Issn Print: 0265-0215

Publication Date: 2007/06/01


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Neuromuscular pharmacodynamics of mivacurium in adult patients with major burns: 9AP2-2

A. Han; J AJ. Martyn

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Background and Goal of Study: Burned patients are resistant to nondepolarizing muscle relaxants (NDMRs). Mivacurium, however, has not been shown to be resistant in burned children. Neuromuscular (NM) response to mivacurium in burned adults is unknown. This study examined the pharmacodynamics of mivacurium bolus in relation to size of burn, time after burn, plasma pseudocholinesterase (PCHE) activity and dibucaine number, in adult major burns.
Materials and Methods: Adults (M/F = 22/8), aged 44.0 ± 10 years, with total burn area (TBA) 35.0 ± 13%, were studied at 40 ± 29 postburn days. Age and sex matched 30 nonburns served as controls. Anesthesia consisted of propofol and fentanyl infusion with N2O and O2. Mivacurium 0.2 mg/kg bolus was given. T1 of TOF Watch® monitored NM block. Onset time was the interval from beginning of drug administration to maximal twitch suppression. Intubation at 1 minute was attempted to simulate rapid sequence induction with recording of either failure or success. Spontaneous recovery profiles from paralysis were measured. Pearson correlations assessed relationship of recovery profiles to PCHE activity, dibucaine number, TBA and elapsed time after the injury.
Results and Discussions: Demographics of patients were similar in both groups. Onset time and all recovery profiles were prolonged in the burned patients. Intubation was successful with difficulty in approximately 70% of both groups. PCHE activity was significantly decreased in burns. Dibucaine number was similar in both groups. Recovery profiles showed high negative correlation to PCHE activity and positive correlation to TBA and time after the burn injury.
Conclusion(s): Unlike children and adolescents who have onset of NM paralysis similar to unburned, mivacurium onset time was prolonged in adult burns. Prolonged onset time suggests resistance to the NM effects. Conversely, prolonged recovery profiles suggest increased sensitivity. These contradictory findings can be explained by AChR proliferation and decreased level of plasma PCHE activity, which seem to depend on time after injury. In view of the prolonged onset time of almost two minutes for maximal paralysis, mivacurium does not appear to be a good drug for rapid onset of paralysis in burned adults.
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