Pulse Oximeters Miss Low Oxygen Levels Nearly Three Times More Often in Blacks Than Whites

By Gene Emery

December 17, 2020

NEW YORK (Reuters Health) - Pulse oximeters are nearly three times more likely to miss oxygen starvation in Blacks than in whites, according to a large new study.

Among 1,609 patients treated earlier this year at the University of Michigan Hospital, in Ann Arbor, 11.7% of Blacks had an alarming arterial oxygen saturation of less than 88%, as measured directly in the blood, even though their pulse oximetry levels were in the normal range of 92% to 96%.

The devices, originally designed for people with light skin, missed low oxygen levels in only 3.6% of whites, a statistically significant difference.

When the researchers expanded their evaluation to look at data from 8,392 other patients treated at 178 intensive-care units during 2014 and 2015, they found that pulse oximeters missed low blood oxygen levels in 17.0% of Black patients versus 6.2% of whites, also a significant difference.

"Thus, in two large cohorts, Black patients had nearly three times the frequency of occult hypoxemia that was not detected by pulse oximetry as white patients," Dr. Michael Sjoding of the University of Michigan Medical School and colleagues write.

"Given the widespread use of pulse oximetry for medical decision making, these findings have some major implications, especially during the current coronavirus disease 2019 (Covid-19) pandemic," they warn. "Reliance on pulse oximetry to triage patients and adjust supplemental oxygen levels may place Black patients at increased risk for hypoxemia."

The analysis is published in the New England Journal of Medicine.

The devices use red and infrared light to gauge the color of hemoglobin, which darkens to purple-red when oxygen levels drop. Because pulse oximeters were mostly tested on whites when they were developed, they are calibrated for people with light skin. They are approved by the U.S. Food and Drug Administration (FDA).

The racial discrepancy was seen even after the team excluded people with diabetes and elevated carboxyhemoglobin levels.

"People at the FDA and device companies should re-evaluate how they assess the accuracy of these devices," Dr. Sjoding told Reuters Health by phone, expressing surprise at the discovery that "one of the most commonly used devices in health care . . . has a potentially small but clearly measurable bias."

"There's a long history of patients who are Black or other minorities not having as good an outcome when they develop things like COVID-19 or other severe lung conditions," he said. "This is an interesting new finding and a potential explanation nobody has thought about before. Maybe it's good news that might explain some of these disparities. But it's bad news that it has this inaccuracy."

The study was undertaken because Dr. Sjoding and his colleagues were noticing discrepancies in what the devices were reporting and what arterial blood gas monitoring was showing.

At the same time, a member of the team read an August 5 article in Boston Review reporting on past evidence - some of it more than 20 years old - warning that the developers of pulse oximeters had failed to make their devices accurate for people with darker skin.

"We were in a position to really answer this question because we have access to this data," said Dr. Sjoding.

"Our findings highlight an ongoing need to understand and correct racial bias in pulse oximetry and other forms of medical technology," the researchers write.

SOURCES: https://bit.ly/3gDRjrZ and https://bit.ly/3gNjncy The New England Journal of Medicine, online December 16, 2020

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