Covidien Nellcor Series, Operator'S Manual

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Measured versus Calculated Saturation
Operator’s Manual 10-3
10.5
Measured versus Calculated Saturation
When calculating saturation from a blood gas partial pressure of oxygen (PO2), the
calculated value may differ from the SpO
2
measurement of a monitoring system.
This usually occurs when saturation calculations exclude corrections for the effects
of variables such as pH, temperature, the partial pressure of carbon dioxide (PCO2),
and 2,3-DPG, that shift the relationship between PO2 and SpO
2
.
Figure 10-1. Oxyhemoglobin Dissociation Curve
functional saturation %carboxyhemoglobin
fractional saturation %methemoglobin


100
 
+
 
–
--------------------------------- 100

=


 
1 % Saturation Axis 3 Increased pH; Decreased temperature, PCO2, and 2,3-DPG
2 PO2 (mmHg) Axis 4 Decreased pH; Increased temperature, PCO2, and 2,3-DPG