Electrolyte Disorders USMLE Step 1 Practice Question
A 34-year-old man with a 3-day history of severe watery diarrhea presents with complaints of weakness and dizziness. Physical examination reveals dry mucous membranes, decreased skin turgor, and tachycardia. Vital signs: heart rate 108/min, blood pressure 98/62 mmHg, respiratory rate 16/min, temperature 37.2°C. The patient denies vomiting. Laboratory studies show: Serum electrolytes:
- Sodium: 138 mEq/L
- Potassium: 3.0 mEq/L
- Chloride: 88 mEq/L
- Bicarbonate: 30 mEq/L Arterial blood gas:
- pH: 7.48
- PCO2: 38 mmHg
- PO2: 95 mmHg Urine electrolytes:
- Urine chloride: 12 mEq/L Which of the following best explains this patient's acid-base disturbance?
Answer choices
- ARespiratory alkalosis from acute volume depletion triggering hyperventilation
- BMetabolic acidosis from bicarbonate loss in diarrheal fluid
- CMetabolic alkalosis from volume contraction and loss of hydrogen ions in diarrheaCorrect answer
- DMixed metabolic acidosis and respiratory alkalosis from concurrent diarrheal illness
- EHyperchloremic normal anion gap metabolic acidosis from GI chloride wasting
- FRespiratory acidosis with inadequate metabolic compensation in chronic diarrheal disease
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