Home pulse oximeters were the personal tech device of 2020 and a calming way for patients to monitor their health at home during Covid-19.
However, a new study found that even in a hospital, pulse oximetry machines can sometimes be inaccurate, especially with black patients. The finding has raised questions about whether people with darker skin should rely on home surveillance.
Doctors say the devices that measure blood oxygen levels are still extremely useful in detecting deterioration in health in all Covid-19 patients, including those with darker skin, before they become seriously ill. If the device is wrong, it is likely that the reading is only a few percentage points different. It is important that all patients, especially those with darker skin, watch out for a downward trend in oxygen levels rather than fixating on a specific number.
“I think having information from a pulse oximeter is better than not having no information,” said Dr. Michael W. Sjoding, Assistant Professor of Internal Medicine in the University of Michigan Medical School and lead author of the new report that appeared in the New England Journal of Medicine. “I would also say that one has to understand that a pulse oximeter is an imperfect device.”
A pulse oximeter looks like a chip clip. When you insert your finger into a pulse oximeter, it emits different wavelengths of light through your skin. The amount of light that is absorbed reflects how much oxygen is in your blood. It has long been known that dark nail polish, cold skin and darker skin pigment can affect the reading. However, the new study suggests that the problem is more common in black patients than most doctors thought.
The analysis, which was based on 1,333 white patients and 276 black patients hospitalized at the University of Michigan earlier this year, used a hospital-based pulse oximeter and compared it to the gold standard test for measuring oxygen saturation known as arterial blood gas Exam. The study found that pulse oximetry overestimated oxygen levels in white patients 3.6 percent of the time, but was incorrect in almost 12 percent of the cases in black patients. Usually the pulse oximetry reading was overstated by a few percentage points.
Apr. 23, 2020, 5:24 p.m. ET
Researchers suspect the inaccurate readings may be due to the way the light is absorbed by darker skin pigments.
A normal reading on a pulse oximeter is usually between 96 and 100. Because patients with Covid-19 can quietly develop low oxygen levels without realizing it, patients are advised to monitor their oxygen levels at home. If the oxygen level drops to 93 or 92, patients are advised to check with their doctor. However, as the Michigan study shows, when a pulse oximeter sometimes overestimates oxygen saturation levels, there is concern that if the monitor reads 94 or 95 incorrectly, a patient with dark skin and self-monitoring at home may delay care if the patient’s actual oxygen level can be 92 or 93.
According to Dr. Sjoding’s solution is for patients to know their baseline values on their home device and watch out for downward trends. If you’re sick with Covid-19 at home and your normal reading drops by four points or more, this is a good reason to call your doctor.
While seeking care is important, you don’t need to panic. Oxygen saturation levels in their low 90s are an issue for people with Covid-19, but can be treated with assistive oxygen placed on the stomach to increase the flow of oxygen to your lungs and possibly other therapies.
“I would say if you happen to have a pulse oximeter at home, make sure you know what your normal level is so you know what a change is for you,” said Dr. Sjoding. “If your home pulse oximeter reads 98 when you purchase it and you are healthy and you are 94 years old and unwell, that is a pretty strong sign that you are sick and should see a doctor. ”
While the study focused on a group of patients who reported themselves as African American, it is reasonable to assume that the risk of error would be similar in other darker-skinned patients. The results are particularly worrying given that the pandemic is disproportionately affecting Black and Hispanic Americans. Studies have found that African Americans were hospitalized more often, suggesting delays in accessing medical care.
While the new data on the accuracy of the pulse oximeter is important in helping doctors better interpret oxygen levels in color patients, Dr. Sjoding states that the results should not deter consumers from using the devices at home as long as they know the limits of the information a pulse oximeter can provide.
“My study is more about the emergency doctor who has to decide whether a patient should be hospitalized or taken to the intensive care unit,” said Dr. Sjoding. “For people at home, the pulse oximeter is still a worthwhile device and there is still valuable information to be found.”
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