In a patient with metabolic acidosis and a serum bicarbonate of 12 mEq/L, what is the expected respiratory compensation PaCO2 predicted by Winter's formula?
Answer and explanation
Correct answer: A. 26 mmHg with a range of 24 to 28 mmHg
- Step 1: Winter's formula calculates the expected respiratory compensation for simple metabolic acidosis: Expected PaCO2 = 1.5 * [HCO3] + 8 +/- 2.
- Step 2: Substituting HCO3 = 12 gives: 1.5 * 12 + 8 = 18 + 8 = 26 mmHg, yielding an expected range of 24 to 28 mmHg.
Answer
26 mmHg with a range of 24 to 28 mmHg.
Why not the others: A PaCO2 of 40 mmHg indicates failure of respiratory compensation and represents a superimposed respiratory acidosis. A PaCO2 of 12 mmHg indicates profound overventilation beyond expected physiological compensation. A PaCO2 of 50 mmHg represents significant hypoventilation.
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