Functional Versus Fractional Saturation; Measured Versus Calculated Saturation - Nellcor OxiMax N-65 Service Manual

Technical Discussion

Functional versus Fractional Saturation

Measured versus Calculated Saturation

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This pulse oximeter measures functional saturation -- oxygenated hemoglobin
expressed as a percentage of the hemoglobin that can transport oxygen. It does not
detect significant amounts of dysfunctional hemoglobin, such as
carboxyhemoglobin or methemoglobin. In contrast, hemoximeters such as the
IL482 report fractional saturation -- oxygenated hemoglobin expressed as a
percentage of all measured hemoglobin, including measured dysfunctional
hemoglobins. To compare functional saturation measurements to those from an
instrument that measures fractional saturation, fractional measurements must be
converted as follows:
functional saturation =
When saturation is calculated from a blood gas partial pressure of oxygen (PO
the calculated value may differ from the SpO
This usually occurs because the calculated saturation was not appropriately
corrected for the effects of variables that shift the relationship between PO
pH, temperature, the partial pressure of carbon dioxide (PCO
fetal hemoglobin. See Figure 25.
Figure 25: Oxyhemoglobin Dissociation Curve
fractional saturation
100 - (% carboxyhemoglobin + % methemoglobin )
measurement of a pulse oximeter.
2
x100
),
2
and
2
), 2,3-DPG, and
2
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