OMISSION OF NITROUS-OXIDE DURING ANESTHESIA REDUCES THE INCIDENCE OF POSTOPERATIVE NAUSEA AND VOMITING - A METAANALYSIS

Background: Postoperative nausea and vomiting are important causes of morbidity after general anesthesia. Nitrous oxide has been implicated as an emetogenic agent in many studies. However, several other trials have failed to sustain this claim. The authors tried to resolve this i ssue through a meta-analysis of randomized controlled trials comparing the incidence of postoperative nausea and vomiting after anesthesia w ith or without nitrous oxide. Methods: Of 37 published studies retriev ed by a search of articles indexed on the MEDLINE database from 1966 t o 1994, 24 studies (26 trials) with distinct nitrous-oxide and non-nit rous oxide groups were eligible for the meta-analysis. The pooled odds ratio and relative risk were calculated. Post hoc subgroup analysis w as also performed to qualify the result. Results: The pooled odds rati o was 0.63 (0.53 to 0.75). Omission of nitrous oxide reduced the risk for postoperative nausea and vomiting by 28% (18% to 37%). In the subg roup analysis, the maximal effect of omission of nitrous oxide was see n in female patients. In patients undergoing abdominal surgery and gen eral surgical procedures, the effect of omission of nitrous oxide, alt hough in the same direction, was not significant. Conclusion: Omission of nitrous oxide reduced the odds of postoperative nausea and vomitin g by 37%, a reduction in risk of 28%.