Why peak flow readings are higher than normal?

The following is a question I recently received:

Question: mom with asthma wrote:

I was recently diagnosed with bronchitis on top of my asthma in the ER. When the nurse took my oxygen level it was 99%. My husband made a comment about it, and assumed that meant there wasn't a problem. I remember she said that it didn't mean a whole lot, just that I had good oxygen saturation in my blood. I don't remember what she said after that. Could you explain what the oxygen level means when you are having an asthma attack? Why do they monitor it?

Since having this problem, I have begun to notice that often when I use my peak flow meter, I get a high number, like 100 higher, than has been normal for me. Can you make any suggestions as to what is going on? I mentioned it when I saw the doctor, but didn't really get an answer.

My humble answer: Good questions. An oxygen level (SpO2 or sat) of 99% is perfectly normal. Usually we like to see it at 90% or better, so 99% is great. A normal SpO2 is usually about 98%, while it is impossible to be at 100% unless you are on supplemental oxygen.

We monitor sats on all patients who come in with respiratory problems, even asthmatics. However, I find that it is rare that an asthmatics sats decrease, this can happen with severe asthma attacks. For this reason, it is important to monitor.

I wrote a post recently about peak flow meters. You can read it by clicking here. One reason your peak flow rates might be higher after you seek treatment for an asthma attack is because you are getting better asthma control now. Perhaps you're on some good asthma medicines (perhaps systemic steroids?), and this can work to improve your lung function. This would be my theory.

Maybe your above normal peak flows are what you are really capable of. I'm sure you know this, but there are medicines meant to improve lung function in asthmatics and prevent asthma flare ups, such as Advair and Symbicort, or Singulair, and sometimes Spiriva. By working with your doctor, and by trial and error, perhaps the right combination of these medicines (all with very few side effects) will help you maintain your higher peak flow readings.

Keep in mind I don't know you as well as your doctor, and this is just my guess. It surprises me, however, that your doctor didn't have a better answer for you.