BLOOD-FLOW AND MIVACURIUM-INDUCED NEUROMUSCULAR BLOCK AT THE ORBICULARIS OCULI AND ADDUCTOR POLLICIS MUSCLES

We have studied the pattern of blood flow and pharmacodynamic profile of mivacurium-induced block at the adductor pollicis and orbicularis o culi muscles. We studied 30 adult patients anaesthetized with fentanyl , thiopentone, nitrous oxide-isoflurane, and mivacurium 0.2 mg kg(-1). Neuromuscular transmission was monitored with accelerometry (TOF Guar d, Biometer, Denmark). Blood flow was measured at the two muscles with the use of a laser Doppler flowmeter (Laserflo BPM2, Vasamedics, USA) . All patients developed 100% neuromuscular block at the adductor poll icis muscle. Mean maximum neuromuscular block at the orbicularis oculi was 96.4 (SD 3.5) % (ns). Onset time, time required for 25% and 75% r ecovery of the first twitch in the train-of-four (T1), and a train-of- four ratio (T4/T1) of 90% at the orbicularis oculi were respectively, mean 130.4 (SD 28.5) s, 9.1 (3.2) min, 16.2 (3.9) min and 20.2 (4.3) m in and were significantly shorter than the corresponding values at the adductor pollicis: 202.7 (37.2) s, 12.9 (3.9) min, 21.1 (5.1) min and 30.8 (7.4) min. For a given T1, there was significantly less train-of -four fade (T4/T1) at the orbicularis oculi than at the adductor polli cis muscle during recovery. Blood flow was comparable at the two muscl es before induction of anaesthesia. Thiopentone significantly increase d thenar muscle blood flow from 2.9 (1.5) to 12.3 (6.8) ml 100 g(-1) m in(-1), with a further increase to 22.7 (8.0) ml 100 g(-1) min(-1) aft er isoflurane (P<0.001). Blood flow at the orbicularis oculi was not a ltered by thiopentone or isoflurane and was consistently lower than th at at the adductor pollicis muscle. We conclude that the different pha rmacodynamic profiles of mivacurium-induced block at the orbicularis o culi and adductor pollicis muscles were not related primarily to a dif ference in blood flows.