Acid-Base Disorders USMLE Step 1 Practice Question
A 70-year-old man with systolic heart failure presents with dyspnea and orthopnea. He receives aggressive loop diuretic therapy and becomes euvolemic within 48 hours. Vitals: BP 128/76, HR 92, RR 16, SpO2 98% on room air. He now reports generalized weakness without dyspnea. Labs show pH 7.49, HCO3− 34 mEq/L, chloride 90 mEq/L, and potassium 3.2 mEq/L. Urine chloride is 8 mEq/L. Which mechanism best explains his alkalosis?
Answer choices
- ARetention of ketoacids
- BBicarbonate loss in the stool
- CLoss of chloride-rich fluid with volume contractionCorrect answer
- DRetention of hydrogen ions due to hypoventilation
- EFailure of distal H+ secretion
- FExcessive aldosterone secretion due to volume depletion leading to increased proximal tubule bicarbonate reabsorption
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.