Modified double burst stimulation of varying stimulating currents.

BACKGROUND

Using modified double burst stimulation (modified DBS), sufficient 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 stimulating current decreases, the neurostimulation-induced discomfort becomes less for awake subjects. It is relevant to investigate the usefulness of the modified DBS delivered at low currents.

METHODS

One hundred and twenty-one adult patients undergoing nitrous oxide-oxygen-isoflurane anesthesia were randomly divided into one of four groups: group 50 (n = 40), group 30 (n = 40), group 20 (n = 40), and supramaximality group (n = 1). After administration of vecuronium, in one hand and forearm (fixed arm), the degree of neuromuscular blockade was quantified mechanically. 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 absence of fade in response to the modified DBS applied at 50, 30, and 20 mA. In one patient (the supramaximality group), modified DBS ratios (D2/D1) were examined at 50, 40, 30, 20, and 10 mA before administration of vecuronium. Moreover, discomfort associated with modified DBS applied at 50, 30, and 20 mA was evaluated using a 10-cm visual analog scale (VAS) in 15 awake volunteers.

RESULTS

Probabilities of detection of fade in response to modified DBS in groups 50, 30, and 20 were 90, 86, and 96% (TOF ratios of 0.61-0.70), 62, 73, 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 to group 30. Supramaximal responses to D1 and D2 could be elicited at a current > or = 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.

CONCLUSION

Modified DBS-induced discomfort becomes less as the stimulating current decreases. However, when stimulated at 30 or 20 mA, fade in response to modified DBS is felt in too many cases, even after neuromuscular blockage subsides to an adequate level.