Service manual

Technical Supplement
S-2
S2.1 Functional Versus Fractional Saturation
The NPB-190 measures functional saturation, that is, oxygenated hemoglobin
expressed as a percentage of the hemoglobin that is capable of transporting
oxygen. It does not detect significant levels of dyshemoglobins. In contrast,
hemoximeters such as the IL482 report fractional saturation, that is, oxygenated
hemoglobin expressed as a percentage of all measured hemoglobin, including
measured dysfunctional hemoglobins.
Consequently, before comparing NPB-190 measurements with those obtained by
an instrument that measures fractional saturation, measurements must be
converted as follows:
functional
saturation
=
fractional
saturation
x
100
100-(% carboxyhemoglobin +%methemoglobin)
S2.2 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 the
NPB-190 SpO
2 measurement. This is because the calculated saturation may not
have been corrected for the effects of variables that can shift the relationship
between PaO
2 and saturation.
Figure S2-1 illustrates the effect that variations in pH, temperature, partial
pressure of carbon dioxide (PCO
2), and concentrations of 2,3-DPG and fetal
hemoglobin may have on the oxyhemoglobin dissociation curve.
0
100 50
Saturation (%)
pH
Temperature
PCO
2
2,3-DPG
PO
2
(mmHg)
100
50
pH
Temperature
PCO
2
2,3-DPG
Fetal Hb
Figure S-1: Oxyhemoglobin Dissociation Curve