Cp50 of propofol for laryngeal mask airway insertion using predicted concentrations with and without nitrous oxide

This study sought to determine the predicted Cp50 of propofol required for laryngeal mask airway insertion (Cp50LMA) and to investigate whether nitrous oxide reduces these required concentrations. Using target-controlled infusion and incorporating the standard Diprifusor pharmacokinetic model, 46 unpremedicated patients were randomly assigned to one of two groups. The patients received either 40% oxygen in air (control group: n = 23), or 60% nitrous oxide in oxygen (nitrous oxide group: n = 23). The target concentration for each patient was determined using the up and down method. Following equilibration between the predetermined blood and effect site concentrations, had been established for > 10 min, laryngeal mask airway insertion was attempted without neuromuscular relaxants. The data were analysed using a probit analysis to obtain Cp50LMA levels. The values for Cp50LMA were 3.24 micro g.ml-1 in the control group and 1.93 microg.ml-1 in the nitrous oxide group.