Acid-base homeostasis · USMLE Step 1

Which of the following best describes metabolic acidosis on arterial blood gas analysis?

  1. pH high, HCO₃⁻ high, PaCO₂ low
  2. pH low, HCO₃⁻ low, PaCO₂ normal or low
  3. pH high, HCO₃⁻ low, PaCO₂ high
  4. pH low, HCO₃⁻ high, PaCO₂ normal
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Correct answer: pH low, HCO₃⁻ low, PaCO₂ normal or low

Metabolic acidosis is evidenced by low bicarbonate (primary disturbance), resulting in reduced pH; respiratory compensation may lower CO₂ (low PaCO₂), but pH remains acidic.

Difficulty: Medium Question 16 of 19

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