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?