Myasthenia gravis and thymic surgery-anaesthetic considerations

Myasthenia gravis is an uncommon condition but it is of particular interest to the anaesthetist because it involves the neuromuscular junction causing a decrease in the margin of safety of neuromuscular transmission. Early thymectomy is the treatment of choice for most patients with MG but the surgical approach to the thymus (transcervical or transsternal) remains controversial. The anaesthetic technique for thymectomy must consider the sensitivity of MG patients to certain drugs used in anaesthesia. While potent inhalational agents are probably the most popular approach, competitive muscle relaxants may be safely used, provided that reduced doses are carefully titrated against effect with the aid of a neuromuscular transmission monitoring system. Of the non-depolarizing relaxants, atracurium would seem to be the ideal because of its short duration of effect and reliable pharmacokinetics. Elective tracheotomy, once routine in all MG patients undergoing thymectomy, is now the exception. Attempts to identify those MG patients who will require prolonged mechanical ventilation postoperatively have produced inconsistent results and each patient must therefore be treated on her/his own merit. Thymectomy averts the progression of disease in most MG patients, speeds the onset of remission, and appears to exert a protective effect against the development of certain extrathymic neoplasms.