What can you assume about a patient who has a mismatch and exhibits hypercapnia?

a. The central nervous system is not re-sponding to the increased PCO2.
b. The patient cannot sustain the high E to overcome the high VD.
c. The patient is compensating for an acute metabolic alkalosis.
d. The patient is compensating for a chronic metabolic acidosis.

ANS: B
An increase in dead space ventilation is caused by either (1) rapid, shallow breathing (an increase in anatomical dead space per minute) or (2) increased physiologic dead space (/ = 0). In either case, the proportion of wasted ventilation increases. Without compensation, this lowers alveolar ventilation per minute and impairs carbon dioxide removal.