Anesthesia and critical care of thymectomy for myasthenia gravis

Myasthenia gravis is an autoimmune disease resulting from the production of antibodies against the ACh receptors of the neuromuscular synapse. The thymus gland is involved in the autosensitization process, and the disease frequently is associated with thymic morphologic abnormalities. There is a consensus that all adults with generalized MG should have a thymectomy. This recommendation has been propagated by the safety of the procedure and excellent outcome. Removal of as much thymic tissue as possible (anterior mediastinal exenteration) by transsternal approach is the logical goal of thymectomy in the treatment of MG. Transcervical approach and VATS, however, are less invasive and have been used in patients who have MG unaccompanied by thymoma. Optimization of the condition of the myasthenic patients can markedly decrease the risk of surgery and improve the outcome. Two techniques have been recommended for general anesthesia in the myasthenic patient. Because of the unpredictable response to succinylcholine and the marked sensitivity to nondepolarizing muscle relaxants, some anesthesiologists avoid muscle relaxants and depend on deep inhalational anesthesia, such as halothane, isoflurane, or sevoflurane, for tracheal intubation and maintenance of anesthesia. Others, however, use a balanced technique of anesthesia that includes the use of carefully titrated muscle relaxants. The most important preoperative factor predicting the need for postoperative mechanical ventilation is the severity of bulbar involvement (Ossermann group 3 and 4), usually indicated by significant dysphagia and dysarthria associated with borderline respiratory dysfunction. Thymectomy benefits nearly 96% of patients: 46% develop complete remission, 50% are asymptomatic or improve on therapy, and 4% remain the same. The time from diagnosis to surgery is shorter than 8 months, and mild or moderate myasthenic symptoms are the main prognostic factors that predict the best outcome after thymectomy.