PPI-guided Postoperative Pain Therapy in the OR

The pupillary dilatation reflex (PDR), induced by a standardized noxious stimulus will be measured as Pupillary Pain Index(PPI,11-point numeric scale, 0= no pain, 10= worst pain) determined with a portable pupillometer. Patients experiencing mild or more severe pain (PPI\> 3) will receive intravenous opioid titration (piritramid, 3 mg bolus steps) and PPI measurement performed before and after intravenous opioid titration.