Lack of Sex Difference in Minimum Local Analgesic Concentration of Ropivacaine for Ultrasound-Guided Supraclavicular Brachial Plexus Block

Sex differences, which may be an important variable for determining anesthetic requirements, have not been well investigated in the aspect of local anesthetic. This investigation aimed to compare the minimum local analgesic concentration (MLAC) of ropivacaine for ultrasound-guided supraclavicular brachial plexus block (US-SCB) between men and women. Patients aged 18-45 years undergoing elective forearm, wrist, or hand surgeries under US-SCB were divided into 2 groups according to sex. The initial concentration was 0.375% ropivacaine 20 mL and the concentration for the next patient was determined by the up-down technique at 0.025% intervals. Success was defined as the absence of any pain in response to a pinprick in the region of all 4 terminal nerves and the skin incision within 45 min. The primary outcome was the MLAC of ropivacaine, which was estimated by the Dixon and Massey method. The analgesia duration, which was defined as the time from the end of the US-SCB injection to the time of feeling discomfort and need for additional analgesics, was observed for each patient. The MLAC of ropivacaine 20 mL for US-SCB was 0.2675% (95% confidence interval [CI], 0.2512-0.2838%) in men and 0.2675% (95% CI, 0.2524-0.2826%) in women. There was no significant difference in MLAC or the analgesia duration between the 2 groups (P>0.05). We found no significant sex-related differences in MLAC or analgesia duration of ropivacaine for US-SCB.