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Operating Principles IĆ29
Oxygen content is determined, using NCCLS recommendations,
26
from the
following relationship:
ctO
2
= FO
2
Hb × 1.xx × ctHb + 0.00314 × pO
2
where ctHb is expressed in g/dL.
If FO
2
Hb is unavailable, oxygen content is derived from estimated oxygen
saturation (O
2
SAT) according to the following equation:
O
2
CT = O
2
SAT × 1.39 × ctHb + .00314 × pO
2
If ctHb is not measured or entered,O
2
CT is not displayed or printed.
NOTE: Clinically significant errors can result from incorporation of an estimated
value for oxygen saturation in further calculations, such as oxygen content and
shunt fraction (Q
sp
/Q
t
), or by assuming that the value obtained (O
2
SAT) is
equivalent to fractional oxyhemoglobin.
26
Oxygen Content of Hemoglobin
The oxygen content of hemoglobin, ctO
2
(Hb), is the volume of oxygen actually
bound to hemoglobin.
38
The oxygen content of hemoglobin, with hemoglobin
oxygen saturation and oxygen capacity, is a useful parameter for determining the
amount of oxygen in the blood that is actually available to the tissues and for
determining the effectiveness of oxygen therapy. The oxygen content reference
range for arterial blood for a normal population is 15.0 to 23.0 mL/dL.
The oxygen content of hemoglobin for a sample analyzed only for CO-ox
parameters on an 800 system is determined using the following equation:
ctO
2
(Hb) = 1.xx × FO
2
Hb × ctHb
where 1.xx represents the oxygen binding factor of hemoglobin and is a value in
the range of 1.30 to 1.40 as specified in the CO-ox module setup.
The oxygen content of a sample analyzed for blood gas and CO-ox parameters on
an 800 system is determined using the following equation:
ctO
2
(B) = 1.xx × FO
2
Hb × ctHb + 0.00314 × pO
2
where the additional equation component represents the dissolved oxygen (0.00314
is the solubility coefficient).