Determining the optimal ropivacaine concentration for spinal anaesthesia during day surgery for anorectal procedures:...

Ropivacaine is a commonly utilized local anesthetic for spinal anesthesia (SA); however, its optimal concentration for elective anorectal surgery has not been thoroughly estimated. This study investigated the minimum effective concentration (MEC₉₀) of ropivacaine required to achieve successful SA in patients aged 18-65 years undergoing elective anorectal procedures. Fifty-one patients received SA with 1.5 ml of ropivacaine hydrochloride, utilizing a biased coin design and an up-and-down method, commencing at an initial concentration of 0.30% and adjusted in increments of 0.05%. The results demonstrated that the MEC₉₀ of ropivacaine for SA was 0.2482% (3.7320 mg, 95% CI: 0.1500-0.3000%). Moreover, MEC₉₉ was extrapolated to 0.2926% (4.4389 mg, 95% CI: 0.2500-0.3000%) for 1.5 ml. These findings suggest that a concentration of 0.2482% (3.7320 mg) effectively induces SA in 90% of patients, while a higher concentration of 0.2926% (4.4389 mg) may be recommended to achieve a 99% efficacy rate.Clinical trial registration ChiCTR2300074796 ( https://www.chictr.org.cn/ ).