Base excess reflects the metabolic (kidney-related) component of a patient's acid-base status on an ABG, separate from the respiratory component that PaCO₂ represents.
Normal metabolic balance.
Mild base deficit or excess.
Significant metabolic acidosis or alkalosis.
Severe metabolic derangement.
They're related but not identical. Base excess is a calculated value that accounts for buffering across the whole blood system, giving a cleaner isolated view of the metabolic component than HCO₃⁻ alone.
Roughly −2 to +2 mEq/L. A negative value (base deficit) suggests a metabolic acidosis component; a positive value suggests a metabolic alkalosis component.
An ABG reflects both respiratory (PaCO₂) and metabolic (base excess) contributions to pH. Isolating them tells you whether an acid-base problem is being driven by the lungs, the kidneys/metabolism, or both.
It often reflects lactic acidosis from poor tissue perfusion (shock), making it a useful marker of severity and resuscitation response in critically ill patients.