[The effect of isoflurane on plasma concentration-response curve of vecuronium determined with continuous infusion method].

To investigate the interaction between vecuronium and isoflurane at the neuromuscular junction in man, I determined the plasma concentration-response curve of vecuronium both under balanced and isoflurane (0.7% and 1.2% end-tidal) anesthesia. In addition, I also determined clinically the infusion rate of vecuronium that made a suitable sustained relaxation possible. I used train-of-four (TOF) stimulation to monitor neuromuscular blockade by vecuronium. Plasma isoflurane concentration was kept constant throughout the observation period. Plasma clearances of vecuronium calculated from the infusion rate and resulting plasma concentration were also found not to be different among the three groups. A significant leftward shift of the concentration-response (T1 inhibition) curve was found both between 1.2% isoflurane group and NLA group, and between 1.2% isoflurane group and 0.7% isoflurane group. The relationship between T1 inhibition and TOF ratio reduction was found not to be different among the three groups. I conclude that 1.2% isoflurane potentiates vecuronium-induced T1 inhibition, but it does not affect the relationship between T1 inhibition and TOF ratio reduction in man. It is helpful for clinical determination of the infusion rate to measure the time period from bolus administration of vecuronium 0.1 mg.kg-1 to reappearance of T3.