Pulse oximeters are calibrated by manufacturers using data collected from healthy volunteers
In general, pulse oximeters are accurate within +/- 2% for sats > 70%
In the critically ill, however, the accuracy of pulse oximetry diminishes when sats drop below 90%
Also, there may be a significant lag time between a hypoxic event and the actual display of the event - most commonly seen in low flow states, hypotension, mild hypothermia, and when using vasoactive medications
Prolonged lag times are more common with finger probes
Pitfall - pulse oximetry does not provide any assessment regarding ventilation (PaCO2) or acid-base status (pH) - it is simply an estimate of arterial oxgyen saturation
Pearl: anemia does not affect the accuracy of pulse oximetry
