Objective This study aimed to identify the median effective volume of ropivacaine 0.5% for ultrasound-guided adductor canal block (ACB). Methods Thirty-two patients received ultrasound-guided ACB for knee arthroscopic meniscectomy. The criterion for successful ACB was the loss of pinprick sensation in the saphenous area (medial knee, leg, and foot). The volume of ropivacaine 0.5% in each case was determined using the up-down method and used for calculating the median effective dose. Results The mean age, weight, and height of patients were 28.6 ± 7.1 years, 68.2 ± 10.6 kg, and 172.5 ± 6.4 cm, respectively. Among patients who received 18- and 15-mL doses, ACB was successful in all four cases. Among patients who received a 12-mL dose, ACB was effective in eight and ineffective in two cases. Among patients who received a 10-mL dose, ACB was successful in six and unsuccessful in seven cases. In patients who received an 8-mL dose, ACB was ineffective in all five cases. The median effective volume of ropivacaine 0.5% was 10.4 mL (95% confidence interval, 9.1-11.4 mL). In all effective cases, the median quadriceps strength was grade 5. Conclusions The median effective volume of ropivacaine 0.5% is 10.4 mL for ultrasound-guided ACB.
Keywords: Adductor canal block; effective dose; knee arthroscopic meniscectomy; quadriceps femoris muscle; ropivacaine; saphenous nerve; ultrasonography.