Median effective concentration of ropivacaine for preoperative analgesia under ultrasound-guided supra-inguinal fascia Iliaca compartment block in hip fracture patients

Ultrasound-guided supra-inguinal fascia iliaca compartment block (FICB) is increasingly used for preoperative analgesia in elderly hip fracture patients. However, the median effective concentration (50% effective concentration, EC₅₀) of ropivacaine required for supra-inguinal FICB for preoperative analgesia has not been determined. This study was designed to evaluate the EC₅₀ of 30 mL ropivacaine to maintain preoperative analgesia for at least 24 h. Twenty-eight consecutive patients aged 75 years or older with acute hip fracture were enrolled. All patients received 30 mL ropivacaine for preoperative analgesia. Dixon's up-and-down sequential method was used to determine the concentration of ropivacaine. The initial concentration was 0.35%. Successful analgesia was defined as a Numerical Rating Scale (NRS) score for pain less than 4 during movement within the first 24 h after the block. The concentration in each subsequent patient was determined by the response of the previous patient, and concentrations were adjusted at 0.025% intervals. The 50% and 95% effective concentrations (EC₅₀, and EC₉₅) of ropivacaine were calculated using probit regression. The EC₅₀ and EC₉₅ of 30 mL ropivacaine for at least 24-hours effective preoperative analgesia via ultrasound-guided supra-inguinal FICB were 0.248% (95% confidence interval [CI], 0.233-0.262%) and 0.276% (95% CI, 0.262-0.343%), respectively. No adverse events occurred. A single dose of ropivacaine was found to provide effective preoperative analgesia via ultrasound-guided supra-inguinal FICB in elderly patients with hip fracture. The EC₅₀ (95% CI) of 30 mL ropivacaine for preoperative analgesia lasting at least 24 h was 0.248% (0.233-0.262%).Trial Registration: This trial was registered on UMIN Center Clinical Trials Register (registration number UMIN000050676, date of first trial registration 25/03/2023).