Acid-Base Disorders USMLE Step 1 Practice Question
A 69-year-old man with severe COPD presents with worsening dyspnea. Vital signs show BP 152/88 mm Hg, HR 102/min, RR 28/min, temperature 37.2°C, and SpO2 88% on room air. Arterial blood gas reveals pH 7.36, PaCO2 60 mm Hg, and HCO3− 33 mEq/L. Serum chloride is 98 mEq/L. He denies recent vomiting. Which mechanism best explains the elevated bicarbonate concentration?
Answer choices
- ACompensation for chronic respiratory alkalosis
- BAcute intracellular buffering only
- CRenal retention of bicarbonate in chronic respiratory acidosisCorrect answer
- DPrimary metabolic alkalosis from vomiting
- ELoss of bicarbonate in the urine
- FIncreased bicarbonate production from hepatic metabolism of organic acids
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