Appropriate compensatory PaCO₂ or HCO₃⁻ changes in acid-base disorders

Metabolic acidosis
(acute or chronic)

Expected PaCO₂ = (1.5 × HCO₃⁻) + 8 ± 2 (Winters formula)

Metabolic alkalosis
(acute or chronic)

~7 mm Hg ↑ in PaCO₂ per 10 mEq/L ↑ in HCO₃⁻

Respiratory acidosis
(chronic only*)

~4 mEq/L ↑ in HCO₃⁻ per 10 mm Hg ↑ in PaCO₂

Respiratory alkalosis
(chronic only*)

~4 mEq/L ↓ in HCO₃⁻ per 10 mm Hg ↓ in PaCO₂

*Compensation for respiratory disturbances is minimal in the acute setting.  The full level of chronic compensation is achieved after ~72 hr.  For simplicity, normal baseline PaCO₂ & HCO₃⁻ should be considered 40 mm Hg & 24 mEq/L, respectively.