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OxyMag_rev26
7.
Oximeter (Masimo)
The encapsulated pulse oximeter Masimo MS-2040 is a self-sufficient solution that enables the secure measurement even in motion
and low perfusion to measure: SpO2, heart rate, perfusion index and PVI. This oximeter is compatible with all Masimo LNCS® sensors.
It is intended for use with neonatal, pediatric and adult patients. In adults and pediatrics the sensor is used on the finger, while in
neonatal patients the sensor is multisite and may be used on the hand, foot or fingers and toes.
The LNCS DC-I and LNCS YI oximetry sensors were tested and validated with the USpO2 MASIMO SET OXIMETRY CABLE and the
OXYMAG equipment, in order to comply with the ABNT NBR ISO 80601-2-61 standard.
7.1
Operation Principle
The MS board of Masimo SET ® pulse oximeter is based
on three principles:
1
Differential of oxyhemoglobin and deoxyhemoglobin
absorption
of
red
and
infrared
light
(spectrophotometry).
2
Volume of arterial blood in the tissue and the light
absorbed in blood changes (plethysmography).
3
Arteriovenous shunt is highly variable and its
absorbance fluctuation by the venous blood is the
most noise component during the pulse.
4
MS board of Masimo SET pulse oximeter as well as
the traditional pulse oximeter determines SpO2 by
passing red and infrared light into a capillary bed
and changing the measurement during the pulsatile
cycle. Red and infrared light emitting diodes (LED)
in oximetry sensors serve as light source; the
photodiode serves as a photodetector.
Traditionally, the pulse oximetry assumes that all pulsations in
the light absorbance signal are caused by fluctuations in
arterial blood volume. It is assumed that the blood flow in the
sensor region passes entirely by the capillary bed rather than
via some arteriovenous shunt. Traditional pulse oximetry
calculates the ratio of pulsatile absorbance (AC) in relation to
average absorbance (DC) in each of the two wavelengths,
660nm and 905nm:
S(660)=AC(660)/DC(660)
S(905)=AC(905)/DC(905)
The oximeter then calculates the ratio between
these two signals of arterial absorbance pulse:
R=S(660)/S(905)
This R value is used to find the SpO2 saturation in a check
table provided by the oximeter software. The values in this
table are based on studies with human blood versus those
from a co-oximetry laboratory in healthy adult volunteers in an
induced hypoxia study.
The MS board of Masimo SET pulse oximeter assumes that
the arteriovenous shunt is highly variable in the floating
absorbance due to venous blood being part of the noise
component during the pulse. The MS board decomposes
S(660) and S(905) into an arterial signal plus a noise
component and calculates the ratio of arterial signal without
noise:
S(660)=S1+N1
3S(905)=S2+N2
R= S1/S2
Again, R is the ratio between two signals of pulsed arterial
absorbance and its value is used to find the SpO2 saturation
in an empirically derived equation in the oximeter software.
The values in the equation empirically derived are based on
