A client has a large pulmonary embolism and is started on oxygen. The nurse asks the charge nurse why the client's oxygen saturation has not significantly improved. What response by the nurse is best?

Rationale: A. Rapid breathing (tachypnea) alone does not significantly prevent oxygenation. While it may cause fatigue over time, it is not the primary reason oxygen saturation remains low in pulmonary embolism. B. Acute respiratory distress syndrome (ARDS) is a different condition. While ARDS also impairs oxygenation, the patient has a pulmonary embolism, so the cause of hypoxemia is different. C. Immediate intubation is not automatically indicated for every patient with pulmonary embolism. Many patients can maintain adequate oxygenation with supplemental oxygen unless they develop severe respiratory failure. D. A pulmonary embolism obstructs blood flow in the pulmonary arteries, causing a ventilation-perfusion (V/Q) mismatch. Oxygen can reach the alveoli, but blood flow is blocked, so oxygen cannot be effectively transferred into the circulation, resulting in persistent hypoxemia despite supplemental oxygen.