ATRACURIUM-INDUCED NEUROMUSCULAR BLOCK IN THE ISOLATED ARM

A modification of the isolated arm technique was applied in 10 females under opioid-based i.v. anaesthesia for comparison of the offset of an atracurium-induced neuromuscular block in an isolated arm to an arm with maintained circulation. The neuromuscular blocking effect of a bolus dose of atracurium 0.5 mg . kg-1 was measured bilaterally using the integrated adductor pollicis EMG response (integrated T1 EMG response in % of baseline value and T4/T1 ratio) after bilateral ulnar nerve train-of-four (TOF) stimulation. At 10% T1 recovery, one arm was isolated from the general circulation for 20 min by means of a tourniquet cuff (isolated arm), while normal circulation was maintained in the other arm (control arm). In both arms, the TOF response, peripheral skin temperature, mixed peripheral venous pH and plasma concentrations of atracurium and laudanosine were then measured and compared. Core and peripheral skin temperatures in both arms remained stable and normal throughout the study, and mixed peripheral venous pH stayed within physiological limits in both arms in all subjects. In the isolated arm, recovery of the neuromuscular block was markedly delayed compared to the control arm, the integrated EMG T1 response and TOF ratio being significantly reduced in the isolated arm after 20 min of isolation. The decline in plasma concentration of atracurium was less in the isolated arm than in the control arm, whereas laudanosine levels increased in the isolated and decreased in the control arm. Normal peripheral circulation is of major importance for termination of an atracurium-induced neuromuscular block. The contribution of Hofmann elimination to termination of an atracurium-induced neuromuscular block appears to be of minor importance.