Automatic Calibration; Functional Versus Fractional Saturation; Measured Versus Calculated Saturation - Nellcor OXIMAX N-600X Series Service Manual

Theory of Operations
absorption by pulsatile arterial blood, eliminating the effects of nonpulsatile
absorbers such as tissue, bone, and venous blood.

Automatic Calibration

Because light absorption by hemoglobin is wavelength dependent and because the
mean wavelength of LEDs varies, an oximeter must know the mean wavelength of
the OxiMax pulse oximetry sensor's red LED to accurately measure SpO
During monitoring, the oximeter's software selects coefficients that are appropriate
for the wavelength of that individual sensor's red LED; these coefficients are then
used to determine SpO
Additionally, to compensate for differences in tissue thickness, the light intensity of
the sensor's LEDs is adjusted automatically.
Note:
During certain automatic calibration functions, the OxiMax N-600x pulse oximeter may
briefly display a flat line on the plethysmographic waveform. This is a normal operation and
does not require any user intervention.

Functional versus Fractional Saturation

This pulse oximeter measures functional saturation where oxygenated hemoglobin
is 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 where oxygenated hemoglobin is expressed as a
percentage of all measured hemoglobin, including measured dysfunctional
hemoglobins. To compare functional saturation measurements to those from an
oximeter that measures fractional saturation, fractional measurements must be
converted using the listed equation.

Measured versus Calculated Saturation

When calculating saturation from a blood gas partial pressure of oxygen (PO
calculated value may differ from the SpO
usually occurs when saturation calculations exclude corrections for the effects of
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Figure 12. Fractional Saturation Conversion Equation
10030881 Rev. B 12-2008
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measurement of a pulse oximeter. This
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Service Manual