FRCA Notes

Post-Operative Nausea and Vomiting

This topic appeared as an SAQ in March 2017, with the bulk of the marks on offer for knowing the risk factors for, and unwanted effects of, PONV.

An abysmal 36% pass rate on a CRQ on PONV from September 2020 left examiners 'surprised at the lack of knowledge in what is a very common anaesthetic topic'.

A repeat CRQ on the topic in 2024 was 'well answered' except for the side effects of ondansetron.

Relevant Primary FRCA topics

Resources

  • Post-operative nausea and vomiting is any nausea, vomiting or retching that occurs within 48hrs of surgery
  • 33% of patients undergoing elective surgery will experience N&V if no prophylaxis is given
    • Incidence as high as 80% if multiple risk factors present

  • NB PONV in paediatric patients is covered separately

Patient Organisational
Distress and reduced satisfaction Delayed return to baseline mobility
Raised ICP/IOP from retching Delayed day-case discharge
Dehydration from reduced oral intake Unplanned admission following day surgery
Secondary haemorrhage due to raised venous pressure Increaed healthcare costs
Wound dehiscence
Aspiration
Oesophageal trauma
Electrolye abnormalities



Patient factors Anaesthetic factors Surgical factors
Female gender Volatile anaesthetic agents Long duration of surgery
Non-smoker Use of nitrous oxide Laparoscopic surgery
History of motion sickness or PONV Use of opioids intra-/post-operatively Gynaecological surgery
Paediatric patient Middle ear ENT surgery
Dehydration Posterior fossa neurosurgery
Delayed gastric emptying Strabismus (squint) surgery
Breast surgery

  • Why does smoking reduce PONV? The mechanism appears to be via down-regulation of nicotonic acetylcholine receptors

  • There are a few risk-scoring systems available e.g.  Apfel, Koivuranta or Palazzo
  • The Apfel and Koivuranta scores are perhaps better than the Palazzo score in predicting PONV (Anaesthesiologica Scandinavica, 2001)
  • They are at best moderately accurate and don't provide a risk threshold above which anti-emetics should be administered, or below which they should not (Anaesthesia, 2005)
  • The Apfel is probably the most widely used, as it is marginally simpler than the Koivuranta score

Apfel score

  • Score 1 point for each of:
    • Female gender
    • Non-smoker
    • Previous history of motion sickness or PONV
    • Planned post-operative use of opioids

  • Higher score is associated with higher risk of PONV:
Score Risk of PONV in 24hrs post-op.
0 10%
1 21%
2 39%
3 61%
4 79%

  • This is reasonably similar to the outcome of the Koivuranta score, wich adds an extra possible point (for surgery duration >1hr)
  • Scoring full marks on the Koivuranta score nets you a PONV risk of 87%

Perioperative approach to reduce incidence of PONV


  • Identify patients at risk of PONV at anaesthetic (pre-)assessment
  • Anxiolysis with benzodiazepine premedication may reduce PONV in at-risk patients
    • Anxiety is not a robustly proven risk factor for PONV, but treating it may help
    • Benzodiazepines may modulate central inputs to the vomiting centre, or reduce anticipatory nausea, thus helping prevent PONV
  • Keeping starvation times to a minimum and use of peri-operative IV fluid hydration

Address modifiable risk factors

  • Avoid GA altogether i.e. use a regional or neuraxial technique
  • If GA is required, still use regional/neuraxial techniques in order to reduce both opioid and maintenance anaesthetic requirements

  • Use a TIVA technique
    • Reported absolute risk reduction in the region of 15 - 25%
    • A 2018 meta-analysis found propofol maintenance was associated with a relative risk of PONV of ~0.6 vs. volatile maintenance
    • Even employing a mixed propofol-volatile technique is superior to volatile agents alone with regards to incidence of PONV

    • Using sub-hypnotic doses of propofol (17mcg/kg/min) during volatile anaesthesia is mooted to reduce incidence of PONV
    • This has not been replicated and it seems sensible to just use TIVA if avoidance of PONV is the goal

  • Don't use nitrous oxide

  • Use sugammadex reversal of NMBA, which is associated with a significantly lower incidence of PONV vs. neostigmine reversal (BJA, 2022)

  • Use generous fluid hydration, especially in those undergoing day surgery

Anti-emetic prophylaxis

  • Use a multimodal anti-emetic approach; each additional antiemetic reduces risk of PONV by ∽30%
    • Some brave (American) souls used a five-drug combination in their "Aim for Zero" PONV and achieved ∽90% success

  • Which drug is best? One should naturally choose the drug(s) which offer the most benefit (effectiveness, pleiotropic effects) and least harm (side-effects, cost, availability)
  • If you can only plump for a single agent, it seems a NK1 receptor antagonist is probably your best bet in terms of efficacy, though isn't readily available in most UK trusts
  • Combination therapy is, however, de rigueur and a triple-whammy of dexamethasone, ondansetron and metoclopramide is about as good as it gets

  • Dexamethasone + ondansetron is probably the modal anti-emetic combination; its efficacy (risk ratio 0.3), cost (about £5 for the two), minimal side-effects and the other benefits of dexamethasone make it a suitable combination

  • Use of ye olde multimodal, opioid-sparing analgesic approach to minimise opioid-induced nausea/vomiting

  • Once established, it seems ondansetron is most efficacious at treating PONV, especially in those who haven't received any prophylaxis (Anesthesia & Analgesia, 2022)