Acid-Base Disorders USMLE Step 1 Practice Question
A 35-year-old woman with anxiety disorder presents to the ER following a panic attack with hyperventilation. She reports dizziness, perioral paresthesias, and hand tetany. Vital signs: BP 128/76 mmHg, HR 110/min, RR 28/min, Temp 37.2°C, SpO2 98% on room air. Arterial blood gas shows pH 7.51, PCO2 28 mmHg, HCO3− 22 mEq/L. Serum calcium is normal. She denies recent diuretic use. Which mechanism best explains her neurological manifestations?
Answer choices
- ADecreased ionized calcium from respiratory alkalosisCorrect answer
- BHypophosphatemia from metabolic acidosis
- CHyperkalemia from respiratory compensation
- DHypercalcemia from metabolic alkalosis
- EHyponatremia from excessive water loss
- FIncreased ionized magnesium from hyperventilation-induced alkalosis
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