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ABG Interpretation
 
 

Assessing Base Excess

 
 
 
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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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