Antiemetics and PONV Prophylaxis: Who Gets What
CA-1 · draft
CA-1 Bootcamp day 4. Authored from cited abstracts; every claim carries a PMID.
Not reviewed. This deck cannot be opened, downloaded or sent
until you approve it. Read every point and its source first — they were drafted
from search results, not from clinical judgement.
Before induction
The simplified risk score rests on four predictors - female sex, a history of motion sickness or previous postoperative nausea and vomiting, non-smoking status and the use of postoperative opioids - and with none, one, two, three or four of them present the incidence of nausea and vomiting was 10%, 21%, 39%, 61% and 79%.
In the 4,123-patient factorial trial ondansetron, dexamethasone and droperidol each cut the risk of postoperative nausea and vomiting by about 26%, propofol by 19% and omitting nitrous oxide by 12%, and because the interventions acted independently of one another their relative risks simply multiply.
Because the interventions are similarly effective and independent, prophylaxis is rarely warranted in low-risk patients, moderate-risk patients may benefit from a single intervention, and multiple interventions should be reserved for high-risk patients - which is the multimodal approach the fourth consensus guidelines recommend for all at-risk surgical patients.
Pooled across 60 trials, 4 to 5 mg of dexamethasone reduced 24-hour nausea and vomiting as effectively as 8 to 10 mg, with a number needed to treat of about 3.7 when used alone - so the bigger dose buys you nothing extra for this indication.
In 8,725 patients having noncardiac surgery, a single 8 mg dose of dexamethasone was noninferior to placebo for surgical-site infection at 30 days (8.1% versus 9.1%), including in patients with diabetes, so the infection worry that keeps residents from giving it is not supported.
Adding a single antiemetic to an inhalational anaesthetic gave the same overall risk of postoperative nausea and vomiting as substituting propofol total intravenous anaesthesia with no antiemetic at all (relative risk 1.06), so changing the anaesthetic and adding a drug are alternatives rather than a hierarchy.
Questions in the room
Name her risk factors out loud. Which belong to the patient and which belong to your anaesthetic?
You gave her ondansetron and she is retching in recovery. Do you give her more ondansetron?
Why does the dexamethasone go in at induction and the ondansetron towards the end?
What would you change about the anaesthetic itself, rather than adding another drug on top of it?
Oral boards stem
A 28-year-old non-smoking woman is having a laparoscopic cholecystectomy. She volunteers that she vomited for a full day after her wisdom teeth came out, and that she gets carsick. Your attending asks you how many risk factors she carries, roughly what her chance of postoperative nausea and vomiting is, and how many antiemetics she should leave the operating room having received.
Sources
Apfel et al., Anesthesiology 1999
PMID 10485781
Apfel et al., New England Journal of Medicine 2004
PMID 15190136
Gan et al., Anesthesia and Analgesia 2020
PMID 32467512
De Oliveira et al., Anesthesia and Analgesia 2013
PMID 23223115
Corcoran et al., New England Journal of Medicine 2021
PMID 33951362
Schaefer et al., European Journal of Anaesthesiology 2016
PMID 27454663
Approving says you read this deck, looked at its figures, and checked the board questions — including that every wrong option is actually wrong. Nothing else has checked those.