Mechanical ventilation is an important support strategy for critically ill patients. It could improve gas exchange, reduce the work of breathing, and improve patient comfort. However, patient-ventilator asynchrony, which defined as a mismatch between the patient and ventilator may obfuscate these goals. Studies have shown that a high incidence of asynchrony (asynchrony index > 10%) is associated with prolonged mechanical ventilation and ICU length of stay and high mortality. So far, there have been only a few studies on the epidemiology of asynchrony in brain-injured patients. Investigators conduct a prospective observational study among brain-injured patients to determine the prevalence, risk factors and outcomes of patient-ventilator asynchrony. Esophageal pressure monitoring, a surrogate for pleural pressure, combined with airway pressure and flow waveforms is used to detect patient-ventilator asynchrony.