Noninvasive ventilation in myasthenic crisis

Background: Myasthenic crisis (MC) is often associated with prolonged intubation and with respiratory complications. Objectives: To assess predictors of ventilation duration and to compare the effectiveness of endotracheal intubation and mechanical ventilation (ET-MV) with bilevel positive airway pressure (BiPAP) noninvasive ventilation in MC. Design: Retrospective cohort study. Setting: Academic research. Patients: We reviewed consecutive episodes of MC treated at the Mayo Clinic, Rochester, Minnesota. Main Outcome Measures: Collected information included patients' demographic data, immunotherapy, medical complications, mechanical ventilation duration, and hospital lengths of stay, as well as baseline and preventilation measurements of forced vital capacity, maximal inspiratory and expiratory pressures, and arterial blood gases. Results: We identified 60 episodes of MC in 52 patients. BiPAP was the initial method of ventilatory support in 24 episodes and ET-MV was performed in 36 episodes. There were no differences in patient demographics or in baseline respiratory variables and arterial gases between the groups of episodes initially treated using BiPAP vs ET-MV. In 14 episodes treated using BiPAP, intubation was avoided. The mean duration of BiPAP in these patients was 4.3 days. The only predictor of BiPAP failure (ie, requirement for intubation) was a PCO₂ level exceeding 45 mm Hg on BiPAP initiation (P=.04). The mean ventilation duration was 10.4 days. Longer ventilation duration was associated with intubation (P=.02), atelectasis (P<.005), and lower maximal expiratory pressure on arrival (P=.02). The intensive care unit and hospital lengths of stay statistically significantly increased with ventilation duration (P<.001 for both). The only variable associated with decreased ventilation duration was initial BiPAP treatment (P<.007). Conclusions: BiPAP is effective for the treatment of acute respiratory failure in patients with myasthenia gravis. A BiPAP trial before the development of hypercapnia can prevent intubation and prolonged ventilation, reducing pulmonary complications and lengths of intensive care unit and hospital stay.