Pulse oximeters are becoming increasingly popular for home use, as people buy them to monitor if someone in the family becomes seriously ill with COVID-19.
The devices, which measure the percentage of oxygen in the blood when clipped on to a fingertip, have been praised by doctors because they can alert people who don’t realize they’re gravely ill to the fact that their body is struggling for oxygen.
One of the biggest worries with COVID-19 is when someone doesn’t realize their oxygen levels have dropped because they don’t actually feel unwell – a phenomenon sometimes referred to as happy hypoxia or silent hypoxia.
David Strain, a clinical academic at the University of Exeter Medical School and clinician at the Royal Devon and Exeter Hospital, tells HuffPost UK: “Ordinarily if your oxygen level drops below about 96%, you start to feel short of breath, you start to be aware that you’re struggling to get oxygen in.”
But one of the features he and other clinicians have witnessed with COVID-19 is when patients have had oxygen saturations of around 75-80% ― which ordinarily would make you gasp for air, as if you’d just run a marathon ― “but they’ve been sat on the ward completely fine with no symptoms and not telling us [that anything is wrong],” he says.
How do pulse oximeters work?
A pulse oximeter works by shining a light through a person’s fingertip (or earlobe) and calculating how much oxygen is in the blood.
A normal reading would usually range from 95-100%.
What kind of reading is a red flag?
Experts suggest reaching out to a health care provider if your reading is lower than 95%, or if the number continues to be lower than your usual reading. Some people with lung conditions, for example, might routinely have lower readings but if their percentage drops more, they should seek help.
The U.S. Centers for Disease Control and Prevention recommends going to the emergency room or calling 911 if your reading is at 90% or less.
Nigel Watson, chief executive of Wessex Local Medical Committees, told the BMJ in October 2020 that evidence is fairly strong that if oxygen saturation falls to 94% or 93%, the mortality risk with COVID-19 increases to around 13%. If it falls below that level, the risk increases to about 28%.
Why are pulse oximeters useful?
It’s vital that people seek medical assistance for low oxygen levels. If left unchecked, it could cause further damage to the body.
“When the oxygen in the blood starts to fail, if we can then put oxygen on, it means we can protect the rest of the body from the effects of low oxygen,” Strain says, “and hopefully that may be one of the steps of preventing long COVID and some of the longer term symptoms. Some of the symptoms of long COVID are because of the fact the brain, or the body, has suffered for periods without oxygen.”
Who might need a pulse oximeter?
Most people who get COVID-19 have very few complications, meaning they will be able to recover at home without the need for pulse oximeters.
However, there are a number of patients who might benefit from such devices. For instance, some people who don’t need immediate hospital attention but are at high risk of developing serious symptoms from COVID-19 ― like those with underlying health conditions. Some people might also be at risk of developing infections if they stay in hospital, so the safest option is to send them home with a pulse oximeter.
Prices can vary widely and how well they work might also vary, with different devices offering different readings.
What are the downsides?
Strain explains that the devices used in hospital are all validated and “have a very good track record.” They also cost a lot more than the ones you’d find in your local pharmacy, so the results might be less accurate.
The machines may also work less well monitoring oxygen levels in people of color. One study found the devices can provide misleading results in more than 1 in 10 Black patients.
Researchers analyzed readings from 1,333 white patients and 276 Black patients who were hospitalized earlier in 2020. They found pulse oximeters overestimated oxygen levels 3.6% of the time in white patients, but got it wrong almost 12% of the time in Black patients, the New York Times reported.
“Given the widespread use of pulse oximetry for medical decision making, these findings have some major implications, especially during the current coronavirus disease 2019 (COVID-19) pandemic,” the researchers concluded.
“Our results suggest that reliance on pulse oximetry to triage patients and adjust supplemental oxygen levels may place Black patients at increased risk for hypoxemia [a low level of oxygen in the blood].”
This post originally appeared in HuffPost UK and has been adjusted to reflect U.S. guidance.
Experts are still learning about COVID-19. The information in this story is what was known or available as of publication, but guidance can change as scientists discover more about the virus. Please check the Centers for Disease Control and Prevention for the most updated recommendations.