THENAR MUSCLE BLOOD-FLOW AND NEUROMUSCULAR EFFECTS OF VECURONIUM IN PATIENTS RECEIVING BALANCED OR ISOFLURANE ANESTHESIA

We have tested the hypothesis that isoflurane potentiates non-depolari zing neuromuscular block via an increase in muscle blood flow. Anaesth esia was induced with thiopentone 4-5 mg kg(-1) in 30 adult male patie nts of ASA physical status I or II and was maintained with 70% nitrous oxide in oxygen supplemented with either a bolus dose of fentanyl 4 m u g kg(-1) followed by an infusion of 1 mu g kg(-1) h(-1) (balanced an aesthesia group, n = 15) or 1.1% end-tidal isoflurane (isoflurane grou p, n = 15). Vecuronium 0.1 mg kg(-1) was given for neuromuscular block . The force of contraction of the adductor pollicis of the thumb in re sponse to ulnar nerve stimulation was recorded. Thenar muscle blood fl ow was measured continuously with a laser Doppler flowmeter. Times req uired for the first twitch in the train-of-four (TI) to recover to 25% , 75% and 90% of its control value were mean 26.3 (SD 5), 35.3 (10), 4 3.5 (7) min and 39.2 (15), 53 (12.5), 61.2 (10) min in the balanced an aesthesia and isoflurane groups, respectively (P < 0.01). Recovery ind ex (time between TI 25% and 75%) was prolonged significantly in the is oflurane group. Administration of thiopentone significantly increased thenar muscle blood flow from 2.6 (1.9) and 2.2 (1.5) ml min(-1)/100 g to 19.2 (14) and 21.7 (16) ml min(-1)/100 g in the balanced anaesthes ia and isoflurane groups, respectively (P < 0.001). The addition of fe ntanyl (balanced) or isoflurane to the anaesthetic mixture produced fu rther increases in thenar muscle blood flow to reach, respectively, 26 .2 (16) and 26.8 (13.6) ml min(-1)/100 g during steady state anaesthes ia. Thenar muscle blood flow was comparable in she two groups througho ut the study. We conclude that isoflurane prolonged vecuronium-induced neuromuscular block. This prolongation was not related primarily to i ncrease in muscle blood flow.