01Who is at risk
PONV is one of the most common and miserable side effects of anesthesia, and risk is additive — the more factors, the higher the chance (up to ~80% with several).
Patient factors (the Apfel score): - Female sex - Non-smoker - History of PONV or motion sickness - (Younger age, and) anticipated post-op opioids
Anesthetic / surgical factors: - Volatile anesthetics and nitrous oxide - Long duration of anesthesia - Type of surgery - Intra-op and post-op opioids
- The app's [Apfel calculator](/calculators/apfel) turns these factors into a risk estimate.
02Prevent it — strategy first, drugs second
The most powerful moves avoid the triggers:
- Favor regional anesthesia over general where appropriate.
- Use propofol for induction and as a maintenance infusion (TIVA); avoid volatile.
- Avoid nitrous oxide.
- Minimize opioids — lean on multimodal analgesia.
- Keep the patient adequately hydrated.
- Add prophylactic antiemetics (below), and have a rescue plan.
In a high-risk patient, you layer several of these — each independent measure adds protection.
03The antiemetic drugs
| Drug | Class | Dose | When |
|---|---|---|---|
| Dexamethasone | Steroid | 4 mg IV | At induction (give after the patient is asleep — it can cause intense perineal/genital burning on push) |
| Ondansetron | 5-HT₃ antagonist | 4 mg IV (or 8 mg ODT) | End of case, or as rescue in PACU |
A typical high-risk recipe: pre-op midazolam; intra-op no nitrous, dexamethasone at induction, a propofol infusion, dexmedetomidine and IV acetaminophen to spare opioids, generous fluids, and ondansetron at the end — then sips of clear liquid (slowly) in PACU.