I for one use (In all my d20 games) a crit table that, while not specifically attributing extra damage, lists a number of effects that I just modify by situation. For example, one result on the ranged tabel (I only have a ranged and a melee table) is that any strenuous action causes the loss of 1 additional lifeblood. For a projectile weapon, I'd say that surgury to remove 'the bullet' would halt that damage. Additionally, on the melee and ranged tables both, there are results of lost fingers, hands, feet, or entire limbs. Surgury can reattatch those. Also, there are many situations where, while not even in combat, a character might suffer such a wound (Hand caught in an airlock, hanging from the side of a grav speeder when it sideswipes a building, etc.) These situations call for skilled and immediate surgical attention!