A patient with chronic hypercapnia placed on an FiO2 of 0.6 starts hypoventilating. What is a possible cause of this phenomenon?

a. Decreased cardiac output
b. O2 toxicity
c. O2-induced hypoventilation
d. Absorption atelectasis

ANS: C
When breathing moderate to high O2 concentrations, COPD patients with chronic hypercapnia may tend to ventilate less.