Concentração eficaz mínima de bupivacaína em bloqueio do nervo femoral guiado por ultrassom após meniscectomia artroscópica de joelhoEstudo randomizado, duplo-mascarado

Objectives: One of the requirements for hospital discharge after meniscectomy is adequate analgesia. A femoral nerve block may reduce the need for systemic analgesics, however, motor block can occur. Guided by ultrasound can reduce the local anesthetic concentration required. The primary objective of this study was to obtain the lowest effective analgesic concentration (EC50 and EC90) of bupivacaine in ultrasound-guided femoral nerve block for arthroscopic knee meniscectomy. Methods: This was a randomized, double-blind study, and patients were distributed into groups using the "up-and-down" method. The first patient received 22 ml of 0.25% bupivacaine; upon negative response, the concentration of bupivacaine was increased by 0.05% in the next patient; upon positive response, the next patient randomly received either the same concentration or a 0.05% lower concentration. A total of 52 patients undergoing arthroscopic knee meniscectomy were evaluated. The patients received 0.01 mg/kg midazolam by IV 5 min before the block. They underwent general anesthesia with 30 mcg/kg alfentanil, 2 mg/kg propofol, and maintenance with propofol, and they received remifentanil if needed. Postoperative analgesia supplementation was performed with dipyrone and, if necessary, ketoprofen; tramadol was used (50 mg) if no relief was achieved. There was evaluated: bupivacain CEM 50 and CEM 90, pain intensity, duration of analgesia, supplementary analgesic dose during 24 hours, and remifentanil administration during surgery. Results: The minimum effective concentration in 50% of patients (MEC50) was 0.160 (95% CI: 0.150-0.189), and MEC90 was 0.271 (95% CI: 0.196-0.300). There was no difference in pain intensity for different concentrations of bupivacaine. Block success occurred in 45 patients, with no difference among bupivacaine concentrations. The length of time until request of the first analgesic dose was higher with bupivacaine concentration ? 0.3% (543.8 ± 283.8 min) than with 0.25% (391.3 ± 177.8 min) or < 0.25% (302.3 ± 210.1 min). Conclusions: The MEC50 of bupivacaine for analgesia in administering an ultrasound-guided femoral nerve block was 0.160 (95% CI: 0.150-0.189), and the MEC90 was 0.271 (95% CI: 0.196-0.300).Objetivos: Um dos requisitos para alta hospitalar é a analgesia adequada. O bloqueio do nervo periférico pode reduzir a necessidade de analgésicos sistêmicos; entretanto, pode ocorrer bloqueio motor, dependendo da concentração do anestésico local utilizado. Guiado por ultrassom, a concentração de anestésico local pode ser reduzido. O objetivo primário deste estudo foi obter a concentração analgésica eficaz mínima da bupivacaína no bloqueio femoral guiado por ultrassom para meniscectomia artroscópica de joelho. Métodos: Este estudo foi prospectivo, randomizado, duplo-cego. Um total de 52 pacientes foram submetidos a meniscectomia artroscópica do joelho e receberam bloqueio femoral guiada por ultrassom usando 22 ml de bupivacaína. A concentração de bupivacaína dada a um paciente foi determinada pela resposta do paciente anterior (a biased-coin design up?down sequential method). Se teve uma resposta negativa, a concentração de bupivacaína foi aumentada em 0,05% no próximo paciente. Se teve uma resposta positiva, o próximo paciente foi randomizado para receber a mesma concentração de bupivacaína (com uma probabilidade de 0,89) ou para receber uma concentração de 0,05% menor (com uma probabilidade de 0,11). Sucesso de bloqueio foi definida como dor