A 90-kg man is admitted to the ICU after partial colectomy for surgical management of colon cancer. He also has a history of congestive heart failure with an ejection fraction of 40%, mild chronic obstructive pulmonary disease (COPD), and anemia. On admission to the ICU, his oxygen saturation is 90% on room air. A radial arterial line and an internal jugular central venous line were placed perioperatively. An arterial blood gas study reveals Pao2 of 55 mm Hg and Paco2 of 40 mm Hg. Venous blood for labs is drawn from the tip of the central line and reveals a venous PO2 of 30 mm Hg. Which of the following factors is most likely contributing to this patient's hypoxemia?
A. Obesity hypoventilation syndrome
B. Opiate-induced hypoventilation
C. Hypothermia
D. Decreased cardiac output
E. COPD exacerbation