..... and might not realise the SPO2 is below 50% (seriously!)
I'm no physician, but my understanding is that that person will have some serious problems well before they get down to 50%!!
Speaking as an asthmatic who has seen a lot of my own SpO
2 readings and been able to correlate them to how you feel at different readings I can confirm that. SpO
2 < 90% you won't notice if you're sitting down, and you won't notice walking at a sedate pace but you would notice walking at a normal pace, SpO
2 < 80% and
any walking, even from your bed to the toilet, becomes hard work, < 70% and you won't even get to your feet.
Reliability and repeatability of the inexpensive 'stick on your finger' type SPO
2 probes is, like probing with a meter or scope, all about technique. I've found the inexpensive probes to be as good as the hospital ones, both in terms of repeatability and accuracy, in direct comparison. Basically, that means that the hospital's £2000 non-invasive probes are as crappy as the £15 ones you can buy yourself. Gold standard is an actual arterial blood gas test which involves a junior doctor hunting around inside your wrist for the artery with a needle and hurts like fuck. If you are ever unlucky enough to need ABGs taken, try to get a woman to do the needle sticking - personal experience suggests that they are more competent, less painful, and most importantly if they can't get it 1st or second try have the humility to get a better colleague to do it rather than press on trying hopelessly again and again while the patient suffers.
Edit: Just checked the BTS guidelines for the treatment of acute asthma - if your SpO
2 is less than 92% then they say treat with at least 6L/min oxygen and for someone suffering from an acute asthma attack they would admit you if they can't maintain an SpO
2 > 92% with oxygen treatment and admit to ICU if ABGs show any significant change in blood pH. I know from experience that if your SpO
2 is below 92% they take you from the ambulance straight into resuscitation (where there's a whole team ready to act
now and there are
always eyes on you even if you're apparently stable) rather than a cubicle.