The base excess represents the deviation above or below the normal amount of base compared to acid present in arterial blood. Hence the term acid-base balance. The normal range is within +3 and -3. The bicarbonate ion (HCO3–) concentration and base excess (BE) are referred to as the metabolic parameter indicating how much alkali there is in the blood and therefore how well the patient’s metabolic system (kidneys) is working. As both of these values essentially tell us the same thing it is not necessary to consider both.