Nellcor Oximax NPB-40, Руководство оператора

Страница: 129 / 161

Principles of Operation
NPB-40 121
Functional versus Fractional Saturation
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:
Measured versus Calculated Saturation
When saturation is calculated from a blood gas partial
pressure of oxygen (PO
2
), the calculated value may differ
from the SpO
2
measurement of a pulse oximeter. This
usually occurs because the calculated saturation was not
appropriately corrected for the effects of variables that
shift the relationship between PO
2
and pH, temperature,
the partial pressure of carbon dioxide (PCO
2
), 2,3-DPG,
and fetal hemoglobin. See Figure Figure 11:.