PSV has been increasingly used as a partial ventilatory support for various types of respiratory failure. We experienced premature breath termination and double triggering in a patient with ARDS during PSV, and investigated the cause of this phenomenon using respiratory muscle pressure (Pmus). The analysis confirmed that the respiratory muscles and the ventilator did not coordinate synchronously in the patient with very low compliance of the respiratory system. The limitation of synchronization was attributable to fixed flow termination criteria in the present PSV algorithm. When dissynchronization is not manageable, other ventilatory modes (eg, APRV, PCV) allowing spontaneous ventilation should be considered as an alternative.