From the Research
Base excess is a critical laboratory value that measures the amount of excess or deficit of bicarbonate in the blood, indicating the metabolic component of acid-base balance, and its interpretation is essential for guiding treatment decisions in acid-base disorders, as noted in the most recent study 1. When interpreting base excess, it should be considered alongside other parameters like pH, PaCO2, and bicarbonate levels for a complete acid-base assessment.
- A normal base excess ranges from -2 to +2 mEq/L, with values above +2 indicating metabolic alkalosis (excess bicarbonate) and values below -2 indicating metabolic acidosis (bicarbonate deficit) 1.
- Base excess is particularly useful because it's standardized to a normal PaCO2 of 40 mmHg, making it a more reliable indicator of metabolic acid-base disturbances independent of respiratory compensation.
- The value is calculated rather than directly measured, using the Henderson-Hasselbalch equation based on pH and PaCO2 measurements. In clinical practice, the use of base to treat acute metabolic acidosis is controversial, and treatment should be aimed at the underlying disease or removal of the toxin, as recommended in the latest study 1.
- Metabolic acidosis can be divided into anion gap and non-gap acidosis, with anion gap acidosis caused by the accumulation of organic anions from sepsis, diabetes, alcohol use, and numerous drugs and toxins.
- Treatment of an anion gap acidosis is aimed at the underlying disease or removal of the toxin, and the use of therapy to normalize the pH is controversial, as discussed in 1.
- Non-gap acidoses result from disorders of renal tubular H + transport, decreased renal ammonia secretion, gastrointestinal and kidney losses of bicarbonate, dilution of serum bicarbonate from excessive intravenous fluid administration, or addition of hydrochloric acid, and their treatment consists of addressing the underlying cause.