Residency · Residency · Anesthesiology

PONV Prevention and Treatment: Evidence-Based Multimodal Approach

Introduction

Postoperative nausea and vomiting (PONV) affects 30% of all surgical patients and up to 80% of high-risk patients. Often described as more distressing than postoperative pain, PONV prolongs PACU stays, causes unanticipated admissions after ambulatory surgery, and in rare cases leads to aspiration, wound dehiscence, or esophageal rupture. An evidence-based, multimodal strategy targeting multiple receptor pathways is the modern standard of care.

Pathophysiology of PONV

Emetic Pathways

The chemoreceptor trigger zone (CTZ) in the area postrema (floor of the fourth ventricle) lies outside the blood-brain barrier and detects emetogenic substances in blood and CSF. The nucleus tractus solitarius (NTS) integrates afferent input from the CTZ, vestibular system, and vagal afferents from the GI tract. The vomiting center in the medullary reticular formation coordinates the motor act of emesis. Key neurotransmitter receptors involved include serotonin (5-HT3), dopamine (D2), neurokinin-1 (NK1), histamine (H1), and muscarinic cholinergic (M1).

Nausea vs. Vomiting

Nausea is a subjective sensation mediated by cortical and limbic pathways that can occur independently of vomiting. Retching and vomiting are motor reflexes coordinated by brainstem centers. Different antiemetics may be more effective for nausea versus vomiting.

Risk Factor Assessment

Patient-Related Risk Factors (Apfel Simplified Score)

The Apfel score identifies four independent predictors, each contributing one point: female sex, non-smoking status, history of PONV or motion sickness, and postoperative opioid use.

Anesthetic and Surgical Risk Factors

Volatile anesthetics have dose-dependent emetogenicity, with the greatest risk in the first 2 hours. Nitrous oxide modestly increases PONV risk (NNH approximately 12). Intraoperative opioids carry dose-dependent risk, though less predictive than postoperative opioid use. Higher risk surgeries include laparoscopic, gynecologic, strabismus, middle ear, and breast procedures. Each 30-minute increase in surgical duration raises risk by approximately 60%.

Pharmacologic Prophylaxis

First-Line Agents

Ondansetron (4 mg IV) is a 5-HT3 antagonist administered at the end of surgery with an NNT of approximately 6. It is the most widely used antiemetic with minimal side effects (headache, QTc prolongation at higher doses). Dexamethasone (4 to 8 mg IV) has an unclear mechanism (anti-inflammatory, central effects) and is administered at induction with an NNT of approximately 4. It offers added benefits of improved analgesia and reduced fatigue, though some avoid it in diabetics or when infection risk is a concern. Droperidol (0.625 to 1.25 mg IV) is a D2 antagonist that is effective but carries an FDA black box warning for QTc prolongation that limits use, though the risk is minimal at low doses. Aprepitant (40 mg PO) is an NK1 antagonist given preoperatively that is most effective for preventing vomiting (NNT approximately 5), with higher cost limiting routine use.

Second-Line and Adjunctive Agents

Scopolamine transdermal patch is applied the evening before or 2 to 4 hours preoperatively and is effective for up to 72 hours, with side effects including dry mouth, visual disturbance, and urinary retention. Promethazine (6.25 to 12.5 mg IV) is an H1 antagonist that is sedating and useful as rescue. Dimenhydrinate (1 mg/kg IV) is an H1 antagonist with modest efficacy. Haloperidol (0.5 to 1 mg IV/IM) is a D2 antagonist that is effective at low doses with minimal sedation. Metoclopramide (10 to 20 mg IV) is a weak antiemetic at standard doses and is not recommended as sole prophylaxis.

Multimodal Combination Strategy

Each antiemetic from a different receptor class provides an additive approximately 25% relative risk reduction. The consensus guideline recommendation is to use a number of antiemetics proportional to the Apfel score: no or single-agent prophylaxis for a score of 0 to 1, dual-agent prophylaxis (such as ondansetron plus dexamethasone) for a score of 2, and triple or quadruple prophylaxis plus baseline risk-reduction strategies for a score of 3 to 4.

Non-Pharmacologic Strategies (Baseline Risk Reduction)

TIVA with propofol reduces PONV by approximately 25% because propofol has intrinsic antiemetic properties. Avoiding nitrous oxide eliminates one risk factor. Minimizing intraoperative and postoperative opioids through multimodal analgesia (regional blocks, acetaminophen, NSAIDs, ketamine, lidocaine infusions) is effective. Adequate hydration with liberal IV fluids (20 to 30 mL/kg) reduces PONV compared to restrictive strategies. Acupuncture or acupressure at the P6 (Nei-Guan) point has evidence supporting efficacy equivalent to a single antiemetic agent (NNT approximately 5).

Treatment of Established PONV

Rescue Antiemetics

An agent from a different class than what was given for prophylaxis should be used. If no prophylaxis was given, ondansetron 4 mg IV is first-line rescue. Ondansetron should not be repeated within 6 hours of a prior dose. Low-dose propofol (20 mg IV bolus) provides rapid, short-lived antiemetic rescue in the PACU. Dexamethasone is not effective as rescue therapy due to its slow onset.

Refractory PONV

Underlying causes should be considered, including opioid-related effects (reduce or eliminate opioids), gastric distension (decompress with OG tube), hypotension, or increased intracranial pressure. Low-dose droperidol or haloperidol may be effective when first-line agents fail. NK1 antagonists (aprepitant, fosaprepitant) may be used for truly refractory cases.

PONV in Special Populations

In pediatric patients, risk factors include age greater than 3 years, strabismus surgery, and a history of PONV or motion sickness. Weight-based dosing is used (ondansetron 0.1 mg/kg, dexamethasone 0.15 mg/kg). In ambulatory surgery, PONV is the leading cause of unanticipated admission, warranting aggressive prophylaxis in moderate-to-high risk patients. Postdischarge nausea and vomiting (PDNV) affects up to 35% of patients after discharge, and rescue antiemetics such as ondansetron ODT should be prescribed to take home.

Clinical Pearls

PONV risk should be assessed for every patient using the Apfel score, with prophylaxis tailored accordingly. Multimodal prophylaxis combining agents from different receptor classes is always more effective than increasing the dose of a single agent. TIVA with propofol and avoidance of volatile agents is the most impactful single baseline risk-reduction strategy, providing approximately 25% relative risk reduction. Dexamethasone at induction plus ondansetron at the end of surgery is the most cost-effective two-drug combination for moderate-risk patients. Opioid-sparing analgesia is both a PONV-reduction and an enhanced-recovery strategy.

References

1. Gan TJ, Belani KG, Bergese S, et al. Fourth consensus guidelines for the management of postoperative nausea and vomiting. Anesth Analg. 2020;131(2):411-448.
2. Apfel CC, Laara E, Koivuranta M, et al. A simplified risk score for predicting postoperative nausea and vomiting. Anesthesiology. 1999;91(3):693-700.
3. Habib AS, Kezer T, Gan TJ. Evidence-based management of postoperative nausea and vomiting: a review. Can J Anaesth. 2004;51(4):326-341.
4. Eberhart LH, Morin AM, Wulf H, Geldner G. Patient preferences for immediate postoperative recovery. Br J Anaesth. 2002;89(5):760-761.

Read this lecture as Markdown