Overview
The bicarbonate level is significantly influenced by acid-base buffering system, and can by affected by the presence of a respiratory process. The base excess is an indicator of a metabolic process that is independent of this buffering system.
The base excess is the amount of strong acid that is required to return a patient's sample to a pH of 7.4, pCO₂ to 40mmHg and temperature to 37°.
Normal Range
- -2 to +2
Elevated Base Excess
A base excess greater than +2 suggests the presence of metabolic alkalosis.
Causes of Elevated Base Excess
- Bicarbonate excess - milk alkali syndrome (antacids), massive transfusion, dialysis
- GI acid loss - vomiting, NG aspirates, gastric fistula
- Renal acid loss - diuretics, hyperaldosteronism, Cushing's, steroids
- Compartmental shift - hypokalaemia
Reduced Base Excess
A base excess less than -2 suggests the presence of metabolic acidosis.
Causes of Reduced Base Excess
- Ingestion of acid - methanol, ethylene glycol, salicylic acid
- Acid production - lactic acidosis, ketoacidosis, rhabdomyolysis
- Reduced acid excretion - renal failure, distal RTA
- Loss of alkali - diarrhoea, proximal RTA
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