A 78-year-old woman is admitted to the medical intensive care unit (ICU) with multilobar pneumonia. On initial presentation to the emergency department, her initial oxygen saturation was 60% on room air and only increased to 82% on a non-rebreather face mask. She was in marked respiratory distress and intubated in the emergency department. Upon admission to the ICU, she was sedated and paralyzed. The ventilator is set in the assist-control mode with a respiratory rate of 24 breaths/min, tidal volume of 6 mL/kg, FiO2 of 1.0, and positive end-expiratory pressure of 12 cmH2O. An arterial blood gas measurement is performed on these settings; the results are pH of 7.20, PCO2 of 32 mmHg, and PO2 of 54 mmHg. What is the cause of the hypoxemia?
A. Hypoventilation alone
B. Hypoventilation and ventilation-perfusion mismatch
C. Shunt
D. Ventilation-perfusion mismatch
Answer:C
A 78-year-old woman is admitted to the medical intensive care unit (ICU) with multilobar pneumonia. On initial presentation to the emergency department, her initial oxygen saturation was 60% on room air and only increased to 82% on a non-rebreather face mask. She was in marked respiratory distress and intubated in the emergency department. Upon admission to the ICU, she was sedated and paralyzed. The ventilator is set in the assist-control mode with a respiratory rate of 24 breaths/min, tidal volume of 6 mL/kg, FiO2 of 1.0, and positive end-expiratory pressure of 12 cmH2O. An arterial blood gas measurement is performed on these settings; the results are pH of 7.20, PCO2 of 32 mmHg, and PO2 of 54 mmHg. What is the cause of the hypoxemia?
A. Hypoventilation alone B. Hypoventilation and ventilation-perfusion mismatch C. Shunt D. Ventilation-perfusion mismatch