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Onset and duration of mivacurium-induced neuromuscular block in patients with Duchenne muscular dystrophy.

BACKGROUND
To determine the response to mivacurium, we prospectively studied onset time and complete spontaneous recovery from mivacurium-induced neuromuscular block in patients with Duchenne muscular dystrophy (DMD).


METHODS
Twelve boys with DMD, age 5-14 yr, seven of them wheelchair-bound, ASA II-III, and 12 age- and sex-matched controls (ASA I) were enrolled in the study. Anaesthesia was induced with fentanyl 2-3 microg kg(-1) and propofol 3-4 mg kg(-1) titrated to effect, and maintained by continuous i.v. infusion of propofol 8-12 mg kg(-1) and remifentanil as required. The lungs were ventilated with oxygen in air. Neuromuscular transmission was assessed by acceleromyography using train-of-four (TOF) stimulation every 15 s. After baseline readings, a single dose of mivacurium 0.2 mg kg(-1) was given. The following variables were recorded: (i) lag time; (ii) onset time; (iii) peak effect; (iv) recovery of first twitch from the TOF response to 10, 25 and 90% (T(10), T(25), T(90)) relative to baseline; (v) recovery index (time between 25 and 75% recovery of first twitch); and (vi) recovery time (time between 25% recovery of first twitch and recovery of TOF ratio to 90%). For comparison between the groups the Mann-Whitney U-test was applied.


RESULTS
There were no differences between the groups in lag time, onset time and peak effect. However, all recorded recovery indices were significantly (P<0.05) prolonged in the DMD group. The median (range) for time points T(10), T(25) and T(90) in the DMD and control group was 12.0 (8-16) vs 8.4 (5-15) min, 14.1 (9-20) vs 10.5 (7-17) min and 26.9 (15-40) vs 15.9 (12-23) min, respectively. The recovery index and recovery time were similarly prolonged in the DMD group.


CONCLUSIONS
These results support the assumption that mivacurium-induced neuromuscular block is prolonged in patients with DMD.