NOVA BIOMEDICAL Stat Profile PRIME - Page 99

B-13
Appendix B
Appendix B
P50 or PO
2
(0.5)*
The P50 is dened as the PO
2
of a sample at which the
hemoglobin is 50% saturated with oxygen at pH 7.4, 37°C,
and 40 mm Hg PCO
2
for SO
2
% values between 40% and
80%.
P50
(uncorrected)
=PO
2
/(SO
2
%/(100-SO
2
%))
0.37
Equation 30
For measured SO
2
% between 80 and 96.9%, the equation
is as follows:
Where z = tanh(0.5343
*
x); x = ln(0.133
*
PO
2
/7); y =
ln(SO
2
%/(100-SO
2
%))-1.875
P50
(uncorrected)
=26.902
*
exp(1.121
*
(y-x-3.5z)/(1.87
*
z
2
+
z - 2.87)) Equation 31
The corrected equation is as follows:
log P50
(corrected)
= log P50
(uncorrected)
+ 0.43 (pH – 7.4) –
0.05 (log PCO
2
/40) – 0.0131(T – 37) Equation 32
* The equations are from Reference 4.