An obese 50-year-old woman undergoes a laparoscopic cholecystectomy. In the recovery room, she is found to be hypotensive and tachycardic. Her aerial blood gases reveal a pH of 7.29, PaO2 of 60 mm Hg, and PaCO2 of 54 mm Hg. Which of the following is the most likely cause of this patient's problem?

Because of the ease with which CO2 diffuses across the alveolar membranes, PaCO2 is a highly reliable indicator of alveolar ventilation. In this postoperative patient with respiratory acidosis and hypoxemia, the hypercarbia is diagnostic of alveolar hypoventilation. Acute hypoxemia can occur with pulmonary embolism, pulmonary edema, and significant atelectasis, but in all those situations the PaCO2 should be normal or reduced, as the patient hyperventilates to improve oxygenation. The absorption of gas from the peritoneal cavity may transiently affect the PaCO2 , but should have no effect on oxygenation.