MODIFIED DOUBLE BURST STIMULATION AT VARYING STIMULATING CURRENTS

Background: Using modified double burst stimulation (modified DBS), su fficient level of recovery from neuromuscular blockade (train-of-four (TOF) ratio >0.7) can properly be diagnosed. Modified DBS may often be applied in awake patients in the postanesthetic care unit. As the sti mulating current decreases, the neurostimulation-induced discomfort be comes less for awake subjects. It is relevant to investigate the usefu lness of the modified DBS delivered at low currents. Methods: One hund red and twenty-one adult patients undergoing nitrous oxide-oxygen-isof lurane anesthesia were randomly divided into one of four groups: group 50 (n=40), group 30 (n=40), group 20 (n=40), and supramaximality grou p (n=1). After administration of vecuronium, in one hand and forearm ( fixed arm), the degree of neuromuscular blockade was quantified mechan ically. In the contralateral arm (free arm), modified DBS stimuli were delivered at 50, 30, and 20 mA in groups 50, 30, and 20, respectively . An observer determined tactilely on the free arm the presence or abs ence of fade in response to the modified DBS applied at 50, 30, and 20 mA. In one patient (the supramaximality group), modifed DBS ratios (D 2/D1) were examined at 50, 40, 30, 20, and 10 mA before administration of vecuronium. Moreover, discomfort associated with modified DBS appl ied at 50, 30, and 20 mA was evaluated using a 10-cm visual analog sca le (VAS) in 15 awake volunteers. Results: Probabilities of detection o f fade in response to modified DBS in groups 50, 30, and 20 were 90, 8 6, and 96% (TOF ratios of 0.61-0.70), 62, 73, and 94(#)% (0.71-0.80), 26, 39, and 79(#)% (0.81-0.90), and 4, 33*, and 51(*#)% (0.91-1.00), respectively. P<0.05 as compared to group 50. P-#<0.05 as compared t o group 30. Supramaximal responses to D1 and D2 could be elicited at a current greater than or equal to 30 mA. The mean VAS scores were 8.7, 6.5, and 4.1(*#) when stimulated at 50, 30, and 20 mA, respectively. P<0.05 as compared to 50 mA. P-#<0.05 as compared to 30 mA. Conclusi on: Modified DBS-induced discomfort becomes less as the stimulating cu rrent decreases. However, when stimulated at 30 or 20 mA, fade in resp onse to modified DBS is felt in too many cases, even after neuromuscul ar blockade subsides to an adequate level.