Effects of desflurane and isoflurane on the vecuronium-induced neuromuscular block in the elderly patients

Objective The study was designed to compare the effects of desflurane and isoflurane on the vecuronium-induced neuromuscular block in the elderly patients. Methods Thirty ASA class I - II elderly patients aged over 70 yr undergoing elective surgery under general anesthesia were randomly divided into 3 groups: desflurane group ( I , n = 10) ; isoflurane group ( II , n = 10) and 3 control group ( III , n = 10). Anesthesia was induced with midazolam 0.02-0.05 mg· kg-1 , propofol 0.5-2.0 mg · kg-1 and fentanyl 2-5μg· kg-1 maintained with inhalation of 6% desflurane(1 MAC) +50% N2O in oxygen (group I ) or 1.15% isoflurane + 50% N2O in oxygen(group II ) or 50% N2O in oxygen (group III ) supplemented with intermittent iv boluses of propofol and fentanyl when necessary. Neuromuscular block was monitored using accelograph (TOF GUARD , Denmark) .A total dose of vecuronium 40 mg ·kg-1 was divided with 4 equal doses of 10μg · kg-1 , which was administered accumulatively in each patient. The next dose was given when the effect of the previous dose had reached its peak (T1 was no longer depressed in the height of 3 successive stimuli) .The cumulative dose-response curves of the 3 groups were established. The onset time and maximum depression of T1 of the initial dose and 3 incremental doses were recorded. After the last increment of 10 μg·kg-1, the time for T1 to returned to 25% ,75% ,90% and TOF ratio(T4/T1) to 70% were recorded. The recovery index was also calculated.Results The demographic data were comparable between the 3 groups. The ED50 and ED95 were significantly lower in desflurane and isoflurane groups than those in control group(P 0.05) .There was no significant difference in the onset time between the 3 groups ( P 0.05 ) . The time for T1 to return to 25 % , 75 % and 90 % was significantly longer in desflurane and isoflurane group than that in the control group. The recovery from vecuronium-induced neuromuscular block was slower in desflurane group than that in isoflurane group( P 0.05). But there was no significant difference in the TOF ratio and recovery index between desflurane and isoflurane groups. Conclusions Both desflurane and isoflurane significantly potentiate the neuromuscular block induced by vecuronium and desflurane causes greater potentiation than equipotent isoflurane.