Ultrasound-guided Axillary Plexus Block - Dose Reduction of Prilocaine

Study Overview
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Brief Summary
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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
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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.

Official Title
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Ultrasound-guided Block of the Brachial Plexus Using Prilocaine: Effects of Local-anesthetic Dose Reduction on Parameters of Block Quality and Adverse Effects in Outpatients

Conditions
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Other Surgical Procedures

Intervention / Treatment
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* Drug: midazolam
* Drug: prilocaine 1%
* Drug: prilocaine 1%
* Drug: prilocaine 1%


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: elective surgery on the distal forearm or the hand adult outpatients, age 18-75 years old ASA-risk groups I-II (American Society of Anesthesiologists) Body Mass Index 17-35 informed consent Exclusion Criteria: severe coagulopathy local or systemic inflammatory response ASA-risk groups ≥ Grad III severe anemia heart failure manifest shock other drugs with influence on methaemoglobinemia (nitrates, sulfonamides etc.) domestic care after surgery not ensured drug allergy : local anesthetics severe polyneuropathy pregnancy, lactation period participation in other studies non-cooperative patients addiction to drugs or alcohol

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 75 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Treatment
Allocation: Non-Randomized
Intervention Model: Parallel Assignment
Masking: Single


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Active Comparator: group A : 40ml Prilocaine 1%<br>40 outpatients : 40ml Prilocaine 1% were administered for axillary plexus block | Drug: midazolam<br>* Prior to performing the regional anesthesia the investigators administered midazolam as a premedication by mouth (3,75-7,5mg) or intravenously (2-3mg).<br>* Other names: Dormicum;Drug: prilocaine 1%<br>* 40 outpatients : 40ml prilocaine 1% were administered for axillary plexus block<br>* Other names: Xylonest 1%;|
| Active Comparator: group B : 30ml Prilocaine 1%<br>40 outpatients : 30ml prilocaine 1% were administered for axillary plexus block | Drug: midazolam<br>* Prior to performing the regional anesthesia the investigators administered midazolam as a premedication by mouth (3,75-7,5mg) or intravenously (2-3mg).<br>* Other names: Dormicum;Drug: prilocaine 1%<br>* 40 outpatients : 30ml prilocaine 1% were administered for axillary plexus block<br>* Other names: Xylonest 1%;|
| Active Comparator: group C : 20ml Prilocaine 1%<br>40 outpatients : 20ml prilocaine 1% were administered for axillary plexus block | Drug: midazolam<br>* Prior to performing the regional anesthesia the investigators administered midazolam as a premedication by mouth (3,75-7,5mg) or intravenously (2-3mg).<br>* Other names: Dormicum;Drug: prilocaine 1%<br>* 40 outpatients : 20ml prilocaine 1% were administered for axillary plexus block<br>* Other names: Xylonest 1%;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Number of Participants With Complete Sensory Block | The number of outpatients with complete sensory block of all 4 nerves (n.musculocutaneous, n.radialis, n.ulnaris,n.medianus) was registrated in each group. | 60 minutes after administration of the local anesthetic | 
| Number of Participants With Complete Motor Blocks | To examine the extent of the motor block the manual muscle function test after Vladimir Janda was used. As a complete motor block was defined, when no motion (grade zero after Janda) of muscles innervated by the four blocked nerves (musculocutaneous, median, radial and ulnar nerve) was observed within 60 minutes after administration of the local anesthetic. | Within 60 minutes after administration of the local anesthetic | 
| Onset Time. | Time from beginning of administration of the local anesthetic until complete sensoric block. | within 60 minutes after administration of the local anesthetic | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Maximum Concentrations of Methemoglobin | Concentration of Methemoglobin (Met-Hb) was measured using spectrophotometry prior to the anesthesia (baseline value) and then hourly after performing the block until a clear decrease became apparent. The maximum amount was reached in every case two or three hours after administration of the local anesthetic. | 0,1,2,3,4 hours post-dose | 
| Number of Participants With Objective Adverse Events as a Measure of Safety and Tolerability | In groups A, B and C was determined the rate of objective clinical signs of increased Met-Hb-levels : drops in oxygen saturation <93% using pulseoximetry or lip cyanosis. | Outpatients were followed for the duration of hospital stay, an average of six hours. | 
| Number of Participants With Subjective Adverse Events as a Measure of Safety and Tolerability. | In groups A, B and C was determined the rate of subjective clinical signs of increased Met-Hb-Levels : headaches or dizziness, when correlated with the peak-Met-Hb-Level. | Outpatients were followed for the duration of hospital stay, an average of six hours. | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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regional anesthesia, ultrasound, methaemoglobin, prilocaine, ASA risk groups I-II, adult outpatients, surgical spectrum covered procedures, distal forearm, hand