Ultrasound-guided Axillary Plexus Block - Dose Reduction of Prilocaine
Condition: Other Surgical Procedures
Study type: Interventional
Phase: Phase 4

Summary: 
      Clinical aim: Does reducing the dose of local anesthetic in ultrasound-guided axillary plexus
      anesthesia have any effect on the success rate and additional parameters of block quality?
      Methodology: In this prospective cohort study three groups of 40 outpatients each were
      administered dosages of 1% prilocaine of either 40mL, 30mL or 20mL for axillary plexus
      anesthesia. Met-Hb was measured prior to administration of the block and then hourly until
      the Met-Hb concentration fell. Parameters of block quality and any adverse effects were
      recorded. The level of significance was defined with α ≤ 0.05.
    

Detailed description: 
      Background

      With the availability of high resolution portable ultrasound equipment, the use of sonography
      in the field of anesthesia has become more widespread in recent years. The investigators
      would like to draw attention to a meta-analysis of prospective randomized studies by Abrahams
      et al. as being representative of the numerous publications available. Compared to nerve
      stimulation, ultrasound-guided nerve blocks have a higher success rate with significantly
      fewer vascular punctures and shorter procedure times. However, the administration of
      ultrasound-guided regional anesthesia necessitates considerable equipment acquisition and
      training expenses. Nevertheless, the suggested benefits resulting from savings in time and
      local anesthetic, increased patient satisfaction and avoidance of complications should be
      considered in addition to the results from Abrahams et al.

      The aim of the present work was to investigate whether an ultrasound-guided block combined
      with a reduced dose of the local anesthetic prilocaine altered the success rate or other
      parameters of block quality. Any adverse effects and the methaemoglobin concentration were
      also recorded.

      Methodology

      After receiving ethics committee approval and after informing patients, ultrasound-guided
      axillary plexus anesthesia was carried out on 120 adult outpatients in ASA risk groups I-II.
      The surgical spectrum covered procedures on the distal forearm or the hand (carpal tunnel
      syndrome, ganglion extirpation, removal of material, etc.). Provision of information and
      inclusion in the study was done in the anesthesia outpatients' clinic as part of the standard
      preoperative preparation. Prior to administering the regional anesthesia the investigators
      administered midazolam as a premedication by mouth (3,75-7,5mg) or intravenously (2-3mg).
      Application of the local anesthesia was done prospectively and single blind in 3 cohorts with
      decreasing dosage. The patients received either 400mg (group A), 300mg (group B) or 200mg
      (group C) of prilocaine 1%. The block was performed under sterile conditions using a portable
      ultrasound device (Sonosite S-Nerve) and a 24 G short bevel cannula with flexible tubing. The
      block was performed using combined out-of-plane (n. musculocutaneous) and in-plane techniques
      (n.radialis, n.medianus, n.ulnaris), usually from a single puncture site. The outpatients
      were cared for in the anesthesia care unit preoperatively and postoperatively until their
      discharge. NIBP, pulse oxymetry and ECG were continuously monitored. The discharge criteria
      were widespread regression of the block with a subjective feeling of well-being including
      adequate analgesia and stable vital signs with methemoglobin (Met-Hb) concentrations ≤ 5%.
      Met-Hb levels were measured using spectrophotometry prior to the anesthesia (baseline value)
      and then hourly after performing the block until a clear decrease became apparent. A complete
      sensory block of all 4 nerves within 60 minutes of administration of the local anesthetic was
      rated as a successful block.

      For the statistical analysis the investigators selected distribution-free, nonparametric test
      methods. The Mann-Whitney U test was used when comparing 2 groups and the Kruskal-Wallis test
      or Fisher's exact test was used when comparing more than 2 groups. The level of significance
      was defined with α ≤ 0.05. With multiple paired comparisons the significance level was
      adjusted using the Bonferroni correction. The Bravais-Pearson correlation coefficient rho
      describes the relationship between the maximum Met-Hb value and the weight-based prilocaine
      dose in mg/kg.
    

Intervention name(s): midazolam; prilocaine 1%; prilocaine 1%; prilocaine 1%
Intervention type(s): Drug; Drug; Drug; Drug
Intervention description(s): Prior to performing the regional anesthesia the investigators administered midazolam as a premedication by mouth (3,75-7,5mg) or intravenously (2-3mg).; 40 outpatients : 40ml prilocaine 1% were administered for axillary plexus block; 40 outpatients : 30ml prilocaine 1% were administered for axillary plexus block; 40 outpatients : 20ml prilocaine 1% were administered for axillary plexus block
Other intervention name(s): Dormicum; Xylonest 1%; Xylonest 1%; Xylonest 1%
Intervention MeSH terms: Midazolam; Prilocaine
Allocation: Non-Randomized
Intervention model: Parallel Assignment
Masking: Single (Participant)
Primary purpose: Treatment
Keywords: ultrasound; methaemoglobin; prilocaine; regional anesthesia; ASA risk groups I-II; adult outpatients; surgical spectrum covered procedures; distal forearm; hand