Dear Doctor: What is “pulse ox”? My sister keeps telling our mom and dad (they’re 74 and 77) that they should be keeping keep track of it, especially right now. She hasn’t been too good at explaining why, or even what it does, though. Can you help?
Dear Reader: The term “pulse ox” is short for pulse oximetry. It’s a simple, painless and noninvasive test that measures the oxygen saturation of your blood. More specifically, it reveals how much of the hemoglobin in the blood is carrying oxygen to all of the tissues of the body.
Oxygen saturation is measured with a small clip-on device that looks a bit like a short, chubby clothespin. Known as a pulse oximeter, it has a hinge on one end that allows it to open and gently attach to a part of the body that’s translucent enough to let light pass through. Typically it’s a fingertip, but it may also be an earlobe or even a toe.
The device is equipped on one side with light-emitting diodes, which send out two different types of light, red and infrared. On the other side is a sensor, which measures how much of each type of light has traveled through the tissue. Hemoglobin that is carrying oxygen will allow more red light to pass through. When hemoglobin isn’t carrying oxygen, it allows more infrared light to pass through. The sensor measures this and comes up with a percentage to express blood oxygenation. Readings that range from 95% to 100% are considered normal. Blood oxygenation below 90% is considered low.
Oxygen saturation is a metric of good health, and pulse oximetry has a number of applications. It’s used to identify and monitor respiratory conditions and disorders, to evaluate how well someone handles increased activity levels and to assess the health of people with conditions that affect blood oxygen levels, such as heart attack, congestive heart failure, chronic obstructive pulmonary disease (COPD), asthma and anemia, to name just a few.
Recently -- and perhaps this has played a role in your sister’s advice to your parents -- new information about COVID-19 pneumonia has pushed pulse oximetry into the news. Instead of being alerted to the onset of pneumonia through symptoms like chest discomfort and painful and labored breathing, a number of COVID-19 patients are experiencing a silent onset of the disease. Even with oxygen saturation levels of 80% and lower, they aren’t in physical distress. What has become clear is that by the time breathing problems do show up, these patients are often in critical condition. As with so much about COVID-19, the reason for this silent onset is not yet understood.
Some physicians working with coronavirus patients are now suggesting that people with seemingly mild cases of the illness monitor their oxygen saturation levels in order to seek treatment as soon as oxygen levels begin to drop. But the accuracy of oxygen saturation readings depends on the device and on proper technique. Depending on the error, this can cause undue alarm or a false sense of security.
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