ABSTRACT
Myasthenia gravis is an autoimmune disorder resulting from a decreased number of active acetylcholine receptors at the neuromuscular junction. Thymectomy is one of its current treatments. Due to sensitivity of myasthenic patients to non-depolarizing muscle relaxants and also the interaction of this medication with anti-cholinestrase drugs, determining the dosage of non-depolarizing muscle relaxants for induction of anesthesia is one of the hurdles in thymectomy. Twenty myasthenic patients undergoing transsternal thymectomy were enrolled into the study. They were divided into two groups randomly, and received either 0.25 mg/kg or 0.50 mg/kg of atracurium to facilitate tracheal intubation. Neuromuscular blockade was measured using train of four [TOF] mode of neuromuscular stimulator 15 minutes after administration of atracurium and then each 5 minutes till entered the recovery phase. The time between injection of atracurium and the recovery phase was compared between the two groups. The two groups were similar with respect to age and gender. The time from the onset of myasthenia gravis to surgery, dosage and duration of pyridostegmine used preoperatively were not significantly different between the two groups. The time from administration of atracurium to recovery phase was not significant between the two groups [P=0.24]. There was no difference between two different doses of atracurium regarding entering the recovery phase, and as the effects of nondepolarizing muscle relaxants are unpredictable in myasthenic patients, we recommend the lower dose to prevent profound skeletal muscle weakness and postoperative complications