End-tidal sevoflurane concentration for ProSeal(TM) versus Classic(TM) laryngeal mask airway insertion in unpremedicated anaesthetised adult females.

The optimal end-tidal sevoflurane concentration for successful ProSealTM (Teleflex, Morrisville, NC, USA) laryngeal mask airway (PLMA) versus ClassicTM (Teleflex, Morrisville, NC, USA) laryngeal mask airway (CLMA) insertion in unpremedicated anaesthetised adults is unknown. We determined end-tidal sevoflurane concentrations for successful insertion in fifty percent of anaesthetised adults. This randomised, prospective, double-blind study was conducted in the operating theatre of a government tertiary care hospital. Forty-four unpremedicated American Society of Anesthesiologists physical status I and II women with cervical carcinoma (aged 30 to 60 years), scheduled for intracavity caesium implantation under general anaesthesia with a laryngeal mask airway (LMA) were included in the study. The participants were randomised to one of the two groups, to receive either a PLMA or CLMA. After anaesthetic induction with sevoflurane, a predetermined end-tidal sevoflurane concentration (starting at 2.5%) was sustained for 10 minutes before LMA insertion was attempted. End-tidal sevoflurane concentration was increased/decreased (step-size 0.25%) using Dixon and Massey's up-and-down method for the next patient based on the previous patient's response. Placement without clenching, movement, coughing or biting within one minute was considered successful insertion. The end-tidal sevoflurane concentration required for successful LMA insertion in fifty percent of anaesthetised adults was calculated as the mean of the crossover pairs' midpoints in each group and further confirmed by probit regression analysis. The end-tidal sevoflurane concentration (95% confidence interval) required for successful PLMA insertion in 50% of anaesthetised adults (3.15% [3.12% to 3.18%]) was significantly higher than that for CLMA insertion (2.71% [2.66% to 2.76%], P<0.001). These findings suggest that deeper anaesthesia is required for placement of a PLMA in comparison to a CLMA.