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What Is a Pulse Oximeter and Can It Help Against COVID-19?

Neha Pathak, MD - Blogs
By Neha Pathak, MDBoard-certified internistApril 28, 2020
From the WebMD Archives

Many doctors in emergency rooms are noticing a very concerning finding: Some COVID-19 patients have dangerously low levels of oxygen, but appear completely comfortable. This is being called “silent hypoxia.” While other conditions can cause silent hypoxia, the number of people with COVID-19 presenting this way is making some doctors rethink how we manage COVID-19 patients before they need emergency care.

Some are recommending that COVID-19 patients monitor their oxygen levels at home with a pulse oximeter. A pulse oximeter is a small device that clips onto your finger and measures the oxygen in your blood. After placing the clip on your finger, you get a heart rate reading and blood oxygen level reading (it’s a little more complicated than this – what you are actually getting is a percentage of the oxygen saturation in your blood…. but you get the point).

What is a normal oxygen level?

A normal oxygen level measured by a pulse oximeter is around 97%, unless you have other underlying health problems like COPD. Doctors start to worry when this level drops under 90% because this can affect the amount of oxygen going to your brain and other vital organs. People can experience confusion and lethargy at low levels. Levels below 80% are considered dangerous and increase the risk of organ damage.

What causes “silent hypoxia” in COVID-19?

The short answer is we don’t really know.

The oxygen level in your blood depends on multiple factors. It depends on the amount of oxygen in the air you breathe in and the ability of that oxygen to make it across tiny air sacs at the very ends of the lung into the blood stream. With COVID-19 patients, we know that the virus can damage the tiny air sacs allowing them to fill up with fluid, inflammatory cells and other material that can block the flow of oxygen into the blood.

Usually, people with low oxygen levels appear uncomfortable, sometimes even to the point of appearing to be gasping for air. This can happen if the windpipe is blocked or if too much carbon dioxide builds up in the blood triggering your body’s response to breathe faster to breathe it out.

It’s not really clear why some COVID-19 patients have such low levels of oxygen without appearing uncomfortable. Some experts think it has to do with damage to the blood vessels in the lungs. Normally, when parts of the lung are damaged, blood vessels constrict (or get smaller) to force blood to go to areas of the lung that are not damaged, keeping up the oxygen levels. With COVID-19, this response may not be working, so blood flow continues even to areas with damaged lung, where oxygen can’t make it across to the blood stream. There’s also the newer finding of “microthrombi” or tiny blood clots that can block oxygen flow into the blood vessels in the lungs which may be causing the drop in oxygen levels.

How can measuring oxygen levels at home help?

Doctors are divided on whether home monitoring of oxygen levels with a pulse oximeter may help because we don’t have clear evidence that is can make a difference in the outcome. In a recent opinion piece for The New York Times, one ER doctor recommended home monitoring for patients with COVID-19 because they believed that information about oxygen levels may help some people seek care earlier if their oxygen level begins to drop.

What are the benefits and drawbacks of using a pulse oximeter at home for COVID-19?

Checking oxygen levels at home is beneficial mostly for those who have diagnosed COVID-19 or symptoms that are highly suggestive of infection. Monitoring your oxygen levels can provide reassurance as symptoms of shortness of breath ebb and flow during the course of the illness. If you notice your levels dropping, it can also help you know when to reach out to your doctor for help.

It is important to be aware, though, that it’s possible to get false alarms from an oximeter. Along with the risk of device malfunction, small things like wearing dark nail polish, false nails, and having cold hands can all throw off the reading, and the readings can change a little depending on your position. So, it’s important to track the trend in your levels, not to react to a single reading.

Because many people are now buying these devices, you may notice short supplies of pulse oximeters. If you do choose to buy one, you can check the FDA website to help you decide what oximeter to buy. Stick with the clip-on versions. Other types may use fancier technology, but they may give inconsistent, unreliable information.

What can be done if I have a low oxygen level at home?

If you do notice your oxygen levels dropping, contact your doctor for advice. If they recommend emergency or hospital care, there are many strategies that the health care team can use to increase your oxygen level. Doctors are not rushing to put people who look relatively comfortable onto breathing machines (ventilators).

Many people are being given oxygen through nasal tubes or facemasks and are also being placed in what’s called “prone positioning.” This is basically where you are put on your stomach or side to help open up air sacs at the bottom and back of your lungs to allow for more oxygen exchange into the blood stream.

The key to taking care of yourself at home with COVID-19 is to monitor your symptoms. If you choose to use a pulse oximeter, do not rely on it to measure your condition. Keep a close eye on all your symptoms and be sure to contact your doctor if you experience worsening symptoms like weakness, confusion, chest pain, shortness of breath, regardless of your oxygen levels.

For more about COVID-19 and other public health concerns, you can follow Dr. Pathak on Twitter @NehapathakMD


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About the Author
Neha Pathak, MD

Neha Pathak, MD, is a board-certified internal medicine doctor and part of WebMD's team of medical editors responsible for ensuring the accuracy of health information on the site. Before joining WebMD, Pathak worked as a primary care physician at the Department of Veterans Affairs and was an assistant professor of medicine at Emory University in Atlanta.

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