Technique of Block Administration
All peripheral nerve blocks were performed under the guidance of ultrasound and the patient was under the monitor of HR, BP and SpO2. Local anesthetics toxicity rescue kit was at handside. Sciatic nerve block was performed after femoral nerve block ( 0.2% ropivacaine 20ml). Patients was in lateral decubitus postion with the operative leg on top. The injection site was located in the subgluteal or upper to-middle thigh region. Disinfection of the puncture site and local anesthesia were performed as described above. A 10-cm 21-gauge insulated needle (UniPlex Nanoline; Pajunk, Geisingen, Germany) was used to inject a total of 20 mL of ropivacaine 0.2% around the sciatic nerve using real-time ultrasonography guidance and an in-plane approach. Using the small-sample up-and-down sequential allocation study design, the concentration of local anesthetic (20mL ropivacaine) administered through the block needle was determined. A concentration of 0.2% of 20mL ropivacaine was injected to the first patient. After a successful block (in the initial 8 hours after operation, the VAS score was less than 4), the concentration of local anesthetic in the next patient was decreased by 0.025%. However, if the block was unsuccessful, then the local anesthetic concentration was increased by 0.025% in the next patient. All patients received less than 3 mg/kg of ropivacaine in order to avoid local anesthetic toxicity