Pharmacokinetics of sufentanil in neurosurgical patients undergoing hyperventilation

The pharmacokinetics of sufentanil were determined in 11 hypocapnic (arterial PCO2 2.9-3.7 kPa) and seven normocapnic (arterial PCO2 5.3-6.0 kPa) neurosurgical patients. Following a single i.v. bolus of sufentanil 4 micrograms kg-1, multiple arterial samples were obtained at timed intervals and plasma concentration of sufentanil was measured by radioimmunoassay. Calculation of the pharmacokinetic parameters from the derived compartmental models demonstrated an increased total volume of distribution of sufentanil in hypocapnic patients (mean 5427 (SD 1866) ml kg-1 v. 3518 (1097) ml kg-1; P less than 0.05) in the control patients and a more prolonged elimination half-life (232 (60) min v. 143 (51) min; P less than 0.01). The increased distribution of sufentanil with hyperventilation was probably caused by an increased proportion of opioid in the nonionized state.