Nellcor N-180, Manual

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N-180 Pulse Oximeter Service Manual
2-2
functional SpO
2
=
fractional saturation
100 - (% carboxyhemo % methemoglobin)
x 100
MEASURED VERSUS CALCULATED SATURATION
When saturation is calculated from a blood gas measurement of the partial
pressure of arterial oxygen (PaO
2
), the calculated value may differ from mea-
sured SpO
2
. This is because the calculated saturation may not have been cor-
rected for the effects of variables that shift the relationship between PaO
2
and saturation (figure 2-1). The variables are: pH, temperature, the partial
pressure of arterial carbon dioxide (PaCO
2
), and the concentrations of
2,3 -DPG and fetal hemoglobin.
0
100 50
(%) SpO
2
pH
Temperature
PCO
2
2,3-DPG
}
pH
Temperature
PCO
2
2,3-DPG
}
PaO
2
(mmHg)
100
50
Figure 2-1: Oxyhemoglobin Dissociation Curve