Pulse Oximetry: A Vital Tool with Important Functional Limitations for Patients with Dark Skin Color

Abstract

Pulse oximeters measure SpO2 (percent oxygen saturation of hemoglobin in peripheral blood). SpO2 estimates SaO2 (percent oxygen saturation of hemoglobin in the arterial blood). Thus pulse oximeters are vital tools for critically ill patients. However, they have technical limitations, including reporting SpO2 values that overestimate SaO2 in patients with dark skin color. This review briefly traces the history of pulse oximeter development, reports the extent of this measurement bias (SpO2 – SaO2 = measurement bias), describes the clinical importance of this measurement bias, and discusses approaches to eliminating it. Depending on the population studied, oximeter measurement bias is between 50% and 860% greater for people with dark vs. light skin color. This bias means that patients with dark skin are 75% to 200% more likely to suffer occult hypoxemia (SaO2 < 88% with concurrent SpO2 = 88%) compared to light skinned patients. Occult hypoxemia is associated with between 40% and 196% increased risk of in-hospital mortality. Because the extent of oximeter measurement bias increases as SpO2 decreases, no one adjustment of SpO2 readings will address this issue. Improvements in the algorithms oximeters use to determine SpO2 values based on larger samples of subjects with a greater range of skin colors and/or improved hardware is needed. Nurses should be aware how skin color impacts oximeter measurement bias and can advocate for the adoption of the most accurate oximeters by their institutions.