Which of the following is a cause of increased physiologic dead space?

• A. Decreased Cardiac Output
• B. High PEEP
• C. Hypoxemia
• D. Pulmonary Embolism

Answer: (D)

Physiologic dead space rises when ventilation occurs in lung regions that are not perfused, so gas exchange cannot happen there. A pulmonary embolism directly causes this by blocking blood flow to part of the lung. The alveoli in that region remain ventilated but lack perfusion, becoming alveolar dead space and increasing the overall physiologic dead space. Other factors, like high PEEP, can contribute by changing ventilation-perfusion dynamics, but the embolism is the most direct and classic cause among the options. Decreased cardiac output or hypoxemia relate to overall oxygenation and mismatch but don’t as directly produce a regional increase in physiologic dead space.