Researching for D&D, how deep of a wound requires stitches and where does it become lethal?

I was trying to find wound depths and the severity of them, based on being stabbed right under the ribs, for my upcoming D&D Session (I'm the DM). However, all I keep getting is the suicide/sh prevention lines/sites when trying to look for it. I try to not make it unreasonable and I acknowledge the fact that I am not well versed with wounds, thus the attempt at research and the further attempt to try and ask for help.

Thanks!