Base Excess (BE) is a calculated value:
BE (mEq/l) = HCO3 (observed) + 10 [pH (observed) -7.40] – 24
The BE has a range of normal of -4 to +4.
The reason for this is that the calculation is based on the pH and the bicarbonate, each of which has its own normal range.
The normal range for HCO3 is 21-28 mEq/L, and that of the pH is 7.35-7.45.
Remember that in trauma we deal almost exclusively with metabolic acidosis.
Therefore, we are concerned only with BEs that are MORE NEGATIVE than MINUS FOUR.
A BE less negative than -4 or less, does not need to be treated with sodium bicarbonate.
For example, a 70 Kg patient with a BE of -4 would appear to require ([0.3X70X-4]/50) or 1.7 amps of NaHCO3, when in fact (s)he requires no treatment.
Look also at the chloride and the lactate. When these are more than “mildly” elevated, and there is a BE more negative than -4, then NaHCO3 treatment is indicated.