Abstract: Objective To investigate the clinical effect of ultrasound-guided continuous pericapsular nerve group block (PENGB) in elderly patients undergoing total hip arthroplasty (THA). 
Methods In this study, 50 patients receiving THA via unilateral posterolateral approach under elective general anesthesia in the 960th Hospital of the Joint Logistics Support Force of the Chinese People's Liberation Army were selected and divided into research group (n=25) and control group (n=25) by random number table method. The research group was treated with ultrasound-guided PENGB, while the control group was treated with continuous ultrasound- guided fascia iliaca compartment block (FICB). The operating duration of nerve blocks, hemodynamic parameters, peripheral blood T lymphocytes, serum cortisol (Cor), adrenaline (AD), norepinephrine (NE), interferon- γ (IFN- γ), interleukin-10 (IL-10), and tumor necrosis factor-α (TNF-α) were compared between the two groups. The mean arterial pressure (MAP) and heart rate (HR) of both groups before anesthesia, at the time of laryngeal mask insertion, at 30 min after surgery, at the end of surgery, and at the time of tube removal were monitored. 
Results The time for ultrasound localization, blockade operation, and injection in the research group was shorter than that in the control group, and the difference was statistically significant (P＜0.05); there were significant differences in interaction between time points with respect to the MAP and HR in the two groups (P＜0.05); there was no significant difference in the interaction between groups and time points between groups (P＞0.05). At 24 h after surgery, the CD3+, CD4+, and CD4+/CD8+ levels of both groups were significantly lower than those of the same group before surgery (P＜0.05), and the CD8+ level was significantly higher than that of the same group before surgery (P＜0.05). The AD, NE, IL-10, and TNF-α levels in the research group were lower than those in the control group at 24 h after surgery, and the difference was statistically significant (P＜0.05). The incidence of adverse reactions was 24.00% in the research group and 36.00% in the control group, but there was no significant difference between the two groups (P＞0.05). 
Conclusion The application of ultrasound-guided continuous PENGB is more effective than ultrasound-guided continuous FICB in reducing the duration of operation and inflammatory stress response levels in elderly patients undergoing THA under general anesthesia. 

Key words: arthroplasty, replacement, hip, ultrasound-guided, nerve block