Abstract: Objective To compare the effects of different concentrations of ropivacaine for hip pericapsular nerve group(PENG) block on multimodal analgesia after femoral head replacement in the elderly, and to explore the most appropriate concentration of ropivacaine. 
Methods Sixty patients who underwent elective femoral head replacement in our hospital were selected. They were randomly divided into low concentration ropivacaine group(group L), medium concentration ropivacaine group(group M) and high concentration ropivacaine group(group H), with 20 cases in each group. They were treated with PENG block combined with low-dose ropivacaine subarachnoid block. PENG block was performed at 30 min before subarachnoid block. Patient controlled intravenous analgesia was used after operation. During PENG block, group L was injected with 20 mL of 0.25% ropivacaine, group M with 20 mL of 0.375% ropivacaine and group H with 20 mL of 0.5% ropivacaine. The pain visual analogue scale (VAS) scores of the three groups were recorded immediately after entering the operation room, immediately before, during and immediately after postural placement. VAS pain scores at rest and during exercise at 6, 12, 24 and 48 h after operation were recorded. The time of pressing the analgesic pump for the first time, the total number of pressing the analgesic pump within 48 h and the number of cases of remedial analgesia with flurbiprofen axetil were recorded. The adverse reactions of anesthesia and analgesia in the three groups were recorded. 
Results VAS pain scores in the three groups decreased gradually and then increased immediately after entering the operation room, immediately before, during and immediately after postural placement, and the difference between time points was statistically significant (P＜0.05). There was no significant difference in interaction between groups, and time points between groups (P＞0.05). The VAS pain score at rest and during exercise in group L increased initially and then decreased, which, however, decreased initially and then increased in group M and H. Compared with group L, the VAS pain scores at rest and during exercise in group M and group H decreased significantly at 12 h and 24 h after operation (P＜0.05). There were significant differences in interaction between groups, time points, and time points between groups (P＜0.05). Compared with group L, the time of pressing the analgesic pump for the first time in group M and group H was significantly prolonged (P＜0.05), and the total number of pressing the analgesic pump within 48 h was significantly reduced (P＜0.05). There was no significant difference in the number of cases of remedial analgesia with flurbiprofen axetil among the three groups (P＞0.05). No adverse reaction of anesthesia and analgesia occurred in the three groups. 
Conclusion Different concentrations of ropivacaine for PENG block can reduce the VAS pain score of elderly patients undergoing femoral head replacement in lateral position and reduce the postoperative VAS pain score. Compared with 0.25% ropivacaine, 0.375% and 0.5% ropivacaine have better analgesic effect and longer duration, and reduce the application of postoperative analgesic drugs. Their effects are similar, but considering the safety, 0.375% ropivacaine is recommended.

Key words: femur head, ropivacaine, analgesia