Asthma UK community forum

Blood Oxygen Levels

I've only had Asthma for about 3 years and suffered a very severe attack 2 years ago that put me in hospital for 12 days. Since then i've had about 2 or 3 less severe attacks each year since triggered by colds/flu/viruses etc but this year i must have had 7 'episodes'.

Earlier this year i purchased an oximeter which you attach to your finger to measure the oxygen levels in your blood. I purchased it because i was worried that during attacks that as well as SOB, tight chest etc i was feeling dizzy and suffering from bad headaches. Most of my attacks occur first thing in the morning and i started to record my O2 readings as well as my PF's.

In the last few weeks my PF's have been down to 320 (best 600) but with O2 readings as low as 80% at the worst. The O2 readings do recover to the high 80's about half an hour of taking reliever. If they had stayed at 80% i would have gone to A &E.

Does anyone else record O2 levels and what are your experiences? Are the low levels and headaches something to worry about?

8 Replies

Hi there,

I'm actually a staff nurse, and worked in respiratory medicine for 2 years. generally we don't recommend patients buy SO2 monitors, because it gives a false sense of security. It's not a good idea to wait until your oxygen levels drop before seeking help, because generally once your oxygen levels are reading low, you are already pretty poorly. If your asthma symptoms are worsening, use them as your guide to seek help, not an oxygen saturation monitor. I'd have recommended phoning an ambulance well before your oxygen levels reached 80%! The dizziness, headache and sick feeling you were feeling is because not enough oxygen was reaching your brain, which means you were in a pretty bad way - please call an ambulance if this happens again! The other problems you have there are different reasons why the reading you get on those machines can be inaccurate, and once your oxygen levels drop below 83%, those machines are no longer in accurate in picking the true concentration up. Please please please make sure you seek medical advice before your Oxygen saturation drop. For an asthmatic with no other heart or chronic lung disease, oxygen saturations should be and be maintained at over 94%. Anything below this requires immediate medical attention. The best guide to how bad your asthma is is your symtpoms, monitoring your peak flow,and response to treatment. try keeping a daily peak flow diary and symptoms diary and show your results to your Asthma Nurse. I'd also recommend you see your GP about stategies to deal with your symptoms as you might need a change in medications. Your peak flow currently appears to be well below normal, and really it's best to seek medical advice after a couple of days, not weeks. Please do not allow your oxygen levels to drop below 90% without calling an ambulance. I hope you get better soon, but please please see your GP ASAP about this, or if it happens again call 999. It is not good to have oxygen saturations below 94%, and requires oxygen at this stage. 90% or below requires emergency treatment

good luck and hope you get better soon


I don't think your monitor is working. You simply wouldn't be managing at home at 80%.


re blood oxygen levels

glad you are feeling better :)

I forgot to mention aswell that those SO2 monitors critically don't measure CO2 - carbon dioxide ('waste')., which is as important as your oxygen levels. In asthmatics, once they become very unwell and the inflammation of their airway becomes severe enough to prevent them from exhaling properly aswell as inhale, (and this is often when asthmatics start to 'tire') , it leads to an accumulation of carbon dixioxide in your blood because you can't blow it off (which is what your lungs are for, breathing in air and blowing off waste). when this 'waste' carbon dioxide builds up in your blood it causes your blood to become acidic, which is very bad for your brain. Signs you are becoming acidic are headache, drowsiness, confusion, agitation and twitchy limbs. this condition is as serious as low oxygen levels, and when asthmatics reach this stage they need artificial ventilation and ICU admission. This is also what they are testing for (as well as true oxygen levels) when doctors take ABG's - arterial blood gases. Hence why it is so critically important to seek help early when asthmatics deteriorate to avoid this scenario. and also another limitation to SO2 monitors for home use.

other reasons SO2 monitors may be inaccurate are if you are cold, have an irregular heart rate, have circulation problems, are anaemic, have particularly large fingers (as some cheap finger monitors can squeeze fingers too tightly restricting circulation and give a low reading), coloured skin, scarred skin, and so on. cheap monitors are also less accurate and have high rates of low/high readings.


Oximeters also need regular maintenance/calibration/servicing. And they don't work with if you wear false nails!

Indigobaby- I am curious why they might not work if you have an irregular heart beat, do you know?


sats monitors....

Bryony the irregular heartbeat thing is just something some of us nurses noted on the ward - it mainly gives you a false average pulse reading (so best doing a manual pulse over 1 minute if you ahve a know Atrial Flutter or ectopic beats) and can cause oxygen sats fluctuations. The expensive Sats monitors we use on the wards are excellent, as you say, they are regularly calibrated and maintained by the physics department, and are extremely accurate up to 83% on O2 levels in the blood. And of course I forgot to mention the acrylic nails and nail polish bit (including clear polish) - even nicotine staining on fingers can affect readings! Ironically my father is a consultant in medical physics, and he himself has designed and built superior oxygen saturation monitors for vascular research, and he had a wee look at a finger probe that I'd bought online for £80 and was quite disgusted by it, as it only uses 1 LED to read oxygen saturations and was concerned about it's quality (even thoughit was a reputable make). my dad (obviously an expert in these machines) says that if the machine costs any less than £300 it's not worth it.

hark me going on about my dad (I'm very proud, he's a bit of a mad scientist). But he's an expert on sats monitors, so as far as I'm concerned his word is God :)


Not been on for a while.

Just thought i would update you after your warnings on my low O2 readings.

On 12th November 2011 i went to A & E suffering from sharp central chest pain, lower chest pain, headaches, dizziness and feeling really unwell. I won't go into all the detail but they admitted me after they struggled to get my O2 readings up and my x rays showed shadowing on my lungs!! I saw the consultant on the ward that day and he said i have Pneunonia. He went to say its a are version called Chronic Eosinophilic Pneumonia. He said it can't be cured but can be controlled with long term steroid use. I am still on steroids today but just on a maintenance dose. Apparently i could relapse at any time.

Thank you for your excellent advice.If my O2 readings fall again i will seek immediate help.



OMG indigo baby Im so glad you wrote all those replies, I was freaking out when I just read Johns post! eeeek....

John thats very sound advice. Im sorry to hear you have pneumonia, I hope you are feeling better soon and they get things under control.

Lynda :)


just noticed its an old post with a new reply lol :)


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