance P receptors. That is why antiemetics from different classes act at different sites and are combined. Risk is estimated before surgery, most often with the simplified Apfel score for adults (female sex, non-smoker, history of PONV or motion sickness, postoperative opioids). Prevention has two parts: reducing baseline risk (regional anaesthesia, propofol-based total intravenous anaesthesia, avoiding nitrous oxide and volatile agents when possible, opioid-sparing analgesia, adequate hydration) and giving prophylactic antiemetics, more of them as risk rises. If PONV occurs despite prophylaxis, treatment uses a drug from a different class from the one already given.

Key points

• PONV is defined in the first 24 hours; post-discharge nausea and vomiting is a separate problem after day surgery.
• Surgical factors such as laparoscopy, gynaecological surgery, cholecystectomy and longer operations are linked to higher rates, though patient factors predict risk best.
• Children have their own risk tools; strabismus surgery, age over three and longer operations increase their risk.
• Dexamethasone works best when given early, near induction, because its antiemetic effect takes time to start.
• A transdermal anticholinergic patch is applied before surgery because of its slow onset.

Components

• Vomiting centre: a network in the medulla that coordinates the vomiting reflex.
• Chemoreceptor trigger zone in the area postrema, outside the blood-brain barrier: senses drugs and toxins in the blood (dopamine D2, serotonin 5-HT3, NK1 receptors).
• Gut and vagus nerve: serotonin released from the gut wall after handling or distension activates vagal afferents.
• Vestibular system: movement after surgery triggers nausea through histamine H1 and muscarinic receptors, which is why motion sickness predicts PONV.

How it works

• 5-HT3 antagonists block serotonin at the vagal endings and the trigger zone; they are better at stopping vomiting than nausea.
• Dopamine antagonists (butyrophenones, benzamides) block D2 receptors in the trigger zone.
• NK1 antagonists block substance P at the vomiting centre and have a long duration.
• Corticosteroids reduce PONV by a mechanism not fully known, probably central and anti-inflammatory.
• Antihistamines and anticholinergics act on the vestibular pathway and the vomiting centre.

Step by step

1. Assess risk before surgery with a validated score — the number of factors guides how much prophylaxis to give.
2. Reduce baseline risk where possible: regional anaesthesia, propofol-based anaesthesia, opioid-sparing analgesia — fewer triggers means less PONV.
3. Give prophylaxis from one or more classes according to risk, timing each drug correctly — combinations add effect.
4. If PONV occurs, check for causes such as hypotension, hypoxaemia or pain — the vomiting may be a sign of another problem.
5. Treat with a class not yet given, and reassess — a drug that failed as prophylaxis rarely works soon after as rescue.

In practice

• Before giving an antiemetic, look for treatable causes: hypotension, hypoxaemia, pain, a full stomach, blood in the stomach, bowel obstruction or opioid excess.
• A patient with long QT or on QT-prolonging drugs needs care with 5-HT3 and dopamine antagonists: check the ECG and electrolytes.
• Dopamine antagonists can cause acute dystonia and akathisia and are avoided in Parkinson disease.
• Anticholinergics and sedating antihistamines can cause confusion, dry mouth and urinary retention in older patients.
• Continuing nausea after discharge should be considered in day-case planning: give oral options and clear advice.

Next step

• Record the risk score and the prophylaxis given in the anaesthetic record and in the handover.
• If vomiting continues after two classes, call the anaesthetist and look for a surgical or medical cause.
• In a drowsy patient who vomits, turn them on their side and suction the airway to prevent aspiration.
• Correct dehydration and electrolytes when vomiting has been prolonged.
• Day-case patients with high risk should go home with advice on nausea and a plan for oral antiemetics.

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Elsewhere in DurgiPedia

• Vomiting and its control
• Postoperative complications: recognising them and when to call
• Immediate recovery after anaesthesia: monitoring and discharge criteria

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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: Postoperative Nausea (StatPearls (NCBI Bookshelf), 2022).

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