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1.  Neuromuscular pharmacodynamics of mivacurium in adults with major burns 
BJA: British Journal of Anaesthesia  2011;106(5):675-679.
Background
Mivacurium is metabolized by plasma pseudocholinesterase (PChE) enzyme, which is decreased in burns. We tested whether the decreased metabolism of mivacurium due to decreased PChE activity can overcome the pharmacodynamic resistance to non-depolarizing relaxants previously seen in major burns.
Methods
Thirty adults with 35 (13)% [mean (sd)] burn were studied at 5–91 post-burn days and 31 non-burns matched controls. Mivacurium 0.2 mg kg−1 was administered as a single bolus. Neuromuscular block was monitored with single-twitch response using TOF-Watch™. Onset time (drug administration to maximal twitch suppression) and spontaneous recovery were measured.
Results
Onset time was significantly prolonged in burns when compared with non-burns (115 vs 90 s; P<0.001). The PChE levels were lower in burns [1432 (916) vs 2866 (731) IU litre−1; P<0.001] and the neuromuscular recovery to 50% of baseline twitch height was prolonged in burns (41 vs 26 min; P<0.001). There was a significant correlation between PChE and time to 50% recovery for the whole group together (r=−0.6; P<0.001). The dibucaine numbers were not different.
Conclusions
The prolonged onset time suggests resistance to neuromuscular effects, whereas the prolonged recovery suggests increased sensitivity. This divergent response can be explained by qualitative and quantitative changes in acetylcholine receptor expression causing resistance and decreased PChE activity causing sensitivity. Despite using a relatively large dose of mivacurium (0.2 mg kg−1) in the presence of decreased PChE levels, this did not overcome the resistance resulting from up-regulated receptors.
doi:10.1093/bja/aer023
PMCID: PMC3077750  PMID: 21354998
neuromuscular relaxants, mivacurium; pharmacodynamics; trauma, burns
2.  Onset and effectiveness of rocuronium for rapid onset of paralysis in patients with major burns: priming or large bolus 
Background
Burn injury leads to resistance to the effects of non-depolarizing muscle relaxants. We tested the hypothesis that a larger bolus dose is as effective as priming for rapid onset of paralysis after burns.
Methods
Ninety adults, aged 18–59 yr with 40 (2)% [mean (se)] burn and 30 (2) days after injury, received rocuronium as a priming dose followed by bolus (0.06+0.94 mg kg−1), or single bolus of either 1.0 or 1.5 mg kg−1. Sixty-one non-burned, receiving 1.0 mg kg−1 as a primed (0.06+0.94 mg kg−1) or full bolus dose, served as controls. Acceleromyography measured the onset times.
Results
Priming when compared with 1.0 mg kg−1 bolus in burned patients shortened the time to first appearance of twitch depression (30 vs 45 s, P<0.05) and time to maximum twitch inhibition (135 vs 210 s, P<0.05). The onset times between priming and higher bolus dose (1.5 mg kg−1) were not different (30 vs 30 s for first twitch depression and 135 vs 135 s for maximal depression, respectively). The onset times in controls, however, were significantly (P<0.05) faster than burns both for priming and for full bolus (15 and 15 s, respectively, for first twitch depression and 75 and 75 s for maximal depression). Priming caused respiratory distress in 10% of patients in both groups. Intubating conditions in burns were significantly better with 1.5 mg kg−1 than with priming or full 1.0 mg kg−1 bolus.
Conclusions
A dose of 1.5 mg kg−1 not only produces an initial onset of paralysis as early as 30 s, which we speculate could be a reasonable onset time for relief of laryngospasm, but also has an onset as fast as priming with superior intubating conditions and no respiratory side-effects.
doi:10.1093/bja/aen332
PMCID: PMC2638834  PMID: 19029093
burns; neuromuscular block, rocuronium

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