Prolonged paralysis after neuromuscular blockade

Non-depolarizing neuromuscular blocking agents have been used with increasing frequency in critically ill patients. Recently, numerous reports have described patients with prolonged muscle weakness after use of these agents for more than two days. Brief weakness lasting several hours to several days is likely the result of prolonged neuromuscular blockade, while more prolonged weakness lasting several weeks to months is likely caused by a myopathy. Specific features of this myopathic disorder are reviewed. Clinically, patients have flaccid paralysis with intact sensation and cognition. Electrodiagnostic findings include decreased M-wave amplitudes, mild positive waves and fibrillations and small, polyphasic motor unit potentials. Muscle biopsy findings include atrophy of type I and type II fibers, myofiber necrosis and selective loss of thick myofilaments. This myopathic disorder is felt to be related to the prolonged use of non-depolarizing neuromuscular blocking agents either alone or in combination with other medications or disorders. Many authors feel that the disorder is caused specifically by a combination of prolonged neuromuscular blockade and corticosteroids. Selective loss of thick myofilaments on muscle biopsy has been produced experimentally in rats by combing denervation with high doses of corticosteroids. As this disorder likely leads to additional respiratory compromise, difficulty weaning from the ventilator, and prolonged hospitalization, prevention is warranted. Methods of prevention include minimizing the dosage of non-depolarizing neuromuscular blocking agents and of other drugs with an effect on the neuromuscular junction, twitch monitoring with a peripheral nerve stimulator and allowing patients to come to an unparalyzed state for brief periods.