Quantifying the interaction of vecuronium with enflurane using closed-loop feedback control of vecuronium infusion.

The influence of different levels of enflurane anaesthesia on infusion requirements of vecuronium was studied in 40 adult surgical patients. Ninety percent neuromuscular block was maintained by computer controlled infusion of vecuronium. During the first 90 min study period all patients received fentanyl-nitrous oxide-oxygen (2:1) anaesthesia. For the following 90 min the patients were randomly assigned to receive enflurane at different end-tidal concentrations: group I, control, fentanyl-nitrous oxide anaesthesia; group II, enflurane 0.3%-nitrous oxide; group III, enflurane 0.6%-nitrous oxide; group IV, enflurane 0.9%-nitrous oxide. Every patient served as his/her own control and the changes of vecuronium infusion requirements were determined individually. When the administration of enflurane was started, vecuronium infusion requirements decreased progressively until 90 min. In group II the infusion rate lowered from 80 +/- 28 to 56 +/- 20 micrograms.kg-1.h-1, in group III from 61 +/- 29 to 34 +/- 17 micrograms.kg-1.h-1 and in group IV from 65 +/- 20 to 30 +/- 14 micrograms.kg-1,h-1. In the control group the infusion rate decreased during the three hour study period from 69 +/- 17 (first 90 min period) to 59 +/- 16 micrograms.kg-1.h-1 (second 90 min period). Enflurane reduces the dose requirements of vecuronium administered by continuous infusion in a dose- and time-dependent manner.