Craig Le Moult
Over the past two years, the pulse oximeter has become a crucial tool for monitoring the health status of patients with COVID-19.
The small device clips onto a finger and measures the amount of oxygen in a patient’s blood. But a growing body of evidence shows the device may be inaccurate when measuring oxygen levels in dark-skinned people.
A study published on Monday only adds to this concern.
Researchers analyzing pre-pandemic health data also found that these measures resulted in patients of color receiving less supplemental oxygen than white patients.
“We were fooled by the pulse oximeter,” says the study’s lead author, Dr. Leo Anthony Celi, director of clinical research and principal investigator at the MIT Laboratory of Computational Physiology.
“We were given the false impression that the patients were fine. And what we showed in this study was that we were giving them less oxygen than they needed,” he says.
These sobering results make it more urgent to educate patients and healthcare professionals about pulse oximeter shortcomings – and to design new models that can work reliably regardless of skin color. of somebody.
A doctor fights to get his son treated
It was last September when Dr Sandra Looby-Gordon saw how this flaw in the device could affect her own family.
Looby-Gordon, who is a doctor at Boston Medical Center, found herself on the phone with a triage nurse at a Florida hospital, arguing that her own son – who was very ill with COVID-19 – should be admitted to the hospital. hospital.
“‘Well, yeah, he looks pretty breathless,'” Looby-Gordon recalled, the nurse responding, “‘but his oxygen level is fine.'”
The nurse was basing it on the reading from the pulse oximeter strapped to her finger, but that assessment didn’t seem fair to Looby-Gordon.
She hung up on the phone with the nurse and spoke with other doctors at her medical center. One of them reminded him of a 2020 article in the New England Journal of Medicine showing pulse oximeter tends to be inaccurate in dark skinned people.
“On top of that, my son is – it sounds strange – but very dark, very dark complexion,” says Looby-Gordon.
Sure enough, later when her son underwent a more invasive test to measure blood oxygen, it showed that his oxygen levels were in fact dangerously low.
He was admitted to hospital, treated and ultimately cured of COVID-19. But Looby-Gordon says most patients in their situation are unaware of pulse oximeter shortcomings.
Even as a black doctor herself, she says she wasn’t fully aware of how the device could be so misleading.
Research highlights device shortcomings
On the contrary, the pandemic has highlighted this long-standing problem with the pulse oximeter.
Research published last month by scientists at Johns Hopkins University shows inaccurate pulse oximeter results prevented identifying black and Hispanic patients who needed COVID-19 treatments like the steroid dexamethasone and remdesivir antiviral.
Throughout the COVID-19 crisis, people of color have experienced higher rates of hospitalization and death from COVID-19 than white people. MIT’s Celi says it’s not possible to know to what extent pulse oximeters contributed to the disproportionate impact of COVID-19 on people of color, but he thinks it played a role.
And the question points to a larger issue with how medical devices are researched and approved: “The way we evaluate medical products is primarily based on trials that primarily involve white individuals,” Celi says.
FDA guidelines for approving pulse oximeters state that clinical trials must include at least two people with dark pigmentation, or 15% of the subject group – whichever is greater. But some doctors and scientists say this is insufficient, especially since there is such a range of skin tones.
Several pulse oximeter manufacturers, including Edwards Lifesciences, Masimo, and Nonin, claim that their own versions of the devices provide accurate results that, in fact, take skin tone into account.
In a 2021 editorial in response to New England Journal of Medicine article, the CEO of Masimo Corp. suggested that several hypotheses could explain the disparity between the results of this study and their own internal research, including sickle cell disease and circulatory problems, which disproportionately affect black people.
Scientists are looking for solutions
Increasingly, scientists and engineers are working on new technologies that could revolutionize pulse oximeters so that they work equally well for people with darker skin tones.
At a Brown University optics lab, doctoral student Rutendo Jakachira explains how a pulse oximeter works.
“If you insert your finger into this groove, the LED at the top sends light through your finger,” Jakachira explains. The device can then calculate a patient’s oxygenation by determining the amount of light absorbed by hemoglobin in the blood.
“That’s the key to the problem seen in dark-skinned people,” says Kimani Toussaint, a professor of electrical and computer engineering, biomedical engineering, and mechanical engineering at Brown University. light energy is hemoglobin. .”
But in reality, skin pigmentation also absorbs light, he says. And for people with darker skin, this can result in a pulse oximeter reading that overestimates the amount of oxygen in their blood.
Toussaint stands next to a table full of technology that he hopes will solve the problem.
“I wouldn’t even call it a device yet,” he says.
Unlike current pulse oximeters, this not-quite-a-device uses polarized light that isn’t absorbed by skin pigmentation. If it works well, Toussaint says they’ll partner with manufacturers to whittle everything down to a device that could be marketed.
Craig LeMoult/Craig LeMoult
At Tufts University, Valencia Koomson is working to solve this problem using a different approach.
His device uses the same type of light as currently available pulse oximeters, but includes technology that can measure a person’s skin tone (people with darker skin pigmentation have lower levels of melanin higher).
“We can send more light if there’s a higher level of melanin, so that melanin doesn’t become a confounding factor that obscures our results,” says Koomson, an associate professor of electrical and computer engineering.
Koomson, who is black, says the history of the pulse oximeter — and ongoing efforts to redesign it — underscore the need for greater diversity in engineering and medicine.
“We are shaped by our environment, who we are and our identity,” she says. “It informs what kind of research is going on. It’s the people who do the research, who decide what research is done.”
Koomson and other scientists also pushed the Food and Drug Administration to take action to address the issue.
“When a patient is at home and not being closely monitored in the hospital, we need to make sure those numbers are as accurate as possible so that clinical assessments can be made,” says Dr. Sandra Kane-Gill, president of the Society for Critical Care Medicine, who sent two letters to the FDA about problems with the pulse oximeter.
The agency begins to react.
Last winter, the FDA issued a warning that skin pigmentation and other factors could impact pulse oximeter results. It is now funding research into the matter and will bring together expert advisers later this year to discuss how to ensure the devices are accurate for everyone.
Despite years of publications on the matter, Koomson says it’s not as well known as it should be.
She says a national legacy of racist and pseudo-scientific studies has left scientists hesitant to explore the physical differences between people of various races.
“People are afraid to talk about physical differences because they don’t want to sound discriminatory,” says Koomson. “But I think we need to talk about the aspects that affect people’s health and impact the care they receive.”
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