Ear Pulse Oximeters as a Cause of Pressure Ulcers

Background:  Pressure ulcer prevalence surveys in the adult intensive care units at an academic medical center showed that pressure ulcers occurred on patients’ earlobes despite  rotation of pulse oximeter location. This observation, combined with the shape and location of these pressure ulcers, suggested that earclip-style probes may exert pressure on soft tissue that exceeds capillary pressure, leading to pressure ulcer formation. Although clinicians commonly consider 25-32 mm Hg the pressure below which capillary perfusion ceases, studies of capillary perfusion pressure actually vary widely in their findings, ranging from 5-70 mm Hg. Moreover, generalizability of these studies to the critical care population must be done with caution.

Objectives:  The aim of this study was to quantify the pressure exerted on the earlobe by an earclip-style pulse oximetry probe for comparison to values of capillary perfusion pressure found in the literature.

Methods:  Seven probes were selected from among those in use in the trauma intensive care unit. A one-pound electronic load cell calibrated with standard weights was used to measure force in pounds exerted by the probes. Each probe was tested twice. The area of the earclip probe that contacts the tissue was calculated to determine pounds per square inch of pressure, which was then converted to mm Hg.

Results: The area of each arm of the probe that contacted the earlobe was .3 square inches. Mean force exerted was .24 ±.06 pounds. Mean combined pressure exerted by the arms of the probes equaled 41.9 ± 10.3 mm Hg.

Conclusions: Earclip-style pulse oximetry probes, often used when low peripheral perfusion prevents accurate oxygen saturation measurement from peripheral sites,  may exert pressure on tissue that exceeds capillary closing pressure, causing earlobe pressure ulcers. Alternative products or sites should be considered when reliable peripheral pulse oximetry values cannot be obtained from peripheral anatomical sites.