Pulse Oximeter: Everything You Need To Know

pulse oximeter

Pulse oximeters have existed in the market for long. They are often found in hospitals, clinics and in the ownership of the people who have chronic lung conditions or certain respiratory disorders. They are also used when you go for high altitude treks. However, pulse oximeters started becoming a household name after medical experts shared an insight that this small, portable tool may prove helpful in detecting COVID-19, especially in people who are asymptomatic(do not show any symptoms).

So, what exactly is a pulse oximeter?

Pulse oximeter is a medical device that helps to check the oxygen levels of the blood in a non-invasive way that too within seconds. This is a completely painless technique, where a clip-like device called probe is placed usually on your fingers. The idea is to place it on any of the body parts that lie farthest to the heart, so some devices may need their probes to be placed on the earlobe, toe, forehead, etc.

The oxygen level calculated by a pulse oximeter is a percentage of how much oxygen your blood is carrying compared to the maximum amount it can carry. This percentage is called oxygen saturation levels (also called SpO2). This number should ideally be above 90-92%[1]. In case it is lower than that, you may need to consult your doctor.

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How does it work?

The device emits beams of light that pass through the body part you have clipped it on. These beams calculate the amount of oxygen by measuring the changes in the absorption of light. It also calculates your heart rate or pulse.

Expert Tip: To make sure that your oximeter is giving the correct reading, when you use your oximeter, count your pulse simultaneously. Same readings mean your oximeter is working well[2].

Can pulse oximeters be helpful in COVID-19?

Though most people (80%) get mild illness of COVID-19, the virus can cause some patients to get moderate or serious disease. COVID-19 can cause the lungs to be filled with pus or fluid. This is called COVID pneumonia. A person infected with COVID-19 may not see any symptoms of breathlessness in early stages even though their blood oxygen levels may be falling down vigorously. This is called silent hypoxia.

Using pulse oximeters can help in detecting this silent hypoxia and getting it treated before it takes a rough turn.

Should you buy a pulse oximeter?

A pulse oximeter acts as an early-detection device and can be a wise option to track your lung health regularly at home. Doctors often recommend patients with lung diseases or respiratory problems to invest in a good pulse oximeter. This helps them keep a track of how well their treatment procedure is working and whether their oxygen levels are optimum or not.

Buying an oximeter won’t do any harm unless you don’t depend on it. Always remember that pulse oximeter is just an equipment and can in no way replace the guidance and treatment of a doctor.

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What to look for when buying a pulse oximeter?

Accuracy: Before buying, make sure that the pulse oximeter doesn’t depict a deviation of more than +2 or -2. Though highly accurate, this deviation commonly exists. It means that if it reads 92%, your actual saturation may be anywhere between 90%-94%[2].

Apt for all patients: Certain pulse oximeters may not give proper results if the patient’s skin is extremely dark or if the finger size is very small or very large. Make sure to choose one that suits your needs.

Warranty, durability and reliability: All these are important. If you’re investing in something, make sure it is durable, has warranty and is reliable.

Easy-to-use, large and easy-to-use display: Since it all depends on accurate reading, the display should be clear and the fonts should not be confusing.

Alerts when finger is not placed properly: This can be an added benefit as not placing the finger properly can give inaccurate results.

When you might need to worry?

Pulse oximeter reading should always be compared with the person’s baseline oxygen level, which varies from person to person. The maximum value of SpO2 a healthy person can get is 100%. Your doctor can guide you on how to calculate your baseline oxygen level.

So, if a person has a baseline oxygen saturation of 90%, then it means that it is the highest value they can get. Hence, a pulse oximeter reading of less than 90% doesn’t necessarily mean that they need to rush to hospital, especially if they don’t show any warning signs that warrant to seek immediate medical care. These warning signs could include difficulty breathing, bluish discolouration of nails or skin. So, to sum up, if someone normally has a baseline oxygen saturation of 94%, and they are now reading at 90%, that’s much more concerning than someone who has a baseline of 90%

How to get accurate results?

There are certain factors that can interfere with the correct function of a pulse oximeter. Knowing about these can help you prevent falsely low readings. These may include:

-Artificial nails/nails that are too long that affect the placement of the pulse oximeter

-Dark nail polish

-Cold hands

-Bright light (such as the sunlight) when falls directly on the probe.

-Shivering or movement, making it difficult for the probe to pick up a signal

-Carbon monoxide poisoning, only an issue in patients following smoke inhalation from a fire.

-Having high levels of lipids in the blood

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Here’s how to rectify these mistakes to get accurate results

-Nail polish, artificial nails, reduced circulation & cold hands may affect readings. Rectify this by placing the probe at the base of the nail or by clipping the probe sideways or by clipping it on the earlobe[2].

-For accurate results, hand should be warm, relaxed and lower than your heart’s level. Also, make sure the blood is flowing through your hands properly[2].

-No smoking. Smoking increases the amount of carbon monoxide in blood and pulse oximeters cannot differentiate between oxygen and carbon monoxide. This can lead to inaccurate results, showing a percentage that’s higher than the actual oxygen level in your body[2].

-Inaccurate results may be obtained if the probe doesn’t work properly. In such a case, contact your doctor.

(The article is reviewed by Dr. Swati Mishra, Medical Editor)

Recommended Reads:

Is It Safe To Use Air Conditioners Amid The Coronavirus Pandemic?

Coronavirus And Respiratory Health: A Pulmonologist Answers Common Questions


1. Pulse Oximetry. American Lung Association. https://www.lung.org/lung-health-diseases/lung-procedures-and-tests/pulse-oximetry

2. Pulse Oximetry. American Thoracic Society. https://www.thoracic.org/patients/patient-resources/resources/pulse-oximetry.pdf

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