Pulse oximeters were less accurate in Black and Hispanic patients, according to a recent study published in JAMA Internal Medicine, which led to delayed care for severe Covid-19.

Study details

Pulse oximeters are electronic devices that estimate a patient's blood oxygen saturation and pulse rate. The devices, typically clipped on a fingertip, shine lights through the finger and analyze the results.

For the study, researchers looked at data on 7,448 patients from five hospitals in the Johns Hopkins Health System between March 4, 2020, and Nov. 21, 2021. All of the patients received pulse oximeter measurements, and blood gas measurements were taken for around 1,200 of the patients.

The researchers then compared the measurements from arterial blood gas tests to the pulse oximeter readings and found significant discrepancies for patients of color. On average, pulse oximeters overestimated Black patients' oxygen saturation by 1.2 percentage points, 1.1 percentage points for Hispanic patients, and 1.7 percentage points for Asian patients.

The researchers also found that nearly 24% of the patients in the study were unrecognized for Covid-19 treatment despite being eligible based on their actual oxygen levels. Of those patients, 54.8% were Black and 27.1% were Hispanic.

Using statistical models on the patients who received arterial blood gas tests, the researchers also found that Black patients were nearly 30% less likely to be recognized as being eligible for severe Covid-19 treatment than white patients, while Hispanic patients were more than 20% less likely.

Discussion

In April, CDC said that Black and Hispanic patients were nearly twice as likely to die of Covid-19 than white patients, a finding that could have been partly caused by inaccurate oxygen measurements, according to Ashraf Fawzy, co-lead author of the study and an assistant professor of medicine at Johns Hopkins University.

"If it's not recognized that a patient is at a point when they should receive treatment, then they're not going to get that therapy," said Michael Sjoding, a pulmonologist at the University of Michigan.

According to A. Ian Wong, a critical care and lung doctor at Duke University, a potential cause of the inaccurate pulse oximeter readings is the skin pigment melanin, which absorbs light and can have an impact on the oximeter's readings.

Even if the pulse oximeters are slightly off, that can have a significant impact on the treatment options available to a patient, said Tianshi David Wu, co-lead author of the study and an assistant professor of medicine at Baylor College of Medicine.

"An inaccurately high oxygen saturation…would disqualify a patient for more-aggressive Covid-19 therapies," he said, including treatments like dexamethasone or remdesivir.

Thomas Valley, an assistant professor of medicine at the University of Michigan, said the study is another addition to the growing body of evidence suggesting the inaccuracies of pulse oximeters is taking a large toll on patients.

"We've been searching for reasons Black and Hispanic people were more likely to die early in the pandemic," he said. "This is pretty depressing that we had treatments available, many of those treatments tied to oxygen levels. Decisions on whether or not people were admitted to hospitals or put on ventilators, those were all based on blood oxygen levels."

"If the main device you're using to measure the severity of Covid is the pulse oximeter and the device is intrinsically biased against people of color, it's not surprising that mortality is going to be higher in patients of color," said Martin Tobin, a professor of medicine at Edward Hines, Jr. VA Hospital.

Valley added that he'd like to see a study examining how decisions to send patients home from the ED or tell them to come to the hospital based on their oxygen levels impacted darker-skinned patients. "We were recommending that all the time, 'If your O2 levels are not low, don't come to the hospital,'" he said. "We don't know how much harm that caused."

In an accompanying editorial, Valeria Valbuena, from the University of Michigan, and colleagues wrote that racial disparities in pulse oximeter measurements are "a known design flaw" and added that, until the flaw is corrected through "market pressure," health care providers should take those inaccuracies into account with other strategies, including "lowering the threshold for suspected disease and obtaining more arterial blood gases."

"Although the device measurement error is real and based purely on optics, the decision to do nothing about a faulty device is a human one, and one that can and should be corrected," the authors wrote. (Mosbergen, Wall Street Journal, 5/31; McFarling, STAT News, 5/31; Walker, MedPage Today, 5/31; Wetsman, The Verge, 5/31; Beals, The Hill, 5/31)