Pulse oximeters have been flying off the shelves during the COVID-19 pandemic. We decode how they work

Pulse oximeters have been flying off the shelves during the COVID-19 pandemic. We decode how they work

Back when TikTok reigned strong in India, there were hundreds of videos of people showing that wearing a mask did not inhibit oxygen saturation. One user Emily Lyoness, who has moderate persistent asthma, recorded herself wearing a spectrum of masks — from a reusable fabric mask to a P100 mask — and tested her oxygen levels by clipping a pulse oximeter to her index finger. The oxygen reading on the device wavered between 98 and 99.

People with COVID-19 often need oxygenation support, so this tool, a staple for many doctors, has become something of a necessity for the layperson. Oximeters have been flying off the shelves for many households’ first aid kits, largely because they are non-invasive, low-cost, easy to use, and effective at detecting hypoxemia (low blood oxygen levels).


Device must-know’s
It comprises a monitor which contains the batteries and display; a probe, which consists of light emitting diodes or LEDs and a light detector called a photo-detector. This probe senses the user’s pulse.

There are two important readings: the pulse rate, recorded as beats per minute (60 to 100 is the safe range); and the oxygen saturation of haemoglobin in arterial blood, the reading of which is recorded as SpO2). Normal readings range from 95% to 100%; anything less, and the user should get medical assistance from a doctor. If your oximeter has alarms, atypical readings will set them off.

The mechanism clips onto the user’s forefinger, though some oximeters have been known to be clipped onto one’s big toe or even the ear, depending on the model. According to the World Health Organization’s Pulse Oximetry Training Manual, one must use the oximeter with patience. Once clipped on, it requires about 10 seconds to get an accurate reading.

A pulmonologist based in Jaipur and chief editor of Lung India, Dr Virendra Singh points out that pulse oximeters are not COVID-19 detectors. He states, one cannot use the pulse oximeter as a sole detector for any respiratory issues. It is only meant to give readings for a small time interval