Abstract: We reran the searches and included one new study (100 participants) in this updated review. In total, we included 11 studies with 829 participants, although most analyses were based on data from fewer participants and evidence of low quality. We noted substantial heterogeneity in the included trials. Thus, our results should be read with caution. It was not possible to combine trials for the primary outcome (LOER), but individual trials reported faster induction times (typically 24 to 82 seconds faster, 41 seconds (31.37 to 50.62)) with high initial concentration sevoflurane (six studies, 443 participants, low-quality evidence). Apnoea appeared to be more common in the high initial concentration sevoflurane group (risk ratio (RR) 3.14, 95% confidence interval (CI) 1.72 to 5.7, two studies, 160 participants, low-quality evidence). We found no evidence of differences between the two groups in the incidence of cough (odds ratio (OR) 1.23, 95% CI 0.53 to 2.81, eight studies, 589 participants, low-quality evidence), laryngospasm (OR 1.59, 95% CI 0.16 to 15.9, seven studies, 588 participants, low-quality evidence), breath holding (OR 1.16, 95% CI 0.47 to 2.83, five studies, 389 participants, low-quality evidence), patient movement (RR 1.14, 95% CI 0.69 to 1.89, five studies, 445 participants, low-quality evidence) or bradycardia (OR 0.8, 95% CI 0.22 to 2.88, three studies, 199 participants, low-quality evidence), and the overall incidence of complications was low. A high initial concentration sevoflurane technique probably offers more rapid induction of anaesthesia and a similar rate of complications, except for apnoea, which may be more common with a high initial concentration. However, this conclusion is not definitive because the included studies provided evidence of low quality.

Plain-language summary: We included in our review 11 randomized controlled trials (829 participants). These trials were conducted between 1997 and 2014 and differed with regard to participants (adults vs children), concentrations of sevoflurane used, addition of nitrous oxide and opioids and other factors. Some elements of the methods suggested low-quality evidence would be obtained. The studies could not always be combined, and study results cannot be stated with certainty. The high initial concentration technique shortened induction time (six studies, 443 participants, low-quality evidence) and led to similar rates of cough (eight studies, 589 participants, low-quality evidence), sudden sustained closure of the vocal cords that prevented breathing (seven studies, 588 participants, low-quality evidence), breath holding (five studies, 389 participants, low-quality evidence), sudden movements (five studies, 445 participants, low-quality evidence) and slow heart rate (three studies, 199 participants, low-quality evidence). The high initial concentration technique showed greater suspension of breathing when compared with the low initial concentration technique (two studies, 160 participants, low-quality evidence). The included studies provided low-quality evidence, and study results should be interpreted with caution. More studies are needed to enable firm conclusions.