Pulse oximeter: How it works, use, reading chart

Pulse oximeter: How it works, use, reading chart

Pulse oximeter definition

A pulse oximeter is a medical device that helps to measure the saturation of oxygen in the blood and pulse rate. It is a small, portable, and clip-like device, runs on a battery. In this pandemic era, it becomes one of the must-have health devices at home as like a thermometer.

However large screened and different models also available but this is mostly used in professional setups like in hospitals, emergency care units, etc. Such professional devices come with a large screen and have multiple jobs like can also take ECG graphs. This machine is connected to the body with different kinds of probes.

How pulse oximeter works?

Spectrophotometry is the working principle behind the pulse oximeter. When a probe or clip-like pulse oximeter is placed on the fingertip, toe, or earlobe it throws visible red light which is called as light emitter part of the device. This light passes through the blood and on the opposite side it is detected by another part of the device known as a photo-detector and likewise, we obtain oxygen saturation.

Our red blood cells carries oxygen in all parts of the body. Light sensors in the device detect these red blood cells carrying oxygen also known as oxygenated blood and can also detect deoxygenated blood. The oxygenated blood looks darker than deoxygenated blood and light sensors are highly sensitive to this change in the blood. It measures variations of light absorbed from oxygenated and deoxygenated blood and shows in form of reading on the device screen.

How to read pulse oximeter?

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When you keep the pulse oximeter on a fingertip, the screen shows you 2 readings on it. One is for oxygen saturation and is marked usually as %Spo2. This indicates your oxygen levels in your blood in percentage.

Another reading is marked with a heart symbol or PRbpm. This reading indicates heart or pulse rate. In PRbpm PR means pulse rate that is your heart rate, at which rate your heart is beating and bpm means beats per minute. So this reading measures how much time your heart beats in one minute.

Pulse oximeter reading chart

Now you understand very well about the 2 readings on the device screen. The next question that arises in our mind is – What are the normal spo2 and PRbpm?


In a normal healthy individual oxygen saturation is more than 95% that is between 95% to 100%. It may have variations of 2% than the actual level in our body. For example, if your oxygen level reading on the device is 95%, then it may be actually 93% or 97% in our body.

Sometimes in COVID-19 patients, there may be low oxygen saturation but patients don’t have any symptoms regarding this. This is also called as Happy Hypoxia syndrome in COVID-19. In this case, you should also consult the doctor for any emergency care needed.

when we talk about oxygen levels in some health conditions like COPD, chronic bronchitis, and other lung diseases it may constantly remain below normal limits. In these conditions, it may range between 88% to 95%. Any abnormal reading with symptoms such as difficulty in breathing or shortness of breath, confusion, chest pain, etc., you should consult health care personnel immediately for further treatment.


In a normal healthy individual, the normal pulse rate is between 60 to 100 beats per minute. When your beats very fast that is more than 100 bpm is called tachycardia. It may be caused by many health issues such as anxiety, stress, overuse of alcohol, caffeine, or tobacco, fever, imbalance in electrolytes, adverse effects of some medicines, etc. After vigorous physical activity or exercise, it may also increase above 100 bpm, but it settles down quickly after rest.

when our heart beats slow that is below 60 bpm is referred to as bradycardia. In athletes, it may be normal. But in others, some causes for it include adverse effects of medicines, imbalance in electrolytes, obstructive sleep apnea, etc.

What are the different uses of the pulse oximeter?

The device has different uses such as…

  • Evaluation of various health diseases like COPD full form is Chronic Obstructive Pulmonary Disease, lung diseases like lung cancer, asthma, pneumonia, chronic or acute bronchitis, heart diseases like myocardial infarction or heart attack, congenital heart diseases, anemia, etc. In all these conditions there may be abnormal reading on the pulse oximeter.
  • It helps to access the efficacy of medications. For example, it evaluates the condition of a patient with asthma after giving medicine to relieve spasms of bronchi, whether it is effective or not.
  • It is helpful to access oxygen saturation on a patient who is on a ventilator.
  • To access patients with shortness of breath or breathing difficulties.
  • To evaluate oxygen saturation for the patient going for surgery or during and after surgery when the patient is under sedation.
  • To monitor how much effective the given oxygen supply is.
  • To evaluate oxygen levels and pulse rate for tolerance to physical activity.
  • It is helpful for sleep apnea patients to evaluate breathing patterns.

How to use a pulse oximeter properly?

To obtain the correct reading first of all put the pulse oximeter on the fingertip, toe, or earlobe. Measurement from a finger is the most suitable site.

Before placing on the finger remove nail paint if any. Dry the finger if it is wet and after placing it don’t put pressure on the device to measure accurate results.

After placing on finger click button on the device to power on it. After power on the device will take reading within few seconds.

Keep it in the position until 30 to 60 seconds to observe any variation in the reading.

Note the result shown on the device screen. If there is abnormal reading and other symptoms in your body please contact your doctor for further advice.

In some cases, the device probe is kept in the position for a certain period of time to monitor oxygen levels and to evaluate the condition of the patient whenever required.

Usage risk of pulse oximeter

A pulse oximeter is a painless, non-invasive, and safe device. Ideally, no risk involved in using it.

During continuous usage, there may be pressure on the finger or pinch like pain due to the clipping effect of the device.

Sometimes for longer use, it may be fixed with an adhesive bandage, which may irritate your skin. Otherwise, no other risk is involved in its use.

Pulse oximeter for children

The same pulse oximeter can be used for kids also. Children have thin fingers. So it should be placed on the thumb, toe, palm, or feet. But for accurate results, both the ends that are light emitter and photo-detector part must face each other in opposite direction.

A pulse oximeter for kids is also available in the market. Have a look at it here on Amazon.

Pulse Oximeter FAQs

Can a pulse oximeter measure respiratory rate?

No. It doesn’t measure respiratory rate. It is made to obtain heart rates and oxygen saturation. But many respiratory diseases and increased respiratory rates may affect pulse rate and spo2 that will reflect on the device. Otherwise, it directly doesn’t indicate respiratory rate.

Can a pulse oximeter detect heart problems?

Heart attack and other heart problems may affect pulse rate and oxygen saturation. But only on this basis, heart attack and other heart diseases can’t be ruled out. We need further evaluation and investigations to detect these problems. We can take quick emergency actions if there is major abnormal reading on the pulse oximeter and having symptoms of a heart attack.

Can pulse oximeter give false reading?

Pulse oximeter reading may not be accurate or may show errors in certain conditions such as…
If the device is improperly placed.
If there is thick nail polish, tattoos, or henna dye on the finger or on the placed part.
During measurement, there is much movement of the finger or much trembling of hands. So keep your finger steady while using the device.
In heavy cold, there may be wrinkling of finger skin or if your fingers are wet, there may not be accurate results. So dry and warm up your hand before taking a reading.
Before using the device confirm that it is in working condition and the battery is not drained.

On which finger pulse oximeter should be placed?

Many people ask questions about the placement of a pulse oximeter on the left or right hand or on different fingers. The index finger has a blood supply from the deep palmer artery which is branched from the radial artery. While the middle finger is supplied by both ulnar and radial artery branches. So, there may be a slight highest average spo2 in the middle finger. But this change is not significant. Mostly in every finger spo2 level will be the same without a major difference. You can read a detailed study here regarding this, which explains what will be the difference in spo2 measurement in different fingers and hands.

Which pulse oximeter to buy?

Only buy pulse oximeters from reliable manufacturers. You can take advice from your doctor about this. Here are some pulse oximeters on Amazon with good ratings and good customer reviews.

Note: If you buy products from the links given in this article, we may have little commission. Please ensure product reliability and all details before purchasing it.

This article is for information purposes only. Please take the advice of health care experts before taking any action.

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