Abstract: BACKGROUND: Ropivacaine and dexmedetomidine are two commonly used local anesthetic agents and adjuvants in elderly total hip arthroplasty. They provide sedation and analgesic effects during peripheral hip nerve blocks.
OBJECTIVE: To explore the dose-effect relationship between dexmedetomidine and ropivacaine in continuous sedation during pericapsular nerve group block in elderly patients undergoing total hip arthroplasty.  
METHODS: A total of 120 elderly patients who received total hip arthroplasty in Dongguan Hospital, Guangzhou University of Chinese Medicine from January 2021 to January 2023 were selected as study subjects and randomly divided into two groups 1:1 matching according to propensity matching method. The observation group (n=60) received pericapsular nerve group block by giving 20 mL mixture of ropivacaine and 1 μg/kg dexmedetomidine. The control group (n=60) received received pericapsular nerve group block by giving 20 mL of ropivacaine. The general data, perioperative indexes, postoperative analgesia, hemodynamic indexes, inflammatory factors, stress indexes, postoperative adverse reactions, length of hospital stay, and the occurrence of postoperative complications were compared and analyzed between the two groups. The median effective dose and 95% effective dose concentrations of ropivacaine pericapsular nerve group block were calculated by the Probit method.  
RESULTS AND CONCLUSION: (1) The postoperative analgesia of the observation group was better than that of the control group, and the visual analog scale score at 6-hour dynamic, 12-hour static, 12-hour dynamic, 24-hour static, 24-hour dynamic, 48-hour static, 48-hour dynamic, as well as the time of first patient-controlled analgesia compression and the number of patient-controlled analgesia compression at 24 and 48 hours postoperatively were statistically different (P < 0.05). (2) There were significant differences between the two groups in mean arterial pressure and heart rate at extubation and 12 hours after extubation (P < 0.01). (3) The levels of interleukin-6, tumor necrosis factor-α, epinephrine, and noradrenaline in the observation group were significantly lower than those in the control group at 24 and 48 hours after surgery (P < 0.01). (4) There was significant difference in the length of hospital stay between the two groups (P < 0.01), and no difference was detected in the occurrence of postoperative complications (P > 0.05). (5) The median effective dose and 95% effective dose values of dexmedetomidine combined with ropivacaine were 0.164% and 0.188%, respectively, while the median effective dose and 95% effective dose values of ropivacaine alone were 0.194% and 0.276%, respectively. (6) It is concluded that using dexmedetomidine combined with ropivacaine in pericapsular nerve group block can effectively alleviate postoperative analgesia in elderly patients with total hip arthroplasty, help maintain the hemodynamic stability of patients, reduce postoperative inflammation and stress response, and shorten the length of hospital stay. In addition, dexmedetomidine can reduce the dosage of ropivacaine under the condition of effective pericapsular nerve group block reaction.

中国组织工程研究杂志出版内容重点：人工关节；骨植入物；脊柱；骨折；内固定；数字化骨科；组织工程

Key words: total hip arthroplasty, dexmedetomidine, ropivacaine, pericapsular nerve group block, sustained sedation