01Why It Matters
- Up to 1/3 of all GA patients experience PONV without prophylaxis (80% in high-risk).
- Patients rank avoiding PONV higher than postop pain.
- Leading cause of delayed PACU discharge and unanticipated hospital admission.
- Risk for aspiration, dehydration, ↑ ICP/CVP, wound dehiscence, suture/mesh disruption, venous bleeding.
02Major Risk Factors
Patient: - Female > male - History of PONV or motion sickness - Young > old - Non-smoker > smoker
Anesthetic: - Volatile anesthetics (including N₂O) - Postoperative opioids - Neostigmine - Aggressive hydration (gut edema)
Surgical: - Duration > 2 h - Type of surgery has less effect than once taught; laparoscopic, ENT, neuro, breast, plastics, strabismus all generally high-risk in classic teaching
03Simplified Apfel Score
Count of: Female + Non-smoker + History of PONV/motion sickness + Postoperative opioids.
| Risk factors | PONV risk |
|---|---|
| 0 | ~10% |
| 1 | ~20% |
| 2 | ~40% |
| 3 | ~60% |
| 4 | ~80% |
Apfel meta-analysis ORs: - Female 2.57 - History of PONV/motion sickness 2.09 - Non-smoking 1.82 - Volatile anesthetics 1.82 - Postop opioids 1.39 - Younger age 0.88 per decade
04Prophylaxis Strategy
- 0–1 risk factors: no prophylaxis or single agent
- 2: two-drug prophylaxis (5-HT3 + steroid)
- 3: multimodal — 5-HT3 + steroid + TIVA, ± scopolamine patch
- 4: aggressive multimodal — TIVA + ≥ 3 agents (5-HT3, steroid, NK1, scopolamine, droperidol)
Pearls: - Combinations must be different mechanisms to be additive - Do not redose the prophylactic agent for PACU rescue — choose a different class - Use regional anesthesia over GA where possible - Use propofol for induction; consider TIVA - Avoid N₂O and high-dose neostigmine
05Antiemetic Classes
5-HT3 antagonists (Ondansetron, Granisetron): Zofran 4–8 mg IV ~30 min before emergence. SE: headache, QT prolongation. More effective at preventing emesis than nausea.
Steroids (Dexamethasone): 4–10 mg IV at induction (NOT awake — causes severe perineal itch). Mechanism unclear. Cheap; for prolonged relief. Use cautiously in DM, sepsis.
Anticholinergics (Scopolamine patch): 1.5 mg TD q72h posterior to ear; place 2–4 h before case. SE: dry mouth, blurred vision, urinary retention, confusion in elderly. Warn patients not to touch patch then eye → pupil dilation.
Dopamine antagonists: - Metoclopramide (Reglan): 10–20 mg IV; ↑ GI motility; CI in bowel obstruction, Parkinson's; extrapyramidal SE - Promethazine (Phenergan): 12.5–25 mg IV; sedating; H1 antagonist also - Prochlorperazine: 5–10 mg
Butyrophenones (Droperidol, Haloperidol): Droperidol 0.625–1.25 mg IV at end of case. Effective but FDA black-box for QT (based on doses 50–100× standard). CI in Parkinson's.
NK1 antagonists (Aprepitant, Fosaprepitant): Most effective for refractory PONV and posterior-fossa neuro cases. Expensive; pre-order from pharmacy. PO 3 h before induction.
Propofol sub-hypnotic doses (10–20 mg IV PACU rescue) or background TIVA.