Simplified Algorithm for the Prevention of Post-operative Nausea and Vomiting: A Before and After Study

Dewinter G, Staelens W, Veef E et al.

British Journal of Anaesthesia 2018: 120 (1): 156-163.


Would a simplified algorithm for PONV prophylaxis reduce the incidence of PONV in adult patients undergoing elective non-cardiac non-day-case surgery under general anaesthesia?

Study design

Quasi-experimental design

Single-centre, before and after study

2 x 5-working day audits (excl. Sat/Sun)

Initial audit using original algorithm Jan 12-18, 2016

Follow-up audit using simplified algorithm Nov 28 – Dec 2, 2016

University Hospitals Leuven, Belgium

Adult patients (Audit 1: 257 screened, 46 included, n=211. Audit 2: 231 screened, 30 excluded, n = 201) undergoing general anaesthesia

Inclusion criteria:

All adult patients >18 years old

Admitted to our post-anaesthesia care unit (PACU)

Undergoing elective, non-cardiac, non-day-case surgery, under general anaesthesia

Exclusion criteria:

Emergency procedures

Admitted to ICU/HDU

Patients expected to require overnight ventilation


Fisher’s exact and Manne Whitney U tests were used to compare groups

Uni and multivariable logistic-regression models with a binomial logit link function were used for all binary outcomes

Poisson regression was used for count data

Primary outcome a p-value of 0.025

24 h PONV incidence, the multivariable logistic regression was risk adjusted

Logistic-regression analyses, the 10% and 20% Apfel risk strata were combined



Initial algorithm

study design1

Simplified algorithm

study design2

Primary outcome

PONV incidence 1h and 24 h post-op

Secondary outcomes

  • Incidence of PON & POV
  • Accurate Apfel score
  • Compliance with guidelines
  • Anti-emetics administered
  • Use of a rescue medication


211 (1st) v 201 (2nd)

Primary outcome

Reduction in PONV over 24h (33% (69/211) vs 22% (45/201) P=0.02) RRR 33%, ARR 11%

Statistically significant when controlling for different confounders

Secondary outcomes

  • No difference in PON & POV over 1h or POV over 24h
  • Apfel score predicts PONV risk
    • But was poorly calculated (correct in 36% v 42%)
  • Simplified algorithm improved compliance with guidelines from 18% to 46%
  • Use of rescue medication reduced during 2nd audit
    • 58 pts (102 anti-emetics doses) v 30 (61), P=0.002


  • Low adherence to PONV guidelines is a well-known problem
  • Uncertain how best to improve compliance with guidelines
  • Electronic prompts/reminders rely on accurate calculation of risk – which was demonstrably poorly done – and have been shown not to work
  • Simplification is effective
  • Some patients will be over-treated but risk of harm is low


  • Relevant question
  • PONV an issue
  • Non-compliance with guidance is recognised issue
  • Sample reflective of KH
  • Reflective of KH practice
    • Similar drugs, similar groups
  • Well matched groups with bias minimised by lack of awareness of audit
  • Significant difference in PONV rates over 24h



  • Short observation periods
  • Study sample might not reflect the population incidence
  • Clinical guidelines are introduced by means of a lecture given to the residents in their preparation year; the first audit occurred 5 months, and the second audit occurred 4 months, after their commencement.
  • Poor calculation of PONV risk may have caused “non-compliance”
    • Correct calculation and knowledge/reminder of guidelines may have improved performance
  • Unclear cause of the reduction of the PONV incidence
    • Introduction of the simplified algorithm
    • Improved compliance with algorithm
    • Increased number of anti-emetics given


  • The beta-error (power) of the study is not specified
  • No data on ethnicity – ?generalisable
  • Majority of patients non-smokers and planned post-op opioid use
  • No mention of N2O
  • Significant number given no antiemetic (35% in initial audit)
  • No mention of cost analysis or SEs of anti-emetics
  • Un-blinded study with no control group
    • Risk of Reporting validity – measurement method/accuracy changed between audits
    • Risk of Regression-to-the-mean – particularly good or bad weeks
    • Risk that audit itself improved awareness and improved performance
    • Risk that introduction of novel guidelines (irrespective of content) improved awareness and improved performance

Study conclusions

The introduction of a radically simplified and mainly sex-centred PONV algorithm for the prophylaxis of PONV resulted in a significant reduction of PONV incidence and in a better compliance with the institutional algorithm.

Summary by Dr A Feben. Journal Club Meeting 27 June 2019.


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