Generalized Paralysis in the Intensive Care Unit: Emphasis on the Complications of Neuromuscular Blocking Agents and Corticosteroids

Abstract

Generalized weakness in intensive care unit (ICU) patients is increasingly recognized as a frequent complication and a common cause of prolonged ventilator dependency. Intravenous corticosteroids and neuromuscular blocking agents, sepsis, and multiorgan failure have been strongly implicated in the ICU paralysis syndromes, but the pathophysiology of these disorders is poorly understood. The combination of neuromuscular blocking agents and corticosteroids may induce three distinct syndromes of generalized weakness in ICU patients: acute myopathy, prolonged neuromuscular blockade, and critical illness polyneuropathy. More than one syndrome may occur simultaneously, and the distinctions may be difficult in a particular patient, but a specific diagnosis usually can be established after careful clinical, electrodi-agnostic, and histological evaluation. Acute myopathy with generalized weakness, preserved eye movements, elevated creatine kinase levels, and myopathic motor units on electromyography (EMG) have developed in asthmatics requiring neuromuscular blockers and steroids. Muscle biopsy has shown distinctive changes, with fiber atrophy, scattered necrosis, and thick (myosin) filament depletion on ultrastructural studies. Patients who have had a prolonged ICU stay or sepsis with failure to wean from the ventilator, distal weakness, and areflexia probably have critical illness polyneuropathy. EMG in these patients has demonstrated reduced or absent motor and sensory potentials with neurogenic motor units. Prolonged neuromuscular blockade most commonly has occurred in patients with renal failure who received prolonged infusions of neuromuscular blockers. Severe flaccid, areflexic paralysis with normal sensation, facial weakness, and ophthalmoparesis persists for days or weeks after the neuromuscular blockers have been discontinued. Repetitive nerve stimulation has shown a decrement of the compound muscle action potential, and it establishes a disorder of neuromuscular transmission in most patients. We critically examine the clinical, electrophysiological, and pathological features of each of these syndromes, and we summarize current understanding of the pathophysiology of these disorders and the relationship to neuromuscular blocking agents and corticosteroids.