title: Population pharmacokinetics of remifentanil in infants and children undergoing cardiac surgery.
abstract: BACKGROUND
  The aim of this study was to provide a model-based analysis of the pharmacokinetics of remifentanil in infants and children undergoing cardiac surgery with cardiopulmonary bypass (CPB).
  
  
  METHODS
  We studied nine patients aged 0.5 to 4 years who received a continuous remifentanil infusion via a computer-controlled infusion pump during cardiac surgery with mildly hypothermic CPB were studied. Arterial blood samples taken prior to, during and after CPB were analyzed for remifentanil concentrations using a validated gas-chromatographic mass-spectrophotometric assay. We used population mixed-effects modeling to characterize remifentanil pharmacokinetics. The final model was evaluated by its predictive performance.
  
  
  RESULTS
  The pharmacokinetics of remifentanil was described by a 1-compartment model with adjustments for CPB. Population mean parameter estimates were 1.41 L for volume of distribution (V) and 0.244 L/min for clearance. V was increased during CPB and post-CPB to 2.41 times the pre-CPB value. The median prediction error and the median of individual median absolute prediction error were 2.44% and 21.6%, respectively.
  
  
  CONCLUSIONS
  Remifentanil dosage adjustments are required during and after CPB due to marked changes in the V of the drug. Simulations indicate that a targeted blood concentration of 14 ng/mL is achieved and maintained in 50% of typical patients by administration of an initial dose of 18 mug remifentanil followed by an infusion of 3.7 mug/min before, during and post-CPB, supplemented with a bolus dose of 25 mug given at the start of CPB.
authors.affiliation: Department of Anesthesia, Stanford University, Stanford, California USA. ddrover@stanford.edu.
authors.forename: Wai Johnn
authors.initials: WJ
authors.lastname: Sam
authors.forename: Gregory B
authors.initials: GB
authors.lastname: Hammer
authors.forename: David R
authors.initials: DR
authors.lastname: Drover