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Calculated PaCO2Aka: Winter's Formula

Calculated PaCO2 in Respiratory Conditions
1. Increase PaCO2 by 10 mmHg
  1. Acute Respiratory Acidosis: decreases pH 0.08
  2. Chronic Respiratory Acidosis: decreases pH 0.03
2. Decrease PaCO2 by 10 mmHg
  1. Acute Respiratory Alkalosis: increases pH 0.08
  2. Chronic Respiratory Alkalosis: increases pH 0.03
Calculated PaCO2 in Metabolic Conditions
1. Metabolic Acidosis with expected compensation
  1. PaCO2 = 1.5 x HCO3 + 8 (+/- 2)
2. Metabolic Alkalosis with expected compensation
  1. PaCO2 = 0.7 x HCO3 + 20 (+/- 1.5)
Interpretation: Elevated Anion Gap Metabolic Acidosis
1. Measured PaCO2 > Calculated PaCO2
  1. Metabolic Acidosis with Respiratory Acidosis
2. Measured PaCO2 < Calculated PaCO2
  1. Metabolic Acidosis with Respiratory Alkalosis

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This page was written by Scott Moses, MD. This page was last revised before 5/10/08, prior to consistent tracking of revision date. This page was last published on 6/1/2008. Please send comments and questions to the editor. Contact information may be found on the page About the Family Practice Notebook. These pages are best viewed with Microsoft Internet Explorer 6.0.