蛛网膜下腔注射罗哌卡因与布比卡因运动神经阻滞效力的比较

Objective To determine the median effective doae (ED50) for motor block after intrathecal ropivacaine and bupivacaine. Methods Sixty ASA Ⅰ or Ⅱ patients, aged 18-64, weighing 46-75 kg, undergoing elective urological surgery under combined spinal-epidural anesthesia, were randomized into 2 groups ( n = 30each) receiving intrathecal 0.5% ropivacaine and 0.5% bupivacaine respectively. The ED50 was determined by up-down sequential allocation. The initial dose was 4 mg. Each time the dose increased/decreased by 1 mg. Efficacy was determined by the occurrence of any motor block in either lower extremity (modified Bromage scale > 0)within 5 or 10 min after the spinal injection. Results The intrathecal ED50 for motor block was 6.68 mg for ropivacaine (95% confidence interval 6.27-7.13 mg) and 4.07 mg for bupivacaine (95% confidence interval 3.56-4.47mg) . The relative motor blocking potency ratio was ropivacaine/bupivacaine 0.61. Conclusion The potency of intrathecal ropivacaine is lower than that of bupivacaine for motor block.     

蛛网膜下腔注射罗哌卡因与布比卡因运动神经阻滞效力的比较

Objective To determine the median effective doae (ED50) for motor block after intrathecal ropivacaine and bupivacaine. Methods Sixty ASA Ⅰ or Ⅱ patients, aged 18-64, weighing 46-75 kg, undergoing elective urological surgery under combined spinal-epidural anesthesia, were randomized into 2 groups ( n = 30each) receiving intrathecal 0.5% ropivacaine and 0.5% bupivacaine respectively. The ED50 was determined by up-down sequential allocation. The initial dose was 4 mg. Each time the dose increased/decreased by 1 mg. Efficacy was determined by the occurrence of any motor block in either lower extremity (modified Bromage scale > 0)within 5 or 10 min after the spinal injection. Results The intrathecal ED50 for motor block was 6.68 mg for ropivacaine (95% confidence interval 6.27-7.13 mg) and 4.07 mg for bupivacaine (95% confidence interval 3.56-4.47mg) . The relative motor blocking potency ratio was ropivacaine/bupivacaine 0.61. Conclusion The potency of intrathecal ropivacaine is lower than that of bupivacaine for motor block.     

妇科手术患者蛛网膜下腔注射布比卡因与左旋布比卡因运动阻滞效应的比较

Objective To determine the median effective dose (ED50) for motor block after intrathecal bupivacaine and ievobupivacaine and define their motor-blocking potency ratios. Methods In this study ED50 was determined by up-down sequential allocation. Sixty ASA Ⅰ or Ⅱ patients aged 20-60 yr with body mass index <30 kg/m2/ undergoing elective gynecological surgery under combined spinal-epidural anesthesia were randomized into 2 groups receiving intrathecal 0.5% bupivacaine and levobupivacaine respectively. The initial dose was 5 mg.Each time the dose increased/decreased by 1 mg. Efficacy was determined by the occurrence of maximum motor block (Bromage scale = 3) in both lower limbs within 20 min after the spinal injection. Results Intrathecal ED50for motor block was 6.04 mg for bupivacaine (95% CI 5.30-6.93 mg), 9.55 mg for levobupivacaine (95% CI 8.62-10.97 mg) (P <0.01). The relative motor blocking potency ratio was levobupivacaine/bupivacalne 0.63 (95 % CI 0.52-0.75). Conclusion The potency of intrathecal levobupivacaine is lower than that of bupivacaine for motor block. The ratio is 0.63.     

罗哌卡因混合舒芬太尼用于剖宫产术患者腰麻的半数有效剂量

目的 确定剖宫产术患者混合舒芬太尼时罗哌卡因腰麻的半数有效剂量(ED50).方法 择期行剖宫产术患者28例,ASA分级Ⅰ或Ⅱ级,经L2,3间隙行脊椎.硬膜外联合穿刺.蛛网膜下腔注射罗哌卡因混合舒芬太尼5 μg,注射时间30 s.第1例患者罗哌卡因剂量为11 mg,采用序贯法,根据腰麻是否成功确定下一例患者的罗哌卡因剂量,相邻剂量梯度为1 mg.采用序贯法计算罗哌卡因腰麻的ED50(95%可信区间).结果 罗哌卡因腰麻的ED50为7.780 mg(95%可信区间为6.850～8.836 mg).结论 罗哌卡因混合舒芬太尼5 μg用于剖宫产术腰麻的ED50为7.780 mg.

Abstract：

Objective To determine the median effective dose (ED50 ) of ropivacaine for spinal anesthesia when combined with sufentanil in patients undergoing caesarean section. Methods Twenty-eight ASA Ⅰ or Ⅱ parturients, aged 18-40 yr, weighing 50-110 kg, undergoing cesarean section under combined spinal-epidural anesthesia, were enrolled in this study. Combined spinal-epidural anesthesia was performed at L2,3 interspace. The mixture of ropivacaine and 5 fig sufentanil was injected into the subarachnoid space over 30 s. The initial dose of ropivacaine was 11 mg. The dose was increased/decreased by 1 mg in the next patient. The ED50 and 95% confidence interval were calculated by up-and-down method. Results The ED50 of ropivacaine was 7.780 mg (95% confidence interval 6.850-8.836 mg). Conclusion When combined with sufentanil 5 μg, the ED50 of ropivacaine for spinal anesthesia is 7.780 mg in patients undergoing caesarean section.     

0.5%罗哌卡因与布比卡因10mg在蛛网膜下腔阻滞的比较

目的观察0.5%罗哌卡因、布比卡因10 mg蛛网膜下腔阻滞对感觉、运动神经的阻滞效果及对血流动力学影响。方法随机选取择期行下肢、下腹或肛肠手术病人48例,ASAⅠ~Ⅱ级,分为布比卡因组(BP组)和罗哌卡因组(RP组),于L2~3、L3~4间隙行腰硬联合穿刺,蛛网膜下腔穿刺成功后于蛛网膜下腔分别注入0.5%的布比卡因或罗哌卡因10 mg,之后于硬膜外腔向头侧置管4 cm以备蛛网膜下腔阻滞不能满足手术需要时追加局麻药。观查并记录感觉阻滞平面,运动神经阻滞程度及血流动力学变化。结果两组病人血流动力学稳定,麻醉平面均能满足手术要求。BP组感觉平面高于RP组,RP组术后下肢运动恢复快于BP组。结论0.5%罗哌卡因、布比卡因10 mg用于腰硬联合麻醉可作为肛肠、部分下腹、下肢手术的麻醉选择;其中罗哌卡因术后下肢运动恢复快,较快恢复自主排尿为其优点。     

超声引导下罗哌卡因臂丛神经阻滞的半数有效浓度

目的 超声引导下罗哌卡因臂丛神经阻滞的半数有效浓度.方法 择期上肢手术患者50例,年龄19～72岁,体重45～83 ks,身高150～181 cm,ASA分级Ⅰ或Ⅱ级.超声引导下行臂丛神经阻滞,定位成功后注入罗哌卡因30 ml,初始浓度0.50%,浓度变化梯度为O.05%,阻滞有效则下一例采用低一级浓度,阻滞无效,则下一例采用高一级浓度.采用Prebit法计算超声引导下罗哌卡因臂丛神经阻滞的半数有效浓度及其95%可信区间.结果 超声引导下罗哌卡因臂丛神经阻滞的半数有效浓度为0.436%,95%可信区间为0.393%～0.477%.结论 超声引导下罗哌卡因臂丛神经阻滞的半数有效浓度为0.436%.

Abstract：

Objective To determine the median effective concentration (EC50) of ropivacaine for ultrasound-guided brachial plexus block.Methods Fifty ASA Ⅰ or Ⅱ patients of both sexes, aged 19-72 yr, weighing 45-83 kg, scheduled for upper extremity surgery under brachial plexus block guided by ultrasound, were enrolled in this study. Brachial plexus block was performed under the guidance of ultrasound. After successful location, ropivacaine 30 ml was injected. EC50 of ropivacaine was determined by up-and-down sequential method. The initial concentration was 0.50% . Each time the concentration increased/decreased by 0.05% . EC50 of ropivacaine required for ultrasound-guided brachial plexus block and 95% confidence interval were calculated using Probit analysis.Results The EC50 of ropivacaine resulting in complete block of the brachial plexus nerve was 0.436%(95% confidence interval 0.393%-0.477% ). Conclusion The EC50 of ropivacaine is 0.436% for ultrasoundguided brachial plexus block.     

罗哌卡因蛛网膜下腔阻滞用于剖宫产的量效关系

目的 研究罗哌卡因蛛网膜下腔阻滞用于剖宫产的量效关系.方法 择期剖宫产患者100例,随机、双盲分为四组.于L2-3间隙蛛网膜下腔穿刺成功后,分别注射罗哌卡因15 mg(A组)、17.5 mg(B组)、20 mg(C组)、22.5 mg(D组).采用针刺法测定感觉阻滞平面,改良Bromage评分法测定下肢运动神经阻滞程度,VAS评分评估患者疼痛程度,术者评定腹壁松弛度,记录麻醉后不良反应.采用Probit法计算50%和95%患者镇痛有效的罗哌卡因剂量(ED50和ED95)及其95%可信区间(CI).结果 随着剂量加大,运动阻滞起效时间逐渐缩短,Bromage评分逐渐增高,感觉和运动恢复时间逐渐延长.四组镇痛有效率分别为36%、64%、96%、100%,腹壁松弛度"很松"的分别为24%、48%、92%、100%.麻醉后不良反应少.罗哌卡因的ED50为15.95 mg(95%CI 15.31～16.62 mg),ED95为18.76 mg(95%CI 17.67～19.54 mg).结论 国大罗哌卡因用于剖宫产蛛网膜下腔阻滞的ED50为15.95 mg,ED95为18.76 mg.     

剖宫产术患者蛛网膜下腔注射不同等比重局麻药的药效学

目的 探讨剖宫产术患者蛛网膜下腔注射不同等比重局麻药的药效学.方法 拟在脊椎-硬膜外联合阻滞下行剖宫产术患者96例,孕37～41周,ASA分级Ⅰ或Ⅱ级,体重50～85kg,随机分为3组(n=32):布比卡因组、左旋布比卡因组和罗哌卡因组分别于蛛网膜下腔注射等比重0.5%布比卡因、等比重0.5%左旋布比卡因和等比重0.5%罗哌卡因.采用序贯法进行试验,初始剂量为9 mg,相邻剂量比为0.9,麻醉有效,则下一例患者采用低一级剂量;麻醉无效,则下一例患者采用高一级剂量.麻醉有效的标准:注射局麻药后15 min内感觉阻滞平面达到T7或以上、术中无牵拉痛、注射局麻药后45 min内硬膜外不需要追加局麻药.计算3种局麻药麻醉的半数有效剂量(ED50)和95%有效剂量(ED95)及其95%可信区间(95%CI).结果 布比卡因麻醉有效的ED50(95%CI)、ED95(95%CI)分别为6.15(5.48～6.68)mg、7.62(6.91～11.82)mg;左旋布比卡因麻醉有效的ED50(95%CI)、ED95(95%CI)分别为8.06(7.46～8.62)mg、9.59(8.86～13.42)mg;罗哌卡因麻醉有效的ED50(95%CI)、ED95(95%CI)分别为10.55(9.73～11.49)mg、12.80(11.66～21.42)mg.布比卡因、左旋布比卡因和罗哌卡因的效价比为1.00:0.76:0.58.结论 剖宫产术患者蛛网膜下腔注射等比重布比卡因、左旋布比卡因和罗哌卡因麻醉有效的效价比为1.00∶0.76∶0.58.     

经尿道前列腺电切术老年患者鞘内注射不同局麻药的药效学

目的 探讨经尿道前列腺电切术老年患者鞘内注射不同局麻药的药效学.方法 择期拟在脊椎-硬膜外联合阻滞下行经尿道前列腺电切术的老年患者90例,ASA分级Ⅰ～Ⅲ级,年龄69～82岁,体重指数＜30 kg/m2,随机分为3组(n=30):左旋布比卡因组(L组)、罗哌卡因组(R组)和布比卡因组(B组)分别于蛛网膜下腔注射0.5%左旋布比卡因、0.5%罗哌卡因、0.5%布比卡因.采用序贯法进行试验,初始剂量分别为7、10、6 mg,相邻剂量比均为0.9.阻滞有效,则下一例采用低一级剂量;阻滞无效,则下一例采用高一级剂量.阻滞有效的标准为:蛛网膜下腔注药后20 min内感觉阻滞平面达T10.计算3种局麻药半数有效剂量(ED50)及其95%可信区间(95%CI).结果 经尿道前列腺电切术老年患者鞘内注射左旋布比卡因、罗哌卡因和布比卡因阻滞的ED50及其95%CI分别为6.781(6.561～7.024)mg、9.135(8.670～9.616)mg和5.170(5.012～5.333)mg.左旋布比卡因、罗哌卡因和布比卡因的效价比为0.76∶0.57∶1.00.结论 经尿道前列腺电切术老年患者鞘内注射左旋布比卡因、罗哌卡因和布比卡因阻滞的效价比为0.76∶0.57∶1.00.     

妇科手术患者蛛网膜下腔注射布比卡因与左旋布比卡因运动阻滞效应的比较

目的 比较妇科手术患者蛛网膜下腔注射布比卡因与左旋布比卡因运动阻滞的的效应.方法 拟在脊椎-硬膜外联合麻醉下行妇科手术的患者60例,ASA Ⅰ或Ⅱ级,年龄20～60岁,身高155～170 cm,体重指数<30 kg/m2,随机分为2组(n=30),布比卡因组(B组):蛛网膜下腔注射等比重0.5%布比卡因;左旋布比卡因组(L组):蛛网膜下腔注射等比重0.5%左旋布比卡因.采用序贯法进行试验,每组第1例患者局麻药剂量均为5 mg,剂量变化梯度为1 mg.运动阻滞有效定义为蛛网膜下腔注药结束后20 min内双下肢改良Bromage评分均达到3分.若上1例有效,则下1例采用低一级剂量;若无效,则下1例采用高一级剂量.采用概率单位回归法计算两药运动阻滞的半数有效剂量(ED50)及其95%可信区间(95%CI).结果 布比卡因运动阻滞的ED50及其95%CI为6.04(5.30～6.93)mg,左旋布比卡因运动阻滞的ED50及其95%CI为9.55(8.62～10.97)mg,布比卡因运动阻滞的ED50低于左旋布比卡因(P<0.01);左旋布比卡因与布比卡因运动阻滞的效价比及其95%CI为0.63(0.52～0.75).结论 左旋布比卡因蛛网膜下腔麻醉时运动阻滞的效应低于布比卡因.     

鞘内注射罗哌卡因、左旋布比卡因和布比卡因后运动阻滞效能的比较

目的测定罗哌卡因、左旋布比卡因和布比卡因鞘内注射后运动阻滞的半数有效量（ED50）及其运动阻滞的相对效能。方法104例在腰麻、硬膜外联合麻醉下行择期剖宫产的产妇随机分为3组，分别鞘内注射0．5％（质量／体积）的罗哌卡因、左旋布比卡因和布比卡因，起始剂量是4mg，试验递增剂量为1mg.有效的定义是：鞘内注药5分钟内任一下肢出现运动阻滞（改良的Bromage评分和臀部运动功能评分）。结果鞘内注射罗哌卡因运动阻滞的ED50值为5．79mg（95％CI：4．62～6．96）；左旋布比卡因的ED50为4．83mg（95％CI：4．35～5．32）；布比卡因的ED50为3．44mg（95％CI：2．55～4．34）（P〈0．0007）。运动阻滞效能的相对比例：罗哌卡因／布比卡因为0．59（95％CI：0．42—0．82）；罗哌卡因／左旋布比卡因为0．83（95％CI：0．64～1．09）；左旋布比卡因／布比卡因为0．71（95％CI：0．51～0．98）。结论3种酰胺类局麻药鞘内注射后运动阻滞效能由低到高分别是：罗哌卡因、左旋布比卡因和布比卡因。     

The relative motor blocking potencies of intrathecal ropivacaine: effects of concentration

This study established the median effective dose (ED(50)) for motor block of intrathecal 1% and 0.1% ropivacaine and determined the effects of the concentration of the solution injected on the motor block obtained. We enrolled into this prospective, randomized, double-blind, sequential allocation study 54 parturients undergoing elective Cesarean delivery under combined spinal-epidural technique. Parturients were randomized to receive intrathecal ropivacaine either 1% or 0.1%. The initial dose was chosen to be 4 mg, with subsequent doses being determined by the response of the previous patient (testing interval, 1 mg). The occurrence of any motor block in either lower limb within 5 min from the intrathecal injection of the study solution was considered effective. The motor block at 5 min was 6.1 mg for 1% ropivacaine (95% confidence interval [CI], 5.1-7.1) and was 9.1 mg (95% CI, 7.8-10.3) for 0.1% ropivacaine (P = 0.0013; 95% CI difference, 1.3-4.7). The relative efficacy ratio of the 2 concentrations was 1.5 (95% CI difference, 1.2-1.9) in favor of the larger concentration. The ED(50) of spinal ropivacaine to produce motor block in pregnant patients was significantly influenced by the concentration of the local anesthetic, with dose requirements being increased by 50% for the smaller concentration. IMPLICATIONS: The minimum local anesthetic dose for motor block with 0.1% ropivacaine is 50% larger than the 1% concentration with a relative efficacy ratio of 1.5. Our findings suggest that more diluted local anesthetic solutions determine less motor block, and this may be considered in ambulant laboring parturients.     

Minimum local analgesic doses of ropivacaine, levobupivacaine, and bupivacaine for intrathecal labor analgesia

BACKGROUND: Doses for intrathecal opioid-local anesthetic mixtures have been arbitrarily chosen. The aim of this study was to compare the analgesic efficacies of intrathecal ropivacaine, levobupivacaine, and bupivacaine for labor analgesia and to determine the analgesic potency ratios for these three drugs. For this purpose, the authors used the up-down sequential allocation model, which estimates the minimum local analgesic dose for intrathecal local anesthetic. METHODS: Ninety-seven nulliparous term parturients in spontaneous labor, requesting combined spinal-epidural analgesia, were randomly allocated to one of three groups to receive 0.25% spinal ropivacaine, levobupivacaine, or bupivacaine. The initial dose of the local anesthetic drug was chosen to be 2.5 mg, and the testing interval was set at 0.25 mg. The subsequent doses were determined by the response of the previous parturient. Efficacy was accepted if the visual analog pain score decreased to 10 mm or less on a 100-mm scale within 30 min. The minimum local analgesic dose was calculated using the method of Dixon and Massey. RESULTS: The intrathecal minimum local analgesic dose was 3.64 mg (95% confidence interval, 3.33-3.96 mg) for ropivacaine, 2.94 (2.73-3.16) mg for levobupivacaine, and 2.37 (2.17-2.58) mg for bupivacaine. The relative analgesic potency ratios were 0.65 (0.56-0.76) for ropivacaine:bupivacaine, 0.80 (0.70-0.92) for ropivacaine:levobupivacaine, and 0.81 (0.69-0.94) for levobupivacaine:bupivacaine. There were significant trends (P levobupivacaine > ropivacaine.     

Minimum Local Analgesic Doses of Ropivacaine, Levobupivacaine, and Bupivacaine for Intrathecal Labor Analgesia

Background: Doses for intrathecal opioid-local anesthetic mixtures have been arbitrarily chosen. The aim of this study was to compare the analgesic efficacies of intrathecal ropivacaine, levobupivacaine, and bupivacaine for labor analgesia and to determine the analgesic potency ratios for these three drugs. For this purpose, the authors used the up-down sequential allocation model, which estimates the minimum local analgesic dose for intrathecal local anesthetic.

Methods: Ninety-seven nulliparous term parturients in spontaneous labor, requesting combined spinal-epidural analgesia, were randomly allocated to one of three groups to receive 0.25% spinal ropivacaine, levobupivacaine, or bupivacaine. The initial dose of the local anesthetic drug was chosen to be 2.5 mg, and the testing interval was set at 0.25 mg. The subsequent doses were determined by the response of the previous parturient. Efficacy was accepted if the visual analog pain score decreased to 10 mm or less on a 100-mm scale within 30 min. The minimum local analgesic dose was calculated using the method of Dixon and Massey.

Results: The intrathecal minimum local analgesic dose was 3.64 mg (95% confidence interval, 3.33-3.96 mg) for ropivacaine, 2.94 (2.73-3.16) mg for levobupivacaine, and 2.37 (2.17-2.58) mg for bupivacaine. The relative analgesic potency ratios were 0.65 (0.56-0.76) for ropivacaine:bupivacaine, 0.80 (0.70-0.92) for ropivacaine:levobupivacaine, and 0.81 (0.69-0.94) for levobupivacaine:bupivacaine. There were significant trends (P <= 0.021) for greater motor block with bupivacaine and levobupivacaine.     

Determination of the full dose-response relation of intrathecal bupivacaine, levobupivacaine, and ropivacaine, combined with sufentanil, for labor analgesia

BACKGROUND: Ropivacaine and levobupivacaine are local anesthetics that produce less motor block and greater sensory-motor separation when compared with equal milligram doses of bupivacaine. Although minimum local analgesic concentration studies suggested that they are less potent than bupivacaine, full dose-response studies have not been performed. The current trial describes the dose-response relation of levobupivacaine, ropivacaine, and bupivacaine, combined with sufentanil, when used for intrathecal labor analgesia. METHODS: Four hundred fifty term parturients in active labor were included in this double-blind, randomized trial. Combined spinal-epidural anesthesia was performed, and ropivacaine, levobupivacaine, or bupivacaine was intrathecally administered in a dose of 1.0, 1.5, 2.0, 2.5, 3.0, or 3.5 mg, always combined with 1.5 microg sufentanil. Patients were considered responders to spinal analgesia if the visual analog scale score for pain was less than 25 mm within 15 min and the visual analog scale score remained less than 25 mm for 45 min. Patient demographics, obstetric data, maternal side effects, and fetal and neonatal well-being were noted. Group-specific dose-response curves were constructed using a probit regression model. RESULTS: The ED95 of bupivacaine was 3.3 mg (95% confidence interval, 2.9-4.1). The ED95s of ropivacaine and levobupivacaine were 4.8 mg (95% confidence interval, 4.0-6.7) and 5.0 mg (95% confidence interval, 4.1-7.0), respectively. Racemic bupivacaine was significantly more potent than ropivacaine (P=0.0027) and levobupivacaine (P=0.0006). Ropivacaine and levobupivacaine were of similar potency (P=0.91). CONCLUSIONS: This full dose-response study suggests that ropivacaine and levobupivacaine are of similar potency, whereas bupivacaine is more potent than both other drugs.     

Determination of the Full Dose-Response Relation of Intrathecal Bupivacaine, Levobupivacaine, and Ropivacaine, Combined with Sufentanil, for Labor Analgesia

Background: Ropivacaine and levobupivacaine are local anesthetics that produce less motor block and greater sensory-motor separation when compared with equal milligram doses of bupivacaine. Although minimum local analgesic concentration studies suggested that they are less potent than bupivacaine, full dose-response studies have not been performed. The current trial describes the dose-response relation of levobupivacaine, ropivacaine, and bupivacaine, combined with sufentanil, when used for intrathecal labor analgesia.

Methods: Four hundred fifty term parturients in active labor were included in this double-blind, randomized trial. Combined spinal-epidural anesthesia was performed, and ropivacaine, levobupivacaine, or bupivacaine was intrathecally administered in a dose of 1.0, 1.5, 2.0, 2.5, 3.0, or 3.5 mg, always combined with 1.5 [mu]g sufentanil. Patients were considered responders to spinal analgesia if the visual analog scale score for pain was less than 25 mm within 15 min and the visual analog scale score remained less than 25 mm for 45 min. Patient demographics, obstetric data, maternal side effects, and fetal and neonatal well-being were noted. Group-specific dose-response curves were constructed using a probit regression model.

Results: The ED95 of bupivacaine was 3.3 mg (95% confidence interval, 2.9-4.1). The ED95s of ropivacaine and levobupivacaine were 4.8 mg (95% confidence interval, 4.0-6.7) and 5.0 mg (95% confidence interval, 4.1-7.0), respectively. Racemic bupivacaine was significantly more potent than ropivacaine (P = 0.0027) and levobupivacaine (P = 0.0006). Ropivacaine and levobupivacaine were of similar potency (P = 0.91).     

Median effective local anesthetic doses of plain bupivacaine and ropivacaine for spinal anesthesia administered via a spinal catheter for brachytherapy of the lower abdomen

BACKGROUND AND OBJECTIVES: Continuous spinal anesthesia via a spinal catheter allows adjusting the duration and extent of anesthesia to surgical needs, maintenance of hemodynamic stability, and good postoperative analgesia. This study was designed to determine the median effective local anesthetic dose of plain ropivacaine and bupivacaine administered intrathecally for interstitial brachytherapy of the lower abdomen using the Dixon up-and-down method. METHODS: Forty patients were randomly allocated to receive either intrathecal bupivacaine 5 mg per mL or ropivacaine 10 mg per mL via a 24-gauge spinal catheter at the L3-4 interspace. The initial dose was 10 mg of bupivacaine or 20 mg of ropivacaine; the dosing intervals were 1 mg and 2 mg, respectively. Doses for subsequent patients were determined by the response of the previous patient in that group. Successful anesthesia was defined as a loss of sensation to a cold stimulus at the T6 level and full motor blockade within 20 minutes after administration of the local anesthetic. RESULTS: The median effective local anesthetic dose for intrathecal bupivacaine was 11.2 mg (95% confidence interval [CI], 10.3-12.1) and 22.6 mg for ropivacaine (95% CI, 20.5-24.6). A relative analgesic potency ratio of 0.50 (95% CI, 0.44-0.56) was calculated between the median effective local anesthetic dose of intrathecal bupivacaine and ropivacaine. CONCLUSIONS: Bupivacaine and ropivacaine are appropriate for continuous spinal anesthesia for interstitial radiation therapy procedures of the lower abdomen. In the dose-ranges investigated, intrathecal ropivacaine is approximately half as potent as bupivacaine.