[Show abstract][Hide abstract] ABSTRACT: We have reviewed randomized controlled trials to assess the effectiveness and safety of anaesthetics which omitted nitrous oxide (N2O) to prevent postoperative nausea and vomiting (PONV). Early and late PONV (6 and 48 h after operation, respectively), and adverse effects were evaluated using the numbers-needed-to-treat (NNT) method. In 24 reports with information on 2478 patients, the mean incidence of early and late vomiting with N2O (control) was 17% and 30%, respectively. Omitting N2O significantly reduced vomiting compared with a N2O regimen; the combined NNT to prevent both early and late vomiting with a N2O-free regimen was about 13 (95% confidence intervals (CI) 9, 30). The magnitude of the effect depended on the incidence of vomiting in controls. In studies with a baseline risk higher than the mean of all reports, the NNT to prevent both early and late vomiting with a N2O-free anaesthetic was 5 (95% CI 4, 10). When the baseline risk was lower than the mean, omitting N2O did not improve outcome. Omitting N2O had no effect on complete control of emesis or nausea. The NNT for intraoperative awareness with a N2O-free anaesthetic was 46 compared with anaesthetics where N2O was used. This clinically important risk of major harm reduces the usefulness of omitting N2O to prevent postoperative emesis.
BJA British Journal of Anaesthesia 03/1996; 76(2):186-93. DOI:10.1093/bja/76.2.186 · 4.85 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: All obtainable investigations that have compared the incidence of vomiting in groups of patients who received nitrous oxide (N2O) and in patients who received anesthetics or analgesics without N2O were examined for a single, dichotomous variable: whether patients who received N2O experienced an absolutely higher incidence, as distinct from a statistically significantly higher incidence, of vomiting. The null hypothesis is that N2O has no effect on emesis, such that an increased incidence of vomiting should occur in about half of the studies examined. However, patients receiving N2O experienced an absolutely higher incidence of emesis in 24 of 27 investigations. The two-tailed probability that this result occurred by chance is < 0.00005. It follows that N2O increases the incidence of emesis compared to alternative anesthetics.
[Show abstract][Hide abstract] ABSTRACT: 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.
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