COPD USMLE Step 1 Practice Question
A 24-year-old man on mechanical ventilation post-motor vehicle collision presents with BP 118/76, HR 92, RR 16 (set), temp 37.2°C, and SpO2 98% on FiO2 0.4. Measured minute ventilation is 8 L/min, but alveolar ventilation is substantially lower due to increased dead space. Chest X-ray shows bilateral lung contusions without pneumothorax. ABG reveals pH 7.38, PaCO2 42 mmHg. Which intervention most directly decreases the minute-to-alveolar ventilation difference?
Answer choices
- ADecrease physiologic dead spaceCorrect answer
- BIncrease fraction of inspired oxygen
- CIncrease pulmonary capillary hydrostatic pressure
- DIncrease respiratory rate while keeping tidal volume constant
- EDecrease hemoglobin affinity for oxygen
- FIncreasing tidal volume at constant respiratory rate
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