A 50-year-old COPD patient on home oxygen has: pH 7.36, PaCO2 58 mmHg, HCO3- 32 mEq/L. This blood gas pattern represents:

• A Acute respiratory acidosis without compensation
• B Mixed metabolic alkalosis and respiratory acidosis
• C Metabolic alkalosis with respiratory compensation
• D Fully compensated respiratory acidosis (chronic) ✓

Explanation

Expected HCO3- compensation in chronic respiratory acidosis = 24 + 3.5 × (PaCO2 − 40)/10 = 24 + 3.5 × 1.8 = 24 + 6.3 ≈ 30.3 mEq/L; actual HCO3- is 32 mEq/L, which is within the expected range for chronic compensation, and pH is near normal (7.36), confirming full compensation. Acute respiratory acidosis would have minimal HCO3- rise. A pH near normal with elevated PaCO2 and elevated HCO3- in a COPD patient is classic chronic respiratory acidosis.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.