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KEY CONCEPTS
Weakness associated with myasthenia gravis is due to autoimmune destruction or inactivation of postsynaptic acetylcholine receptors at the neuromuscular junction, leading to reduced numbers of receptors and degradation of their function and to complement-mediated damage to the postsynaptic membrane.
Patients who have myasthenia gravis with respiratory muscle or bulbar involvement are at increased risk for pulmonary aspiration and pneumonia.
Many patients with myasthenia gravis are exquisitely sensitive to nondepolarizing neuromuscular blockers (NMBs).
Patients who have myasthenia gravis are at risk for postoperative respiratory failure. Disease duration of more than 6 years, concomitant pulmonary disease, a peak inspiratory pressure of less than –25 cm H2O (eg, –20 cm H2O), a vital capacity less than 4 mL/kg, and a pyridostigmine dose greater than 750 mg/d are predictive of the need for postoperative ventilation following thymectomy.
Patients with Lambert–Eaton myasthenic syndrome and other paraneoplastic neuromuscular syndromes are very sensitive to both depolarizing and nondepolarizing NMBs.
Respiratory muscle degeneration in patients with muscular dystrophy interferes with an effective cough mechanism and leads to retention of secretions and frequent pulmonary infections.
Degeneration of cardiac muscle in patients with muscular dystrophy is common but results in dilated or hypertrophic cardiomyopathy in only 10% of patients.
Succinylcholine should be avoided in patients with Duchenne or Becker muscular dystrophies because of unpredictable response and the risk of inducing severe hyperkalemia or triggering malignant hyperthermia.
Anesthetic management in patients with periodic paralysis is directed toward preventing attacks. Perioperative management must include frequent determinations of plasma potassium concentration and correction of abnormal values, with careful electrocardiographic monitoring to detect arrhythmias.
In patients with periodic paralysis, the response to NMBs is unpredictable, and neuromuscular function should be carefully monitored during their use. Increased sensitivity to nondepolarizing NMBs is likely to be encountered in patients with hypokalemic periodic paralysis.
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Neuromuscular diseases adversely affect muscle function either primarily or via nerve or neuromuscular junction abnormalities. They include myasthenia gravis; Lambert–Eaton syndrome; amyotrophic lateral sclerosis (ALS, or Lou Gehrig disease); infectious motor neuronopathies including acute flaccid paralysis, tetanus, and botulism; Guillain-Barré syndrome, Becker, Duchenne, facioscapulohumeral, and myotonic muscular dystrophies; Charcot–Marie–Tooth disease; polymyositis; and a large number of other pathological conditions. Although relatively uncommon, patients with these diseases will present to the operating room and to non–operating room procedure areas for diagnostic studies, treatment of complications, or procedural management of related or unrelated disorders, and they may also be evaluated and managed by anesthesia providers in the emergency department, intensive care unit, and on hospital wards in response to a rapidly progressive and life-threatening decline in respiratory status. Overall debility, with diminished respiratory muscle strength and increased sensitivity to neuromuscular blockers (NMBs), predisposes these patients to postoperative ventilatory failure, pulmonary aspiration, and pneumonia and may slow their postprocedure recovery because of difficulty with ambulation and increased risk of falling. Cardiac involvement may include cardiomyopathy or dysrhythmias. A basic understanding of the major disorders and their potential ...