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Postoperative nausea and vomiting (PONV)
Risk is estimated from four simple factors, the baseline risk is lowered, and combined prophylaxis from several drug classes is given — and when prophylaxis fails, rescue comes from a different class.
Why it matters in the exam
The exam presents a young non-smoking woman with previous nausea coming for laparoscopic surgery and asks what the risk is and what the prophylaxis should be. It also asks about the side effects of each drug (QT prolongation, raised glucose, anticholinergic effects), the timing (dexamethasone at induction, ondansetron at the end of surgery) and the principle that the rescue drug must come from a different class.
The four adult risk factors are female sex, non-smoking, previous PONV or motion sickness, and opioids after surgery; each factor adds about 20%, from about 10% with none to about 80% with all four. Halogenated agents and N2O, long surgery and laparoscopy increase the risk; propofol intravenous anaesthesia, a nerve block instead of opioids and adequate fluids reduce it. Under the 2020 consensus, a patient with 1–2 factors receives two prophylactic drugs, and with more — three or four.
Postoperative nausea and vomiting are not just discomfort: they lengthen the stay in recovery, delay eating and discharge, and in some operations endanger the result — for example strain on sutures or bleeding. In children somewhat different risk factors are used, such as long surgery, age three or more and strabismus surgery. In exam questions an answer that offers only one drug for a patient with all the risk factors is usually not enough.
Key points
- Four risk factors: female, non-smoker, previous PONV or motion sickness, postoperative opioids.
- Each factor adds about 20% risk.
- Combined prophylaxis: 1–2 factors → two drugs; 3 or more → three or more.
- Ondansetron at the end of surgery, dexamethasone at induction, scopolamine in advance.
- Rescue from another class.
Summary table
| Class | Example and dose | Timing | Side effect |
|---|---|---|---|
| 5-HT3 antagonists | Ondansetron 4 mg IV | End of surgery | QT prolongation, constipation, headache |
| Steroid | Dexamethasone 4–8 mg IV | Induction | Raised glucose |
| Dopamine antagonists | Droperidol 0.625–1.25 mg, haloperidol, amisulpride | End of surgery | QT prolongation, extrapyramidal effects |
| NK1 antagonists | Aprepitant 40 mg PO | Before induction | Long-acting |
| Anticholinergic | Scopolamine patch | The evening before or 2 hours before | Dry mouth, blurred vision, confusion in the elderly |
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Sources
- Fourth Consensus Guidelines for the Management of Postoperative Nausea and Vomiting, 2020 — Risk assessment, prophylaxis and rescue
- Miller's Anesthesia, 9th edition (2020) — Postoperative Nausea and Vomiting
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.