Dose-response and concentration-response relation of rocuronium infusion during propofol nitrous oxide and isoflurane nitrous oxide anaesthesia

The dose-response and concentration-response relation of rocuronium infusion was studied in 20 adult surgical patients during proporfol-nitrous oxide and isoflurane (1 MAC) -nitrous oxide anaesthesia. Neuromuscular block was kept constant, initially at 90% and then at 50% with a closed-loop feedback controller. At 90% block the steady-state infusion of rocuronium was 0.55 +/- 0.16 mg kg(-1) h(-1) and the corresponding concentration 1714 +/- 281 ng mL(-1) in patients receiving propofol. At 50% block the corresponding infusion rate was 0.27 +/- 0.11 mg kg(-1) h(-1) and the concentration 1077 +/- 244 ng mL(-1), respectively. At 50% block isoflurane reduced the rate of infusion by 52% (P <0.005) and the concentration by 59% (P <0.001); at 90% block both the mean infusion rate and the concentration of rocuronium were reduced by 35% (P <0.005). The mean rocuronium clearance at 50% block was unaffected by the type of anaesthesia; it was 4.1 +/- 1.6 and 4.9 +/- 2.7 mL kg(-1) min(-1) in the groups receiving propofol and isoflurane anaesthesia, respectively. We conclude that isoflurane reduces the infusion requirements of rocuronium by changing the pharmacodynamic behaviour.