Objective To determine the median effective background volume ( MEBV50 ) of 0.2%ropivacaine in ultrasound-guided continuous sciatic nerve block in the elderly patients with knee ankylosing after surgery releasing .Methods Twenty-two elderly patients (aged 65-79 years, weighed 58-90 kg, ASA Ⅰ-Ⅲ) who underwent arthrolysis of knee joint after total knee arthroplasty in our department from January 2014 to May 2016 were recruited in this study .All patients received ultrasound-guided continuous sciatic nerve block by means of subgluteal approach after manipulation with intravenous general anesthesia .After catheter placement , the volume of the injected solution was varied for consecutive patients using the Dixon ’ s up-and-down stair-case method according to the response of the previous patient ( initial volume: 5 ml/h; up-and-down steps: 0.5 ml/h).We recorded the blockade situation of sensory at 24 and 48 h after the placement of the stimulation catheter .Results For ultrasound-guided continuous sciatic nerve block with subgluteal approach , the MEBV50 of 0.2%ropivacaine was 4.3 ml/h (95%confidence interval:4.0-4.6 ml/h) for analgesia in the elderly after arthrolysis of knee joint .Conclusion When 0.2%ropivacaine is used for ultrasound-guided subgluteal continuous sciatic nerve block in elderly patients after knee arthrolysis , the MEBV50 is 4.3 ml/h.%目的：本研究旨在测定老年患者超声引导下以0．2％罗哌卡因连续坐骨神经阻滞应用于膝关节松解术后镇痛的半数有效背景量。方法选取宣武医院2014年1月至2016年5月全膝关节置换术（ TKA）后行膝关节僵直手法松解术患者22例，年龄65～79岁，体质量58～90 kg，美国麻醉医师协会（ASA）评分Ⅰ～Ⅲ级，静脉全身麻醉下手法松解后行超声引导下经臀下入路定位，定位成功后置入连续刺激导管，采用Dixon序贯法0．2％罗哌卡因连续坐骨神经阻滞，开始背景流量为5 ml／h，如术后24、48 h患者阻滞效果完善，则下一例患者背景量减少0．5 ml／h；如果阻滞效果不完善，则下一例患者背景流量增加0.5 ml／h。结果超声引导经臀下入路0．2％罗哌卡因连续坐骨神经阻滞的半数有效背景量为4.3 ml／h，95％可信区间为4.0～4．6 ml／h。结论0．2％罗哌卡因在超声引导下用于老年患者膝关节手法松解术后连续坐骨神经阻滞，半数有效背景量为4．3 ml／h。
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