Available evidence does not support the claim that nitrous oxide affects mortality or cardiovascular morbidity.

pearl

• G Imberger, A Orr, K Thorlund, J Wetterslev, P Myles, and A M Møller.
• Copenhagen Trial Unit, Centre for Clinical Intervention Research, Rigshospitalet, Blegdamsvej 9, Copenhagen Ø DK-2100, Denmark.
• Br J Anaesth. 2014 Mar 1;112(3):410-26.

BackgroundThe role of nitrous oxide in modern anaesthetic practice is contentious. One concern is that exposure to nitrous oxide may increase the risk of cardiovascular complications. ENIGMA II is a large randomized clinical trial currently underway which is investigating nitrous oxide and cardiovascular complications. Before the completion of this trial, we performed a systematic review and meta-analysis, using Cochrane methodology, on the outcomes that make up the composite primary outcome.MethodsWe used conventional meta-analysis and trial sequential analysis (TSA). We reviewed 8282 abstracts and selected 138 that fulfilled our criteria for study type, population, and intervention. We attempted to contact the authors of all the selected publications to check for unpublished outcome data.ResultsThirteen trials had outcome data eligible for our outcomes. We assessed three of these trials as having a low risk of bias. Using conventional meta-analysis, the relative risk of short-term mortality in the nitrous oxide group was 1.38 [95% confidence interval (CI) 0.22-8.71] and the relative risk of long-term mortality in the nitrous oxide group was 0.94 (95% CI 0.80-1.10). In both cases, TSA demonstrated that the data were far too sparse to make any conclusions. There were insufficient data to perform meta-analysis for stroke, myocardial infarct, pulmonary embolus, or cardiac arrest.ConclusionThis systematic review demonstrated that we currently do not have robust evidence for how nitrous oxide used as part of general anaesthesia affects mortality and cardiovascular complications.

This article appears in the collection: Is nitrous oxide use safe in anesthesia?.

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