Summary of findings for the main comparison. Summary of findings’ table 1.
| Nitrous oxide‐based compared to nitrous oxide‐free for general anaesthesia | ||||||
| Patient or population: adult patients 18 years and above undergoing standard general anaesthesia Settings: operating room Intervention: nitrous oxide‐based techniques Comparison: nitrous oxide‐free techniques | ||||||
| Outcomes | Illustrative comparative risks* (95% CI) | Relative effect (95% CI) | No of participants (studies) | Quality of the evidence (GRADE) | Comments | |
| Assumed risk | Corresponding risk | |||||
| nitrous oxide‐free | Nitrous oxide‐based | |||||
| Inhospital case fatality rate | Study population | OR 0.87 (0.61 to 1.26) | 10148 (8 studies) | ⊕⊕⊕⊝ moderate1 | — | |
| 12 per 1000 | 11 per 1000 (8 to 16) | |||||
| Moderate | ||||||
| 0 per 1000 | 0 per 1000 (0 to 0) | |||||
| Pneumonia | Study population | OR 1.68 (1 to 2.81) | 2699 (8 studies) | ⊕⊕⊝⊝ low2,3 | The sensitivity analysis suggested that the results of meta‐analysis was not robust. | |
| 17 per 1000 | 27 per 1000 (17 to 45) | |||||
| Moderate | ||||||
| 11 per 1000 | 18 per 1000 (11 to 30) | |||||
| Pulmonary atelectasis | Study population | OR 1.57 (1.18 to 2.1) | 2400 (5 studies) | ⊕⊕⊕⊕ high | — | |
| 79 per 1000 | 119 per 1000 (92 to 153) | |||||
| Moderate | ||||||
| 50 per 1000 | 76 per 1000 (58 to 100) | |||||
| Myocardial infarction | Study population | OR 1.01 (0.84 to 1.22) | 9246 (6 studies) | ⊕⊕⊕⊕ high | — | |
| 51 per 1000 | 51 per 1000 (43 to 61) | |||||
| Moderate | ||||||
| 65 per 1000 | 66 per 1000 (55 to 78) | |||||
| Stroke | Study population | OR 1.47 (0.86 to 2.53) | 9142 (4 studies) | ⊕⊕⊕⊝ moderate3 | — | |
| 5 per 1000 | 7 per 1000 (4 to 12) | |||||
| Moderate | ||||||
| 3 per 1000 | 4 per 1000 (3 to 8) | |||||
| Severe nausea and vomiting | Study population | OR 1.44 (0.97 to 2.15) | 11045 (10 studies) | ⊕⊕⊝⊝ low4,5 | The sensitivity analysis suggested that the results of meta‐analysis was not robust. | |
| 95 per 1000 | 131 per 1000 (92 to 184) | |||||
| Moderate | ||||||
| 108 per 1000 | 148 per 1000 (105 to 207) | |||||
| Length of hospital stay | The mean length of hospital stay in the intervention groups was 0.36 higher (0.69 lower to 1.4 higher) | 1103 (6 studies) | ⊕⊕⊕⊝ moderate5 | — | ||
| *The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% CI) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; OR: odds ratio. | ||||||
| GRADE Working Group grades of evidence High quality: further research is very unlikely to change our confidence in the estimate of effect. Moderate quality: further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. Low quality: further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. Very low quality: we are very uncertain about the estimate. | ||||||
1Serious imprecision: 95% CI of OR includes both 1.0 and 0.75/1.25. Downgraded by one level. 2Serious risk of bias: all studies were described as randomized but details were only provided by three; four studies described allocation concealment. Two studies blinded participants and personnel; six studies blinded outcome assessors. Downgraded by one level. 3Serious imprecision: 95% CI of OR includes both 1.0 and 1.25. Downgraded by one level. 4Serious risk of bias: all studies were described as randomized but details were only provided by three; four studies described allocation concealment. Four studies blinded participants and personnel; seven studies blinded outcome assessors. Downgraded by one level. 5Serious inconsistency: substantial heterogeneity with I² statistic > 50%. Downgraded by one level.