A patient has arterial blood gas results showing pH 7.28, PaCO2 50 mmHg, and HCO3− 22 mEq/L. What is the primary acid-base disorder?
- A Respiratory acidosis with no compensation ✓
- B Metabolic acidosis with respiratory compensation
- C Respiratory alkalosis
- D Mixed metabolic and respiratory acidosis
Correct answer: A. Respiratory acidosis with no compensation
Explanation
The pH is low (acidosis), and PaCO2 is elevated (>40 mmHg), indicating respiratory acidosis as the primary disorder. Bicarbonate is near-normal at 22 mEq/L (expected range 22-26), suggesting no significant metabolic compensation has occurred yet — this is consistent with acute respiratory acidosis. In chronic respiratory acidosis, bicarbonate rises by approximately 3.5 mEq/L per 10 mmHg rise in PaCO2.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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