Figure 4

Comparison of intraoperative additional sufentanyl requirements during surgery among four groups. Group R_0.2 = 0.2% ropivacaine, Group R_0.33 = 0.33% ropivacaine, Group R_0.5 = 0.5% ropivacaine, Group C = normal saline. **P = 0.001, ***P < 0.001.