I have similar asthma to you as well as various mobility aids. I am stubbornly independent. In April 2014 I had to have my gallbladder removed by general anaesthetic.
I was told to get my asthma as best under control as I could. The doctor arranged surgery for a better time of year. Just before pollen but after winter.
A bed on itu was reserved for me.
And my asthma behaved itself and i did not need any treatment for asthma the who time.
Try to relax lots before and think positive.
I hope it all goes well for you and be sure to rest after surgery your body will take longer to heal thanks to pred.