How a Pulse Oximeter Works

Dear COPD Coach, My husband has been diagnosed with COPD but has not yet had pulmonary function tests to determine the type/severity. We purchased a pulse oximeter to monitor his 02 levels (he was sent home from the hospital on 4 liters but is now reduced to 2). My question is, do you take the first reading that comes up when the pulse oximeter is put on or do you wait 15 seconds and use that reading? Also, I would like to say this is one of the most informative websites I have found on COPD and I certainly appreciate the support it provides.

—Curious about Pulmonary Function Testing

Dear Curious, A pulse oximeter can be a very useful tool for a COPD patient, providing you use it correctly and realize it has limitations.

The pulse oximeter measures two distinct things: The first number that comes up is most often the pulse rate. Usually this number is marked by a small heart. The second number that comes up is the level of oxygen in the blood. Both numbers are needed to assess your present levels.

At this point, it is important to discuss the limitations of the device. The pulse oximeter only gives you a limited amount of information, and is in reality just a snapshot of your functioning at that particular time. For example, it does not tell you the concentration of CO2 (Carbon Dioxide, the waste product of your breathing and something that is not healthy in high levels) in your blood stream. This means that you could be retaining a large amount of CO2, which could be limiting the amount of usable oxygen in your blood.

In other words, the pulse oximeter is not a substitute for more extensive tests that give you and your doctor a better idea of your exact pulmonary function.

The second limitation is that all pulse oximeters “are not equal.” Less expensive units often do not have the accuracy of other more expensive units. It is never a bad idea to take your unit with you to your doctor’s appointment and compare the readings with his unit. I was at a trade show one time and a company there was selling very inexpensive pulse oximeters. I tried 6 different units and never once was able to get a reading! In order to get an accurate oxygen saturation reading, the device must sense every beat of a fairly strong pulse – if your pulse is irregular, weak or not being sensed for some reason, the pulse oximeter may show an oxygen reading, but it is not necessarily accurate. It is also important to keep in mind that many things can affect the reading, such as nail polish, cold or heat, or even which finger you are using it on. If your hands are cold, warm them before taking a reading. If you get a suspicious reading, take it again, or maybe use another finger.

Now for the question of understanding the readings. Ideally, a reading should show a relatively normal heart rate (between 60-100 beats per minute) and an oxygen reading in the middle to high nineties. If the heart rate is higher than usual, but the oxygen number is normal, it means that the heart is working harder to keep your saturations high which could indicate a problem if it remains that way on subsequent readings. If the heart rate is high and the oxygen reading is low, it could also indicate a problem. The important thing is to not panic! Wait a few minutes, and take another reading. If the abnormal readings continue, and you are feeling out of breath, contact your doctor.

To get more information on pulse oximeters, check out our educational materials, which has a lot of good information that can really help you!

Thanks for writing, and be sure to stay in touch!

-The COPD Coach

Coaches Corner is aimed at providing information for individuals with COPD to take to your doctor, and is not in any way intended to be medical advice. If you would like to submit a question to the Coaches Corner email us at coachescorner@copdfoundation.org. We would love to hear your questions and comments. You can address your emails to The COPD Coach.

This article was reviewed by Senior Director of Community Engagement and COPD360social Community Manager, Bill Clark, as well as certified staff Respiratory Therapists on January 23, 2020.

41 Comments

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valiejean

Hi. Well, I"m not technical but I have been using a pulse oximeter for a decade now. When I am exercising or out of breath if my sats fall below 90 I stop what I'm doing and start pursed lip breathing. I continue this until I reach 90 again. I have had very severe COPD for a decade now, since I was 55.
I purchased mine for forty dollars from a pharmacy. When I go to the doctor it is alway very close in numbers.
Best advice ever. Keep exercising and build your muscles to help you breathe. I know, you say I'm out of breath. So was I, but the more I work on it, the better it becomes.
Good luck and keep on keeping on.
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- Jean IA State Captain
  
  Use PLB all the time and you'll find you may not go below 90 at all.
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- Pieit
  
  Hi Jean, I have the same problem,my oxygen drops if I am exercising or running around like a crazy woman,which is always. Question is when it falls to 89 or 88,do i need to put on oxygen or just do pursured breathing. It always comes back up in a couple of seconds/ minutes.Thank you
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- pammy68
  
  I also work out and the better you exercise and build especially your upper muscles the better able are you lungs to take in and release a breath. Having strong legs is like having a 2nd heart, they help the blood get pumped up.
  
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vansmith

In answer to the question originally posted above: "My question is, do you take the first reading that comes up when the pulse oximeter is put on or do you wait 15 seconds and use that reading?" , yes you should wait for a brief time for it to settle ... and yes 15 seconds sounds reasonable if rested. If your husband has been moving around just prior to taking the reading, there can be quite a time before you see his 02 level come back up on resting. Remember your pulse ox reading is always playing catch up - eg. if I jump up and down for 10 seconds and immediately take a reading it can look like my usual rested reading for 30 seconds or so before it dips for a few seconds before climbing back up again - hope that makes sense ;) From your question though I would say you likely already have a good idea of how to use it :)
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- Caroline West Virginia State Captain
  
  It depends on the oximeter, but the first reading is usually not accurate. I have one that no matter what it comes up 88 and then settles into the correct reading.
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Ken Benson-California Lung Health Advocate and State Captain

A detailed look at how a pulse oximeter works.

http://www.howequipmentworks.com/pulse_oximeter

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- SSK
  
  Thank you, Ken
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di545

Thanks to the COPD coach for a very informative explanation. I like the way you explained the heart rate verses the saturation. Sometimes my heart rate is high and my oxygen is in the 90's but I am having hard time breathing. This helped me understand better, really like this board.

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Shanna Kronk

I love you question and the information provided. I tried buying an OTC pulse ox meter & had to return it due to poor accuracy. Do the research & compare with your doctor's for accuracy. Better to spend a little more on a better unit that's more accurate.
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Merry

I am not promoting a certain very popular shopping website that starts with A and often proceeds the word "jungle," or "river," but I found that a good place to shop for a pulse oximeter. Not only do they have a variety to choose from, but you can also see which ones have been highly rated by other purchasers.

I got one from there for under $30 and it seems to provide results very similar to the doctor's office.
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philoz

I got one on e-__y very resonable
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I do think waiting 15 seconds sounds like a good average rule of thumb. Typically I only check when exercising. Soon as I see the same one or two numbers repeating I go with that result. I look for the consistency. For example when I first put in on, it might ready 97 or 98... I wish:) Within a couple of seconds I might see it alternating between 93 and 94 or 91 and 90. As I breathe (big plb breathing) I will see the number change, I typically see two repeating numbers rather than one steady number. I wait for a consistent result and go with that.

Also make sure the lanyard is not between your finger and the light, I've done that more than once and wondered why my O2 was so incredibly low.
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edpe77

Thanx for the discussion. I took particular not of the "pulse" #'s I frequently see a pulse of 120 w/O2 either in the mid 90's or near 88. But like you said, take another reading and/or wait for the pulse to settle down. I also find that PLB helps normalize both #'s.
ed

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Michael55

My resting pulse/ox never gets above 96. With minimal movement or exertion, like walking around the house, fixing a meal, or washing dishes, it drops to around 87. Walking to the car from the house, it drops to around 84. I take a breathing treatment with my Nebulizer before I leave the house when going to appointments or to the store for groceries, etc.
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- Michael55
  
  ...and I meant to say -- this is on 4 liters of continuous oxygen.
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Jean IA State Captain

Pleit, I think if you use pursed lip breathing from the beginning of your exercise or whatever you're doing, you'll find that your O2 sats won't fall as quickly and you won't have to stop so much. If you know it's going to fall, start the activity with it on, then you won't have to worry. You won't do yourself any harm, and you won't have to stop what you're doing either.
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- Jean IA State Captain
  
  I should have said, start the activity with your O2 on, and then you won't have to start, stop, etc.
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Babsie

Lately, my Oximeter has started going blank on me. The numbers disappear, replaced by dashes, but the lights stay on, so it's not the battery. Does anyone know what this means? It's very inconvenient in the middle of an exercise session!

I have also wondered about brands. I'm willing to spend more on a better one--but not for no reason! Any recommendations?
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- It could be that the battery is low but not dead. Have you changed it to be sure? Maybe it needs to be cleaned, I would just wipe it with a damp (not dripping wet) paper towel. Are you wearing nail polish, that would be a problem, as would cold hands.
  
  I like Nonin Go Achieve. They are medically calibrated. Not all Nonins but the Go Achieve has a different fit, to me it seems more ergonomic. The display goes on the palm side of your hand, a more natural position for your arms and hands. I don't fumble as much with it which matters when you are short of breath on a stationary bike. If you are sitting on a couch it probably doesn't matter as much. I also get less wacky results with it, its pretty consistently gives me a stable reliable reading within 2-3 seconds.
  
  In all fairness, other people are happy with less expensive ones.
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- Tina Hsu
  
  Hello, I am a Respiratory Therapist. It is possible that the pulse ox shows dashes when it can't get a reading. It needs a steady pulse, no light interference, and ideally no movement. It is common for a pulse ox to "have trouble" getting a reading when someone is moving. The reading should be checked when you are still. If you need to get a reading during exercise for some reason, hold your hand still for a few seconds and that should help.
  When exercising, you can check intensity by doing a talk test or using a modified BORG scale. We do not recommend checking O2 levels during activity because the pulse oximeters are not made for that and will often show an inaccurate reading. Glad to hear you are exercising!! Keep it up!
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edpe77

Because of curiosity, I tried my pulse-Oxs on all fingers - results were generally in agreement.
Then, I tried it with finger nail facing down - no effect.
And surprisingly, inserting the finger in sideways also has no effect. For you ladies, with nail polish, just rotate the finger 90deg!
ed
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- Sharo
  
  Edpe pass this on to Jean, Jean do you mean to keep the oxy meter on when first starting to exercise.???? there was no place to ask on your page. another question how many times a day should you do PLB , I have been using my oxygen more than usual since this terrible weather, air up North is usually over 50, here its 13 to 19 at most..
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I had issues from the high grade one they use at the Doctors office and we couldnt get a good reading, it was very jumpy!
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- I wonder what brand it was so we can avoid it.
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RoseMcK

I just checked a half-dozen sites for the Nonin Go2 Achieve Pulse Oximeter. The manufacturer has placed it "On Indefinite Backorder." Other results include "Cannot be ordered at this time"; "Out of Stock." Sounds pretty final, unfortunately.

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- That’s too bad, that was a favorite.
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I should of posted more clearly that the high grade pulse ox at the Doctors office was jumpy because of me and not bad equipment, sometimes I hit the post comment before I proofread.
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- I know about posting too fast, I am always doing that. btw what is proof reading:)
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For an acxurate reading, pulse oximeter should be placed on the right middle finger. If that is not an option, use the right thumb. Wait one minute before taking a reading. Research has shown that nail polish only barely impacts the reading. Source: NIH
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celinaredden

The global Pulse Oximeters Market is anticipated to grow magnificently in the forecast period (2017 to 2023). It should record an approximate CAGR of 6.5 percent during the said period. These devices would observe rapid growth in the coming years, owing to the ability of pulse oximeters to check the health of patients at their homes & convenience and accurate detection of significant ailments. Taking into account the worldwide scenario, the industry has a huge potential for further expansion.
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celinaredden

The global Pulse Oximeters Market is anticipated to grow magnificently in the forecast period (2017 to 2023). It should record an approximate CAGR of 6.5 percent during the said period. These devices would observe rapid growth in the coming years, owing to the ability of pulse oximeters to check the health of patients at their homes & convenience and accurate detection of significant ailments. Taking into account the worldwide scenario, the industry has a huge potential for further expansion.
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cheeto

What if your O2 is above 97 but your heart rate is in the low 50s upper 40s? Thats how mine is, and I am not healthy by any means and am not an athlete.
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- Jean IA State Captain
  
  That heart rate is low for someone who has COPD. You might try changing the battery in the oximeter to be sure you're getting a high powered reading. The other thing would be to take the oximeter to your next appt and check it against their readings. If you're really concerned, call your doc and ask about it. They can find your most recent visit and tell you what your heart rate was then. It may be something they'll want to see you for.
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- Stephanie Williams, RRT (COPDF VP of Education and Engagement)
  
  Another thing to consider is that some medications cause you to have a slow heart rate. There are actually several of them that can do this. You can find your pulse in your neck or wrist and count your beats per minute and see if it actually that low or if the pulse ox is just not picking up every beat. Sometimes they are not accurate due to low blood pressure or an abnormal heart rhythm. Taking your device to your next doctor appt. would be a good idea.
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SpiritualCrone61

I am a tad concerned. Noticed my heart rate increased all of a sudden .... Used my oximeter which read 95/107!!! I waited a few minutes. 94/102. Help! Before I call tele Doctor ... any advice? Ty !
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- Bill Clark - Community Manager
  
  A pulse oximeter only gives you a snapshot in time. Generally when your heart rate goes up it means it is working to keep your oxygen sats up...at that particular time. Before you panic, wait to see if there is a regular pattern over several hours. If there is then call your doctor or go to ER. The heart rate you describe doesn't appear to be dangerous . It would also help to know what you were doing prior to taking the reading and while you were taking the reading
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- SpiritualCrone61
  
  Thank you. I am bed bound so simply resting. Same while taking reading.
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- DannyBoy¡Hola!52+
  
  I don’t think it means anything. It happens to me sometimes, and I take a deep breath from my diaphragm, exhale and purse my lips while lowering my shoulders and lowing my head toward my lap. I close my eyes, and imagine relaxing on a peaceful beach. Number? 98. Try this technique if you want to.
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Norso

Hello Spiritual Clone,
Like you my heart rate goes high and it concern me. I've told my doctor (uk,) and I think maybe you should tell yours or pcp if that is what it is in USA.

Mine seems far less concerned than I am so I'm only saying tell your Dr as a precaution rather than anything else.

My heart rate goes very high at times. But it also goes very low.

Climbing stairs 96, 104 or 114 if I hurry. As high as 134 on fast long walk.

You mention bed bound and I have a theory ... I first became aware of my fluctuating heart rate when I dozed on sofa and took readings straight after.... I was shocked as heart rate was 114.

Since then I've noticed if i lounge my heart rate goes up!!! If I sit straight it goes down.

I tested this in car by adjusting seat. In normal driving position upright... Fine bpm heart rate is 72 or 74.
Move seat to relaxed position and sp02 goes down and heart rate up.

I suspect lying and resting can put us in a scrunched position and lungs may find it more difficult to work hence heart tries to compensate.

Be on the safe side and tell your health care person but I've been like this for 2 months and drs in uk don't seem worried! Best of luck anyway to you

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