1-58 Rapidlab 1200 Operator’s Guide: System Overview and Intended Use
02087462 Rev. V
p50
Half saturation of hemoglobin by oxygen (p50) indicates the partial pressure of oxygen
when oxygen has saturated 50% of the available hemoglobin. The p50 value indicates the
position of the oxygen-hemoglobin dissociation curve:
21
•Low p50 shifts
the curve to the left and indicates increased oxygen-hemoglobin
affinity
•High p50 shifts the curve to the right and indicates decreased oxygen-hemoglobin
affinity
The p5
0 value is useful in indicating the presence of abnormal hemoglobin that affects the
oxygen transport mechanism, and as an indirect measure of the 2,3 DPG concentration.
The p50 can also indicate changes in pH, pCO
2
, and temperature.
19,21
The p50 value is reported for sO
2
values between 20% and 90% and is determined using
the following equation:
p50 = 26
.6 x (pO
2
c / pO
2
s)
where
pO
2
c = pO
2
× 10
–[0.48 x (7.4–pH(37)) + 0.0013BE(B)]
and pO
2
s is calculated with an interactive program.
31
Oxygen Saturation (Estimated)
Oxygen saturation is a ratio, expressed as a percentage, of the volume of oxygen carried to
the maximum volume of oxygen that the hemoglobin can carry. When combined with
knowledge of oxygen content, oxygen saturation is useful for evaluating the amount of
oxygen actually available for the tissues. Oxygen saturation can also be used to evaluate
th
e effectiveness of oxygen therapy.
The system estimates oxygen saturation using t
he relationship described by Kelman
32
and
Thomas
33
as follows:
()
100*
104.2311002400015
2000204515
6234
234
2
×+−+−
++−
=
NNNN
NNNN
estSATO
where
N = pO
2
× 10
[0.48(pH(37)–7.4)–0.0013 BE(B)]
To Next Page
Loading...
