Siemens RAPIDLAB 248 Operator's Manual page 132

Page G-8
Base Excess
Base excess is an empirical expression that approximates the amount of
acid or base required to titrate one litre of blood back to a normal pH of 7.4.
The base excess in blood with a pH of 7.4, pCO
total haemoglobin of 15 g/dL and a temperature of 37°C is zero. Base
excess is useful in the management of patients with acid-base disorders as
it allows the estimation of the number of equivalents of sodium bicarbonate
or ammonium chloride required to correct the patient's pH to normal.
There are two versions of base excess, available in the System Set Up
menu.
Base Excess of Extracellular Fluid (BE(ecf))
The base excess of extracellular fluid, formerly known as in vivo base
excess, reflects only the non-respiratory component of pH disturbances
Base Excess of Blood (BE(B))
The base excess of blood, formerly known as in vitro base excess, is
calculated from the following equation
If no ctHb value has been entered, a value of 15g/dL is assumed.
Oxygen Content (O
Oxygen content is the concentration of the total oxygen carried by the
blood, including oxygen bound to haemoglobin as well as oxygen dissolved
in plasma and in the fluid within red cells.
Oxygen content is calculated, using NCCLS recommendations
If no ctHb value has been entered, O
Clinically, dissolved oxygen is for most situations analytically unimportant.
However, at very low levels of haemoglobin or in patients receiving
hyperbaric oxygen therapy, dissolved oxygen may be a very significant
contributor to oxygen transport.
BE(ecf) = cHCO –
3 act
BE(B) = (1 – 0.014ctHb) (cHCO
O CT = (1.39ctHb x O
2
where ctHb is expressed in g/dL.
– 24.8 + 16.2 (pH – 7.4)
– – 24.8 + (1.43ctHb + 7.7) (pH – 7.4))
3 act
CT)
2
SAT/100) + (0.00314pO
2
CT is not calculated.
2
248 Operator's Manual
of 40 mm Hg (5.33 KPa),
2
18
, as follows:
)
2