Anesthesia

When you cast this spell at a creature, they fall under the effect of an extremely powerful anesthetic, completely blocking their sense of pain. If a creature affected by this spell falls below 0 hit points, they don't fall unconscious. They can keep going as normal, with a special pool of hit points equal to your spell ability modifier x 5. After these hit points end, the spell ends and the creature falls unconscious. If the target is stabilized after falling unconscious, they take 1 level of exhaustion, otherwise suffer no exhaustion if healed past 0 hit points.

At Higher Levels. When you cast this spell using a spell slot of 5th or higher the hit point pool the target gains, increases by 5 for each spell level.