I've had them done with 96% oxygen levels with bad shortness of breath, yet I've barely been able to speak with 90% sats and not had them done, had sats into low 80s and got out of blood gases, I've also had them done for 90-92% sats with NO breathing difficulties.
is there a generalised thing of when they're done or does it all depend on your doctor in A&E/wards?