Question, when a character is injured up to Rendering critical 4 wich is says "A torrent if blood spills from the deep cuts" it implies that you have "blood loss" and probably on the ground holding you stomach or the character can act "rambo-like" and continue fighting?

Rending critical 4's effect is 1d5 fatigue and a pool of slippery blood that requires an agility test or to fall prone. The target is not suffering from the Blood Loss special effect.

Yes you can rambo through it, assuming the amount of Fatigue you suffer by the end of it isn't greater than your toughness bonus. See page 251 for effects of fatigue.