Ultrasound-guided Axillary Plexus Block - Dose Reduction of Prilocaine

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

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.

Study Overview

• Status: Completed
• Conditions: Other Surgical Procedures
• Intervention / Treatment: Drug: midazolam; Drug: prilocaine 1%; Drug: prilocaine 1%; Drug: prilocaine 1%

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.

• Study Type: Interventional
• Enrollment (Actual): 120
• Phase: Phase 4

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years to 75 years (Adult, Older Adult)
• Accepts Healthy Volunteers: No
• Genders Eligible for Study: All

Description

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

Study Plan

How is the study designed?

Design Details

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

Number of Arms

3

Arms and Interventions

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

What is the study measuring?

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.

Collaborators and Investigators

• Sponsor: Helios Research Center
• Investigators: Study Director: Georg Rehmert, Dr.med., Klinik für Anästhesiologie und Intensivtherapie, Helios Kliniken Schwerin, Wismarsche Strasse 393-7, DE-19049 Schwerin

Study record dates

Study Major Dates

• Study Start: September 1, 2009
• Primary Completion (Actual): April 1, 2010
• Study Completion (Actual): April 1, 2010

Study Registration Dates

• First Submitted: March 4, 2011
• First Submitted That Met QC Criteria: March 4, 2011
• First Posted (Estimate): March 7, 2011

Study Record Updates

• Last Update Posted (Estimate): July 12, 2011
• Last Update Submitted That Met QC Criteria: July 6, 2011
• Last Verified: June 1, 2011

More Information

Terms related to this study

• Keywords: ultrasound; hand; regional anesthesia; prilocaine; methaemoglobin; ASA risk groups I-II; adult outpatients; surgical spectrum covered procedures; distal forearm
• Additional Relevant MeSH Terms: Physiological Effects of Drugs; Neurotransmitter Agents; Molecular Mechanisms of Pharmacological Action; Central Nervous System Depressants; Peripheral Nervous System Agents; Sensory System Agents; Anesthetics, Intravenous; Anesthetics, General; Anesthetics; Tranquilizing Agents; Psychotropic Drugs; Hypnotics and Sedatives; Adjuvants, Anesthesia; Anti-Anxiety Agents; GABA Modulators; GABA Agents; Anesthetics, Local; Midazolam; Prilocaine
• Other Study ID Numbers: A 2009 24