Publications

Retrospective clinical trials of pulse oximeter accuracy report more frequent missed diagnoses of hypoxemia in hospitalized Black patients than White patients, differences that may contribute to racial disparities in health and health care. Retrospective studies have limitations including mistiming of blood samples and oximeter readings, inconsistent use of functional versus fractional saturation, and self-reported race used as a surrogate for skin color. Understanding the cause of biased readings by pulse oximetry in patients with darkly pigmented skin is high priority given the essential nature of pulse oximetry. Objective: To prospectively measure the contributions of skin pigmentation, perfusion index, sex, and age on pulse oximeter errors. Design: We studied two pulse oximeters (Nellcor N-595TM and Masimo Radical 7TM) in prevalent use in North America, Europe, and Asia-Pacific regions. We analyzed 9,763 matched pulse oximeter readings (SpO2) and arterial oxygen saturation (hemoximetry SaO2) during stable hypoxemia (SaO2 68-100%). Perfusion index (PI) was measured as percent infrared light modulation by the pulse detected by the pulse oximeter probe, with low perfusion categorized as PI <1%. Setting: Clinical research laboratory Participants: 146 healthy subjects, including 25 with light skin (Fitzpatrick class I-II), 78 with medium (class III-IV), and 43 with dark (class V-VI) skin. Exposures: Controlled hypoxemia Main Outcomes: Pulse oximeter bias (difference between SaO2 and SpO2) by skin pigment category in a multivariable mixed-effects model incorporating repeated-measures and different levels of SaO2 and perfusion. Results: Skin pigment, perfusion index and degree of hypoxemia significantly contributed to errors (bias) in both pulse oximeters. The combined frequency of missed diagnosis of hypoxemia (pulse oximeter readings 92-96% when arterial oxygen saturation was <88%) in low perfusion conditions was 1.1% for light, 8.2% for medium and 21.1% for dark skin. Conclusions and Relevance: Low peripheral perfusion combined with darker skin pigmentation leads to clinically significant high-reading pulse oximeter errors and missed diagnoses of hypoxemia. Darkly pigmented skin and low perfusion states are likely the cause of racial differences in pulse oximeter performance in retrospective studies. Both skin pigmentation and low perfusion should be accounted for in regulatory standards for pulse oximeters.

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It has long been known that many pulse oximeters function less accurately in patients with darker skin. Reasons for this observation are incompletely characterized and potentially enabled by limitations in existing regulatory oversight. Based on decades of experience and unpublished data, we believe it is feasible to fully characterize, in the public domain, the factors that contribute to missing clinically important hypoxemia in patients with darkly pigmented skin. Here we propose 5 priority areas of inquiry for the research community and actionable changes to current regulations that will help improve oximeter accuracy. We propose that leading regulatory agencies should immediately modify standards for measuring accuracy and precision of oximeter performance, analyzing and reporting performance outliers, diversifying study subject pools, thoughtfully defining skin pigmentation, reporting data transparently, and accounting for performance during low-perfusion states. These changes will help reduce bias in pulse oximeter performance and improve access to safe oximeters.

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