Pulse oximeters are essential in the fight against Covid. They may not work on dark skin

Pulse oximeters are essential in the fight against Covid. They may not work on dark skin

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The pulse oximeters, which increased during the pandemic, could produce inaccurate results, the U.S. Food and Drug Administration warned Friday.
Earlier this week, the U.S. Centers for Disease Control and Prevention also updated its coronavirus clinical guidelines to warn doctors and nurses that data from several studies suggest that skin pigmentation may affect the accuracy of the devices.

“Although pulse oximeters can be useful for estimating blood oxygen levels, these devices have limitations that can lead to inaccurate readings,” said Dr. William Maisel, director of the product evaluation and quality office at the FDA’s Center for Devices and Radiological Health, said in a statement.

Pulse oximeters are small clamp-like devices that attach painlessly to a patient’s finger and constantly monitor the amount of oxygen in their blood. Covid-19 is a respiratory disease, which means that it first attacks the lungs, so low oxygen levels are a sign that the patient may be getting worse. CDC data show that black, Latino, and Native Americans are four times more likely to be hospitalized with Covid-19 than others.
The recent warnings come after a study published in the New England Journal of Medicine in December. Dr. Michael Sjoding and several colleagues from the University of Michigan analyzed data from more than 10,000 patients. For each patient, they compared the oxygen levels recorded by a pulse oximeter with those measured with arterial blood gas – a much more accurate but painful and invasive procedure.

The researchers wanted to know how often the pulse oximeter displayed a relatively normal oxygen level if it had to be something more worrying.

In white patients, the pulse oximeter gave a deceptive number 3.6% of the time. In black patients, it was 11.7% of the time.

The downside, says Dr Sjoding, is that pulse oximeters were three times as likely to miss significantly low oxygen levels – or hypoxemia – in black patients. According to the study, one in ten black patients can get misleading results.

Why the readings are not exact

There is a relatively simple explanation for why. Pulse oximeters work by sending two types of red light through your finger. A sensor on the other side of the device picks up this light and uses it to detect the color of your blood; bright red blood is very oxygen-like, while blue or purple blood is less. If the device is not calibrated for dark skin, the pigmentation may affect the way light is absorbed. Dark nail polish can cause a similar effect.

Experienced physicians do not rely on the pulse oximeter alone to make a diagnosis or to determine a patient’s treatment, says Dr. Michelle Ng Gong, head of critical care medicine and head of pulmonary medicine at Montefiore Medical Center in New York.

“They will never tell a patient that I do not care how bad you feel, as long as the number is in order, you should not worry about it,” says Dr. Gong. “It’s a tool. And as a tool we need to be able to use it properly in the context of other information.”

But, says dr. Gong, during the pandemic, when hospitals are overwhelmed and doctors who are not normally in the emergency are brought in to see and examine patients, the numbers of a pulse oximeter can carry more weight. Inaccurate reading can be particularly problematic if the patient’s oxygen level is limitless.

Doctors must also be aware of their own unconscious prejudice, says dr. Gong. Studies show, for example, that when African Americans complain about pain, they are less likely to get as much (or any) pain medication as Whites. If a patient says he is struggling to breathe, physicians should not dismiss it simply because the pulse oximeter is normal.

“The only way in which health inequalities can be reduced,” says Dr. Gong, “is when we attack it from different angles, from both the larger contributions as well as our personal interaction.”

Doctors are also not the only ones who use pulse oximeters. As hospitals reached capacity during the pandemic, some Covid-19 patients with less severe symptoms were sent home to monitor their progress. According to market research, sales of pulse oximeters at home have increased by 500% since the new coronavirus arrived in the US.

Amy Moran-Thomas, a professor of anthropology at MIT, began researching pulse sock meters last year when her husband was sent home with one.

The findings are not new

Moran-Thomas discovered investigations into the 1990s that indicated that there was a problem with pulse oximeters in patients with dark skin.

In 2005, a study at the University of California, the Hypoxia Laboratory in San Francisco, found that three different models of pulse oximeters overestimated oxygen levels in dark-skinned patients. They conducted a follow-up study in 2007 with similar results.

“A reading of 77 like my husband’s can hide a true saturation of as low as 69 – even greater immediate danger. But EMTs or intake nurses cannot detect the differences. The number seems objective and race-neutral,” Moran- Thomas wrote in Boston Review.

Moran-Thomas asked her why the problem, which had been identified decades ago, had not yet been rectified.

“I am a physician for lung and critical care,” said Dr. Sjoding, who began his studies after reading Moran-Thomas’ article. “One of our co-authors is a leading Black Doctor from the University of Michigan. None of us knew it. None of us knew about these studies from the mid-2000s. It was not a part of our training. “

The public’s attention is increasing. On January 25, several U.S. senators sent the FDA a letter requesting them to investigate the matter. The FDA is responsible for approving medical pulse oximeters before it goes on the market. The agency currently requires pulse oximeters to be tested on different skin tones, meaning “at least 2 dark pigmented (subjects) or 15% of the subject coil, whichever is greater.”
The FDA says it is reviewing the available data carefully to determine if additional guidance or studies are needed from the agency. It recently approved a smartphone pulse oximeter that claims to work on all skin tones, with an automatic calibration period of 10-20 seconds to accurately measure how light moves through the user’s skin.

“These devices are not intended as the exclusive or primary use of information to make a clinical diagnosis or treatment,” said Dr. Maisel said in an interview with CNN on Wednesday. “One should not rely too much on a pulse oximeter reading, even if it is the most accurate product.”

“Just make sure you are aware of it when making decisions,” says Dr Sjoding. “The pulse oximeter reading may be a few points off. And if so, would you care for this patient in a different way?”

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