Cardinal Health Alaris 8000 Series, Directions For Use Manual

Page: 275 / 378

Principle of Operation (Continued)
General Information
4-31 Alaris
®
System Directions for Use
SpO
2
Modules Section
blood is related to hemoglobin oxygen saturation to identify
the oxygen saturation of arterial hemoglobin, the monitor uses
the pulsatile nature of arterial flow. 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
S
p
O
2
Module bases its
S
p
O
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, venous blood, tissue and
bone.
Because light absorption by hemoglobin is wavelength
dependent and the mean wavelength of
LED
s varies, an
oximeter must know the mean wavelength of the sensor’s red
LED
to accurately measure
S
p
O
2
. During monitoring, the
instrument’s software selects coefficients that are appropriate
for the wavelength of that individual sensor’s red
LED
. Those
coefficients are then used to determine
S
p
O
2
.
To compensate for differences in tissue thickness, the light
intensity of the sensor’s
LED
s is adjusted automatically.
The
S
p
O
2
Module measures functional saturation (oxygenated
hemoglobin expressed as a percentage of the hemoglobin
that can transport oxygen). It does not detect significant
amounts of dysfunctional hemoglobin; such as,
carboxyhemoglobin or methemoglobin. In contrast,
hemoximeters (such as,
IL482
) report fractional saturation
(oxygenated hemoglobin expressed as a percentage of all
measured hemoglobin, including measured dysfunctional
hemoglobin).
To compare functional saturation measurements to those from
an instrument that measures fractional saturation, fractional
measurements must be converted as follows:
functional saturation=
fractional saturation
x
100
100
- (
%
carboxyhemoglobin
+ %
methemoglobin)
8210 Series (Continued)
(8210)