Winter's Formula Calculator - Expected PaCO2 in Metabolic Acidosis

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Measured from arterial blood gas or basic metabolic panel. Normal range is approximately 22-26 mEq/L.
mEq/L
Patient's actual measured arterial PaCO2 from blood gas analysis. Enter this to get the clinical interpretation of whether compensation is appropriate.
mmHg
Expected PaCO2Concurrent respiratory alkalosis
35

Central expected value from the formula

Compensation range - low33
Compensation range - high37
Expected PaCO2 range33.0 - 37.0 mmHg
Compensation statusBelow expected range: concurrent primary respiratory alkalosis (over-compensation)
Expected PaCO2 (kPa)4.67
Compensation range - low (kPa)4.4
Compensation range - high (kPa)4.93
35 mmHg
Very low PaCO2<20Compensation zone20-35Normal range35-45Elevated45-60High60+

PaCO2 below expected range: over-compensation detected

  • For a bicarbonate of 18.0 mEq/L, appropriate respiratory compensation should produce a PaCO2 of 33.0 to 37.0 mmHg.
  • Measured PaCO2 (32.0 mmHg) is below 33.0 mmHg, suggesting a concurrent primary respiratory alkalosis on top of the metabolic acidosis.
  • Winter's formula applies only to metabolic acidosis. Do not use it to assess compensation for metabolic alkalosis or primary respiratory disorders.

Next stepEvaluate for causes of primary respiratory alkalosis: anxiety, pain, sepsis, salicylate toxicity, liver failure, or mechanical ventilation settings.

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