The Relationship Between Needle Position and Injection Pressure During Femoral Nerve Block

Study Overview
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Brief Summary
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Recent evidence suggests that injection pressure monitoring may be able to predict needle nerve contact in the brachial plexus nerve block model, but little is known about multifascicular nerves. The investigators hypothesize that injection pressure monitoring can reliably predict needle-nerve contact during femoral nerve block.

Detailed Description
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Single center, observational study. Patients scheduled for elective lower limb surgery with femoral nerve block will be recruited. Femoral nerve will be identified using a linear ultrasound transducer. A 22 GA 5 cm nerve block needle will be inserted with bevel downward and advanced to the following conditions: Needle tip slightly indenting the fascia iliaca lateral to the femoral nerve Needle tip advanced through fascia iliaca Needle tip slightly indenting the anterior surface of the femoral nerve Needle tip withdrawn 1 mm from nerve. At each of these conditions, 1 ml of dextrose solution will be injected via an automated pump at 10 ml/min and the spread of injectate observed sonographically. Simultaneously, a blinded observer will measure opening injection pressure using both an electronic and a mechanical transducer. If opening pressure reaches 15 psi, this investigator will halt the injection. In addition, minimum threshold current required to elicit a motor response will be recorded for conditions 3 and 4. Patients will be contacted at 7 days and asked about any adverse effects.

Official Title
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The Relationship Between Needle Position and Injection Pressure During Femoral Nerve Block

Conditions
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Orthopedic Disorders

Intervention / Treatment
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* Procedure: Apposition of needle bevel against femoral nerve


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Age 18-65 ASA physical status I-III scheduled for lower limb surgery where femoral block is part of intended analgesic plan Exclusion Criteria: Contraindication to femoral nerve block (e.g. infection) BMI > 35 kg/m2 inability to communicate postoperative symptoms pre-existing neurologic deficits in the operative extremity allergy to local anesthetics history of opioid dependence

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 65 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

Intervention Model: Single Group Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Intervention<br>A 22 GA 5 cm nerve block needle will be advanced to the following conditions: Needle tip slightly indenting the fascia iliaca Needle tip advanced through fascia iliaca Needle tip slightly indenting the anterior surface of the femoral nerve Needle tip withdrawn 1 mm from nerve. At each of these conditions, 1 ml of dextrose solution will be injected and spread of injectate observed sonographically. A blinded observer will measure injection pressure. If opening pressure reaches 15 psi, this investigator will halt the injection. In addition, minimum threshold current required to elicit a motor response will be recorded for conditions 3 and 4. | Procedure: Apposition of needle bevel against femoral nerve<br>* Indentation of femoral nerve and fascia iliaca by block needle and measurement of opening injection pressure during the controlled injection of 1 ml of dextrose (D5W) solution<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Incidence of high opening injection pressure (15 psi or greater) when needle tip in contact with nerve |  | 1 minute | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Incidence of high opening injection pressure (15 psi or greater) at other needle locations |  | 1 minute | 
| Minimum threshold current to elicit a motor response with needle-nerve contact and needle disengagement |  | 1 minute | 
| Incidence of paresthesias |  | 1 week | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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opening injection pressure, femoral nerve block, fascia iliaca, ultrasound guided nerve block