Acid-Base Disorders USMLE Step 1 Practice Question
A 28-year-old woman with a 6-month history of Crohn's disease presents with persistent diarrhea. She reports approximately 4-6 loose stools daily but denies vomiting or recent antibiotic use. Vital signs are stable: BP 110/68 mmHg, HR 92 bpm, RR 18 breaths/min, temperature 37°C. Laboratory studies show: pH: 7.32
PaCO2: 35 mmHg
HCO3−: 16 mEq/L
Serum K+: 3.2 mEq/L
Serum Cl−: 92 mEq/L
Serum Na+: 138 mEq/L
Anion gap: 8 mEq/L Which of the following best explains the pathophysiologic mechanism underlying this patient's acid-base disturbance?
Answer choices
- ALoss of gastric HCl with contraction metabolic alkalosis
- BAccumulation of lactate and ketoacids from malabsorption
- CNormal anion gap metabolic acidosis from bicarbonate wasting in stool with secondary hyperchloremiaCorrect answer
- DRespiratory acidosis from diaphragmatic weakness secondary to hypokalemia
- EImpaired renal ammonia excretion leading to hyperammonemia-induced acidosis
- FSecondary hyperparathyroidism causing increased urinary acid excretion
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