Siemens Rapidlab 1200, Operator'S Manual, Page: 75 / 448

Rapidlab 1200 Operator’s Guide: System Overview and Intended Use 1-55
02087462 Rev. V
Base excess permits the estimation of the number of equivalents of sodium
bicarbonate or of ammonium chloride required to correct the blood pH to normal.
A negative value for base excess indicates a base deficit.
Two versions of base excess exist:
•
Base excess of extracellular fluid [BE(ecf)], formerly known as in vivo base
excess, determined as follows:
BE(ecf) = HCO
3
–
act–24.8 + (16.2 × (pH(37)–7.40))
• Base excess of blood (BE(B)), formerly known as in vitro base excess,
determined as follows:
BE(B) = (1–0.014 × tHb) × [(HCO
3
–
act–24.8) + ((7.7 + 1.43 × tHb) ×
(pH(37)–7.40))]
NOTE:
If c tHb is not available as an entered value or a measured value, the
system uses 15 g/dL as a default value.
The equations for base excess are derived from CLSI recommendations.
19
Total Carbon Dioxide
Total carbon dioxide ( c tCO
2
) is the sum of the dissolved carbon dioxide and the
plasma bicarbonate. When evaluated with pH and p CO
2
, total carbon dioxide is
useful in distinguishing between metabolic and respiratory acid-base disorders.
The system determines total carbon dioxide according to the following equation:
c tCO
2
= (0.0307 × p CO
2
) + HCO
3
–
act
Hematocrit
Hematocrit (Hct) is the ratio of the volume of packed red blood cells to the
volume of human whole blood. Hematocrit, with other parameters such as total
hemoglobin, is useful in the evaluation of anemia.
The estimated hematocrit value is determined using the following equation:
Hct = c tHb × 2.941
where 2.941 is a factor calculated by dividing 100 g/dL by a normal MCHC
(mean corpuscular hemoglobin concentration) of 34%.
Estimated hematocrits should not be used as the sole consideration in the
diagnosis of hematological disorders.