11-1
11 Monitoring SpO
2
11.1 Introduction
SpO
2
monitoring is a non-invasive technique used to measure the amount of oxygenated
haemoglobin and pulse rate by measuring the absorption of selected wavelengths of light.
The light generated in the probe passes through the tissue and is converted into electrical
signals by the photodetector in the probe. The SpO
2
module processes the electrical signal
and displays a waveform and digital values for SpO
2
and pulse rate.
This device is calibrated to display functional oxygen saturation. It provides four
measurements:
(1) Pleth waveform (Pleth): visual indication of patient’s pulse. The waveform is not
normalized.
(2) Oxygen saturation of arterial blood (SpO
2
): percentage of oxygenated hemoglobin in
relation to the sum of oxyhemoglobin and deoxyhemoglobin.
(3) Perfusion index (PI): gives the numerical value for the pulsatile portion of the measured
signal caused by arterial pulsation. PI is an indicator of the pulsatile strength. You can
also use it to assess the quality of SpO
2
measurement.
Above 1 is optimal,
Between 0.3 and 1 is acceptable.
Below 0.3 indicates low perfusion; When PI is below 0.3, a question mark (?) is
displayed to the right of the SpO
2
value, indicating that the SpO
2
value may be
inaccurate. Reposition the SpO
2
sensor or find a better site. If low perfusion persists,
choose another method to measure oxygen saturation if possible.
PI value can be displayed under the PR value in larger characters if [PI Zoom] is
enabled.
(4) Perfusion indicator: the pulsatile portion of the measured signal caused by arterial
pulsation.
(5) Pulse rate (derived from pleth wave): detected pulsations per minute.
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