My siblings and I have used a D30 for the last 13 or so years. Anytime a character drops to or below 0 Hit Points, you roll D30 vs. Con Score to stay awake. Every Round you are unconscious you can roll a D30 to wake back up. You bleed 1 Hp a round while in Negatives.
Additional House Rules.
Cavalier Class can fight in negatives without a roll.
Also play -9 +Level worth of Negatives. (Ex. Level 9 = Max Negative -18)
Have a couple more uses for the d30 but that is for the most part the only one that comes up each session.