Ilfeld Brian M, Le Linda T, Ramjohn Joanne, Loland Vanessa J, Wadhwa Anupama N, Gerancher J C, Renehan Elizabeth M, Sessler Daniel I, Shuster Jonathan J, Theriaque Douglas W, Maldonado Rosalita C, Mariano Edward R
Department of Anesthesiology, University of California San Diego, San Diego, California 92037-7651, USA.
Anesth Analg. 2009 Jan;108(1):345-50. doi: 10.1213/ane.0b013e31818c7da5.
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 infraclavicular brachial plexus block.
Preoperatively, an infraclavicular 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 postoperative 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.
Patients given 0.4% ropivacaine (n = 27) experienced an insensate limb, a mean (sd) of 1.8 (1.6) times, compared with 0.6 (0.9) times for subjects receiving 0.2% 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-75th percentiles) of 10.0 (8.0-10.0) in Group 0.2% and 7.0 (5.3-8.9) in Group 0.4% (P = 0.018). Analgesia was similar in each group.
For continuous infraclavicular 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 continuous popliteal-sciatic nerve blocks. The interaction between local anesthetic concentration and volume is thus complex and varies among catheter locations.
局部麻醉药浓度或总药物剂量是否为连续周围神经阻滞效果的主要决定因素仍不清楚。此前唯一一项专门针对此问题的研究，涉及连续腘窝坐骨神经阻滞，报告称与相对高浓度罗哌卡因低容量相比，相对低浓度罗哌卡因高容量导致肢体感觉丧失更为常见。然而，这种关系是否特定于腘窝处的坐骨神经，或者是否因解剖位置而异仍不清楚。因此，我们检验了零假设，即在连续锁骨下臂丛神经阻滞中，以不同浓度和速率但总基础剂量相等的方式给予罗哌卡因，会产生相似的效果。
术前，采用喙突入路为肘部远端接受中度疼痛骨科手术的患者插入锁骨下导管。患者被随机分配在术后第二天接受0.2%（基础量8 mL/h，推注量4 mL）或0.4%（基础量4 mL/h，推注量2 mL）的罗哌卡因经神经周围输注。因此，两组每小时均接受16 mg罗哌卡因，并且可通过患者自控推注剂量每30分钟追加8 mg。我们的主要终点是术后次日早晨开始的24小时内肢体感觉丧失的发生率。次要终点包括镇痛效果和患者满意度。
给予0.4%罗哌卡因的患者（n = 27）肢体感觉丧失的平均（标准差）次数为1.8（1.6）次，而接受0.2%罗哌卡因的患者（n = 我们的主要终点是术后次日早晨开始的24小时内肢体感觉丧失的发生率。次要终点包括镇痛效果和患者满意度。
给予0.4%罗哌卡因的患者（n = 27）肢体感觉丧失的平均（标准差）次数为1.8（1.6）次，而接受0.2%罗哌卡因的患者（n = 23）为0.6（0.9）次（估计差异 = 1.2次发作，95%置信区间，0.5 - 1.9次发作；P = 0.001）。0.2%组术后镇痛满意度（0 - 10分，10分为最高分）的中位数（第25 - 75百分位数）为10.0（8.0 - 10.0），0.4%组为7.0（5.3 - 8.9）（P = 0.018）。两组的镇痛效果相似。
对于连续锁骨下神经阻滞，除了局部麻醉药的总用量外，局部麻醉药的浓度和容量也会影响经神经周围输注的效果。相对高浓度罗哌卡因小容量时肢体感觉丧失更为常见。这与先前报道的连续腘窝坐骨神经阻滞的关系相反。因此，局部麻醉药浓度和容量之间的相互作用很复杂，并且因导管位置而异。
