Theory of Operation
Efficia CM Series Service Guide A-7
Measurement Modules
light during the pulsations. The ratio of light absorbed is translated into a measurement
of functional oxygen saturation (SpO2).
Ambient conditions, sensor application, and patient conditions can influence the
ability of the monitoring system to accurately measure SpO
2.
Pulse oximetry is based on two principles: oxyhemoglobin and deoxyhemoglobin
differ in their absorption of red and infrared light (measured using spectrophotometry),
and the volume of arterial blood in tissue (and hence, light absorption by that blood)
changes during the pulse (registered using plethysmography). A monitoring system
determines SpO2 by passing red and infrared 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 arterial 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 SpO2 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.
Masimo SpO
2
The Masimo SpO
2
module contains a Masimo
®
SET board with a rainbow option that
uses a multi-wavelength sensor to distinguish between oxygenated blood,
deoxygenated blood, oxidized blood, and blood plasma.
Note — The Masimo features available depend on the purchased options for the
monitor. The following description may not apply to all monitors.
The module performs pulse oximetry by using a sensor with various light-emitting
diodes (LEDs) that pass light through the measurement site to a diode (detector).
Signal data is obtained by passing various visible and infrared lights (LEDs, 500 nm to
1400 nm) through a capillary bed (for example, a fingertip, a hand, a foot) and
measuring changes in light absorption during the blood pulsatile cycle. This
information may be useful to clinicians. The maximum radiant power of the strongest
light is rated at 25 mW. The detector receives the light, converts it into an electronic
signal, and then sends it to the Masimo rainbow board for calculation.
The Masimo rainbow board uses proprietary algorithms to calculate the patient's
functional oxygen saturation (SpO
2
[%]), total hemoglobin concentration (SpHb [g/dL]),
and pulse rate (PR). The SpHb measurements rely on a multi-wavelength calibration
equation to quantify the concentration of total hemoglobin in arterial blood.
Pulse CO-Oximetry is a continuous and noninvasive method of measuring the levels of
total hemoglobin (SpHb) and carboxyhemoglobin concentration (SpCO) in arterial
blood. It relies on the same principles of pulse oximetry to make its SpHb and SpCO
measurement. The measurement is taken by a sensor capable of measuring SpHb,
usually on the fingertip for adult and pediatric patients. The sensor connects directly to
the Pulse CO-Oximeter or with a patient cable. The sensor collects signal data from the
To Next Page
Loading...
