Pulse Oximetry & Oxygen Saturation: What Oxygen Therapy Users Need to Know

pulse oximeter

A pulse oximeter is a handy medical device that uses two frequencies of light – red and infrared – to determine the percentage of hemoglobin in the blood that is saturated with oxygen, otherwise known as your oxygen saturation level (O2 sat level). If you have ever been in a doctor’s office and heard your health care providers talking about SpO2 and SaO2, you might be left wondering, “What is SpO2 and how is it different from SaO2?” When oxygen saturation is measured using a pulse oximeter, it is referred to as SpO2, which stands for percutaneous oxygen saturation. When it is measured by way of a blood test known as an arterial blood gas study, it is referred to as SaO2, or arterial blood oxygen saturation.

What Is the Normal Oxygen Saturation Level?

Your oxygen saturation level is dependent upon a number of factors including your health condition, breathing rate and activity level. When measured by pulse oximeter, normal oxygen levels range between 95-100%. O2 sat values under 90% are considered low.[1]  When measured by arterial blood gas analysis, a typical healthy O2 saturation is generally between 75-100 mm Hg.

If one or both of your oxygen saturation readings fall below healthy O2 saturation levels, oxygen therapy will likely be recommended. Supplemental oxygen is generally covered by Medicare and other insurance companies when your oxygen saturation level, as measured by pulse oximetry, is at or below 88% at rest and/or your partial pressure of oxygen (Pa02), as measured by arterial blood gas study, is at or below 55 mm Hg.

Pulse Oximetry and Oxygen Therapy

A pulse oximeter can be a useful and reassuring tool if you are using home oxygen therapy. Not only will using a pulse oximeter at home help you better manage your health condition by allowing you to track your oxygen saturation throughout the day, but it will allow you to properly measure and adjust your oxygen flow rate – under the strict guidance and direction of your doctor only – according to your activity level. If you think you need to adjust your flow rate or the frequency or amount of oxygen you receive, talk with your doctor first and record your fluctuating O2 saturation. Never adjust your flow rate or the amount of oxygen you receive on your own.

Tips for Using Pulse Oximetry at Home

You can purchase a home oximeter either online, from a reputable supplier like Inogen, or from a medical supply company or pharmacy. Most models made for in-home use are inexpensive and easy to use so you can track your oxygen saturation level on your own. Simply attach the pulse oximeter probe to your finger and wait until the LED screen indicates your SpO2. It should only take a couple of seconds. The pulse oximeter will also measure and display your heart rate. You may want to record your daily SpO2 readings in a health journal or on a piece of paper to later show your health care provider, particularly if you are experiencing O2 sat fluctuations throughout the day. This way, your doctor can determine if your oxygen flow rate is meeting your needs properly during all of your activities.

Why You Should Know Your Oxygen Saturation Level

It is important to know your oxygen saturation level if you have a health condition that affects how much oxygen is in your blood. When your blood oxygen level is low, the cells and tissues of your body receive less oxygen, which means your body cannot function the way it should. This can negatively impact all your bodily functions and can also put a strain on your heart and your brain.[2]

According to the American Thoracic Society, most people need an oxygen saturation level of at least 89% to keep their cells healthy. Having a blood oxygen level lower than this for short periods of time is not believed to be dangerous. However, your cells and tissues may become damaged if your oxygen saturation level runs low many times or continuously.2 As such, anyone with a lower oxygen saturation or with an O2 sat that drops during certain activities, like exercise or sleep, should be monitoring their O2 saturation regularly. 

How to Obtain an Accurate Pulse Oximetry Reading

To get the most accurate O2 sat reading from your pulse oximeter, there needs to be enough blood flow to the hand and finger wearing the device. This means the best reading occurs when your hand is warm, relaxed and below the level of your heart.2

Factors that May Influence an SpO2 Reading

Most oximeters are reasonably accurate, giving you a reading of 2% over or 2% under what your oxygen saturation would be if measured by an arterial blood gas study.2 A pulse oximeter reading may be less accurate, however, if any of the following apply:

  • If you have poor circulation and/or cold hands.
  • If you wear nail polish or artificial nails.
  • If you are shivering or your hands are trembling.
  • If you have heart arrhythmias.
  • If you smoke.
  • If you have very dark skin.

Because SpO2 levels vary from person to person, the best way to ensure you are getting accurate readings is to begin by recording your oxygen saturation level at rest and at different activity levels over a period of time. Getting a baseline O2 saturation allows you to see your typical range throughout the day, which then allows you to see when there are any abnormal drops in your SpO2. Generally speaking, a drop of about 3 or 4% from your usual oxygen saturation is a concern.

Tips for Getting a Better Reading

An inaccurate pulse oximetry reading can be misleading and alarming. To get the best oxygen saturation reading possible, consider the following tips:

  • Make sure the probe is functioning properly and that it is securely attached to the finger.
  • If you are having difficulty getting a reading, try another finger or the opposite hand.
  • Warm your hands first by placing them inside a warm towel or under warm, running water.
  • Remove nail polish or artificial nails before taking a reading.
  • Do not smoke.

It is also important to know how to read your pulse oximeter correctly. Your pulse oximeter takes two readings, so it is critical that you know which is which and do not mix up the two. So, what are the two readings on a pulse oximeter? This device measures both your pulse rate and your blood oxygen saturation. Usually, your pulse rate appears on the device first and may be indicated by a small heart or another symbol. Your blood oxygen saturation, which may be labeled as your SpO2, will usually appear second. 

Keep in mind that a normal heart rate typically falls between 60 and 100 beats per minute, while a normal oxygen saturation rate should be between 95-100%. If you have a weak or irregular pulse, your pulse oximeter may not sense it properly. If your numbers are worrisome, try waiting a few minutes, making sure your hands are warm, and try again on another finger.[3]

Frequently Asked Questions: Oxygen Saturation

What is SpO2?

SpO2 is a measure of the amount of oxygen-carrying hemoglobin in your blood as measured by a pulse oximeter. This oxygen saturation measurement tells you whether your body is getting the oxygen you need and, particularly for people who struggle with maintaining normal O2 saturation, knowing your SpO2 could help prevent hypoxia and hypoxemia. 

What does oxygen saturation indicate?

Your oxygen saturation level tells you whether you are getting the oxygen you need for your body to function properly. A healthy person’s normal O2 saturation reading should fall between 94 and 99%. If your oxygen saturation is below 90%, it is likely that your doctor will recommend supplemental oxygen to improve your O2 sat levels and provide your body with the oxygen it needs. For people with chronic lung diseases like COPD, however, their normal oxygen saturation may be lower than the usual range. It is good to be aware of this, and it is still important to watch for significant fluctuations (specifically, drops of 3-4% or more). 

What causes oxygen saturation to drop?

Your oxygen saturation can drop for any number of reasons, depending on your overall health, activity level, location and breathing. Some very normal activities, like sleeping, can cause your O2 saturation to drop, though your O2 sat levels are likely to remain within the normal range. Changes in oxygen availability, as experienced in an airplane or at high altitudes, can also cause drops in your oxygen saturation level. If you have a lower concentration of hemoglobin, like those with iron deficient anemia have, you may also experience lower O2 saturation. Finally, illnesses and conditions that affect your breathing, your lungs’ ability to absorb enough oxygen or that cause problems with gas exchange within the body can cause significantly lower oxygen saturation.

What are the two readings on a pulse oximeter?

Pulse oximeters take two readings, measuring both your blood oxygen saturation and your pulse rate. Typically, the first number you will see is your pulse rate. While pulse oximetry is primarily used to measure your oxygen saturation, knowing your heart rate can help determine potential problems. In many cases, your pulse rate gives information about how much oxygen your body is receiving, as well as whether your heart and lungs are working the way they should and getting the blood they need. The second number you will see, your blood oxygen saturation, tells you how much oxygen the hemoglobin in your blood is carrying. This indicates whether you’re getting the oxygen you need throughout your body. A pulse oximeter can gives you a picture of your oxygen saturation and pulse rate right in that moment, which can be quite helpful information.[3]

Cited Sources

[1] “Hypoxemia (Low Blood Oxygen).” Mayo Clinic, Mayo Foundation for Medical Education and Research, 1 Dec. 2018, www.mayoclinic.org/symptoms/hypoxemia/basics/definition/sym-20050930. 

[2] Fahy, Bonnie, et al. “Pulse Oximetry.” ATS Patient Education Series, American Thoracic Society, Updated Mar. 2018, https://www.thoracic.org/patients/patient-resources/resources/pulse-oximetry.pdf.

[3] “How a Pulse Oximeter Works.” COPD Foundation, COPD Foundation, 23 Jan. 2020, www.copdfoundation.org/COPD360social/Community/COPD-Digest/Article/309/How-a-Pulse-Oximeter-Works.aspx. 

Additional Sources

Hegg, Jessica. “Understanding SpO2 and Normal Oxygen Levels.” HomeCare Magazine, Cahaba Media Group, Inc., 28 Sept. 2016, www.homecaremag.com/understanding-spo2-and-normal-oxygen-levels. 

Leader, Deborah. “Understanding Oxygen Saturation.” Verywell Health, About, Inc., 7 May 2020, www.verywellhealth.com/oxygen-saturation-914796.

16 thoughts on “Pulse Oximetry & Oxygen Saturation: What Oxygen Therapy Users Need to Know”

  1. Avatar Evelyn says:

    This was very informative. Thanks!

  2. Avatar Larry says:

    Very informative. Have a better understanding of the importance of oxygen levels in my body

  3. Avatar Joseph hynes says:

    When using pulse technology what would trigger the pulse oxygen. What would be the oximeter number have to be for the pulse oxygen to start

    1. Inogen Inogen says:

      Hi Joseph, Pulse-dose oxygen therapy is triggered when a patient inhales oxygen. When you breathe in, you create a vacuum which our sensors detect. Your doctor will determine what flow setting you should be on. Your oxygen level, what an oximeter detects, does not have an affect on the amount of oxygen you will receive. Only your flow setting will determine the amount of oxygen you will receive. To increase the amount of oxygen, you increase your flow setting. Again, your doctor will work with you to determine the appropriate flow setting based on your oxygen needs. For more information on pulse-dose oxygen please visit: https://www.inogen.com/oxygen-therapy/clinical-efficacy/

  4. Avatar Mathew says:

    Who else wants the best quality Pulse Oximeter?

    1. Inogen Inogen says:

      Hi Mathew, Portable pulse oximeters are simply and easy to use. For more information on the Inogen pulse oximeter, please visit: https://www.inogen.com/product/pulse-oximeter/

  5. Avatar Rosemary Fogle says:

    Does Medicare cover the cost of a Imogen Oxygen Concentrator and what is the process of getting one?

    1. Inogen Inogen says:

      Hi Rosemary, Depending on your medicare coverage, the region you live in, how long you've been on oxygen, and what portable oxygen concentrator (POC) is right for you, Inogen One may or may not be covered by Medicare. To have an Oxygen Specialist check your Medicare insurance and to learn more about the process, please call us at 1-800-374-9038.

  6. Avatar bev says:

    should the PRbpm number on an oximeter be similar to the number on the pulse rating line on a blood pressure monitor?

    1. Inogen Inogen says:

      Hi Bev, Under normal circumstances, the pulse rate on an oximeter and the pulse rate on a blood pressure monitor should be about the same. This is assuming the pulse oximeter is able to get a good signal from the finger you're putting it on and the person has a regular heart rhythm that is strong enough to register on either device. When the heart rate is irregular or erratic, the hands are really cold or there's another reason for a poor pulse ox signal, or the heart isn't pumping efficiently enough to give you a strong signal, the monitors may not record an accurate reading or they may register an error message. That said, the best way to take your pulse rate is to use two fingers – your index and middle fingers – and place them firmly on the skin above an artery, such as the radial artery on your wrist or the carotid artery on the side of your neck. Using the second hand on a clock, start counting for a full minute. If your heart rate is regular, you can just count for 10 seconds and multiply the result by 6. I hope this helps and please let us know if you have any more questions.

  7. Avatar Patricia Thurman says:

    I have had asthma since 1999 when I contracted blastohistocist. Last Aug 2018 I was dc with cryptogenic organizing pneumonia with a mass in right lung, steaming out if or close first mainstream bronchis. After 5million baths of 80mg steroids daily the mass is 70%smaller but still large enough to be hinder my rtf lung capacity. So many questions and I adore your articles but for now I want to know how my pulse ox in ER upon discovery of mass could have been 99%on room air but the ABG had a PaO2 of 59? I have been an RN for 38 years and I had to insist they do the bag. Of course after that can chest Cray and ct scan and a mass 5X7cm or maybe mms. Anyway even the thoracic surgery and pulmonologist sway that bag was wrong, altered, contaminated. Meanwhile I don't qualify for O2 because the guidelines are based on pulse ox reading. Thank you for listening and I h you will respond. I am sure you understand my inherent need for knowledge.

  8. Avatar Colleen says:

    My o2 monitor will read around 98% immediately after putting the probe on my finger. It will trend down and finally settle out at around 93%. Which reading do I use. I am breathing normally and sitting quietly.

    1. Inogen Inogen says:

      Hi Colleen, It’s best to use the reading after giving the oximeter a chance to stabilize. If you have any questions on the readings, please contact your physician's office or the pharmacy you go to.

  9. Avatar Linda says:

    Thank you! Verified my thoughts on the times I do not get an accurate reading from my patients. I will do the warm towel trick next time one of my pts has cold finger.
    Have a great week!
    Linda RN

  10. Avatar Shannon says:

    Hello my boyfriend was in the hospital a few months back with damage to his lungs and low oxygen levels of 87. Once he was release he was placed on home oxygen for a couple weeks. Its been almost 3 months since he has been off the at home care. When we check his reading on the finger pulse ox he will be completely random. Sometimes it will read 88, 96, 90, 93. And even if we leave it on a little bit he will go from 88-96-90 in a matter of a couple minutes. Is this something to be concerned about and what reading do we go by. I dont want to have to rush him to the hospital every time it reads lower. I wasnt sure if there could be another cause to it fluxuating so much or not. When we check him its normally just when we are sitting at home and not after any activities. I have checked myself as well just to see if there is a problem. But i stay consistant

  11. Avatar John says:

    Very informative and presented good data to measure oneself.

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