Low perfusion and missed diagnosis of hypoxemia by pulse oximetry in darkly pigmented skin: A prospective study

Abstract

Abstract Importance: 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.

Competing Interest Statement

The authors have declared no competing interest.

Clinical Protocols

https://www.OpenOximetry.org/protocols

Funding Statement

Supported by the Gordon and Betty Moore Foundation, The Patrick J. McGovern Foundation, and funds generated from the testing of pulse oximeters.

Author Declarations

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

IRB of the University of California at San Francisco (UCSF Committee on Human Research)

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Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable.

Yes

Data Availability

All data produced in the present study are available upon reasonable request to the authors

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