A pediatric patient intubated with a 3.5-mm endotracheal tube is receiving pressure support ven-tilation. The respiratory therapist notes patient-ventilator asynchrony and a rapid deceleration of flow that prematurely ends inspiration

The most appropriate action to alleviate this is which of the following?
a. Increase the PS level.
b. Increase the rise time.
c. Decrease the PS level.
d. Increase the flow cycle.

ANS: B
ET tubes smaller than 4.5 mm may provide excessive resistance during PS. This can cause pres-surization of the ventilator circuit before sufficient flow enters the patient's airway. The result is a rapid deceleration of flow, which may prematurely end the inspiratory phase (premature pres-sure support termination [PPST]). This phenomenon does not allow the augmentation of VT, and patient-ventilator asynchrony may result. When PPST is suspected, a slower rise time can be used, which may reduce or eliminate the problem.