How should postoperative nausea and vomiting be prevented and managed in adult surgical patients, including risk assessment and prophylactic and rescue antiemetic therapy?

Postoperative Vomiting Management

All surgical patients should receive risk-stratified prophylactic antiemetic therapy with at least 2 antiemetic drugs from different classes before emergence from anesthesia, rather than waiting for vomiting to occur. 1

Risk Assessment

Assess every patient preoperatively using the Apfel score, which evaluates four key risk factors: 1, 2

• Female sex
• Non-smoking status
• History of motion sickness or previous PONV
• Expected use of postoperative opioids

Patients with ≥2 risk factors require multimodal prophylaxis with 2-3 antiemetics from different pharmacologic classes. 1

Prophylactic Antiemetic Regimen

Standard Risk (1 Risk Factor)

Administer ondansetron 4 mg IV plus dexamethasone 4-5 mg IV before the end of surgery. 2 This combination provides superior prevention compared to either agent alone through synergistic mechanisms targeting different receptor pathways. 3

High Risk (≥2-3 Risk Factors)

Use triple prophylaxis: ondansetron 4 mg + dexamethasone 4-5 mg + a third agent from a different class (such as droperidol, metoclopramide, or scopolamine). 1, 2 The combination approach is significantly more effective than monotherapy because these agents block different receptors (5-HT3, glucocorticoid, dopamine D2, muscarinic). 4, 5

Timing of Administration

Administer all prophylactic antiemetics before emergence from anesthesia, ideally 1 hour before surgery completion or after intubation for dexamethasone. 3 This timing ensures peak drug levels during the highest-risk period. 2

Rescue Therapy for Breakthrough Vomiting

If vomiting occurs despite adequate prophylaxis, immediately switch to an antiemetic from a different pharmacologic class than those used prophylactically. 2, 3 Using the same drug class for rescue reduces effectiveness. 3, 4

Rescue Algorithm

If ondansetron was used prophylactically, administer: 2, 3

• Haloperidol 0.5-2 mg IV/PO (dopamine antagonist), or
• Metoclopramide 10 mg IV (dopamine antagonist with prokinetic effects), or
• Prochlorperazine 5-10 mg IV/PO (dopamine antagonist)

These dopaminergic agents work through completely different mechanisms than 5-HT3 antagonists, providing additive benefit. 3

Adjunctive Risk Reduction Strategies

Beyond pharmacologic prophylaxis, implement these evidence-based measures: 1, 6

• Use total intravenous anesthesia (TIVA) with propofol rather than volatile anesthetic gases 1, 2, 4
• Implement multimodal opioid-sparing analgesia with acetaminophen and NSAIDs to reduce opioid requirements 1, 2
• Maintain adequate intravenous hydration and avoid hypotension 4, 6
• Facilitate early oral intake within 2-4 hours post-surgery when the patient is lucid 1, 2

Critical Pitfalls to Avoid

Never use single-agent prophylaxis in patients with multiple risk factors - this approach is insufficient and leads to preventable PONV. 2 Studies consistently demonstrate that combination therapy is significantly more effective than monotherapy in high-risk patients. 4, 5

Never underdose dexamethasone - doses below 4 mg are less effective. 2 The evidence supports 4-5 mg as the optimal dose for PONV prevention, with 8 mg reserved for specific high-risk scenarios. 3

Never wait for vomiting to occur before treating - prophylaxis is far more effective than rescue therapy. 2 The paradigm has shifted from reactive treatment to proactive prevention based on risk stratification. 7, 6

Never repeat the same antiemetic class for rescue therapy - if ondansetron was used prophylactically and PONV develops, switching to ondansetron again provides minimal additional benefit. 3, 4 Always use a different mechanism of action.

Never use liberal opioids without multimodal analgesia - opioids are a major modifiable risk factor for PONV. 2, 6, 8 Opioid-sparing techniques significantly reduce PONV incidence.

Special Considerations

Diabetic Patients

Monitor blood glucose when using dexamethasone, as it causes transient dose-dependent hyperglycemia in the first 24 hours. 3 Consider using the 4 mg dose rather than higher doses in diabetic patients, combined with another antiemetic class. 3

QT Prolongation Risk

Use ondansetron cautiously in patients with cardiac conduction abnormalities due to potential QT interval prolongation. 3 Consider alternative 5-HT3 antagonists or different antiemetic classes in high-risk cardiac patients.

Persistent Vomiting

For intractable PONV despite multimodal therapy, consider continuous infusion of antiemetics and ensure no underlying surgical complications (such as ileus, bowel obstruction, or increased intracranial pressure) are present. 3