Median effective concentration of ropivacaine blocking motor nerve in aged patients of different age stratification / 中华麻醉学杂志

ABSTRACT

Objective To determine the median effective concentration (EC50) of ropivacaine blocking the motor nerve in aged patients of different age stratification.Methods Ninety-six patients of both sexes,aged 66-85 yr,of American Society of Anesthesiologists physical status Ⅰ-Ⅲ,with body mass index of 20-27 kg/m2,scheduled for elective hip replacement,were divided into 4 groups (n=24 each) according to the agegroup Ⅰ 66-70 yr,group Ⅱ 71-75 yr,group Ⅲ 76-80 yr and group Ⅳ 81-85 yr.The concentration of ropivacaine was determined by up-and-down sequential trial.In each group,0.2％ ropivacaine 10 ml was epidurally injected in the first patient,and the difference between two successive concentrations was 0.025％.Each time the concentration of ropivacaine increased or decreased in the next patient depending on whether or not the Bromage score was 0 at 30 min after epidural injection.The EC50 and 95％ confidence interval of epidurally administered ropivacaine blocking the motor nerve were determined using probit analysis.The sensory block level and development of intraoperative hypotension and nausea and vomiting were recorded.Results The EC50 (95％ confidence interval) of ropivacaine was 0.24％ (0.19％-0.29％),0.22％ (0.17％-0.26％),0.19％ (0.15％-0.24％) and 0.17％(0.14％-0.22％) in Ⅰ,Ⅱ,Ⅲ and Ⅳ groups,respectively,and the EC50 of epidurally administered ropivacaine blocking the motor nerve was gradually decreased with increasing age stratification (P＜0.05).The sensory block level was all at T7.8-S1 in the four groups.There were no significant differences between the four groups in the incidence of intraoperative hypotension or nausea and vomiting (P＞0.05).Conclusion For aged patients of different age stratification,the EC50 of epidurally administered ropivacaine blocking the motor nerve is as follows0.24％ in patients aged 66-70 yr;0.22％ in patients aged 71-75 yr;0.19％ in patients aged 76-80 yr;0.17％ in patients aged 81-85 yr.