I have treated several patients who have had asthma & been on beta blockers. If the patient does not respond to oxygen therapy & nebulized Albuterol then I add Ipratropium bromide, if they still do not respond then I usually move on to
Epinephrine 1:1,000 0.3mg IM/SC & Fluids.
FYI: There are quite a few relative contraindications to beta blockers, including Asthma, Bradycardia with a heart rate less than 60 beats per minute, CHF, COPD, emphysema, hypotension 2nd or 3rd degree heart block & immunotherapy just to name a few.