Key Facts

PONV is one of the most common complications of anaesthesia, causing patient distress, delayed discharge, and increased healthcare costs. A multimodal approach to prevention and treatment significantly improves outcomes.

Epidemiology

Overall PONV incidence is approximately 30% without prophylaxis. In high-risk patients (Apfel score 3-4), incidence reaches 60-80%. PONV costs the NHS millions annually through prolonged recovery, unplanned admissions, and additional treatments. Patient surveys consistently rank PONV as one of the most undesirable post-operative outcomes.

Aetiology

Patient risk factors:

• Female sex (strongest patient factor)
• Non-smoker
• History of PONV or motion sickness
• Young age

Anaesthetic risk factors:

• Volatile anaesthesia (vs TIVA)
• Nitrous oxide (modest effect)
• Post-operative opioids
• Duration of anaesthesia (each 30 min increases risk by ~60%)

Surgical risk factors:

• Gynaecological (laparoscopy), ENT (middle ear, tonsillectomy), strabismus surgery, laparoscopic surgery

Pathophysiology

Vomiting is controlled by the vomiting centre in the lateral reticular formation of the medulla. Input arrives from:

• Chemoreceptor trigger zone (CTZ): Area postrema (outside BBB) — dopamine (D2), serotonin (5-HT3), NK1 receptors
• Vestibular system: Histamine (H1), muscarinic (M1) receptors — motion sickness component
• GI tract: Vagal afferents — 5-HT3 receptors on enterochromaffin cells
• Higher cortical centres: Anxiety, pain, smell

Antiemetics target these different receptor pathways, which is why combination therapy from different classes is more effective than single-agent therapy.

Risk Assessment (Apfel Score)

Clinical Presentation

• Nausea with or without vomiting in the first 24 hours post-operatively
• May be accompanied by retching, pallor, sweating
• Can lead to dehydration, electrolyte imbalance, aspiration risk
• Delayed discharge, unplanned overnight admission

Red Flags

• Persistent vomiting >24 hours — consider surgical complication (obstruction, ileus)
• Bilious vomiting — consider bowel obstruction
• Projectile vomiting — consider raised ICP (neurosurgical patients)
• Signs of aspiration — cough, wheeze, desaturation

Bedside

• Apfel score: Pre-operative risk assessment
• Observations: HR, BP (hypotension can cause nausea), temperature
• Fluid balance: Assess hydration status
• Abdominal examination: If persistent vomiting — exclude surgical cause

Bloods

• U&Es: If prolonged vomiting — electrolyte derangement (hypokalaemia, metabolic alkalosis)
• FBC: If concerned about post-operative complication

Imaging

• AXR/CT abdomen: If surgical cause suspected (obstruction, ileus)

Special Tests

• Not routinely required for straightforward PONV

Non-pharmacological

• Adequate hydration: IV fluids perioperatively
• Minimise opioids: Multimodal analgesia, regional anaesthesia
• TIVA: Propofol-based anaesthesia reduces PONV by ~30% vs volatile
• Avoid nitrous oxide: In high-risk patients
• Adequate analgesia: Pain itself is emetogenic
• Acupressure/acupuncture: P6 (Neiguan) point — some evidence of efficacy

Pharmacological

Prophylaxis (based on Apfel score):

• Low risk (0-1): No prophylaxis or single agent
• Moderate risk (2): Combination of 2 agents from different classes
• High risk (3-4): Combination of 2-3 agents + TIVA + minimise opioids

Antiemetic agents:

• Ondansetron 4mg IV (5-HT3 antagonist): At end of surgery — most commonly used
• Dexamethasone 6.6mg IV (steroid): At induction — cheap, effective, long-acting (DREAMS trial)
• Cyclizine 50mg IV (H1 antagonist): Effective for vestibular-mediated nausea
• Droperidol 0.625-1.25mg IV (D2 antagonist): Effective but risk of sedation, QT prolongation
• Prochlorperazine 12.5mg IM (D2 antagonist): Alternative
• Aprepitant 40mg PO (NK1 antagonist): For high-risk patients; expensive

Rescue antiemetic: Use agent from a DIFFERENT class to prophylaxis given

Surgical/Interventional

• Not applicable

Referral Criteria

• Persistent vomiting >24h — surgical review to exclude complication
• Severe PONV causing dehydration/electrolyte imbalance — IV fluids and electrolyte correction
• Recurrent PONV with subsequent anaesthetics — anaesthetic review for future planning

• Prophylaxis reduces PONV incidence by 40-60% compared with no treatment
• Combination therapy is more effective than single-agent prophylaxis (NNT 3-5 for combination vs 5-8 for single agent)
• TIVA + combination antiemetics can reduce high-risk PONV from 80% to <20%
• Day case impact: PONV is the most common cause of unplanned overnight admission (5-10% of day cases)
• Patient satisfaction: Effective PONV management significantly improves patient experience scores

Antiemetic Receptor Targets

Prophylaxis Strategy by Risk

Key Trials