Covidien Nellcor Series, Руководство оператора

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Theory of Operations
10-2 Operator’s Manual
blood enters the vascular bed, and blood volume and light absorption increase.
During diastole, blood volume and light absorption reach their lowest point. The
monitoring system bases its SpO
2
measurements on the difference between
maximum and minimum absorption (measurements at systole and diastole). By
doing so, it focuses on light absorption by pulsatile arterial blood, eliminating the
effects of nonpulsatile absorbers such as tissue, bone, and venous blood.
10.3
Automatic Calibration
Because light absorption by hemoglobin is wavelength dependent and because the
mean wavelength of LEDs varies, a monitoring system must know the mean wave-
length of the pulse oximetry sensor's red LED to accurately measure SpO
2
.
During monitoring, the monitoring system’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 monitoring system may briefly display a
flat line on the plethysmographic waveform. This is a normal operation and does not require
any user intervention.
10.4
Functional versus Fractional Saturation
This monitoring system measures functional saturation where oxygenated hemo-
globin is expressed as a percentage of the hemoglobin that can transport oxygen. It
does not detect significant amounts of dysfunctional hemoglobin, such as carboxy-
hemoglobin 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 a monitoring system
that measures fractional saturation, fractional measurements must be converted
using the listed equation.