Payn, I'm assuming that you're refering to significant combat penalties inflicted on combattants once their hit points fall below a given threshold.
Dangerous stuff, that. Unless your plan is for the penalty not to apply to PCs. Because additional numerical handicaps to PCs because their hitpoints are low will lead to far more frequent deaths and TPK events. I can recall many fights where the entire party (except perhaps the wizard) down in single-digit hit points when they finally managed to eliminate their adversaries.
RPGs, regardless of the game system, have a high degree of abstraction concerning the accumulation of wounds leading to unconsciousness or death. IMHO, it's best not to question such things too closely. A 1st-level character suffering 30 hit points of damage is going to be down and out, but for a 12th-level character, it's hardly a scratch.
If you really want fights to be deadly, I can recommend the ICE/Rolemaster/MERP/Arms Lore books from the early 80s. Pages & pages of super detailed (and super-debilitating) critical hit tables. Not as much fun as some might think.