Mallinckrodt NPB-190 Manuale dell'Operatore Scaricare il pdf (Pagina 92)

Principles of Operation

During monitoring, the instrument’s software reads this resistor

value and selects coefficients that are appropriate for the

wavelength of that individual sensor’s red LED; these

coefficients are then used to determine SpO

2. This resistor value

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 light intensity of the sensor’s LEDs is 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 (PO2), the calculated value may differ from the SpO

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 PO2 and

saturation (Figure 21): pH, temperature, the partial pressure of

carbon dioxide (PCO2), 2,3-DPG, and fetal hemoglobin.

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Mallinckrodt NPB-190 Manuale dell'Operatore Pagina 92