Henry Schein HS-Vet, Instructions For Use Manual

Page: 52 / 279

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measurement of SpO
2
is dependent upon light from the sensor,
excessive ambient light can interfere with this measurement.
Pulse oximetry is based on two principles:

Oxyhemoglobin and deoxyhemoglobin differ in their
absorption of red and infrared light
(spectrophotometry).

The volume of arterial blood in tissue (hence light
absorption by the blood) changes during the pulse
(plethysmography).
The oximeter determines SpO
2
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) serve as light sources; a photonic
diode serves as the photo detector.
Because oxyhemoglobin and deoxyhemoglobin differ in light
absorption, the amount of red and infrared light absorbed by blood
is related to hemoglobin oxygen saturation. To identify the oxygen
saturation of arterial hemoglobin, the oximeter 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 oximeter bases its SpO
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 non-pulsatile
absorbs such as tissue, bone and venous blood.
Wavelength
The sensor contains LEDs that emit red light at a wavelength of
approximately 660 nm and infrared light at a wavelength of
approximately 900 nm.
8.2 Functional Versus Fractional
Saturation