Principles Of Operation; Oximetry Operating Principles; Automatic Calibration; Functional And Fractional Saturation - Nellcor N-20 Operator's Manual

PRINCIPLES OF OPERATION
vgs/ Oximetry Operating Principles
w OXIMETRY OPERATING PRINCIPLES
^ Many times each second, the N-20/N-20P passes red and
^ infrared light into the sensor site and determines absorption.
Measurements that are taken during the arterial pulse reflect
^ absorption by arterial blood, nonpulsatile blood, and tissue.
w Measurements that are obtainedbetween pulses reflect
absorption by nonpulsatile blood and tissue. By correcting
**" "during-pulse'' absorption for "between-pulse" absorption, the
^ N-20/N-20P determines red and infrared absorption by
pulsatile arterial blood. Because oxyhemoglobin and
^ deoxyhemoglobin differ in red and infrared absorption, this
^ corrected measurement can be used to determine the
percentage of oxyhemoglobin in arterial blood: Sp02 is the ratio
*** of corrected absorption at each wavelength.
Automatic Calibration
The N-20/N-20P is automatically calibrated each time it is
turned on and whenever a new sensor is connected: it sets
\ws sensor-specific calibration coefficients by reading a calibration
resistor in the sensor. Also, the intensity of the sensor's light
sources are adjusted automatically to compensate for
differences in tissue thickness and darkness.
Vgjj^
*igii>>
Functional and Fractional Saturation
The N-207N-20P measures functional saturation, i.e.,
*** oxygenated hemoglobin expressed as a percentage of the
vgpz hemoglobin that is capable of transporting oxygen. It does not
detect significant levels of dyshemoglobins. In contrast,
^ instruments such as the IL282 CO-Oximeter measure
^ fractional saturation, i.e., oxygenated hemoglobin expressed as
a percentage of all measured hemoglobin, including
^ dyshemoglobins.
25
^iiai/