I have asthma and a pulse oximeter. i use it to check when i get an asthma attack. what spo2 is normal? so i know when to go to the er. i am 25.

Peak flow meter: You are better off checking your peak flow since by the time the O2 sat drops you could be in serious trouble. Normal SaO2 is >95%. Asthma specialists use peak flow meters to determine the degree of obstruction. Maintenance medications should keep it above 90%. Intervention should begin early before it drops below 80%. A peak flow below 50% is a medical emergency. Start steroids and go to ER.

Peak flow better...: Instead of a pulse oximeter use peak flow measurements to gauge asthma control at home. Peak flow meters a inexpensive, easy to use, and a great way to track your respiratory function at home. Talk to your doctor about your specific asthma action plan and how to use peak flows properly and pick one up soon. Pulse oximeters are not a reliable way to track asthma control.

When it gets worse: I agree with Dr Grieve that pulse oximetry is useless in monitoring asthma .The rule of thumb is symptoms . If you are waking up at night from asthma more than 2x/wk, using your rescue inhaler nearly daily, or the breathing is getting progressive worse, you need to see your doctor. Lung function monitoring helps but the readings do not always correlate with severity of your asthma.