Association between nitrous oxide and the incidence of postoperative nausea and vomiting in adults: a systematic review and meta-analysis.

Some, but not all studies have suggested intra-operative use of nitrous oxide is correlated with postoperative nausea and vomiting. We performed a meta-analysis of randomised controlled trials to compare the incidence of nausea and vomiting in adults following general anaesthesia with or without nitrous oxide. We retrieved 30 studies (incorporating 33 separate trials) that investigated a 'nitrous oxide group' (total 2297 patients) vs a 'no-nitrous oxide group' (2301 patients). Omitting nitrous oxide significantly reduced postoperative nausea and vomiting (pooled relative risk 0.80, 95% CI 0.71-0.90, p = 0.0003). However, the absolute incidence of nausea and vomiting was high in both the nitrous oxide and no-nitrous oxide groups (33% vs 27%, respectively). In subgroup analysis, the maximal risk reduction was obtained in female patients (pooled relative risk 0.76, 95% CI 0.60-0.96). When nitrous oxide was used in combination with propofol, the antiemetic effect of the latter appeared to compensate the emetogenic effect of nitrous oxide (pooled relative risk 0.94, 95% CI 0.77-1.15). We conclude that avoiding nitrous oxide does reduce the risk of postoperative nausea and vomiting, especially in women, but the overall impact is modest.