Abstract: We included eight RCTs that involved a total of 829 participants (416 and 413 participants in the pLMA and cLMA groups, respectively). We identified six cross-over studies that are awaiting classification; one is completed but has not been published, and data related to the first treatment period for the other five studies were not yet available. Seven included studies provided data related to the primary outcome, and eight studies provided data related to more than one secondary outcome. Our analysis was hampered by the fact that a large proportion of the included studies reported no events in either study arm. No studies reported significant differences between devices in relation to the primary review outcome: failure to adequately mechanically ventilate. We evaluated this outcome by assessing two variables: inadequate oxygenation (risk ratio (RR) 0.75, 95% confidence interval (CI) 0.17 to 3.31; four studies, N = 617) and inadequate ventilation (not estimable; one study, N = 80). More time was required to establish an effective airway using pLMA (mean difference (MD) 10.12 seconds, 95% CI 5.04 to 15.21; P < 0.0001; I² = 73%; two studies, N = 434). Peak airway pressure during positive pressure ventilation was lower in cLMA participants (MD 0.84, 95% CI 0.02 to 1.67; P = 0.04; I² = 0%; four studies, N = 259). Mean oropharyngeal leak (OPL) pressure was higher in pLMA participants (MD 6.93, 95% CI 4.23 to 9.62; P < 0.00001; I² = 87%; six studies, N = 709). The quality of evidence for all outcomes, as assessed by GRADE score, is low mainly owing to issues related to blinding and imprecision. Data show no important differences between devices with regard to failure to insert the device, use of an alternate device, mucosal injury, sore throat, bronchospasm, gastric insufflation, regurgitation, coughing, and excessive leak. Data were insufficient to allow estimation of differences for obstruction related to the device. None of the studies reported postoperative nausea and vomiting as an outcome. We are uncertain about the effects of either of the airway devices in terms of failure of oxygenation or ventilation because there were very few events. Results were uncertain in terms of differences for several complications. Low-quality evidence suggests that the ProSeal laryngeal mask airway makes a better seal and therefore may be more suitable than the Classic laryngeal mask airway for positive pressure ventilation. The Classic laryngeal mask airway may be quicker to insert, but this is unlikely to be clinically meaningful.

Plain-language summary: We included eight randomized studies that involved a total of 829 participants 18 years of age and older. All participants had elective surgeries and needed general anaesthesia. Researchers directly compared cLMA against pLMA for providing artificial breathing during surgery. We identified six cross-over studies that are awaiting classification; one is completed but has not been published, and five other studies are gathering data related to the first treatment period that are not yet available. Five studies did not report any funding sources. Of the remaining three studies, one reported that the Laryngeal Mask Company sponsored some data but was not involved in study design, data analysis, and manuscript preparation. The Joseph Drown Foundation, in Los Angeles, Califiornia, in the USA, partially supported another study. One of the authors of the final study had received research funds from Intavent Ltd, manufacturer of both types of laryngeal mask airway, but Intavent Ltd did not sponsor this study. We are unsure whether these devices exhibit important differences in providing adequate oxygenation and ventilation because there was not enough data to enable us to draw any firm conclusions. ProSeal laryngeal mask airway may provides a better seal because it leaks at higher pressure, but Classic laryngeal mask airway may be quicker to insert. However, these findings are not important clinically. We assessed all of the included studies as providing low-quality evidence because anaesthetists knew which device was being used on which participants (although this was probably unavoidable), and because it was unclear whether the investigator who collected the data was unaware of the intervention. This fact created the potential for bias.