Pharmacodynamics of mivacurium chloride in 13- to 18-yr-old adolescents with thermal injury

Neuromuscular pharmacodynamics of mivacurium in adults with major burns

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.

Burn injury pain: the continuing challenge

The development of more effective methods of relieving pain associated with burn injury is a major unmet medical need. Not only is acute burn injury pain a source of immense suffering, but it has been linked to debilitating chronic pain and stress-related disorders. Although pain management guidelines and protocols have been developed and implemented, unrelieved moderate-to-severe pain continues to be reported after burn injury. One reason for this is that the intensity of pain associated with wound care and rehabilitation therapy, the major source of severe pain in this patient population, varies widely over the 3 phases of burn recovery, making it difficult to estimate analgesic requirements. The effects of opioids, the most commonly administered analgesics for burn injury procedural pain, are difficult to gauge over the course of burn recovery because the need for an opioid may change rapidly, resulting in the overmedication or undermedication of burn-injured patients. Understanding the mechanisms that contribute to the intensity and variability of burn injury pain over time is crucial to its proper management. We provide an overview of the types of pain associated with a burn injury, describe how these different types of pain interfere with the phases of burn recovery, and summarize pharmacologic pain management strategies across the continuum of burn care. We conclude with a discussion and suggestions for improvement. Rational management, based on the underlying mechanisms that contribute to the intensity and variability of burn injury pain, is in its infancy. The paucity of information highlights the need for research that explores and advances the identification of mechanisms of acute and chronic burn injury pain.

PERSPECTIVE

Researchers continue to report that burn pain is undertreated. This review examines burn injury pain management across the phases of burn recovery, emphasizing 3 types of pain that require separate assessment and management. It provides insights and suggestions for future research directions to address this significant clinical problem.

Neuromuscular pharmacodynamics of rocuronium in patients with major burns

Rocuronium, which has a short onset time and is free of hyperkalemic effects, could be considered for rapid-sequence induction of anesthesia in patients with burns. In this study, we assessed the neuromuscular pharmacodynamics of rocuronium in patients with major burns. Adults aged 18-59 yr who had a major burn injury (n = 56) and a control group of 44 nonburned patients were included. Rocuronium was used at 3 times (0.9 mg/kg) or 4 times (1.2 mg/kg) the 95% effective dose. Anesthesia consisted of propofol and fentanyl with nitrous oxide and oxygen. Neuromuscular block was monitored with an acceleromyograph by using train-of-four stimulation. The onset time to 95% neuromuscular block was prolonged in burned compared with nonburned patients (115 +/- 58 s versus 68 +/- 16 s for 0.9 mg/kg; 86 +/- 20 s versus 57 +/- 11 s for 1.2 mg/kg). Dose escalation shortened the onset time, prolonged the duration of action, and improved intubating conditions in burned patients. All recovery profiles were significantly shorter in burned versus nonburned groups with both doses. Resistance to the neuromuscular effects of rocuronium was partially overcome by increasing the dose. A dose up to 1.2 mg/kg provides good tracheal intubating conditions after major burns.