Fentanyl and propofol uptake by the lung: effect of time between injections

The effect of time between the administrations of fentanyl and propofol on the first pass uptake of propofol in the cat lung was studied using double indicator dilution technique. The pulmonary first pass uptake of propofol (mean +/- s.e. mean) was 58 +/- 6% in six cats (control group) that had received no fentanyl prior to propofol (1 mg/kg) administration. The uptake was significantly reduced to 32 +/- 3% in animals pretreated with fentanyl (1 microgram/kg) 30 seconds before propofol administration (n = 6). However, when fentanyl was administered 3 minutes (n = 6) or 10 minutes (n = 6) prior to propofol, the pulmonary uptake of propofol (45 +/- 5%, 50 +/- 7% respectively) was not significantly reduced. The results demonstrate that the ability of fentanyl to inhibit pulmonary removal of propofol depends on its time of administration prior to propofol. These data may have clinical implication with respect to timing of the preinduction opiate injection.