Electrolyte Disorders USMLE Step 1 Practice Question
A 55-year-old man with a 3-day history of acute kidney injury presents to the emergency department with generalized weakness and palpitations. He has been taking lisinopril for hypertension. Vital signs are BP 142/88 mmHg, HR 108 bpm with an irregular rhythm, RR 20, temperature 37.2°C, and SpO2 98% on room air. Laboratory studies reveal serum potassium 6.8 mEq/L, creatinine 4.2 mg/dL (baseline 0.9), and blood glucose 95 mg/dL. Troponin is negative. An ECG shows peaked T waves with a normal QRS duration. The patient is immediately given intravenous calcium gluconate. Which of the following best explains the rationale for administering calcium gluconate first, before insulin-dextrose or sodium bicarbonate?
Answer choices
- ACalcium gluconate reduces serum potassium concentration by inhibiting renal tubular reabsorption
- BCalcium gluconate shifts potassium intracellularly by activating Na-K-ATPase pumps more rapidly than insulin
- CCalcium gluconate stabilizes the cardiac myocyte membrane by decreasing the resting membrane potential gradientCorrect answer
- DCalcium gluconate directly chelates serum potassium ions, converting them to a non-bioavailable complex
- ECalcium gluconate buffers intracellular hydrogen ions and prevents arrhythmogenic acidosis in myocardial cells
- FCalcium gluconate enhances glomerular filtration rate and promotes renal potassium excretion in acute kidney injury
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