Abstract: We included nine RCTs in this review involving 517 participants. Studies had a high or unclear risk of bias. The main reason for this was low methodological quality or missing data, even after study authors were contacted. Study size was generally small, with a minimum of 40, and a maximum of 73 participants. In one study (40 participants), three deaths in the LMA group and two deaths in the ETT group were reported, although none of the deaths were related to the procedure (very low-quality evidence). Five studies (281 participants) reported on procedure-related deaths, stating that no procedure-related death occurred at all (very low-quality evidence). It is uncertain whether there is a difference in the number of people experiencing one or more serious adverse event(s) between LMA and ETT (risk ratio (RR) 0.86, 95% confidence interval (CI) 0.41 to 1.80; 467 participants, 8 studies, very low-quality evidence). The duration of the procedure may be shorter in the LMA group (mean difference (MD) -1.46 minutes, 95% CI -1.92 to -1.01 minutes; 6 studies, 324 participants, low-quality evidence). However failure of procedure, as allocated by randomization, requiring conversion to any other procedure, may be higher in the LMA group (RR 2.82, 95% CI 1.22 to 6.52; 8 studies, 439 participants, low-quality evidence). We did not find any clear evidence of a difference between ETT and LMA groups for all other outcomes. Only one study provided follow-up data for late complications related to the intervention, showing no clear evidence of benefit for any treatment group. Evidence on the safety of LMA for PDT is too limited to allow conclusions to be drawn on either its efficacy or safety compared with ETT. Although the LMA procedure may shorten the period during which the airway is insecure, it may also lead to higher conversion rates. Also, late complications have not been investigated sufficiently. These results are primarily based on single-centre trials with small sample sizes, and therefore the level of evidence remains low. Studies with low risk of bias focusing on late complications and relevant patient-related outcomes are necessary for definitive conclusions on safety issues related to this procedure. The dependency of the successful placement of a LMA on the type of LMA used should also be further assessed. There are two studies awaiting classification that may alter the conclusions once assessed.

Plain-language summary: The evidence is current to January 2018. We included nine randomized controlled trials (517 participants). The trials included between 40 and 73 participants. Although use of the LMA procedure may shorten the period during which the airway is insecure, the procedure is more likely to have to be changed. Only one small study of 40 participants reported the number of people who died from any cause during their stay in hospital, without any difference between treatment groups. No deaths were caused by the procedure itself in the five studies (281 participants) that reported this outcome. Eight studies reported the number of participants with one or more serious adverse events, showing no clear evidence of a benefit for a laryngeal mask airway or endotracheal tube (467 participants). Serious adverse events that occurred were irregular rhythm of the heart beat, low blood oxygen concentrations, accidental displacement of the ETT or LMA, damage of parts of the ETT, minor bleeding and reflux of swallowed food into the airways. Neither method was superior in terms of preventing any adverse event. The duration of the procedure was clearly shorter in the laryngeal mask group, by well over a minute (6 studies, 324 participants). This benefit was associated with a higher risk of needing to change over to a different procedure (8 studies, 434 participants). Longer-term complications were not sufficiently investigated. We judged the quality of evidence to be very low or low because we could not obtain important information on the methods used to conduct these studies. We had serious concerns about study limitations, the small number of participants in the studies and the variation in findings within and between studies (imprecision). Most studies were limited in reporting on patient relevant outcomes. The first study was published in 2002 and techniques have improved over time since then.