Measured And Calculated Saturation; Oxyhemoglobin Dissociation Curve - Nellcor N-20 Operator's Manual

Principles of Operation
26
Consequently, before comparing N-20/N-20P measurements
with those obtained by an instrument that measures fractional
saturation, measurements must be converted as follows:
functional
saturation
fractional saturation
x 100
100 - (%carboxyhemog]obin+ %methemoglobin)
Measured and Calculated Saturation
When saturation is calculated from a blood gas measurement of
the partial pressure of oxygen (P02), the calculated value may
differ from the N-20/N-20P Sp02 measurement. This is because
the calculated saturation may not have been corrected for the
effects of variables that shift the relationship between PO2 and
saturation: temperature, pH, the partial pressure of carbon
dioxide (PCO2), and the concentrations of 2,3-DPG and fetal
hemoglobin.
100 —I
t pH 1
4 Temperature
4 PCO2
' ' ^"""^"^- " "
4 2,3-DPG
' J^ •»''
Fetal Hb J
/ +- s '
' /-**'
' / '
^ ^
1 / *
5*
' / '
c
' / / I * PH
1 50-
1 1
/ 1 t Temperature
S
\ t PCO2
2
, J / [ t 2,3-DPG
CO
1 / ,
(0
' / '
>/'
1 / '
1 / '
' / '
/ /
0
V*
1
50 100
PO2 (mmHg)
Figure 10: Oxyhemoglobin Dissociation Curve
vast/