PONV: Multimodal by Apfel Score

Pharmacology II · 7 min read

Match the number + class of antiemetics to risk. Score Apfel pre-op, choose 0/2/3/4 agents, layer non-pharmacologic strategies. Single-agent prophylaxis is undertreatment in high-risk patients.

Why this matters

PONV affects 20-30% of all anesthesia patients and up to 80% of high-risk patients. It causes patient dissatisfaction, delays discharge from PACU, increases unanticipated admission from ambulatory surgery, and complicates wound healing (vomiting tension on closures). Multimodal prophylaxis — combining 2-4 agents from different mechanism classes — is more effective than maximizing one class. The dominant modern framework is RISK-STRATIFIED prophylaxis using the Apfel score.

Apfel score — 30 seconds at the bedside

Four predictors, each worth 1 point. (1) FEMALE SEX. (2) NON-SMOKER. (3) HISTORY of PONV or motion sickness. (4) ANTICIPATED postoperative OPIOID use. Score → risk: 0 factors = 10%, 1 factor = 21%, 2 = 39%, 3 = 61%, 4 = 79%. Recalculate when surgery type changes (laparoscopy, gynecologic, otologic, ENT all add risk). Apfel beats individual surgeon predictions in published data — the score forces you to count.

Match agents to score

0 factors → no prophylaxis (or single low-cost agent in some protocols). 1-2 factors → 2 agents from DIFFERENT mechanism classes. 3-4 factors → 3-4 agents + non-pharmacologic strategies (TIVA, regional). Why different classes matters: mechanism saturation. Giving two 5HT3 antagonists doubles the cost without adding much benefit — the receptors saturate. Combining ondansetron (5HT3) + dexamethasone (steroid) + droperidol (D2) hits three independent pathways and the effects are additive.

Pharmacologic class menu

(1) 5HT3 ANTAGONIST — ondansetron 4 mg IV at end of case (peak effect at emergence); palonosetron 0.075 mg longer-acting alternative. Modest QT prolongation. (2) STEROID — dexamethasone 4-10 mg IV at INDUCTION (effect develops over hours, not minutes). Also analgesic + antiinflammatory adjunct. (3) D2 ANTAGONIST — droperidol 0.625 mg IV (FDA black box for QT but low-dose safe per modern data); haloperidol 0.5-2 mg alternative; metoclopramide 10 mg also gives prokinetic effect. EPS in young/female patients — pretreat with diphenhydramine if higher dose. (4) NK1 ANTAGONIST — aprepitant 40-80 mg PO 1-3 h pre-op; long-acting (24-48 h coverage); expensive — reserve for highest-risk + prolonged surgery. (5) ANTICHOLINERGIC — scopolamine patch 1.5 mg behind ear pre-op (4 h onset, 72 h effect); CAUTION in elderly + glaucoma + BPH (delirium + retention). (6) ANTIHISTAMINE — diphenhydramine 12.5-25 mg IV; sedating; useful for vestibular component.

Non-pharmacologic — multiplier

TIVA with PROPOFOL reduces PONV by 25-50% vs volatile-based anesthesia — single biggest non-pharmacologic intervention. AVOID N2O when feasible (especially >50% concentration, prolonged use). REGIONAL ANESTHESIA / EPIDURAL when appropriate — reduces opioid dose by 50-80% in major thoracic + abdominal surgery, eliminating one of the four Apfel factors. ADEQUATE HYDRATION peri-op (dehydration worsens PONV). P6 ACUPRESSURE wristband (Sea-Band) — modest but real evidence; cheap + safe; let the patient apply pre-induction. Avoid prolonged NPO (start clear liquids 2 h pre-op per ASA fasting guidelines). Treat post-op pain aggressively — pain itself is emetogenic and pain medications add another opioid hit.

Rescue when prophylaxis fails

Rescue with a DIFFERENT mechanism class than was used prophylactically. If ondansetron given prophylactically → use droperidol or dexamethasone for rescue (not more ondansetron — receptors already saturated). If only dexamethasone given prophylactically → use ondansetron 4 mg IV. CHECK the obvious: pain (treat first), hypoxia, hypotension, full bladder, gastric distention (NG decompression if intubated for prolonged surgery), hypoglycemia. Persistent PONV despite multimodal rescue → consider haloperidol 1-2 mg IV or rare cases olanzapine.

Pearl — score, then layer

The single biggest mistake in PONV prophylaxis is reflexive single-agent treatment regardless of risk. A Apfel-4 patient getting 4 mg ondansetron alone is being undertreated. The corollary is overprophylaxis: an Apfel-0 patient doesn't benefit from triple-class drugs. Score, layer, document. PONV is one of the most reliably preventable patient dissatisfactions in anesthesia.

References

· SAMBA 4th Consensus PONV Guidelines 2020
· Apfel CC, NEJM 2003 (multimodal antiemetic strategies)
· Stoelting Pharmacology 6e Ch 23