The quality of evidence is downgraded by indirectness (direct comparisons not available).
A Cochrane review 1[Abstract] included 7 studies with a total of 547 patients, comparing nitrous oxide to placebo or active comparators in elective colonoscopic procedures. Patients with known underlying causes of pain/discomfort were excluded.
A statistical meta-analysis was not possible on the included studies because the results of the data could not be pooled or compared for all the studies. 257 patients were randomized to receive the N2O/O2 mixture (7 studies), while 225 patients received some form of sedation with or without other analgesia (6 studies), and 65 patients received a placebo (3 studies). Four studies showed that N2O/O2 is as good in controlling pain/discomfort as conventional methods, while one showed sedation was better and another study showed N2O/O2 was better. Six of the studies showed that N2O/O2 groups had quicker recovery times and shorter lengths of hospital stays while one study showed that there was no difference between the two groups. Two studies showed that N2O/O2 was safer while one reported that sedation was safer.
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