What Is Pulse Oximetry and How to Measure It At Home

What is a Pulse Oximeter?

The pulse oximeter, also sometimes referred to as a Pulse Ox, is a small electronic device that looks like a clip. It is often attached to the fingers but can be attached to other body parts such as the earlobe, toes, foot, nose, or even the forehead. The device, available in both disposable and reusable forms, measures the body’s oxygen saturation level or the level of oxygen in the blood. A pulse oximeter can show exactly how efficient your body is at carrying oxygen to the body parts furthest from the heart, and it can reveal changes in your oxygen saturation level.

Doctors often use the device in their clinics, and you might notice it when visiting hospitals and emergency rooms. In a formal healthcare setting, the device allows doctors and nurses to determine if they need to administer extra oxygen to their patients.

People who have to check their heart and breathing conditions or a regular basis are likely to have a pulse oximeter at home for personal use. 

Why Do You Need Pulse Oximetry?

According to Johns Hopkins Medicine, a pulse oximeter is necessary for use during surgical procedures and in conjunction with ventilator use, lung medicine, and sleep studies. For patients with lung conditions who are taking medicine, a pulse oximeter is also used to determine whether the medication is working as expected. During surgery, pulse oximeters track the patient’s oxygen level to ensure that the patient is receiving an adequate level of oxygen while sedated. Pulse oximeters can also help track oxygen levels for people suffering from sleep apnea, a disorder in which breathing suddenly stops and starts during sleep. Individuals with heart and lung conditions and anemia also make use of pulse oximeters to monitor their health.

How Does a Pulse Oximeter Work?

When we breathe in oxygen, that oxygen is carried by our blood to the rest of our body. This is primarily accomplished by hemoglobin molecules that travel through our blood vessels. Hemoglobin without oxygen is called deoxygenated hemoglobin, and hemoglobin with oxygen is called oxygenated hemoglobin. SpO2, or blood oxygen saturation, refers to the percentage of oxygenated hemoglobin in the body. 

A pulse oximeter, which is non-invasive and painless, can measure SpO2 by differentiating between the light absorbed in oxygenated and deoxygenated blood. It follows Beer’s Law, which states that the concentration of a solution is proportional to its absorption of light. It also follows Lambert’s Law, which states that the intensity of transmitted light is proportional to the distance the light has to travel.

When used on the fingertip, a pulse oximeter uses a cold light source to send two wavelengths of light through the fingertip, making it seem red. The light that pulse oximeters use is generated with LEDs, or light-emitting diodes, normally found in electronics. The LEDs send red and infrared wavelengths, but the two lights are never lit at the same time. The oximeter then analyzes the light that has passed through the fingertip, allowing it to rapidly measure how much light has been absorbed. It ignores any room light and light absorbed by the tissues surrounding the arterial blood because skin and surrounding tissues do not pulsate.

The pulse oximeter gathers these measurements without the use of an actual blood test. The pulse oximeter’s screen will then show the reading in the form of pulse rate and SpO2.

Pulse Rate and SpO2

A person’s pulse rate is calculated as the number of times the heart contracts per minute. According to the American Heart Association, a human’s resting pulse rate should be between 60 to 100 beats per minute (bpm), but a pulse rate lower than 60 is common among people who are active or who may take medicines that slow their pulse.

A person’s SpO2 reading, on the other hand, is considered normal if it is 95% or greater. If one’s SpO2 is at 92% or less, their blood may be poorly saturated with oxygen, causing multiple symptoms, including shortness of breath and chest pain.

A pulse oximetry test is completed in only a few seconds, but it is essential to stay still while the oximeter is attached to the body, as motion can alter light levels and cause the device to provide an inaccurate reading. 

Are There Any Risks Involved with Pulse Oximetry?

The American Lung Association states that there are no known risks or dangers of using a pulse oximeter, at least “when the values are reviewed and monitored by a competent health professional.” However, the risks that pulse oximetry poses are quite minimal, such as skin irritation from adhesive or an incorrect reading if the pulse oximeter falls off of the body. Risks encountered will depend on each person’s health, so individuals must speak to their healthcare professional while monitoring their pulse oximetry.

Pulse Oximeter Use Today

In an opinion piece for The New York Times, Dr. Richard Levitan, an emergency room physician, wrote that pulse oximeter screening could detect some forms of pneumonia and respiratory illness, leading to early treatment. He noted that, by the time patients feel shortness of breath, they have already had pneumonia for days.

Using a pulse oximeter at home makes sense if you want to regularly monitor your blood oxidation level for potential signs of illness, just like how many households have their own thermometers to detect fever. However, what is most important is that a pulse oximeter is not used as a substitute for consulting official medical staff.