Influence of nitrous oxide added to general anaesthesia on postoperative mortality and morbidity: a systematic review and meta-analysis.

BACKGROUND

Nitrous oxide (NO) is a common adjuvant to general anaesthesia. It is also a potent greenhouse gas and causes ozone depletion. We sought to quantify the influence of NO as an adjuvant to general anaesthesia on postoperative patient outcomes.

METHODS

We searched Medline, EMBASE, and Cochrane Central for works published from inception to July 6, 2023. RCTs comparing general anaesthesia with or without NO were included. Risk ratios (RRs) and standardised mean differences (SMDs) were calculated, along with 95% confidence intervals (CIs), using a random-effects model. Outcomes were derived from the Standardised Endpoints for Perioperative Medicine (StEP) outcome set. Primary outcomes were mortality and organ-related morbidity, and secondary outcomes were anaesthetic and surgical morbidity.

RESULTS

Of 3305 records, 179 full-text articles were assessed, and 71 RCTs, totalling 22 147 patients, were included in the meta-analysis. Addition of NO to general anaesthesia did not influence postoperative mortality or most morbidity outcomes. NO increased the incidence of atelectasis (RR 1.62, 95% CI 1.24 to 2.12) and postoperative nausea and vomiting (RR 1.27, 95% CI 1.15 to 1.40), and decreased intraoperative opioid consumption (SMD -0.19, 95% CI -0.35 to -0.04) and time to extubation (MD -2.17 min, 95% CI -3.32 to -1.03 min).

CONCLUSIONS

NO did not influence postoperative mortality or most morbidity outcomes. Considering the environmental effects of NO, these findings confirm that current policy recommendations to limit its use do not affect patient safety.

SYSTEMATIC REVIEW PROTOCOL

PROSPERO CRD42023443287.