Neuromuscular Pharmacodynamics of Mivacurium in Patients with Major Burns

Chung, Mi Hwa; Jung, Jin Kyung; Lee, Jin Young; Kwak, In Suk; Choi, Young Ryong; Won, Rim Soo; Han, Tae Hyung

Abstract

BACKGROUND: Burned patients sometimes require rapid onset of neuromuscular paralysis to secure the airway in full stomach patients or to treat laryngospasm. Because of poor lung function and hypermetabolic state, they desaturate quite rapidly. Burned patients are usually resistant to the effects of nondepolarizing relaxants. Mivacurium can be potentially a good alternative for rapid onset of paralysis, since it is metabolized by plasma cholinesterase, an enzyme often decreased in subject with major burns. This prospective study was conducted to define the neuromuscular pharmacodynamic profile of a single bolus dose of mivacurium in adult patients with major burns.
METHODS
Adults (M/F = 22/8), aged 44.0 +/- 10.2 years, with total body surface area (TBSA) burn of 35.0 +/- 12.5% were studied at 39.8 +/- 28.9 post burn days. Age and sex matched 30 non-burned patients served as controls. Anesthesia was consisted of propofol and fentanyl infusion with nitrous oxide and oxygen. Mivacurium 0.2 mg/kg was administered as a bolus. Using TOF Watch, neuromuscular block was monitored with T1 response after the initial tetanic stimulation to recruit all muscle fibers. Onset time was defined as the interval from the beginning of drug administration to maximal twitch suppression. Intubation was attempted at 1 minute after the drug administration to simulate the rapid sequence induction with recording of either failure or success of intubation. By allowing spontaneous recovery without reversal drug, recovery profiles of neuromuscular paralysis were also measured.
RESULTS
Patients demographics were similar in both groups except for the burn. Onset times and all recovery profiles were significantly prolonged in the burned versus non-burned groups. Attempts at intubation at 1 minute after the drug administration were successful with difficulty in approximately 70% of patients in both groups.
CONCLUSIONS
Mivacurium 0.2 mg/kg demonstrated the conflicting dual responses in the burned patients. The prolonged onset time suggests resistance to neuromuscular effects. The prolonged recovery suggests increased sensitivity. This can be partially explained by the acetylcholine receptor proliferation and decreased level of plasma pseudocholinesterase. 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 burns.