Low minimal stimulating current improves infraclavicular brachial plexus block efficacy

Abstract

To investigate if low minimal stimulating current used in nerve stimulator localizing is associated with a greater likelihood of infraclavicular block success. 188 patients, aged 14 to 64, of ASA physical status class I - II, and scheduled for surgical procedures below elbow were assigned to low current group (Group A, n = 118) or regular current group (Group B, n = 70) according to the last figure of admission number. The infraclavicular plexus block was performed using the Wilson's approach 2 cm medial and caudal to the coracoid process guided by nerve stimulator with 30 ml of 0.5% ropivacaine after eliciting distal motor responses. The minimal stimulating current (I) was adjusted to 0.1 mA < or = I < 0.3 mA in Group A or 0.3 mA < or = I < 0.5 mA in Group B. The 2 groups were further sub-divided into 2 subgroups: lateral cord subgroup when motor responses of wrist and finger-flexion and pronation of forearm were induced, and posterior subgroup when extension of wrist and finger was induced. Anesthesia efficacy was assessed 5, 10, 20 and 30 min after the local anesthetic injection. A successful blockade was defined as analgesia in all dermatomes of the five nerves (median nerve, musculocutaneous nerve, radial nerve, ulnar nerve, and medial antebrachial cutaneous nerve). The success rate of Group A was 84.7%, significantly higher than that of Group B (67.1%, P < 0.05). When divided into posterior and lateral cord subgroups, The success rate of the posterior subgroup of Group A was 96.5%, significantly higher than that of the posterior subgroup of Group B (78.9%, P < 0.05). Minimal stimulating current lower than 0.3 mA, significantly lower than the recommended value (0.5 mA), improves the efficacy of infraclavicular brachial plexus block, especially when the posterior cord is stimulated.