A novel technique to determine an 'apparent ke0' value for use with the Marsh pharmacokinetic model for propofol
Debate continues over the most appropriate blood-brain equilibration rate constant (ke0) for use with the Marsh pharmacokinetic model for propofol. We aimed to define the optimal ke0 value. Sixty-four patients were sedated with incremental increases in effect-site target concentration of propofol while using six different ke0 values within the range 0.2-1.2 min-1. Depth of sedation was assessed by measuring visual reaction time. A median 'apparent ke0' value of 0.61 min -1 (95% CI 0.37-0.78 min-1) led to the greatest probability of achieving a stable clinical effect when the effect-site target was fixed at the effect-site concentration displayed by the target-controlled infusion system, at the time when a desired depth of sedation had been reached. By utilising a clinically relevant endpoint to derive this value, inter-individual pharmacokinetic and pharmacodynamic variability may be accounted for. © 2014 The Association of Anaesthetists of Great Britain and Ireland.