Why is it, that if a patient is having an asthma attack, they still have a high pulse ox reading...maybe even 100%? It's quite simple. If you think about the body, and what asthma is, it all makes sense.
When someone has an asthma attack, they have bronchoconstriction, thus trapping air in the lungs. So, with the SpO2 monitoring, we have the oxygen trapped in our lungs, thus causing the high SpO2 reading. When the patient's SpO2 starts to drop, then you know something is wrong...they have been constricted too long.
With these patients, you need to administer Albuterol and Atrovent, via nebulize. Now, personally, I like to take the NRB mask, remove the bag, and attach the nebulizer part to the mask, thus making a nebulizer mask...works great. Now, don't expect the lungs to start to open up right away, it will take a minute for the medication to work it's way down through the bronchioles. As time goes on, you should start to hear the wheezing to fade away. But, if you still hear wheezing, that you need to administer another Albuterol treatment, and even possibly a steroid.
As you are treating your patient, remember, their pulse ox reading, in most cases, will always be high. The best way to properly monitor your patient, is to put them on capnography. Some agencies carry a device that is a NC and a capnography device in one. If you have it, use it! Capnopgrahy is the most accurate way to monitor a patient with respiratory emergencies. Yet, you may still get that crazy reading, because you have the air trapped in the lungs. If you're comfortable with the capnography, use it, and remember, with COPD/asthma, they will present with the shark-fine waveform.
Overall, don't always trust your SpO2 monitor. Capnography is the best device to use, and if you have it, always use it. And always remember this...treat your patient, not the monitor.