UDM
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.