Which of the following modes of mechanical ventilation is/are more likely to produce an altered PaCO2 in patients in response to chemoreceptor input? I. continuous mandatory ventilation II, proportional assist ventilation III. pressure support ventilation IV. assist-control (volume-cycled) ventilation

A. III only
B. II, IV only
C. III, IV only
D. I, II, III only

?ANS: C
A. Incorrect response: In response to increasing levels of FICO2, patients receiving PSV demonstrated increased chemoreceptor response, evidenced by a hypocapnia and a larger tidal volume.
B. Incorrect response: In response to increasing levels of FICO2, patient receiving PAV essentially maintained a constant PaCO2 (eupnea).
C. Correct response: In response to increasing levels of FICO2, patients receiving either ACV or PSV experienced increased chemoreceptor response, demonstrated by hypocapnia and an increased VT.
D. Incorrect response: In response to increasing levels of FICO2, patients receiving ACV demonstrated increased chemoreceptor response, evidenced by a hypocapnia and a greater tidal volume.