Which finding is characteristic of a large saddle pulmonary embolism?

Which finding is characteristic of a large saddle pulmonary embolism?

• A. Fever with normal oxygen
• B. Tachypnea with respiratory alkalosis and hypoxemia
• C. Anorexia
• D. Isolated chest wall tenderness

Answer: (B)

The key idea is that a large saddle pulmonary embolism causes a sudden, major obstruction of the pulmonary arteries, leading to a sharp ventilation-perfusion mismatch. Areas of the lung that are ventilated but not well perfused create dead space, while overall oxygen transfer to the blood drops, producing hypoxemia. In response, the body increases respiratory rate to improve oxygen delivery, so you get tachypnea. This rapid breathing blows off carbon dioxide faster than it’s produced, resulting in a respiratory alkalosis. So the combination of rapid breathing with low oxygen and a high blood pH due to low CO2 is the classic physiologic pattern seen with a large pulmonary embolism. Fever with normal oxygen, anorexia, and isolated chest wall tenderness aren’t typical hallmarks of a large embolus; they don’t reflect this acute V/Q mismatch and hyperventilatory response.

The key idea is that a large saddle pulmonary embolism causes a sudden, major obstruction of the pulmonary arteries, leading to a sharp ventilation-perfusion mismatch. Areas of the lung that are ventilated but not well perfused create dead space, while overall oxygen transfer to the blood drops, producing hypoxemia. In response, the body increases respiratory rate to improve oxygen delivery, so you get tachypnea. This rapid breathing blows off carbon dioxide faster than it’s produced, resulting in a respiratory alkalosis. So the combination of rapid breathing with low oxygen and a high blood pH due to low CO2 is the classic physiologic pattern seen with a large pulmonary embolism.

Fever with normal oxygen, anorexia, and isolated chest wall tenderness aren’t typical hallmarks of a large embolus; they don’t reflect this acute V/Q mismatch and hyperventilatory response.