Postoperative nausea and vomiting

Why examiners ask this

PONV is the complication patients fear most and the most common reason for delayed discharge. Examiners use it to test whether you stratify risk and prophylax by number, and whether you know that rescue needs a drug from a different class. It also hides complications: the vomiting patient after an eye operation, the diabetic with gastroparesis, the vomiting patient whose real problem is hypotension.

The 60-second answer

Decision points and the "why"

• Prophylaxis by number of factors — risk reduction is additive across classes; each drug reduces relative risk by about 25%, so the high-risk patient needs multimodal prophylaxis.
• Dexamethasone — given at induction because its onset is slow; 4–8 mg. In the PADDI trial a single 8 mg dose after induction reduced PONV, did not increase surgical-site infection (including in the 13% with diabetes), and caused slightly more hyperglycemia; I still give it to diabetics with glucose monitoring.²
• Ondansetron — 4 mg; the label says immediately before induction, but I give it at the end of surgery so its effect covers recovery. A second dose after failed prophylaxis adds no benefit.³ It prolongs the QT, so I avoid stacking QT-prolonging drugs in a patient with long QT.
• Droperidol and haloperidol — effective at low doses (0.625–1.25 mg droperidol); the boxed warning concerns QT prolongation and torsades, requires a 12-lead ECG before administration, and caps the initial dose at 2.5 mg.⁴
• Scopolamine patch — the label says apply it the evening before surgery and remove it 24 hours after.⁵ It causes dry mouth, blurred vision and confusion in the elderly; the Beers Criteria list it as highly anticholinergic, so I avoid it over 65.⁶
• Aprepitant — an NK1 antagonist with a long duration, 40 mg orally within 3 hours before induction;⁷ I add it for very high-risk patients and those for whom vomiting is dangerous: wired jaws, fresh fundoplication, or intracranial surgery.
• TIVA — removing volatiles reduces risk by about 25%, as much as one drug.

The complication they will inject

Ninety minutes after a laparoscopic sleeve gastrectomy, the patient, who received dexamethasone and ondansetron, is retching repeatedly. I examine the patient: blood pressure, heart rate, pain, abdominal distension and whether the vomit contains blood. Hypotension, hypoxemia or uncontrolled pain can present as nausea and need treatment first. I avoid repeating ondansetron within 6 hours because a second dose of the same class adds little;³ I give a drug from a different class: promethazine 6.25 mg, haloperidol 1 mg or a small dose of propofol 20 mg. I tell the surgeon, because retching after a sleeve or fundoplication risks a staple-line leak or wrap disruption, and I rule out a surgical cause.

Pitfalls that cost points

• Prescribing the same antiemetic for rescue.
• Giving dexamethasone at the end of surgery.
• Using one drug for a patient with four risk factors.
• Forgetting the children's risk factors: surgery over 30 minutes, age over 3, strabismus surgery, and personal or family history.
• Treating nausea without excluding hypotension or hypoxemia.

Rapid-why

Q: Why does propofol reduce PONV? A: It has an intrinsic antiemetic effect and replacing volatiles removes the main anesthetic cause; the effect is greatest in the first 6 hours.

Q: Why is post-discharge nausea and vomiting separate? A: It occurs after the patient leaves; risk factors include female sex, history of PONV, age under 50, opioids in the PACU and nausea in the PACU.

Q: Why does scopolamine cause confusion in the elderly? A: It is a tertiary amine and crosses the blood-brain barrier, producing central anticholinergic syndrome.

Q: Why give dexamethasone carefully in tumor lysis risk? A: Steroids can precipitate tumor lysis in patients with lymphoma or leukemia.

Numbers to know

Links

• Ambulatory anesthesia and discharge criteria, Volatile agents and nitrous oxide: when and when not, PCA and multimodal analgesia, Tonsillectomy and the bleeding tonsil, Morbid obesity and bariatric surgery
• Fourth Consensus Guidelines for the Management of Postoperative Nausea and Vomiting (2020)