Nitrous oxide (NWe systematically searched PubMed, the Cochrane Library, Embase, Web of science, China National Knowledge Infrastrusture (CNKI) and Wanfang Database up to August 10th, 2021. Randomized controlled trials (RCTs) were included if they compared N14 RCTs with 1751 patients were included. Pooled analysis suggested that NThe present meta-analysis suggested that N