Atracurium‐induced neuromuscular block in the isolated arm

Abstract

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.(ABSTRACT TRUNCATED AT 250 WORDS)

Onset of neuromuscular block after tourniquet inflation: comparison of suxamethonium with vecuronium

“…After 20 min of tourniquet inflation in patients receiving atracurium, peripheral venous pH remained within the physiological range (i.e. 7.34-7.42), and there was no difference between the two arms [8]. In the same study, the EMG response was not affected by tourniquet inflation for 20 min in the absence of neuromuscular blockers.…”

“…In these studies, the drug was injected in the isolated forearm. In another study a tourniquet was inflated to assess recovery after systemic injection of atracurium [8]. The present study differed from these investigations in the role of the tourniquet.…”

“…If muscle blood flow were the only determinant of onset time, interruption of circulation to muscle would be expected to affect intensity of paralysis, and block should remain constant in a muscle with absent blood supply. The application of a tourniquet to interrupt blood flow has been used during recovery after systemic injection of atracurium [8]. In spite of the lack of circulation in the arm, recovery was found to continue, although more slowly in the isolated than in the perfused arm.…”

Recovery of Atracurium and Vecuronium Neuromuscular Block in the Isolated Forearm

“…It is this question that we have examined. The previous suggested explanation, that the metabolism of atracurium in the effect compartment could explain this paradox, is improbable as the effect compartment is of small size and Ericksson and colleagues [6] have demonstrated that Hofmann degradation does not occur to any extent at the neuromuscular junction.…”

“…It has been suggested that, because of the metabolism of atracurium, there is a different treatment of both drugs in the effect compartment [4,5]. However, there is no evidence that this occurs in vivo [6]. Various pharmacokinetic models have been constructed in an attempt to explain this phenomenon.…”