A preferential delivery method to investigate direct neuromuscular blockade effect of inhaled anesthetics on skeletal muscle.

Inhaled anesthetics can enhance the effect of neuromuscular blocker, but whether inhaled anesthetics such as sevoflurane have a direct effect on skeletal muscle contractility is unknown. Selectively blocking skeletal muscle may prevent the interference effect of central nervous system. So we decided to evaluate a local application of neuromuscular blocker (NMB) atracurium to prevent the general effect on skeletal muscle. In part 1, sevoflurane (a inhaled anesthetic) minimum alveolar concentrations (MAC) of 1.0, 1.5 and 2.0 would be applied in succession. Neuromuscular function was assessed at each MAC. In part 2, patients are randomized into four groups: group1 (propofol+NMB, sevoflurane 0 MAC), and groups 2 to 4 (NMB+sevoflurane 1.0, 1.5 and 2.0 MAC respectively). In group 1, patients were anesthetized by propofol, then 0.01mg/kg atracurium was injected into the tested arm intravenously after the arterial blood flow was blocked using a tourniquet. For the other 3 groups, patients inhaled 1.0 MAC, 1.5 MAC, or 2.0 MAC of sevoflurane. Then 0.01mg/kg atracurium was injected. Neuromuscular function was recorded for the 4 groups. Neuromuscular function was assessed by acceleromyography measurement of evoked responses to train-of four (TOF) stimuli (2Hz for 2s applied every 12s) at the adductor pollicis using a TOF-Guard™ neuromuscular transmission monitor. If proven, our hypothesis would demonstrate the inhaled anesthetics have no direct effect on contractility but only by increasing the skeletal muscle sensitivity to NMB.