When adaptive support ventilation (ASV) is being used, how does the Hamilton Galileo minimize air trapping and auto-PEEP?

A. It automatically decreases the exiting VT when necessary to prevent overdistention of the lungs.
B. The ventilator adjusts the flow-cycle criterion on a breath-to-breath basis.
C. It calculates the expiratory time constant and uses the time constant to maintain adequate expiratory time.
D. The ventilator accomplishes this by either increasing or decreasing pressure support.

?ANS: C
A. Incorrect response: During ASV, the ventilator (1) uses the initial ventilator settings (i.e., high-pressure alarm, PEEP, and Fio2), (2) calculates system compliance, airway resistance, and auto-PEEP, and (3) uses the pressure limit of both mandatory and spontaneous breaths to determine the target breath and tidal volume.
B. Incorrect response: The therapist can adjust the rise time and the flow-cycling criterion.
C. Correct answer: The ventilator adjusts the I:E ratio and the inspiratory time of the mandatory breaths to prevent air trapping. These adjustments are accomplished by calculating the patient's expiratory time constants, and maintaining sufficient expiratory time.
D. Incorrect response: Pressure support ventilation is not part of ASV.