10 Theory Of Operations; Overview; Theoretical Principles - Covidien Nellcor Operator's Manual

10 Theory of Operations

Overview

10.1
This chapter explains the theory behind operations of the Nellcor™ Bedside
SpO Patient Monitoring System.
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Theoretical Principles

10.2
The monitoring system uses pulse oximetry to measure functional oxygen sat-
uration in the blood. Pulse oximetry works by applying a Nellcor™ pulse oxim-
etry sensor to a pulsating arteriolar vascular bed, such as a finger or toe. The
sensor contains a dual light source and a photodetector.
Bone, tissue, pigmentation, and venous vessels normally absorb a constant
amount of light over time. The arteriolar bed normally pulsates and absorbs
variable amounts of light during the pulsations. The ratio of light absorbed is
translated into a measurement of functional oxygen saturation (SpO
Ambient conditions, sensor application, and patient conditions can influence
the ability of the pulse oximeter to accurately measure SpO
mance Considerations, p. 6-63.
Pulse oximetry is based on two principles: oxyhemoglobin and deoxyhemoglo-
bin differ in their absorption of red and infrared light (measured using spectro-
photometry), and the volume of arterial blood in tissue (and hence, light
absorption by that blood) changes during the pulse (registered using plethys-
mography). A monitoring system determines SpO
light into an arteriolar bed and measuring changes in light absorption during
the pulsatile cycle. Red and infrared low-voltage light-emitting diodes (LED) in
the sensor serve as light sources; a photo diode serves as the photo detector.
Since oxyhemoglobin and deoxyhemoglobin differ in light absorption, the
amount of red and infrared light absorbed by blood is related to hemoglobin
oxygen saturation.
The monitoring system uses the pulsatile nature of arterial flow to identify the
oxygen saturation of arterial hemoglobin. During systole, a new pulse of arte-
).
2
. Reference Perfor-
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by passing red and infrared
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