Apex Oximeter - GE ApexPro TT Technical Manual

Apex oximeter

Theory of operation - pulse oximetry
2001989-351A
NOTE
The telemetry system supports 2 SpO2 oximeter modules:
Apex Oximeter
Nonin Xpod Oximeter
Pulse oximeters shine light (red and infrared) through perfused tissue and detect the
fluctuating signals caused by arterial blood pressure pulses. Well-oxygenated blood is
bright red, while poorly oxygenated blood is dark red. The pulse oximeter determines
functional oxygen saturation of arterial hemoglobin from this color difference by
measuring the ratio of absorbed red and infrared light as the blood volume fluctuates
with each heart beat. Since steady conditions (steady venous blood flow, skin
thickness, bone, finger nails, etc.) do not cause fluctuations, they do not affect the
saturation reading.
Mathematically:
min
( (
In red
max
SpO = f
min
2
( (
In infrared
max
Anything that affects the intensity of the light such as thick or colored skin affects the
maximum and minimum proportionally and thus the ratio minimum/maximum does
not change. However, if too little light gets through, the pulse oximeter does not
function.
Pulse oximeters use 2 different wavelengths of light (colors) and thus have the ability
to determine 1 component of blood. Pulse oximeters are calibrated to closely
approximate functional oxygen saturation values. Pulse oximeter oxygen saturation
values will closely approximate laboratory instrument fractional saturation values if
the dysfunctional hemoglobin saturation levels are negligible. If the dysfunctional
hemoglobin is carboxyhemoglobin or methemoglobin, then the difference between
the oxygen saturation value displayed by the Pulse oximeter and the oxygen
saturation values determined by the laboratory instrument are greater as the
dysfunctional hemoglobin levels rise approximately in accordance with the following
formulas:
ApexPro™
Equipment Overview
310C
801
2-15