Minimum effective concentration of bupivacaine for axillary brachial plexus block guided by ultrasound

The use of ultrasound in regional anesthesia allows reducing the dose of local anesthetic used for peripheral nerve block. The present study was performed to determine the minimum effective concentration (MEC90) of bupivacaine for axillary brachial plexus block. Patients undergoing hand surgery were recruited. To estimate the MEC90, a sequential up-down biased coin method of allocation was used. The bupivacaine dose was 5mL for each nerve (radial, ulnar, median, and musculocutaneous). The initial concentration was 0.35%. This concentration was changed by 0.05% depending on the previous block; a blockade failure resulted in increased concentration for the next patient; in case of success, the next patient could receive or reduction (0.1 probability) or the same concentration (0.9 probability). Surgical anesthesia was defined as driving force ≤2 according to the modified Bromage scale, lack of thermal sensitivity and response to pinprick. Postoperative analgesia was assessed in the recovery room with numeric pain scale and the amount of drugs used within 4h after the blockade. MEC90 was 0.241% [R2: 0.978, confidence interval: 0.20–0.34%]. No patient, with successful block, reported pain after 4h. This study demonstrated that ultrasound guided axillary brachial plexus block can be performed with the use of low concentration of local anesthetics, increasing the safety of the procedure. Further studies should be conducted to assess blockade duration at low concentrations. O uso do ultrassom na anestesia regional permite a redução da dose de anestésico local utilizada para o bloqueio de nervos periféricos. O presente estudo foi conduzido com o objetivo de determinar a concentração mínima efetiva (CME90) de bupivacaína para o bloqueio do plexo braquial via axilar (BPVA). Pacientes submetidos a cirurgias da mão foram recrutados. Foi usado um método de alocação “biased coin” seqüencial “up-down” para estimar a CME90. A dose de bupivacaína foi de 5mL para cada nervo (radial, ulnar, mediano e musculocutâneo). A concentração inicial de era 0,35%. Essa concentração era alterada em 0,05% dependendo do bloqueio anterior: a falha do bloqueio resultava em aumento da concentração para o próximo paciente; no caso de sucesso, o próximo paciente poderia receber ou redução (probabilidade de 0,1) ou mesma concentração (probabilidade 0,9). A anestesia cirúrgica foi definida como força motora ≤ 2 segundo a escala de Bromage modificada, ausência de sensibilidade térmica e de respos