Resp Care
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In the developed world, Guillain-Barré syndrome and myasthenia gravis account for the majority of cases of acute respiratory failure associated with neuromuscular disease. The 4 components that contribute to respiratory failure are upper-airway dysfunction, inspiratory-muscle weakness, expiratory-muscle weakness, and the pulmonary complications associated with these conditions. ⋯ The morbidity and mortality of patients who require mechanical ventilation are not insubstantial. This paper will review the mechanisms underlying acute respiratory failure, the clinical assessment of patients, the predictors of the need for mechanical ventilation, and the intensive-care-unit morbidity and mortality of patients with Guillain-Barré syndrome or myasthenia gravis.
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Although life-saving, mechanical ventilation is associated with numerous complications. These include pneumonia, cardiovascular compromise, barotrauma, and ventilator-induced lung injury. Recent data from animal studies suggest that controlled mechanical ventilation can cause dysfunction of the diaphragm, decreasing its force-generating capacity--a condition referred to as ventilator-induced diaphragmatic dysfunction (VIDD). ⋯ Whether the decrease in diaphragmatic contractility observed during controlled ventilation contributes to failure to wean from the ventilator is difficult to ascertain. Weaning-failure patients have reasons other than VIDD for respiratory-muscle weakness. Until we have further data, it seems prudent to avoid the use of controlled mechanical ventilation in patients with acute respiratory failure.
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Neuromuscular abnormalities culminating in skeletal-muscle weakness occur very commonly in critically ill patients. Intensive-care-unit (ICU) acquired neuromuscular abnormalities are typically divided into 2 discrete classes: polyneuropathy and myopathy. However, it is likely that these 2 entities commonly coexist, with myopathy being the most common cause of weakness. ⋯ The only intervention proven to reduce the incidence of ICU-acquired neuromuscular abnormalities is intensive insulin therapy. Additional research is necessary to better delineate the causes and pathogenesis of these disorders and to identify potential preventive and therapeutic strategies. In addition, consensus guidelines for its classification and diagnosis are needed.
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Motor weakness in a patient in the intensive care unit (ICU) may be related to (1) pre-existing neuromuscular disorder that leads to ICU admission, (2) new-onset or previously undiagnosed neurological disorder, or (3) complications of non-neuromuscular critical illness. Neuromuscular syndromes related to ICU treatment consist of critical illness polyneuropathy, critical illness myopathy, and prolonged neuromuscular blockade, and are now recognized as a frequent cause of newly acquired weakness in ICU patients. Clinical features include quadriparesis, muscle wasting, and difficulty weaning from the ventilator. ⋯ A subgroup of patients with myasthenia gravis with muscle-specific tyrosine kinase antibody is noted to present as respiratory crisis. Muscle biopsy in ICU paralysis syndromes may be helpful in arriving at a specific diagnosis or to classify the type of critical illness myopathy. Nerve biopsy is only rarely indicated.
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Neuromuscular diseases that affect the respiratory system are a major cause of morbidity and mortality in both acute and long-term settings. This conference examined the pathophysiology and management of neuromuscular diseases in both settings. ⋯ This summary of the conference briefly describes the main points of each presentation and highlights areas that need addressing in the future. Major topics covered include the basic respiratory pathophysiology of neuromuscular disease; respiratory complications and management of amyotrophic lateral sclerosis; techniques of noninvasive ventilation and secretion removal; and evaluation and management of neuromuscular-induced respiratory failure in the acute-care setting, including Guillain-Barré syndrome, myasthenic crisis, and critical-illness myoneuropathy.