Which of the following physiologic and/or mechanical changes can the therapist expect a patient who is receiving volume-controlled ventilation for airflow obstruction to experience as a result of having narrowed airways? I. increased peak airway pressures II. overdistention injury to distal airways III. reduced risk for volutrauma IV. increased alveolar dead space
A. I, IV only
B. II, III only
C. I, II, IV only
D. I, III, IV only
?ANS: C
A. Incorrect response: See explanation C.
B. Incorrect response: See explanation C.
C. Correct response: Narrowed airways produce a high resistance to flow that can cause high peak pressures. Much of this pressure is dissipated in providing gas flow through obstructed airways, and therefore does not overdistend distal alveoli. However, the heterogeneous distribution of airflow obstruction seen in most airways diseases means that less obstructed alveolar regions may be transiently exposed to these high peak pressures and be at risk for overdistention injury. Therefore the therapist should realize that a high peak pressure, even in the presence of a plateau pressure less than 30 cm H2O, should be prevented. Perhaps auto-PEEP causes overdistention injury as well.
D. Incorrect response: See explanation C.?
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