While providing pressure-controlled mechanical ventilation with PSV to a patient having respiratory failure caused by airflow obstruction, the therapist notices that the peak flow of the pressure-controlled breath diminishes and that the decelerating flow profile is slow. What action should the therapist take at this time?

A. Increase the rise time.
B. Decrease the tidal volume.
C. Increase the flow cycling criterion.
D. Decrease the inspiratory flow.

ANS: C
A. Incorrect response: See explanation C.
B Incorrect response: See explanation C.
C. Correct response: A specific cycling problem can occur with PSV in patients with airway obstruction. The peak flow of the pressure-controlled breath may be diminished, and the decelerating flow profile may be slow. This situation may cause prolongation of the pressure support breath because the cycling flow value (often 25% to 35% of the peak flow) may take substantial time to reach. Consequently, shortened expiratory times may cause auto-PEEP. Methods of addressing this issue involve increasing the pressure support flow cycling criterion, for example, from 25% to 50% of the peak flow.
D. Incorrect response: See explanation C