IRCT20140519017756N33 IRCT 2018-01-27 Birjand University of Medical Sciences The effect of adding nitroglycerin to morphine in intravenous pain control pumps Comparison of analgesic and hemodynamic effects of morphine sulphate alone and morphine sulphate plus nitroglycerine in candidates for simple abdominal surgeries using intravenous patient-controlled analgesia 2016-12-21 anticipated 60 Complete https://irct.ir/trial/28032 interventional Randomization: Randomized, Blinding: Single blinded, Placebo: Not used, Assignment: Parallel, Purpose: Prevention, Randomization description: Table of random numbers, Blinding description: Patients are not aware of which study group they are allocated into. 2 Post-operative pain. Intervention 1: Intervention group: (Morphine + Nitroglycerin): Intravenous pain pump of the case group will be filled with 0.5 milligram/kilogram morphine + 3 microgram/minute nitroglycerin. Intervention 2: Control group: (morphine): Intravenous pain pump in the control group will be filled with 0.75 milligram/kilogram morphine . No - There is not a plan to make this available Justification or reason for not sharing IPD is The majority of participants agreed to participate if the confidentiality of data would be guaranteed.