局部麻醉药浓度和剂量对持续锁骨下神经阻滞的影响：一项多中心、随机、单盲、对照研究

背景目前尚不明确局部麻醉药浓度或药物总剂量是否是连续外周神经阻滞效果最主要的决定性因素。此前仅有一项关于胭窝坐骨神经阻滞的研究，该研究报道了使用高容量较低浓度罗哌卡因发生肢体感觉完全阻滞的概率远远高于低容量较高浓度罗哌卡因，但上述现象是否仅限于腘窝处的坐骨神经，或者说是否因解剖部位变化而异尚不清楚。因此，本研究的检验假设定为：在连续锁骨下臂丛阻滞中，以不同的浓度和速率注射总量相等的罗哌卡因，可以产生相似的阻滞效果。方法选择拟行肘关节远端、中等疼痛骨科手术患者，经喙突入路放置锁骨下臂丛阻滞导管。患者经随机分组确定手术后第2天应用罗哌卡因神经周围镇痛的方法：浓度0．2％组（背景剂量8ml／h，单次追加量4ml）或0．4％组（背景剂量4ml／h，单次追加量2ml）。两组患者每小时持续注入罗哌卡因的总量均为16mg，每30分钟可能还有患者自控的追加剂量8mg。主要观察指标为自手术后次日早晨开始的24小时内患侧肢体完全无感觉的发生率，次要观察指标是镇痛效果和患者的满意度。结果给予0．4％罗哌卡因（n=27）的患者发生肢体无感觉的平均次数（标准差）为1．8（1．6）次，而给予0．2％罗哌卡因（n=23）的患者为0．6（0．9），评估差异为1．2次，95％可信区间0．5～1．9次（P=0．001）。手术后镇痛满意度（评分0—10分，10分为最高分）在0．2％罗哌卡因组得分的中位数（25％～75％百分位数）为10．0分（8．0～10．0），0．4％罗哌卡因组为7．0分（5．3～8．9）。镇痛效果两组相近。结论在连续锁骨下神经阻滞时，除了注射局麻药物总量之外，药物的浓度和容量是另两种影响神经周围镇痛辫果的因素。容量偏小而浓度略高的罗哌卡因产生肢体完全无感觉的概率较高，这一结果与此前关于连续胭窝坐骨神经阻滞的研究结果相反。局麻药浓度与容量之间的关系相当复杂，且随置管部位的不同而异。

BACKGROUND： It remains unclear whether local anesthetic concentration or total drug dose is the primary determinant of continuous peripheral nerve block effects. The only previous investigation, involving continuous popliteal-sciatic nerve blocks, specifically addressing this issue reported that insensate limbs were far more common with higher volumes of relatively dilute ropivacaine compared with lower volumes of relatively concentrated ropivacaine. However, it remains unknown if this relationship is specific to the sciatic nerve in the popliteal fossa or whether it varies depending on anatomic location. We therefore tested the null hypothesis that providing ropivacaine at different concentrations and rates, but at an equal total basal dose, produces comparable effects when used in a continuous infradavicular brachial plexus block. METHODS： Preoperatively, an infradavicular catheter was inserted using the coracoid approach in patients undergoing moderately painful orthopedic surgery distal to the elbow. Patients were randomly assigned to receive a postoperative perineural ropivacaine infusion of either 0. 2% （basal 8 ml/h, bolus 4 ml） or 0.4% （basal 4 ml/h, bolus 2 ml） through the second postoperafive day. Both groups, therefore, received 16 mg of ropivacaine each hour with a possible addition of 8 mg every 30 min via a patient-controlled bolus dose. Our primary end point was the incidence of an insensate limb during the 24-h period beginning the morning after surgery. Secondary end points included analgesia and patient satisfaction. RESULTS： Patients given 0. 4% ropivacaine （n = 27） experienced an insensate limb. a mean （SD） of i. 8 （1.6） times, compared with O. 6 （0. 9） times for sub}ects receiving0. 2% ropivacaine （n = 23; estimated difference = 1. 2 episodes, 95% confidence interval, 0. 5 - 1.9 episodes; P = 0. 001 ）. Satisfaction with postoperative analgesia （scale 0 - 10, 10 = highest） was scored a median （25th- 75thpercentiles） of10.0 （8.0-10.0） in Group0.2% and 7.0 （5.3 -8.9） in Group0.4% （P=0.018）. Analgesia was similar in each group. CONCLUSIONS： For continuous infradavicular nerve blocks, local anesthetic concentration and volume influence perineural infusion effects in addition to the total mass of local anesthetic administered. Insensate limbs were far more common with smaller volumes of relatively concentrated ropivacaine. This is the opposite of the relationship previously reported for contin-uous popliteal-sdatic nerve blocks. The interaction between local anesthetic concentration and volume is thus complex and varies among catheter locations.