understood, and i agree that this is the intended design of blood tanking. however, in my example, i was frost-spec'd, and i was still able to self-heal myself through the damage the adds were putting out pretty much indefinitely, relying only on my mitigation cooldowns, death strike, and blood tap to keep me up. i also had a ghoul sacrifice in my back pocket.
That's also the design of blood, however. We're trading damage reduction abilities (Bone Shield, Unbreakable Armor, Dreadplate) in favor of hitpoints and methods to refill those hit points.