A 60-year-old male smoker with COPD is admitted with septic shock. Blood gas reveals: pH 7.18, PaCO2 62 mmHg, PaO2 55 mmHg, HCO3- 23 mEq/L, and lactate 5.2 mmol/L. What mixed acid-base disorder is present?
Answer and explanation
Correct answer: D. Combined acute respiratory acidosis and high anion gap metabolic acidosis
- Step 1: pH 7.18 confirms severe acidemia.
- Step 2: Elevated PaCO2 (62 mmHg) indicates acute respiratory acidosis (alveolar hypoventilation).
- Step 3: Elevated serum lactate (5.2 mmol/L) indicates tissue hypoperfusion causing a high anion gap metabolic acidosis.
- Step 4: Normal bicarbonate (23 mEq/L) reflects acute failure of renal compensation.
Answer
Combined acute respiratory acidosis and high anion gap metabolic acidosis.
Why not the others: Compensation would elevate HCO3- markedly; the disorder is mixed, not pure.
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