Selective versus non-selective neural stimulation in the monitoring of muscular relaxation during general anesthesia

Aim. The depth of muscular relaxation during general anesthesia is monitore d through the analysis of the contraction evoked by selective electrical st imulation of a peripheral nerve. The aim of this study was to compare the m ethod 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) an d to the ventral aspect of the contralateral forearm (NSS). The muscular re sponses of the adductor pollicis brevis (SS) and the forearm supinator long us (NSS) were studied at 30-60 s intervals with piezoelectric transducers b efore and after the administration of atracurium bolus doses of 0.5 mg/kg t o patients under general anesthesia. SS and NSS evoked muscular responses w ere quantitized as percentages of the control response and compared with li near correlation and concordance analysis. Results. Twenty patients were st udied. 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%. Conclu sion. NSS is equivalent to SS for muscular relaxation monitoring during gen eral anesthesia. This has important implications to simplify muscular relax ation monitor design.