IRCT20151012024493N6 IRCT 2023-02-24 Shahid Beheshti University of Medical Sciences comparing fentanyl and remifentanil in liver transplant surgery Comparison between the influence of intraoperative Remifentanil and Fentanyl on postoperative pain following adult orthotopic liver transplant surgery: A randomized clinical trial 2023-02-20 anticipated 32 Complete https://irct.ir/trial/60649 interventional Randomization: Randomized, Blinding: Triple blinded, Placebo: Not used, Assignment: Parallel, Purpose: Treatment, Randomization description: Random-number table In this study, people enter the study groups by lottery; In such a way that the type of injectable drug used is placed in the desired number in the sealed opaque envelopes that are coded. Each of the codes is also written on a piece of paper, folded and placed inside a box. After entering the operating room, each patient takes out one of the pieces of paper from the box. The envelope has the same number as the number inside the selected paper. which is applied to the patient. This work continues until the end of the papers so that the number of patients reaches the desired number in the groups, Blinding description: The patients will be grouped by numeric coding. The patient will not be aware of the type of administered drug. The chief researcher who is responsible for patient's safety and preparing the drugs will be aware of the drug administered. But the resident and the nurse in the operating room will not know which drug is given to the patient. The researcher (responsible anesthesiologist) will prepare two syringes with the same volume and the same appearance (clear fluid in 50 cc- syringe) and these syringes will be given to the nurse/resident in the operating room. The duration of infusion will be the same for both groups. Groups coding is numerical and the intensive care unit personnel and the epidemiologist responsible for analysis of the data will not be aware of coding type. 2-3 Liver Transplantation. Intervention 1: Intervention group: In Fentanyl group, Fentanyl is infused by the rate of 0.03-1 mcgr/Kg body weight/min during surgery. Intervention 2: Intervention group: In Remifentanyl group, Fentanyl is infused by the rate of 0.03-1 mcgr/Kg body weight/min during surgery. No - There is not a plan to make this available Justification or reason for not sharing IPD is No more data is available.