Myasthenia gravis: management of myasthenic crisis and perioperative care.
Myasthenic crisis may be defined as respiratory failure or delayed postoperative extubation for more than 24 hours resulting from myasthenic weakness. Myasthenic crisis results from weakness of upper airway muscles leading to obstruction and aspiration, weakness of respiratory muscles leading to reduced tidal volumes, or from weakness of both muscle groups. About one-fifth of patients with myasthenia gravis experience crisis, usually within the first year of illness. Over the last four decades, prognosis from myasthenic crisis has dramatically improved from a mortality rate of 75% to the current rate of less than 5%. Common precipitating factors for myasthenic crisis include respiratory infections, aspiration, sepsis, surgical procedures, rapid tapering of immune modulation, beginning treatment with corticosteroids, exposure to drugs that may increase myasthenic weakness, and pregnancy. Myasthenic crisis should not be fatal, as long as patients receive timely respiratory support and appropriate immunotherapy to reduce myasthenic weakness of the upper airway and respiratory muscles. Myasthenic patients with oropharyngeal or respiratory muscle weakness should receive preoperative plasma exchange or intravenous immunoglobulin therapy to a minimal level of weakness to prevent postoperative complications.