Aim: The depth of muscular relaxation during general anesthesia is monitored through the analysis of the contraction evoked by selective electrical stimulation of a peripheral nerve. The aim of this study was to compare the method of selective stimulation (SS) to a new method based on non-selective electrical stimulation (NSS) delivered over the muscle.
Method: Electrical stimuli were delivered as train-of-four impulses to the ulnar nerve (SS) and to the ventral aspect of the contralateral forearm (NSS). The muscular responses of the adductor pollicis brevis (SS) and the forearm supinator longus (NSS) were studied at 30-60 s intervals with piezoelectric transducers before and after the administration of atracurium bolus doses of 0.5 mg/kg to patients under general anesthesia. SS and NSS evoked muscular responses were quantitized as percentages of the control response and compared with linear correlation and concordance analysis.
Results: Twenty patients were studied. Basal and post-atracurium muscular responses were similar for the SS and the NSS methods. Precision between SS and NSS was >85% and accuracy >92%. Concordance was: basal <15%, relaxation <5%, recovery <10%.
Conclusion: NSS is equivalent to SS for muscular relaxation monitoring during general anesthesia. This has important implications to simplify muscular relaxation monitor design.