Causes and outcomes of acute neuromuscular respiratory failure

To identify the spectrum of causes, analyze the usefulness of diagnostic tests, and recognize prognostic factors in patients with acute neuromuscular respiratory failure.

We evaluated 85 patients admitted to the intensive care unit (ICU) at Mayo Clinic, Rochester, between 2003 and 2009 with acute neuromuscular respiratory failure, defined as a need for mechanical ventilation owing to primary impairment of the peripheral nervous system. Outcome was assessed at hospital discharge and at last follow-up. Poor outcome was defined as a modified Rankin score greater than 3.

The median age was 66 years; median follow-up, 5 months. The most frequent diagnoses were myasthenia gravis, Guillain-Barré syndrome, myopathies, and amyotrophic lateral sclerosis (27, 12, 12, and 12 patients, respectively). Forty-seven patients (55%) had no known neuromuscular diagnosis before admission, and 36 of them (77%) had poor short-term outcomes. In 10 patients (12%), the diagnosis remained unknown on discharge; only 1 (10%) had regained independent function. Older age was associated with increased mortality during hospitalization. Longer mechanical ventilation times and ICU stays were associated with poor outcome at discharge but not at the last follow-up. Patients without a known neuromuscular diagnosis before admission had longer duration of mechanical ventilation, longer ICU stays, and worse outcomes at discharge. Electromyography was the most useful diagnostic test in patients without previously known neuromuscular diagnoses. The presence of spontaneous activity on needle insertion predicted poor short-term outcome regardless of final diagnosis. Coexistent cardiopulmonary diseases also predicted poor long-term outcome.

Among patients with neuromuscular respiratory failure, those without known diagnosis before admission have poorer outcomes. Patients whose diagnoses remain unclear at discharge have the highest rates of disability.