The role of non-invasive ventilation and factors predicting extubation outcome in myasthenic crisis.

INTRODUCTION: Myasthenic crisis is a great threat to patients with myasthenia gravis. Usage of non-invasive ventilation (NIV) to prevent intubation and timing of extubating of patients in myasthenic crisis are important issues though not well documented.
METHODS: To explore the factors predicting NIV success and extubation outcome in myasthenic crisis, we reviewed the records of 41 episodes of myasthenia crisis.
RESULTS: NIV was applied to 14 episodes of myasthenic crisis and eight (57.1%) of them were successfully prevented from intubation. An Acute Physiology and Chronic Health Evaluation (APACHE) II score of <6 and a serum bicarbonate level of <30 mmol/l were independent predictors of NIV success. For patients undergoing invasive mechanical ventilation, extubation failure was observed in 13 (39.4%) of 33 episodes, and the most common cause was sputum impaction due to a poor cough strength (61.5%). A maximal expiratory pressure (Pemax) of > or = 40 cmH(2)O was a good predictor of extubation success. Extubation failure led to poorer outcomes.
CONCLUSIONS: NIV may be applied to those patients with a low APACHE II score and a lesser degree of metabolic compensation for respiratory acidosis. For patients undergoing invasive mechanical ventilation, extubation failure is associated with significant in-hospital morbidity in myasthenic crisis. Adequate levels of Pemax and cough strength correlate significantly with extubation success.