Before the coronavirus pandemic, most Americans had heard about pulse oximeters only via TV shows where EMTs shout out a patient’s “pulse ox” — or measure of oxygen in the blood. But when multiple news reports mentioned pulse oximeters as a possible tool in the limited arsenal of weapons against covid-19, the low-cost medical devices started flying off shelves almost as quickly as toilet paper.
Typically clipped over a finger (though a toe or ear lobe works, too), a pulse oximeter transmits light from sensors on one side of the device through the body part to sensors on the other side. In about 15 seconds, it calculates how much oxygen is being transported through the person’s bloodstream and displays the results as a percentage (abbreviated SpO₂). Doctors consider a SpO₂ reading of 94 percent and higher to be normal. Low levels of oxygen in the blood (hypoxemia) can lead to low levels of oxygen in the tissue and organs (hypoxia), which can lead to death.