You are answering a USMLE-style medical question. Question: A 70-year-old woman is brought to the emergency department for the evaluation of abdominal pain, nausea, and vomiting for 1 day. Computed tomography shows a small bowel perforation. The patient is prepared for emergent exploratory laparotomy. She is sedated with midazolam, induced with propofol, intubated, and maintained on nitrous oxide and isoflurane for the duration of the surgery. A single perforation in the terminal ileum is diagnosed intraoperatively and successfully repaired. The patient is transferred to the intensive care unit. The ventilator is set at an FiO2 of 50%, tidal volume of 1000 mL, respiratory rate of 12/min, and positive end-expiratory pressure of 2.5 cm H2O. Her temperature is 37.3°C (99.1°F), pulse is 76/min, and blood pressure is 111/50 mm Hg. She is responsive to painful stimuli. Lung examination shows bilateral rales. Abdominal examination shows a distended abdomen and intact abdominal surgical incisions. The remainder of the physical examination shows no abnormalities. Arterial blood gas analysis shows: pH 7.44 pO2 54 mm Hg pCO2 31 mm Hg HCO3- 22 mm Hg Which of the following is the best next step in the management of this patient?" Options: A) Increase the FiO2 B) Increase the tidal volume C) Increase PEEP D) Increase the respiratory rate Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.