Determining the Minimum Effective Volume of Local Anesthetic for Ultrasound-guided Axillary Brachial Plexus Block
Condition: Axillary Brachial Plexus Block
Study type: Interventional

Summary: 
      This is a study to calculate the minimum effective volume of bupivacaine 0,5% with
      epinephrine for successful axillary brachial plexus block for hand surgery in 50% of the
      patients (MEV50).
    

Detailed description: 
      Study Design All patients had their demographic data recorded upon inclusion in the study.
      Routine preoperative monitoring was subsequently performed using ECG, non-invasive blood
      pressure measurements and pulse oximetry. Intravenous access was established and maintained
      with a crystalloid infusion.

      The axillary approach using ultrasound (M-Turbo ® System with HFL 38x linear transducer 13-6
      MHz, SonoSite, Bothell, WA, USA) and peripheral nerve stimulation (Stimuplex ® DIG RC, B.
      Braun, Melsung, Germany) guidance was performed to obtain brachial plexus block with the
      patient lying in the supine position. The needle used was a 22G x 50 mm (AEQ2250, BMD Group,
      Venezia, Italy). The puncture site was infiltrated with lidocaine 1% after asepsis and
      antisepsis skin treatment with chlorhexidine. After that, the ulnar, radial, median and
      musculocutaneous nerves were visualized by ultrasound (Figure 1) and had their identity
      confirmed by nerve stimulation. An initial dose of 5 mL of bupivacaine 0.5% with adrenaline
      (1:200,000) was injected in the proximity of each nerve. If severe pain at the injection was
      referred or, if nerve diameter changed during injection, injection was immediately
      interrupted, patient was removed form study and followed postoperatively for possible
      intraneural injection. The needle was repositioned during injection and perineural injected
      was ensured by ultrasound.

      The efficacy of the block was assessed by an assessor blinded to injected volume. Assessments
      were conducted every 5 min up to a total of 30 min following the end of the injection of the
      local anaesthetic. Block assessment was finished either after surgical anaesthesia was
      achieved or,after 30 min had elapsed.

      Success or failure of the block was used to dynamically reduce or increase, respectively, the
      volume of local anaesthetic that was used for the subsequent patient. When a block was
      achieved, the subsequent patient received a 0.5 mL reduction in the total volume of local
      anaesthetic per nerve. Upon failure of the block, the patient received a complementation of
      nerve blocks at a point distal to the axilla, and the volume of local anaesthetic delivered
      to the next patient was increased by 0.5 mL. After the block was assessed, the patients were
      cleared for surgery. During surgery, an infusion of 25-50 mcg.kg-1.min-1 of propofol was used
      to achieve proper sedation. Also, if during the procedure pain was referred, the block was
      considered failure and a conversion to general anaesthesia was performed.

      After surgery, the patients were admitted to the post-anaesthetic recovery room, where they
      were continuously monitored using ECG as well as non-invasive blood pressure and pulse
      oximetry until the requirements for discharge were met. Postoperative analgesia was evaluated
      in the recovery room using a visual analogue pain scale (VAS) three hours after the block.
    

Intervention name(s): Bupivacaine 0,5%
Intervention type(s): Other
Intervention description(s): The study method was a step-up/step-down sequence model where the dose for following patients was determined by the outcome of the preceding block. The starting dose of bupivacaine was 5 mL per nerve. In the case of block failure, the dose was increased by 0.5 mL per nerve. Conversely, block success resulted in a reduction in dose by 0.5 mL per nerve. Each of the three nerves was treated as a separate entity. Dose adjustments were made to each nerve individually. The volume dose was increased in 0.5 mL at every 5 consecutive cases regardless of the result of the previous block in order to minimize bias occurence. A blinded assistant assessed sensory and motor blockade at 5-min intervals up to 30 min.
Intervention MeSH terms: Bupivacaine
Intervention model: Single Group Assignment
Masking: Single (Outcomes Assessor)
Keywords: Ultrasound; Axillary block; Bupivacaine; Minimum; Volume; Minimum volume of bupivacaine 0,5%