Covid-19: Pulse oximeters lower mortality after positive diagnosis, study finds

New research from South Africa has found that using pulse oximeters to check oxygen saturation levels following a Covid-19 diagnosis saves lives. The researchers gave 8,115 high-risk patients, including the elderly and those with chronic illness, a pulse oximeter each to check their oxygen levels at home after being diagnosed with Covid-19.

A pulse oximeter clips on the finger and measures blood oxygen levels. Many people learned of the device in the early days of Covid-19 after doctors pointed to “silent hypoxia” — a form of oxygen deprivation that occurs so slowly that patients don’t notice — in some Covid-19 victims. Often, these patients are so oxygen deprived and ill by the time they are taken to hospitals that they need ventilator support.

The South African researchers gave the Covid-19 patients in their survey pulse oximeters and regularly followed up with them to ensure that they were correctly using it. The researchers asked the patients to record their saturation level twice daily and told them to get in touch with doctors if the reading fell below 95%.

For a reading below 90%, they were told to immediately go to the emergency room. The patients were all asked to seek emergency medical care if they had trouble breathing, regardless of the oximeter reading.

The researchers then compared the study group with patients in the general population between March and October 2020. During the study, 544 of 38,660 patients succumbed to Covid-19. The deceased included 49 from the study group as well.

However, the risk of death was 52% lower among those instructed to monitor their oxygen saturation at home. Based on the country’s overall mortality rate, 95 people in the study group were expected to die. But the pulse oximeter appears to have saved 46 of those.

Shirley Collie, one of the authors of the study, told The New York Times: “I think it’s important to know that a pulse oximeter makes a difference.”

“You’re monitoring your oxygen because the timing of when you get to the hospital makes a huge difference on your clinical outcome.”

The oximeter’s magnitude of benefit startled even Dr. Richard Levitan, among the first to warn about silent hypoxia. Calling the findings “astounding,” Dr. Levitan told The New York Times: “It’s exceedingly rare in medicine to show such a huge difference in treatment, particularly with such a complicated disease.”

“All of this happened with different management, in different hospitals, while the pandemic was unfolding. To have a 50% mortality difference is phenomenal. We almost never see a benefit as large as that.”

Speaking of the lower mortality rate among the study group, the researchers said constant monitoring at home allowed the patients to seek medical care sooner. Among the patients who visited hospitals, those using pulse oximeters at home displayed lower inflammation when measured by a C-reactive protein test.

The study was conducted before the availability of vaccines. Vaccinated people are at a lower risk of serious illness or hospitalisation. However, some vaccinated people, especially those in high-risk groups, can develop severe illness. According to Dr. Levitan, even those who have completed their vaccination programme should use pulse oximeters after being diagnosed with Covid-19.

“Your odds of getting seriously ill are low, but I’ve hospitalized patients with Covid pneumonia who are vaccinated,” he said.

“Across all of medicine, with earlier treatment people do better. If you come in early and spend three to five days in the hospital, that’s very different than coming in late and landing in the ICU.”

Pulse oximeters also lower anxiety after a Covid diagnosis. Collie said she had first-hand experience after suffering from a breakthrough infection in the summer, despite completing Johnson & Johnson’s vaccination course.

She had tightness in her chest and a cough, but regularly monitored oxygen levels at home. “It does give a lot of comfort in terms of checking where you’re at,” she told The New York Times. “This monitoring can modify your risk of a really bad outcome. I think it’s hugely empowering.”

The oxygen saturation reading for most healthy people is around 95% to 99%. Some people, who have pre-existing medical conditions, can have a lower reading. Doctors suggest seeking medical advice if the reading dips below 94.

However, the device’s accuracy can vary, especially in people with dark skin. A study of Black patients found that the reading was not accurate in 10% of cases. Even dark nail polish can interfere with the device’s reading.