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. SpO
2
measurement can be used for
adults, pediatrics and neonates.
This device is calibrated to display functional oxygen saturation.
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 indicator: the pulsatile portion of the measured signal caused by arterial pulsation.
4. 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 SpO2 measurement.
Above 1 is optimal, between 0.3 and 1 is acceptable. Below 0.3 indicates low perfusion; reposition the SpO2 sensor
or find a better site. If low perfusion persists, choose another method to measure oxygen saturation if possible.
PI is available for Mindray SpO
2
module and Masimo SpO
2
module. When PI is below 03, a question mark (?) is
displayed to the right of the SpO
2
value, indicating that the patient is in low perfusion and SpO
2
value may be
inaccurate.
5. Pulse rate (derived from pleth wave): detected pulsations per minute.
NOTE
A functional tester or SpO2 simulator cannot be used to assess the accuracy of a SpO2 module or a SpO2
sensor.
A functional tester or SpO
2
simulator can be used to determine the pulse rate accuracy.
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