Base excess

Base Excess is a term used in medicine and biochemistry to describe the amount of excess or insufficient bicarbonate (HCO3-) in the blood. The value is compared to the normal bicarbonate concentration in the blood, which should be in the range of 22 to 28 mmol/L. A positive base excess indicates a higher than normal bicarbonate level, often due to metabolic alkalosis, while a negative base excess indicates a lower than normal level, often due to metabolic acidosis.

Definition

The term "base excess" was first introduced by Siggaard-Andersen in 1963 as a measure of the non-respiratory component of acid-base balance. It is defined as the amount of strong acid that must be added to each liter of fully oxygenated blood to return the pH to 7.40, while the temperature and partial pressure of carbon dioxide (pCO2) are held constant at 37 degrees Celsius and 40 mmHg, respectively.

Clinical Significance

Base excess is a valuable parameter in the diagnosis and management of acid-base disorders. It provides information about the body's buffering capacity and the presence of non-respiratory acid-base disturbances. For example, a negative base excess is indicative of a metabolic acidosis, while a positive base excess suggests a metabolic alkalosis.

In critical care medicine, base excess is often used to guide the treatment of patients with severe acid-base disturbances, such as those caused by trauma, sepsis, or drug overdose. It is also used in the interpretation of arterial blood gas analysis.

Measurement

Base excess is typically measured in a laboratory setting using an arterial blood gas analyzer. The analyzer measures the pH and pCO2 of a blood sample, and then calculates the base excess using the Henderson-Hasselbalch equation.

Limitations

While base excess is a useful parameter in the assessment of acid-base balance, it has some limitations. It does not provide information about the respiratory component of acid-base balance, and it may be affected by changes in temperature, pCO2, and the concentration of other strong ions in the blood.

See Also

• Acid-base homeostasis
• Anion gap
• Buffer solution
• Henderson-Hasselbalch equation
• Metabolic acidosis
• Metabolic alkalosis