An 83-year-old woman is found unresponsive by her son approximately 3 hours after she returned to her hospital room following gall bladder surgery. The nurse reported that the patient had asked for her pain medications and said she was going to rest for a while. Arterial blood gases reveal hypercapnia and hypoxemia. Which of the following is the most likely cause of the high arterial PCO₂ ?
a. Decreased alveolar dead space
b. Decreased metabolic activity
c. Hypoventilation
d. Hypoxemia
e. inequality