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Base Excess Calculator
Base Excess (BE) represents the amount of strong acid (in mEq/L) that would need to be added to one liter of blood to return the pH to 7.40, assuming a partial pressure of carbon dioxide (PCO2) of 40 mmHg and a temperature of 37°C.
It is a pure marker of the metabolic component of acid-base disorders, independent of respiratory changes. A positive value indicates Metabolic Alkalosis, while a negative value (Base Deficit) indicates Metabolic Acidosis.
Blood Gas Values
InputsArterial pH
Bicarbonate (mEq/L)
Result
Normal Range: −2 to +2 mEq/L
Clinical Context
Standard Base Excess (SBE):
This calculator estimates Standard Base Excess using the Van Slyke equation approximation, which assumes a hemoglobin concentration of approximately 5 g/dL (modeling the buffering capacity of the entire extracellular fluid, not just whole blood). This is clinically preferred over Actual Base Excess for assessing metabolic status.
Interpretation:
• BE < −2 mEq/L: Metabolic Acidosis (e.g., Lactic acidosis, DKA, Renal failure).
• BE > +2 mEq/L: Metabolic Alkalosis (e.g., Vomiting, Diuretics, Hyperaldosteronism).
Clinical References
How to Use This Calculator
Follow these steps to calculate Base Excess.
Enter pH
Input the arterial pH from the Blood Gas analysis.
Enter Bicarbonate
Input the HCO₃⁻ level in mEq/L.
Interpret
A positive result indicates alkalosis; a negative result indicates acidosis (often called Base Deficit).
Frequently Asked Questions
HCO3 alone is affected by respiratory compensation (CO2 changes). Base Excess is a calculated value that isolates the metabolic component, making it easier to see if a metabolic problem exists regardless of breathing.
SBE (Standard Base Excess) assumes the buffering of the entire extracellular fluid (Hb ~5g/dL), whereas actual BE assumes the buffering of whole blood (Hb ~15g/dL). SBE is generally considered more accurate for clinical use.