[Use of mivacurium chloride during transsternal thymectomy in myasthenic patient]. / Empleo del clorhidrato de mivacurio durante la timectomía transesternal en el paciente miasténico.

ABSTRACT

INTRODUCTION: Myasthenia gravis is an autoimmune disease characterized by the presence of circulating IgG antibodies, which interact with acetylcholine receptors and interfere with neuromuscular transmission. OBJECTIVES: To compare neuromuscular function when mivacurium is used in patients with myasthenia gravis and patients with no impairment of transmission at the neuromuscular synapse. MATERIAL AND METHOD: Prospective study of 40 patients in two groups. Group I (n = 20) consisted of patients with no impairment of neuromuscular transmission who underwent sternotomy or mediastinoscopy and who received 2 ED95 of mivacurium. Group II (n = 20) were patients with myasthenia gravis who underwent transsternal thymectomy and received 0.5 ED95 of mivacurium (50 micrograms/Kg). The neuromuscular function of all patients was monitored by accelerometry of the thumb adductor. RESULTS: All demographic variables except sex were similar in the two groups. Time to maximal block, duration of block and the recovery at T1 25-75 were significantly greater in group II (250 +/- 10 s, 29.1 +/- 2.4 min and 8.1 +/- 1.5 min, respectively) than in group I (188 +/- 13 s, 21.2 +/- 0.4 min and 7.1 +/- 0.2 min in group I). Maintenance doses were given more often in group I. At the end of surgery and before recovery from mivacurium, the mean twitch height in group II was 89.3 +/- 0.5%, such that tracheal tubes were removed from 95% of the patients without complications. The mean time until extubation in group II was 17.8 +/- 1.3 min and was related to the extension of the blocks. The differences were statistically significant (p < 0.05). CONCLUSIONS: The anesthetic effect of mivacurium was twice as great in myasthenic patients, in whom it behaved like an intermediate-level non-depolarizing muscle relaxant. Mivacurium can reduce prolonged mechanical ventilation in patients who are myasthenic or pharmacologically immunosuppressed and at risk of sepsis arising in the respiratory tract.