Minimum Effective Concentration of Bupivacaine in Ultrasound-guided Axillary Brachial Plexus Block

The demographic data of all included patients were recorded. Routine monitoring of the surgical procedure, including electrocardiography, non-invasive blood pressure and pulse oximetry, was performed. Peripheral venous access was established in the nonoperative upper limb and standard intravenous premedication (0.03 mgkg of midazolan) was administered to all patients.

Brachial plexus blocks were performed through the axilla on patients in a supine position using a ultrasound device with a 13-6 MHz linear transducer (SonoSite, Bothell, WA, USA) and a Stimuplex® DIG RC peripheral nerve stimulator (B. Braun, Melsung, Germany).

The end of the local anesthetic injection was considered time 0 for evaluating the effectiveness of the block. A blinded observer, who was not present during the injection and was unaware of the concentration of local anesthetic used, assessed motor, thermal and sensory blocks. These assessments were performed every 5 minutes after the procedure for 30 minutes or until the block was deemed effective.

Motor function was assessed using a modified Bromage scale. The following muscles were assessed: finger flexors (median nerve), finger extensors (radial nerve), finger adductors (ulnar nerve) and elbow flexion (musculocutaneos nerve).The assessment of thermal sensation in the upper limb was performed using gauze and alcohol. Pain sensation was assessed by a pinprick test using a 23 G needle. The thermal and pain sensitivities of the ulnar, median, radial and musculocutaneos were examined.

Surgical anesthesia was defined as a motor scale of 2 or lower, with absent of appreciation of cold and pinprick sensation. Patients who exhibited block failure received an ultrasound-guided complement to the nerve block distal to axilla or conversion to general anestehesia.