Effect of digital pressure on the neurovascular sheath during perivascular axillary block

We have assessed prospectively the influence of digital pressure on the effectiveness of perivascular axillary block using a catheter technique in two groups of patients. Ninety-eight patients received axillary injections of 2% mepivacaine with adrenaline 20 ml mixed with contrast agent 20 ml. During injection firm digital pressure was applied either on the neurovascular sheath (group 1) or 6-8 cm below it (group 2). The patient's arm was then adducted. Axillary radiographs were obtained in 90 patients after 30 min. In the last eight patients radiographs were obtained after injecting 2, 20 and 40 ml of the mixture to study the dynamics of spread. There were no statistically significant differences in proximal flow of mepivacaine or in the success rate of the block between the groups. Signs of flow obstruction by the head of the humerus were seen in only eight patients. In the majority of patients local anaesthetic spread above the coracoid process, which increased the success rate of the block, but did not guarantee an effective block.