Local Anesthetic Concentration and Rebound Pain

Study Overview
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Brief Summary
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The rebound pain after nerve block could interfere with patient's recovery and rehabilitation. It is not known how local anesthetic concentrations affect rebound pain. The aim of this study is evaluation of the effect of local anesthetic concentration on rebound pain after interscalene block for shoulder surgery.

Detailed Description
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Shoulder surgery is related to more than moderate pain after surgery. Interscalene nerve block could reduce the postoperative pain effectively. When the effect of nerve block ends, however, rebound pain could appear. The rebound pain could interfere with patient's recovery and rehabilitation. The mechanism of rebound pain is not well known. One of possible mechanism is that the pain stimulus that was blocked suddenly comes out, and it is perceived as more severe pain. The strength of the block may vary depending on the concentration of the local anesthetic. Therefore, the concentration of local anesthetics could affect rebound pain. The aim of this study is evaluation of the effect of local anesthetic concentration on rebound pain after interscalene block for shoulder surgery.

Official Title
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Evaluation of the Effect of Local Anesthetic Concentration on Rebound Pain After Interscalene Block for Shoulder Surgery

Conditions
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Rebound Pain

Intervention / Treatment
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* Other: Reduced concentration of local anesthetic (ropivacaine)
* Other: Usual concentration of local anesthetic (ropivacaine)


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Elective shoulder surgery under general anesthesia and interscalene block for postoperative pain Exclusion Criteria: Contraindication of interscalene block: pulmonary disease, lung resection history, brachial nerve injury Diabetic neuropathy Adverse drug reaction history to ropivacaine, fentanyl Impaired coagulation

Ages Eligible for Study
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Minimum Age: 19 Years
Maximum Age: 70 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: Randomized
Intervention Model: Parallel Assignment
Interventional Model Description: Randomized controlled trial One group received interscalene block with 0.15% of ropivacaine One group received interscalene block with 0.5% of ropivacaine
Masking: Triple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Low concentration<br>Interscalene block with 0.15% ropivacaine 15 ml | Other: Reduced concentration of local anesthetic (ropivacaine)<br>* Reduced concentration of ropivacaine We usually use 0.5% ropivacaine in our facility. The intervention group used 0.15% ropivacaine 15 ml<br>|
| Active Comparator: Usual concentration<br>Interscalene block with 0.5% ropivacaine 15 ml | Other: Usual concentration of local anesthetic (ropivacaine)<br>* 0.5% ropivacaine 15ml<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Rebound pain score | It is calculated by subtracting the visual analogue scale (VAS) of pain at the last time when the nerve block was effective from the highest VAS for 12 hours from the time when the nerve block effect disappeared. VAS of pain: 0=no pain   10=very severe pain | 48 hours after surgery | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| total postoperative fentanyl dose | Total dose of fentanyl injected (mcg) through patient controlled analgesia (PCA) for 48 hours after surgery | 48 hours after surgery | 
| fentanyl bolus injection time | Number of bolus injection times using patient controlled analgesia (PCA) | 48 hours after surgery | 
| Subjective satisfaction | Patient's subjective satisfaction 48 hours after surgery Use visual analogue scale (0=very unsatisfied, 10= very satisfied) | 48 hours after surgery |