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Factors affecting oxygen saturation readings:
( Haemoglobin, Circulation ): If the haemoglobin is fully saturated with oxygen, the SpO2 will appear normal even if the total haemoglobin level is low. Thus, the person could be severely anaemic and have inadequate oxygen to supply the tissues but the pulse oximeter would return a normal value.
( Circulation, Haemoglobin ): The oximeter will not return an accurate reading if the area under the sensor has impaired circulation, such as occurs in peripheral vascular disease or if a person is very cold.
Activity: Shivering or excessive movement of the sensor site may interfere with accurate readings.
Dark-coloured nail polish or discolouration of the nail bed: False readings typically arise when a person is wearing dark-coloured nail polish or if the nail bed is discoloured by a subdermal haematoma or other sources of nail bed discolouration, such as nicotine stains.
( Carbon monoxide poisoning, Circulation ): Pulse oximeters cannot discriminate between haemoglobin saturated with carbon monoxide versus oxygen. In this case, other measures of oxygenation are needed.