I always ask for DHE at the Er when I have a migraine that won't quit. I get DHE, phenergan, and usually toradol or sometimes demerol in conjunction.
Sometimes the DHE will kick it by itself but sometimes not. It has to be IV for me though. I used the nasal spray for a few months and then it wouldn't work.
I also use imitrex injections and axert and those will sometimes abort if I don't wait too long.
Be careful with the DHE. It makes your heart race and really nauseated. (for me anyway.)
Hope it works. It is my saving grace. I am going to ask my neuro for a rx for the dhe injections that you can give yourself and try to stay out of the ER.