Differences between Pulse Oximetry Readings from Finger vs. Ear Probe Locations in Anesthetized Patients

Background/objectives: Pulse oximetry is a standard of care during the administration of GA and MAC.

The goal of this study is to determine if there are significant differences between PO readings obtained with oximeter probes on a finger versus the ear.

Methods: A PO probe was placed on a finger and the ear. Paired readings were recorded every five minutes. Differences in saturation readings between the finger and ear probe at each time point were entered into categories.

Discussion/Results: SpO2 readings can be decreased by various factors. We undertook this study because of clinical instances when finger SpO2 readings were unexpectedly low, and rapid placement of an ear probe often recorded a higher SpO2. We hypothesized that, when there were differences, SpO2 readings from the ear would be higher than the finger, due to the large amount of blood flow to the head. However, the data indicate that neither the ear probe nor the finger probe provide consistently higher saturation readings.

An SpO2 reading that is falsely low by could result in changes that may impact outcome such as bleeding from insertion of a nasal airway, or hemodynamic changes due to rapid laryngoscopy and intubation. This is troubling if airway maneuvers are performed unnecessarily due to a falsely low SpO2. If SpO2 decreases unexpectedly, usual procedures include checking the probe, seeking possible causes of desaturation, and appropriate corrective airway maneuvers. In addition, placement of a pulse oximeter probe in a second location may provide useful information.