Arterial Blood Gas Analysis (BGA) Algorithm Calculator

Arterial Blood Gas Interpretation: Explanation and Clinical Context This tool provides a structured approach to identify the primary acid base disturbance and to assess whether the observed respiratory or renal compensation is appropriate for a single predominant disorder. The algorithm first classifies the sample as acidemia or alkalemia based on pH. It then uses the relationship between pCO2 and HCO3 to identify a likely primary respiratory or metabolic disorder.

For metabolic acidosis the expected respiratory compensation is calculated using Winter formula, expected pCO2 equals 1.5 times measured HCO3 plus 8, with an accepted small margin of variation. If measured pCO2 approximates the expected value then compensation is appropriate, and deviations suggest a mixed disorder or additional respiratory process. For metabolic alkalosis expected pCO2 can be estimated by the formula expected pCO2 equals 0.7 times the difference between measured HCO3 and 24, plus 40, with a small margin of variation.

For primary respiratory disorders the expected renal compensation is estimated differently for acute and chronic processes. In acute respiratory acidosis HCO3 rises by about 1 mEq per liter for each 10 mmHg rise in pCO2. In chronic respiratory acidosis renal compensation increases HCO3 by about 3.5 mEq per liter for each 10 mmHg rise in pCO2.

In acute respiratory alkalosis HCO3 falls by about 2 mEq per liter for each 10 mmHg fall in pCO2 and in chronic respiratory alkalosis HCO3 falls by about 5 mEq per liter for each 10 mmHg fall in pCO2. Use clinical context and additional laboratory data including electrolytes, anion gap, lactate and clinical history to confirm or refine the diagnosis. If results are inconsistent with expected compensation consider mixed acid base disorder, sample or lab error, or the need for further testing.

Reference Adrogue HJ, Madias NE, Management of life threatening acid base disorders, New England Journal of Medicine, 1998. Winter formula and its clinical application, review articles and teaching resources. Expected compensation in metabolic alkalosis, StatPearls and hospital teaching resources.

Practical rules for respiratory compensation and the Boston approach, recent review and teaching summaries.