Tehran University of Medical Sciences Journal of Orthopedic and Spine Trauma 2538-2330 10 4 2024 12 30 160 5 Mohsen Sabermoghaddamranjbar Departement of anesthesiology, school of medicine, Mashhad University of Medical Sciences, Mashhad, Iran Saeid Jamalie Bastami Departement of anesthesiology, school of medicine, Mashhad University of Medical Sciences, Mashhad, Iran Alireza Sharifian Attar Departement of anesthesiology, school of medicine, Mashhad University of Medical Sciences, Mashhad, Iran Seyed-Hossein Khademi Departement of anesthesiology, school of medicine, Mashhad University of Medical Sciences, Mashhad, Iran Mohammad Alipour Departement of anesthesiology, school of medicine, Mashhad University of Medical Sciences, Mashhad, Iran Mahdieh Samei Orthopedic Research Center, Ghaem Hospital, Mashhad University of Medical Sciences, Mashhad, Iran Omid Shahpari Orthopedics Surgeon, Orthopaedic Research Center, Ghaem Hospital, Mashhad University of Medical Sciences, Mashhad, Iran 2024 05 09 Background: The objective of this study was to assess the effect of adding a very low dose of naloxone to a remifentanil infusion on postoperative pain in patients undergoing hip replacement surgery in the lateral position. Methods: This randomized clinical trial involved 80 patients who underwent hip replacement surgery under general anesthesia and were randomly assigned into two groups through block randomization: group 1 received remifentanil at a dose of 0.3 μg/kg/minute, while group 2 received remifentanil at a dose of 0.3 μg/kg/minute with a very low dose of naloxone administered at 0.05 μg/kg/hour following injection. Postoperative pain [measured using the visual analog scale (VAS)], drowsiness caused by narcotics and analgesics in recovery, and the duration of getting out of bed were all monitored and recorded in the ward. Results: The median [interquartile range (IQR)] of time to administration of the first sedative drug was 0 (0, 4) hours in the control group and 4 (0, 4) hours in the intervention group. The difference between the groups was statistically significant (P < 0.0001). The frequency of pain after surgery at 0, 4, and 8 hours was significantly different between the control and intervention groups (P = 0.003, P < 0.0001, and P = 0.021, respectively). Conclusion: Based on the results, we recommend using a very low dose of naloxone along with remifentanil infusion in patients undergoing complete hip replacement surgery to reduce their pain and the need for painkillers. https://jost.tums.ac.ir/index.php/jost/article/view/591 https://jost.tums.ac.ir/index.php/jost/article/download/591/390