If you need to use your gun to protect yourself, you need to stop the attacked RIGHT NOW. If you don't, the attacker is going to want to kill you RIGHT NOW! Granted, doctors have commented on the amazing amount of damage the lowly .22 does while bouncing around in the human body; BUT, note that these comments were from doctors trying to save the lives of those shot with them, that were still alive. If a .45 were used, we'd be talking with a corroner, not a doctor.
I would never bet my, or my loved ones life on a .22. My bottom limit is a .357 mag. Cheers!