At close range, birdshot might work in many cases.
Might could be an awfully important word though.
Consider cases like the one documented in the article at
https://www.mja.com.au/journal/2000/...ide-difference (it appears the text is no longer available online for non-subscribers). The medical examiner in this case initially thought they were dealing with a homicide, because the deceased had been shot THREE TIMES with a 12 ga. shotgun at contact distance. Turns out to have been a suicide.
One particular case has been documented from Australia. In February 1995, a man committed suicide on parkland in Canberra, Australia. He took a pump action shotgun and shot himself in the chest. The load passed through the chest without hitting a rib, and went out the other side. He then walked fifteen meters, reloaded, leaned the shotgun against his throat, and shot his throat and part of his jaw. He then reloaded, walked 136 meters to a hill slope, lay down on the slope, held the gun against his chest with his hands and operated the trigger with his toes. This shot entered the thoracic cavity and demolished the heart, killing him.[4] --
http://en.wikipedia.org/wiki/Multiple_gunshot_suicide
The loads used in this case were #2 shot IIRC.
Keep in mind there are no guarantees your gunfight will go according to your plan. Chances are it will not, in fact. Consider your situation, what innocents nearby could be in danger from your projectiles if they miss or overpenetrate, and choose your defensive load or loads accordingly. Most of all, train and practice so you can hit under pressure and run the gun reflexively.