Covidien Nellcor OxiMax N-600x, Operator'S Manual

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Theory of Operations
116
Operator’s Manual
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
2
.
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
2
.
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.
Figure 101. Fractional Saturation Conversion Equation
Measured versus Calculated Saturation
When calculating saturation 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 when saturation calculations exclude corrections for the effects of