Postoperative Nausea and Vomiting

Postoperative nausea and vomiting (PONV) is nausea, retching or vomiting in the first 24 hours after surgery. It affects about 30% of surgical patients overall and up to 80% of those at highest risk when no prophylaxis is given. It delays discharge, causes dehydration and electrolyte loss, and can strain wounds and anastomoses.

Epidemiology. Nausea (about 50%) is more common than vomiting (about 30%). Up to a third of ambulatory patients have symptoms after discharge.

Risk factors. The simplified risk score counts female sex, non-smoking status, previous PONV or motion sickness, and expected postoperative opioid use. Scores of 0 to 4 carry risks of about 10%, 20%, 40%, 60% and 80%. Laparoscopic, gynaecological, breast, ENT, strabismus and bariatric surgery, age under 50 years, long operations, volatile agents, nitrous oxide and high dose neostigmine add risk.

Timing. Early PONV occurs within 2 to 6 hours, delayed PONV from 6 to 24 hours, and post-discharge symptoms after leaving hospital.

Pathophysiology.

The vomiting centre in the medulla integrates input from the chemoreceptor trigger zone, the vestibular system, the cortex and vagal afferents from the gut.

Five receptor systems drive it: serotonin 5-HT3, dopamine D2, histamine H1, muscarinic M1 and neurokinin NK1. Combining drug classes works better than increasing the dose of one class.

Triggers are volatile agents, opioids, gut manipulation, hypotension and pain.

Nausea, retching or emesis with pallor, sweating, salivation and tachycardia. Complications are dehydration, hypokalaemia, hypochloraemic alkalosis, aspiration, wound strain or dehiscence, bleeding at the operative site and delayed discharge.

Red flags.

• Vomiting persisting beyond 24 hours, or worsening after initial improvement.
• Abdominal distension, absent bowel sounds or bilious or faeculent vomit.
• Haematemesis, severe headache, new neurological signs or reduced consciousness.
• Chest or interscapular pain with surgical emphysema after forceful retching (oesophageal rupture).

The diagnosis is clinical once other causes are excluded. Check glucose, sodium, potassium, urea and creatinine if vomiting is prolonged. Image the abdomen if distension or pain is present, and the head if neurological features are present.

Differential diagnosis.

• Ileus or bowel obstruction.
• Anastomotic leak or peritonitis.
• Opioid effect.
• Hypotension, hypoglycaemia or hyponatraemia.
• Raised intracranial pressure.
• Adrenal insufficiency.
• Gastric stasis or a blocked nasogastric tube.

Prophylaxis directed by risk. With 0 to 1 risk factors use none or one agent. With 2 factors use two agents. With 3 to 4 factors use two or three agents from different classes plus propofol based total intravenous anaesthesia, avoiding nitrous oxide and volatile agents, with opioid sparing analgesia and adequate hydration.

Drug regimens.

• Ondansetron: 4 mg IV once at the end of surgery; no repeat within 6 hours; maximum 16 mg in a single IV dose; check QTc and electrolytes where risk exists; maximum 8 mg daily in severe hepatic impairment.
• Dexamethasone: 4 to 8 mg IV once after induction; single dose; maximum 8 mg for PONV; monitor glucose for 24 hours in diabetes; use 4 mg in diabetes or older age; avoid in uncontrolled infection.
• Droperidol: 0.625 to 1.25 mg IV once at the end of surgery; maximum 1.25 mg; ECG monitoring for 2 to 3 hours afterwards; avoid with long QT, hypokalaemia, hypomagnesaemia, bradycardia or other QT-prolonging drugs; use the lower dose in older adults.
• Aprepitant: 40 mg orally within 3 hours before induction; single dose; maximum 40 mg; monitor INR if on warfarin and note reduced efficacy of hormonal contraception; no renal adjustment.
• Hyoscine hydrobromide patch (1 mg released over 72 hours): one patch behind the ear the evening before surgery; wear up to 72 hours; maximum one patch; monitor for confusion, dry mouth and urinary retention; avoid in children, glaucoma and frail older adults.
• Cyclizine: 50 mg IV slowly, IM or orally every 8 hours; duration while symptomatic; maximum 150 mg daily; monitor heart rate; avoid in heart failure; reduce dose in older adults.
• Metoclopramide: 10 mg IV or orally every 8 hours; maximum 30 mg daily and 5 days; monitor for extrapyramidal effects; use 5 mg under 60 kg; halve the dose with creatinine clearance 15 to 60 mL/min and quarter it under 15 mL/min; avoid in bowel obstruction, phaeochromocytoma and Parkinson disease.

Rescue. Use a drug from a class not already given. Repeating the same class within 6 hours is ineffective. Propofol 10 to 20 mg IV bolus, repeated once if needed, is an option in the recovery room with airway monitoring. Maximum cumulative rescue dose is 40 mg.

Monitoring. Fluid balance, electrolytes, glucose when steroids are used, and QTc with ondansetron or droperidol where risk is present.

Referral and escalation. Review surgically if vomiting persists beyond 24 to 48 hours or if there is abdominal distension. Urgent neurosurgical review is needed with neurological signs.

Special groups. Children: ondansetron 0.1 mg/kg IV (maximum 4 mg) and dexamethasone 0.15 mg/kg IV (maximum 5 mg); strabismus and tonsillectomy are high risk. Older adults: limit anticholinergics and phenothiazines. Pregnancy: ondansetron and cyclizine are used after the first trimester.