Predictive accuracy of alfentanil infusion in coronary artery surgery: A prebypass study in middle-aged and elderly patients

Abstract

Twenty-three informed and consenting patients scheduled for CABG were anesthetized using computer-controlled infusions of alfentanil, midazolam, and pancuronium. Thirteen middle-aged patients received a preprogrammed infusion scheme of alfentanil, simulated using the population pharmacokinetic set of Maitre et al (Group M), and 10 elderly patients received a preprogrammed infusion scheme simulated using the model of Helmers et al (Group H). The target alfentanil concentrations in groups M and H for tracheal intubation were: 300–500 ng/mL and for sternotomy: 500–700 ng/mL. Blood alfentanil concentrations were measured at tracheal intubation, skin incision, sternotomy, and aortic cannulation. The bias, inaccuracy, and precision of each pharmacokinetic set were assessed by the median performance error (MDPE), the median absolute performance error (MDAPE), and the 10th and 90th percentiles of the performance errors (P10, P90), respectively. The predictive accuracy of seven other alfentanil pharmacokinetic sets selected from the literature was also evaluated retrospectively. The measured alfentanil concentrations were underpredicted when using all the pharmacokinetic sets, except the set of Scott et al (MDPE: −15.9%). The sets of Maitre et al and Helmets et al were found not to be accurate (MDAPE > 40%) in both groups M and H. The set of Scott et al with the lowest clearance (2.4 mL/kg/min) shows the best accuracy (MDAPE: 19.5%) and precision (P10: −40%, P90: 16%). In conclusion, the set of Scott et al should preferably be selected to predict prebypass alfentanil infusion accurately in either middle aged or elderly patients who have normal myocardial function (LVEF > 50%) and are scheduled for CABG.