Mallinckrodt NPB-190 Manual do Operador descarregar pdf (Página 66)

Appendix A: Principles of Operation

determine SpO2. This resistor is read when the monitor is turned

on, periodically thereafter, and each time a new sensor is

connected.

Additionally, to compensate for differences in tissue thickness,

the intensity of the sensor’s LEDs are adjusted automatically.

Functional versus Fractional Saturation

This monitor 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 =

fractional saturation

100 - (% carboxyhemoglobin + % methemoglobin )

x100

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 SpO2

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

saturation (Figure 8): pH, temperature, the partial pressure of

carbon dioxide (PCO

2), 2,3-DPG, and fetal hemoglobin.

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Mallinckrodt NPB-190 Manual do Operador Página 66