Postoperative Nausea & Vomiting

Definition & Importance

Postoperative nausea and vomiting (PONV) is one of the commonest and most distressing complications of anaesthesia and surgery. Besides patient discomfort, it can cause dehydration, electrolyte disturbance, wound strain, aspiration and delayed discharge, so it is actively predicted, prevented and treated.

Risk Factors

Well-recognised patient risk factors (the Apfel score) are female sex, non-smoker, a history of PONV or motion sickness, and postoperative opioid use. Anaesthetic factors include volatile agents, nitrous oxide and opioids; surgical factors include gynaecological, laparoscopic, ENT/middle-ear and squint surgery.

Prevention & Treatment

Management combines reducing risk and anti-emetic drugs. Risk is reduced by using propofol/TIVA (propofol is anti-emetic), avoiding nitrous oxide and minimising opioids (multimodal, opioid-sparing analgesia), and ensuring good hydration. Anti-emetics from different classes are combined for prophylaxis in at-risk patients: ondansetron (5-HT₃ antagonist), dexamethasone, and a dopamine antagonist (e.g. Metoclopramide/droperidol), with additional agents to treat established PONV.

A Multimodal, Risk-stratified Approach

Modern management of postoperative nausea and vomiting is risk-stratified and multimodal: the patient’s risk is estimated from factors such as the Apfel score, and the number of preventive measures is matched to that risk. For the low-risk patient little or no prophylaxis may be needed, whereas the high-risk patient receives a combination of strategies — a propofol-based technique avoiding nitrous oxide and minimising opioids, adequate hydration, and two or more anti-emetics acting at different receptors given prophylactically. This layered approach, attacking the problem at several points rather than relying on a single drug, is far more effective than waiting for nausea to develop and then treating it, and it has become central to enhanced-recovery programmes because nausea and vomiting are major causes of patient distress and delayed discharge.

Anti-emetic Drug Classes

The anti-emetics used against postoperative nausea and vomiting act at different receptors, which is why they are combined for additive effect:

• the 5-HT₃ antagonists such as ondansetron block serotonin receptors and are a mainstay
• corticosteroids such as dexamethasone, given at induction, provide prolonged prophylaxis by an incompletely understood mechanism
• dopamine antagonists such as metoclopramide, droperidol and prochlorperazine block the chemoreceptor trigger zone
• antihistamines and anticholinergics (for example cyclizine and hyoscine) act on the vomiting pathways and vestibular input. Choosing agents from different classes for a high-risk patient attacks the problem at several points and is more effective than increasing the dose of any single drug.

Female, non-smoker, past PONV, opioid use — the four Apfel factors.

• PONV: very common; causes dehydration, electrolyte disturbance, aspiration, wound strain, delayed discharge.
• Apfel risk factors: female, non-smoker, previous PONV/motion sickness, postoperative opioids.
• Anaesthetic/surgical factors: volatiles, nitrous oxide, opioids; gynae/ENT/laparoscopic/squint surgery.
• Reduce risk: TIVA (propofol), avoid nitrous oxide, opioid-sparing analgesia, hydration.
• Prophylaxis: combine anti-emetic classes (ondansetron + dexamethasone ± dopamine antagonist).