Risky Surgery Level 1
Prerequisites: trained in Medicine
Your surgery can bring a patient back from the brink of death, but might push them over the edge. When you Treat Wounds, you can deal 1d8 slashing damage to your patient just before applying the effects of Treat Wounds. If you do, you gain a +2 circumstance bonus to your Medicine check to Treat Wounds, and if you roll a success, you get a critical success instead.
Source: Advanced Player's Guide pg. 208