depends on detecting a pulsatile blood flow. In a trauma patient, this is not always possible. Depending on the state of the patient, there may not be an adequate pulse for the probe to detect. If the patient is cold
or has loss a lot of blood, there may only be a weak pulse in the periphery.
Also, there are inaccuracies in the reading given by pulse oximeters. There needs to be an adequate waveform demonstrated on the monitor before the reading can be considered accurate. There is often an error of +/-2%.
The most accurate measure of oxygen saturation
is an arterial blood
Dr K A Pottinger,