A patient with diabetic ketoacidosis has arterial pH 7.18, HCO3- 8 mEq/L, and PaCO2 20 mmHg. Using the Winter formula, what is the expected respiratory compensation and is it adequate?
- A Expected PaCO2 = 20 +/- 2; adequate compensation ✓
- B Expected PaCO2 = 18 +/- 2; adequate compensation
- C Expected PaCO2 = 20 +/- 2; inadequate compensation, suggesting mixed disorder
- D Expected PaCO2 = 12 +/- 2; there is an additional respiratory acidosis
Correct answer: A. Expected PaCO2 = 20 +/- 2; adequate compensation
Explanation
Winter formula: expected PaCO2 = 1.5 x [HCO3-] + 8 +/- 2 = 1.5 x 8 + 8 = 20 +/- 2 mmHg. The measured PaCO2 of 20 mmHg falls within this range, indicating a purely metabolic acidosis with appropriate respiratory compensation. This is a high-yield acid-base calculation for NEET PG.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.