Base excess

It has been suggested that Base deficit be merged into this article or section. (Discuss)

In human physiology, base excess (see: base) refers to the amount of acid required to return the blood pH of an individual to the reference interval pH (7.35–7.45) with the amount of carbon dioxide held at a standard value. The value is usually reported in units of (mEq/L). The normal reference range is somewhere between −5 to +3. Comparison of the base excess with the reference range assists in determining whether an acid/base disturbance is caused by a respiratory, metabolic, or mixed metabolic/respiratory problem.

Another definition for base excess is the amount of acid or base that must be added to a litre of blood (ECF) to return the pH to 7.4 at a pCO2 of 40 mmHg (5.3 kPa).

The term and concept were first introduced by Poul Astrup and Ole Siggaard-Andersen in 1958.

Interpretation

A base excess value exceeding +3 indicates that a patient has blood that requires abnormally increased amounts of acid to return the pH to neutral, thus indicating alkalosis. More simply, a BE=3 means the body has 3 equivalents more of base than acid—i.e., it has excess base, and is thus alkalotic. Whereas a value below −3 usually indicates that the patient is acidotic, ie excess acid needs to be removed from the blood to return the pH back to normal.

Examples of common situations where you would see a base excess less than −3 would include lactic acidosis (for example after anaerobic metabolism during heavy exercise) and diabetic ketoacidosis. A common example of a situation associated with a base excess exceeding +3 is in persistent vomiting causing loss of acidic gastric fluids.

Calculation/estimation

It can be estimated by the equation:^[1] Base excess = 0.93 (HCO₃ − 24.4 + 14.8(pH − 7.4))

Alternatively expressed:^[1] Base excess = 0.93×HCO₃ + 13.77×pH − 124.58

Actual and standard

Actual base excess is the base excess in the blood.

Standard base excess is the value of base excess when the hemoglobin value is 5 g/dl. This gives a better view of the base excess of the entire extracellular fluid.^[2]

See also

• Metabolic alkalosis
• Base deficit
• Arterial blood gas

References

1. ^ ^{a b} Medical Calculators > Calculated Bicarbonate & Base Excess teven Pon, MD, Weill Medical College of Cornell University
2. ^ Acid-Base Tutorial — Terminology

External links

• acid-base.com
• Base+excess at eMedicine Dictionary
• -321912807 at GPnotebook