MEDLINE (OvidSP) search terms: 1. postoperative complications/ or perioperative care/ or intraoperative complications/ or (intraoperative or perioperative or postoperative).mp. 2. exp clonidine/ or exp dexmedetomidine/ or mivazerol.mp. 3. ((randomized controlled trial or controlled clinical trial).pt. or randomized.ab. or placebo.ab. or drug therapy.fs. or randomly.ab. or trial.ab. or groups.ab.) not (animals not (humans and animals)).sh. 4. 1 and 2 and 3 Embase (OvidSP) search terms 1. postoperative complication/ or postoperative period/ or perioperative period/ or intraoperative period/ or peroperative care/ or peroperative complication/ or (perioperative or intraoperative or postoperative).ti,ab. 2. clonidine/ or dexmedetomidine/ or mivazerol.ti,ab. 3. (randomized‐controlled‐trial/ or randomization/ or controlled‐study/ or multicenter‐study/ or phase‐3‐clinical‐trial/ or phase‐4‐clinical‐trial/ or double‐blind‐procedure/ or single‐blind‐procedure/ or (random* or cross?over* or multicenter* or factorial* or placebo* or volunteer*).mp. or ((singl* or doubl* or trebl* or tripl*) adj3 (blind* or mask*)).ti,ab. or (latin adj square).mp.) not (animals not (humans and animals)).sh. 4. 1 and 2 and 3 CENTRAL search terms #1 clonidine OR dexmedetomidine OR mivazerol #2 perioperative OR preoperative OR postoperative #3 #1 AND #2