| Summary: | Abstract 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).
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