Thenar muscle blood flow and neuromuscular effects of vecuronium in patients receiving balanced or isoflurane anaesthesia

We have tested the hypothesis that isoflurane potentiates non-depolarizingneuromuscular block via an increase in muscle blood flow. Anaesthesiawas induced with thiopentone 4–5 mg kg^–1 in 30 adultmale patients of ASA physical status I or II and was maintainedwith 70% nitrous oxide in oxygen supplemented with either abolus dose of fentanyl 4µg kg^–1 followed by an infusionof 1 7µg kg^–1 h^–1 (balanced anaesthesia group,n=15) or 1.1% end-tidal isoflurane (isoflurane group, n=15).Vecuronium 0.1 mg kg^–1 was given for neuromuscular block.The force of contraction of the adductor pollicis of the thumbin response to ulnar nerve stimulation was recorded. Thenarmuscle blood flow was measured continuously with a laser Dopplerflowmeter. Times required for the first twitch in the train-of-four(T1) to recover to 25%, 75% and 90% of its control value weremean 26.3 (SD 5), 35.3 (10), 43.5 (7) min and 39.2 (15), 53(12.5), 61.2 (10) min in the balanced anaesthesia and isofluranegroups, respectively (P<0.01). Recovery index (time betweenT1 25% and 75%) was prolonged significantly in the isofluranegroup. Administration of thiopentone significantly increasedthenar muscle blood flow from 2.6 (1.9) and 2.2 (1.5) ml min^–1/100g to 19.2 (14) and 21.7 (16) ml min^–11100 g in the balancedanaesthesia and isoflurane groups, respectively (P<0.001).The addition of fentanyl (balanced) or isoflurane to the anaestheticmixture produced further increases in thenar muscle blood flowto reach, respectively, 26.2 (16) and 26.8 (13.6) ml min^–1/1100g during steady state anaesthesia. Thenar muscle blood flowwas comparable in the two groups throughout the study. We concludethat isoflurane prolonged vecuronium-induced neuromuscular block.This prolongation was not related primarily to increase in muscleblood flow.