After undergoing left hemicolectomy for a colonic mass Develops shortness of breath

Two days after undergoing left hemicolectomy for a colonic mass develops shortness of breath, a 60- year-old man develops shortness of breath. His temperature is 38.1C (100.6F), pulse is 80/min, respirations are 22/min, and blood pressure is 120/78 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 88%. Cardiopulmonary examination shows decreased breath sounds and decreased fremitus at both lung bases. Arterial blood gas analysis on room air shows:

pH: 7.35

Pa02: 70m Hg

PaCo2: 40mm Hg

An x-ray of the chest shows collapse of the bases of both lungs. Which of the following is the most likely mechanism of this patient’s hypoxemia?

Increased tidal volume

Decreased hemoglobin oxygen-binding capacity

Increased anatomic dead space Increased rate of oxygen consumption

Decreased ratio of ventilated alveoli

Decreased chest wall compliance