Preoperative variables (e.g. patient characteristics) Surgical/Anesthesia variables (e.g. type/length of surgery, antiemetics) Outcome variables (PONV, worst pain as delineated in the outcomes section), Intraoperative fentanyl measured 1) as a continuous variable and 2) by predefined limits of 0 to 0.2mg, >0.2-0.5mg, >0.5 to 0.8mg, and >8mg.