This post is long as it contains the rules you have all been wanting for your T20 game [those of you who want to maintain a since of danger but not change the primary feel of combat]. i will sumurize below:
basically, there is no more negative life blood, once you hit 0, you make fortitude checks per attack [DC based on damage] or become dying. you continue making checks once dying to actually die.
low level characters really won't notice a huge change, and high level characters will still be out of the fight from lucky shots. rules follow, and are similar to the Unearthed Arcana:
0 Lifeblood
With this variant, characters can’t be reduced to negative lifeblood—0 is the minimum. There is no automatic lifeblood total at which a character dies. Instead, any character who takes damage that reduces his lifeblood to 0 must make a Fortitude save to avoid falling unconscious or dying.
The Fortitude Save
When a character’s lifeblood is reduced to 0, he must attempt a Fortitude save (DC 10, + points of damage dealt by the attack). Success means the character is disabled; failure indicates that he is dying. Failure by 10 or more means the character is dead. (If the character rolls a natural 1, he is dying. Calculate the numeric result; if he missed the DC by 10 or more, he is dead.)
The possible results of the save are as follows.
Disabled
A disabled character is conscious, but can only take a single move or standard action each turn (but not both, nor can she take full-round actions). She moves at half speed. Taking move actions doesn’t risk further injury, but if a disabled character takes any standard action (or any other action the Referee deems strenuous, including some free actions such as casting a quickened spell), she must succeed on a Fortitude save (against the same DC as the save made when reduced to 0 lifeblood) to remain disabled; otherwise, she becomes dying after she completes the action. If a disabled character takes any lethal damage, she must make a new Fortitude save (DC 10, + points of damage dealt by the attack or effect), but any result other than dead means the character is now dying. A disabled character who is dealt (or who is currently suffering from) any nonlethal damage suffers the standard effects for loss of Stamina but does not begin dying.
A disabled character must undergo surgery or to be brought to 1 lifeblood, after which point he heals naturally. After 1 week of being continuously disabled (no back and forth between dying and disabled), a character heals 1 lifeblood and will resume natural healing from that point after.
Dying
A dying character is unconscious and near death. Each round on his turn, a dying character must make a Fortitude save (DC 10, +1 per turn after the first) to become stable.
If the character fails the save, he dies.
If the character succeeds on the save by less than 5, he does not die but does not improve. He is still dying and must continue to make Fortitude saves every round.
If the character succeeds on the save by 5 or more but by less than 10, he becomes stable but remains unconscious.
If the character succeeds on the save by 10 or more, he becomes conscious and disabled.
Another character can make a dying character stable using his medical skill as per the rules in the skill section.
Stable
A stable character is unconscious. Every hour, a stable character must succeed on a Fortitude save (DC 10, +1 per hour after the first) to remain stable.
If the character fails the save, he becomes dying.
If the character succeeds on the save by less than 5, he does not get any worse, but does not improve. He is still stable and unconscious, and must continue to make Fortitude saves every hour.
If the character succeeds on the save by 5 or more, he becomes disabled and has 0 lifeblood.
Another character can grant a stable character a +2 bonus on his Fortitude save to remain stable by tending to him for at least 10 minutes during the hour between saves and by making a DC 15 medical check.
Dead
A dead character’s well… dead. Unless you have access to divine intervention, you can’t do much to a dead character except go through his pockets for loose credits.
Healing
A disabled, stable, or dying character has 0 lifeblood. Healing that raises her above 0 lifeblood makes her conscious and fully functional again, just as if she had never been reduced to 0.
For example, Tirsa is blown up by a marine’s RAM grenade for 26 points of damage, but she only has 14 lifeblood. She is reduced to 0 lifeblood. She must immediately attempt a DC 36 Fortitude save (base DC 10, +26 because the damage dealt). She rolls a 27, so she is unconscious and dying. (Had she rolled any worse, the grenade would have killed her outright.)
On her next turn, she must succeed on a DC 10 Fortitude save to become stable. She rolls a 13, which is enough to remain dying but not good enough to become stable. Next round, the DC increases to 11, and she rolls a 16. Since that result exceeds the DC by at least 5 points, Tirsa becomes stable but remains unconscious. Assuming that she isn’t tended by her friends (or slain by more grenades) in the meantime, she must succeed on a DC 10 Fortitude save 1 hour later to remain stable.