Postoperative nausea and vomiting

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Postoperative Nausea and Vomiting (PONV)

Definition and Incidence

PONV refers to nausea, retching, and/or vomiting occurring in the first 24-48 hours after surgery. Without prophylaxis, it affects approximately 30% of the general surgical population and up to 70-80% in patients with multiple predisposing risk factors. It is one of the most common and distressing complications in the postanesthesia care unit (PACU).

Pathophysiology

The vomiting reflex is coordinated by the vomiting center in the medulla, which receives input from multiple sources including:

Chemoreceptor trigger zone (CTZ) - located in the area postrema (outside the blood-brain barrier), rich in dopamine (D2), serotonin (5-HT3), neurokinin-1 (NK1), and opioid receptors
Vestibular system - histamine (H1) and acetylcholine (muscarinic) receptors dominate
Vagal afferents from the GI tract - 5-HT3 receptors
Higher cortical centers - emotion, pain, smell

Activating any of these receptor systems can precipitate nausea and vomiting, which guides pharmacologic targeting.

Risk Factors

Apfel Score (Adults) - Simplified Risk Prediction

Risk Factor	Points
Female gender	1
Nonsmoker	1
History of PONV or motion sickness	1
Postoperative opioid use	1
Total	0-4

Predicted PONV risk: 0 factors ~10% | 1 factor ~20% | 2 factors ~40% | 3 factors ~60% | 4 factors ~80%

Evidence-Based Risk Factor Classification (SAMBA Guidelines)

Category	Factors
Established risk factors	Female sex, history of PONV/motion sickness, nonsmoking status, younger age, general vs regional anesthesia, volatile anesthetics and N2O, postoperative opioids, longer anesthesia duration, surgery type (cholecystectomy, laparoscopic, gynecologic)
Conflicting evidence	ASA physical status, menstrual cycle, neostigmine for NMB reversal
Disproven/limited relevance	BMI, anxiety, nasogastric tube, supplemental oxygen, perioperative fasting, migraine

Pediatric Risk (Eberhart Score)

Surgery ≥30 min, age ≥3 years, strabismus surgery, history of POV or family history of PONV - scores 0-4 correspond to ~10%, 10%, 30%, 50%, 70% risk.

PONV Management Algorithm

Step 1: Risk Mitigation (Non-Pharmacologic)

Before reaching for antiemetics, reduce baseline risk:

Use regional anesthesia instead of general anesthesia when possible
Use propofol for induction AND maintenance (total intravenous anesthesia, TIVA)
Avoid nitrous oxide in surgeries lasting >1 hour
Avoid volatile anesthetics
Minimize intraoperative and postoperative opioids (multimodal analgesia, enhanced recovery pathways)
Ensure adequate hydration
Use sugammadex instead of neostigmine for neuromuscular blockade reversal

Step 2: Risk Stratification and Prophylaxis

Number of prophylactic agents should match risk level:

1-2 risk factors → 2 antiemetic agents
>2 risk factors (high risk) → 3-4 antiemetic agents

Pharmacologic Prophylaxis and Treatment

Drug Classes and Mechanisms

Drug Class	Agents	Key Notes
5-HT3 receptor antagonists	Ondansetron, granisetron, ramosetron	First-line; headache/constipation as side effects
NK1 receptor antagonists	Aprepitant (40 mg PO), fosaprepitant	Most effective single agent per Cochrane review; given preoperatively
Corticosteroids	Dexamethasone (4-8 mg IV)	Given at induction; risk of glucose intolerance, wound healing concerns
D2 receptor antagonists (butyrophenones)	Droperidol, haloperidol	Droperidol has FDA black box warning for QTc prolongation - requires ECG monitoring
D2 antagonists (phenothiazines)	Prochlorperazine, chlorpromazine	Sedation; extrapyramidal effects
Antihistamines (H1)	Diphenhydramine, promethazine, meclizine	Sedation, dry mouth; useful for motion-sickness-mediated PONV
Anticholinergics	Transdermal scopolamine, atropine	Applied 4 hours preoperatively; dry mouth, sedation, blurred vision
Propofol anesthesia	Propofol infusion	Antiemetic properties at subhypnotic doses; useful in high-risk patients

Key Dosing Points

Ondansetron: 4 mg IV at end of surgery (adults); 50-100 mcg/kg in children
Dexamethasone: 4-8 mg IV at induction
Aprepitant: 40 mg PO preoperatively - most effective single agent for reducing postoperative vomiting
Droperidol: 0.625-1.25 mg IV - effective but requires QTc monitoring due to FDA black box warning

Combination Therapy

Combination of agents from different classes is more efficacious than any single drug. The ondansetron + dexamethasone combination is the most widely used two-drug regimen.

Rescue Treatment

For breakthrough PONV (nausea/vomiting despite prophylaxis):

Use an antiemetic from a different drug class than the prophylactic agent used
If ondansetron was given prophylactically, giving another dose is unlikely to be effective - switch to a D2 antagonist, dexamethasone, or scopolamine patch
Low-dose propofol (20 mg IV boluses) can be used as rescue in the PACU

PONV vs PDNV

Postdischarge nausea and vomiting (PDNV) occurs after hospital discharge (>2 hours postoperatively in ambulatory patients). Risk factors slightly differ - female sex, age <50, history of PONV, opioid use in PACU, and nausea in PACU are the strongest predictors.

Special Considerations

Pregnancy: Ondansetron is the preferred antiemetic; avoid droperidol
Pediatrics: Ondansetron + dexamethasone combination is standard; droperidol is used but requires caution; propofol TIVA reduces risk
Cardiac patients: Avoid droperidol if prolonged QTc; haloperidol at low doses (0.5-1 mg) is safer
Laparoscopic/bariatric surgery: High-risk procedures; opioid-free or opioid-sparing anesthesia significantly reduces PONV (per 2025 meta-analysis, PMID 38578868)

Sources: Morgan and Mikhail's Clinical Anesthesiology 7e, p. 514-517; Sabiston Textbook of Surgery, Table 20.9; Barash Clinical Anesthesia 9e; SAMBA Consensus Guidelines (Gan TJ et al., Anesth Analg 2014)

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