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Meta Analysis
Nitrous Oxide-related Postoperative Nausea and Vomiting Depends on Duration of Exposure.
Post-op nausea & vomiting incidence is related to duration of nitrous oxide exposure, but is clinically insignificant at under 1 hour exposure.
pearl- Philip J Peyton and Christine Yx Wu.
- From the Department of Anaesthesia, Austin Health, Melbourne, Australia (P.J.P. and C.Y.W.); and Department of Surgery, Austin Hospital and University of Melbourne, Melbourne, Australia, and Institute for Breathing and Sleep, Victoria, Australia (P.J.P).
- Anesthesiology. 2014 May 1;120(5):1137-45.
BackgroundInclusion of nitrous oxide in the gas mixture has been implicated in postoperative nausea and vomiting (PONV) in numerous studies. However, these studies have not examined whether duration of exposure was a significant covariate. This distinction might affect the future place of nitrous oxide in clinical practice.MethodsPubMed listed journals reporting trials in which patients randomized to a nitrous oxide or nitrous oxide-free anesthetic for surgery were included, where the incidence of PONV within the first 24 postoperative hours and mean duration of anesthesia was reported. Meta-regression of the log risk ratio for PONV with nitrous oxide (lnRR PONVN2O) versus duration was performed.ResultsTwenty-nine studies in 27 articles met the inclusion criteria, randomizing 10,317 patients. There was a significant relationship between lnRR PONVN2O and duration (r = 0.51, P = 0.002). Risk ratio PONV increased 20% per hour of nitrous oxide after 45 min. The number needed to treat to prevent PONV by avoiding nitrous oxide was 128, 23, and 9 where duration was less than 1, 1 to 2, and over 2 h, respectively. The risk ratio for the overall effect of nitrous oxide on PONV was 1.21 (CIs, 1.04-1.40); P = 0.014.ConclusionsThis duration-related effect may be via disturbance of methionine and folate metabolism. No clinically significant effect of nitrous oxide on the risk of PONV exists under an hour of exposure. Nitrous oxide-related PONV should not be seen as an impediment to its use in minor or ambulatory surgery.
This article appears in the collections: Random Stuff, Is nitrous oxide use safe in anesthesia?, and Debunking anesthetic myths.
Notes
Related confirming the safety of nitrous oxide:
- Myles et al. ENIGMA-II trial (Lancet 2014): The safety of addition of nitrous oxide to general anaesthesia in at-risk patients having major non-cardiac surgery (ENIGMA-II)
- Møller et al. (BJA 2014): Does anaesthesia with nitrous oxide affect mortality or cardiovascular morbidity?
Daniel Jolley
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