Over the past two years, pulse oximetry has become an important tool for tracking the health of COVID-19 patients.
The small device is attached to a finger and measures the amount of oxygen in the patient’s blood. But a growing body of evidence shows the device may be inaccurate when measuring oxygen levels in people with darker skin.
A study published on Monday only adds to this concern.
Researchers who analyzed pre-pandemic health data also found that these measurements resulted in patients of color getting less supplemental oxygen than white patients.
“We tricked the pulse oximeter,” says study lead author Dr. Leo Anthony Sely, director of clinical research and principal research scientist at the MIT Laboratory of Computational Physiology.
“We gave the wrong impression that the patients were fine,” he says. “And what we showed in this study was that we were giving them less oxygen than they needed.”
These shocking findings bring more urgency to educate patients and medical professionals about the shortcomings of pulse oximetry — and to design new models that can work reliably regardless of a person’s skin tone.
A doctor struggles to take care of her son
It was last September when Dr. Sandra Lupe-Gordon saw how this malfunction of the device could affect her family.
Lupe Gordon, a physician at Boston Medical Center, found herself on the phone with a triage nurse at a Florida hospital, arguing that her son — who was very sick with COVID-19 — needed to be hospitalized.
Lupe Gordon recalls the nurse’s response: “Well, he appears to be short of breath, but his oxygen levels are fine.”
The nurse based this on the reading from a fingertip pulse oximeter, but that assessment was not correct for Looby-Gordon.
I got off the phone with the nurse and spoke with other doctors at her medical center. Someone mentioned it in an article published in 2020 in a newspaper New England Journal of Medicine The demonstration of pulse oximetry tends to be inaccurate in dark-skinned people.
“Besides, my son – this sounds weird – but he is very dark skinned and very dark,” says Lupe Gordon.
Sure enough, later when her son underwent a more invasive blood-oxygen test, it showed his oxygen levels were dangerously low.
He was hospitalized, treated, and eventually recovered from COVID-19. But Looby-Gordon says that most patients in their setting would not know the deficiencies of the pulse oximeter.
Even as a black doctor, she says she wasn’t fully aware of how so misleading the device can be.
Research highlights device flaws
If anything, the pandemic has highlighted this long-standing problem with pulse oximetry.
Research published by scientists at Johns Hopkins University last month showed that inaccurate results from pulse oximeters led to a failure to identify black and Hispanic patients who needed COVID-19 treatments such as the antiviral steroid dexamethasone and remdesivir.
Throughout the COVID-19 crisis, people of color have experienced higher rates of hospitalization and death from COVID-19 than white people. It’s not possible to know how much pulse oximetry has contributed to the disproportionate impact of COVID-19 on people of color, says MIT Selye, but he believes it did play a role.
The problem points to a larger issue with how medical devices are studied and approved: “The way we rate medical products is primarily based on trials that primarily involve white individuals,” Seely says.
The US Food and Drug Administration (FDA) guidelines for approval of pulse oximeters state that clinical trials should include at least two dark-pigmented subjects, or 15% of the group of subjects—whichever is greater. But some doctors and scientists say this is not enough, especially since there is a wide range of skin tones.
Many pulse oximeter manufacturers — including Edwards Lifesciences, Masimo and Nonin — claim that their own versions of the devices provide accurate results that actually take skin color into account.
In a 2021 opinion piece in response to New England Journal of Medicine In an article, the CEO of Masimo Corp. Several hypotheses have been proposed that may explain the discrepancy between the results of that study and their internal research, including sickle cell disease and circulatory problems, which disproportionately affect blacks.
Scientists are looking for solutions
Increasingly, scientists and engineers are working on new technologies that could revolutionize pulse oximetry so that it also works for people with darker skin.
At Brown University’s Optics Laboratory, doctoral student Rotendo Jakashira explains how the pulse oximeter works.
“If you insert your finger into this groove, the lamp on top sends light through your finger,” Jakashira says. The device can then calculate the patient’s oxygenation by seeing how much light the hemoglobin in the blood has absorbed.
“This is the key to the problem seen in people with darker skin,” says Kimani Tosan, professor of electrical engineering, computer engineering, biomedical engineering, and mechanical engineering at Brown University. It is assumed that the only absorber of light energy is hemoglobin. ”
But in fact, skin tone also absorbs light, he says. And for people with darker skin, this can result in a reading from the pulse oximeter that overestimates the amount of oxygen in their blood.
Toussaint stands next to a table full of tech hoping to solve the problem.
“I wouldn’t call this device yet,” he says.
Unlike current pulse oximeters, the never-before-seen device uses polarized light that is not absorbed by skin pigmentation. If it works properly, Toussaint says they will partner with manufacturers to reduce all of that to a marketable device.
Craig Lummault / Craig Lummault
At Tufts University, Valencia Comson is working to tackle this problem using a different approach.
Her device uses the same type of light as currently available pulse oximeters, but includes technology that can measure a person’s skin color (people with darker skin pigmentation have higher levels of melanin).
“We can send out more light if there is a higher level of melanin present, so that the melanin does not become a confounding factor obscuring our results,” says Comson, who is an associate professor of electrical and computer engineering.
Comson, who is Black, says the story of the pulse oximeter — and efforts now underway to redesign it — point to the need for greater diversity in engineering and medicine.
“We are shaped by our environment, who we are, and who we are,” she says. “It shows what kind of research is being done. It’s the people who do the research, who decide what to look for.”
Comson and other scientists have pushed the Food and Drug Administration to take steps to address the problem.
Sandra Kane Gill, president of the Society for Critical Care Medicine, says two letters to the Food and Drug Administration regarding pulse oximeter problems.
The agency began to respond.
Last winter, the US Food and Drug Administration (FDA) issued a warning that skin pigmentation and other factors could affect pulse oximetry results. It is now funding research into the problem and will bring together expert advisors later this year to discuss how to ensure the devices are accurate for everyone.
Despite years of publications on the issue, Comson says it’s not as well known as it should be.
She says the national legacy of racist pseudoscientific studies has made scientists wary of exploring the physical differences between people of different races.
“People are afraid to talk about physical differences because they don’t want to appear discriminatory,” Comson says. “But I think we have to talk about the aspects that affect people’s health and have an impact on the care they receive.”
#dark #skin #pulse #oximeters #fall #short