Acid-Base Disorders USMLE Step 1 Practice Question

A 45-year-old man with Child-Pugh class C cirrhosis presents to the emergency department with altered mental status, diffuse muscle weakness, and muscle cramping. He has been taking furosemide 80 mg daily for 2 weeks to manage ascites. Vital signs are BP 136/84 mmHg, HR 102 bpm, RR 16 breaths/min, temperature 37.2°C, and SpO2 98% on room air. He denies vomiting, diarrhea, or respiratory symptoms. Laboratory studies are notable for: pH 7.52 PCO2 43 mmHg PO2 88 mmHg HCO3− 35 mEq/L K+ 2.8 mEq/L Cl− 84 mEq/L Na+ 132 mEq/L Cr 1.0 mg/dL (baseline 0.9) Albumin 2.1 g/dL Which of the following mechanisms most directly perpetuates the metabolic alkalosis in this patient?