Cerebral Blood Flow Evaluation With Trancranial Doppler After Interscalene Nerve Block

Study Overview
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Brief Summary
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The purpose of this study is to assess cerebral blood flow velocity (CBFV) following regional anesthesia for shoulder surgery. The results of this study will help to further understand the physiologic effect of the interscalene nerve block on cerebral blood flow.

Detailed Description
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Traditionally, cerebral blood flow (CBF) is believed to decline when mean arterial pressure (MAP) is below the lower limit of cerebral autoregulation. Cerebral blood flow autoregulation refers to the capacity of the central nervous system to maintain blood flow within a wide range of mean arterial blood pressure. The habitual thinking is that the brain is perfused merely dependent by the blood pressure and that above or below the limits of cerebral autoregularion CBF is pressure passive. Despite this notion, there is evidence showing that parameters other than MAP influence cerebral hemodynamics independent of cerebral autoregulation. One of the physiologic processes that contribute to CBF regulation is cardiac output (CO). However, exactly how an alteration in CO, in the face of a stable blood pressure, leads to a change in CBF is not entirely clear. One of the suggested mechanisms in play is the sympathetic nervous system (SNS)-mediated vasoconstriction of extracranial and proximal intracranial vessels. Cerebral arteries are abundantly innervated by sympathetic nerve fibers originating from the superior cervical ganglion. Studies have shown that CBF reduction is attenuated by pharmacologic blockade or extirpation of the cervical sympathetic chain. The anesthetic protocol for patients undergoing major shoulder surgery include an interscalene nerve block (ISNB) combined with general anesthesia in the sitting position. The ISNB involves injecting local anesthetic at the level of the cervical spinal roots. One of the most common side effects encountered after ISNB is Horner syndrome, which is characterized by ptosis, myosis, and enopthalmia. Horner's syndrome results from the diffusion of the local anesthetic solution to the ipsilateral sympathetic cervical chain (stellate ganglion). The presence of Horner's syndrome indicates spread of local anesthetic to the sympathetic chain. Whether this degree of sympatholytic following interscalene block is associated with an observable change in CBF is unknown. Studies in baboon have shown that cervical surgical sympathectomy maintained CBF in the face of hemorrhagic hypotension and CBF did not decrease until MAP was 35% of the baseline value. These results suggest that sympathectomy induced by the block of the sympathetic chain by the local anesthetic injected for the ISNB might alter CBF. Therefore, the aim of our study is to evaluate the effect of unilateral interscalene nerve block on CBF by measuring CBF velocity non-invasively with Transcranial doppler (TCD).

Official Title
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Cerebral Blood Flow Evaluation With Trancranial Doppler After Unilateral Interscalene Nerve Block: Observational Prospective Study

Conditions
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Regional Anesthesia, Horner Syndrome, Cerebral Blood Flow

Intervention / Treatment
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* Device: TCD Measurement


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Patients undergoing orthopedic surgery and with an indication for preoperative insertion of interscalene nerve block 18-85 years old Give consent to participate in study Exclusion Criteria: Cannot give consent Patients who are clinically unstable or require urgent/emergent intervention

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 85 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Treatment Arm<br>Patients ages 18-85 years old presenting with orthopedic shoulder surgery with indication to receive preoperative insertion of interscalene nerve block. | Device: TCD Measurement<br>* CBFV measurements will be acquired continuously with the patient supine and the head neutral. Analysis of CBFV measurements will be undertaken at 3 timepoints: Patient awake and supine in the holding area After sedation After interscalene nerve block<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Cerebral Blood Flow Velocity before and after interscalene nerve block | The TCD automatically measures blood flow velocity in the main cerebral arteries of the circle of Willis. We will target the MCA which is the closest to the temporal bone therefore the most easily accessible for insonation and monitoring. We will do a bilateral monitoring. | baseline, after 30 minutes | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Systolic, diastolic, mean blood pressure changes before and after interscalene nerve block | Will be measured before/during/after interscalene nerve block placement | baseline, after 30 minutes | 
| Heart Rate | Will be measured before/during/after interscalene nerve block placement | baseline, after 30 minutes | 
| Respiratory Rate changes before and after interscalene nerve block | Will be measured before/during/after interscalene nerve block placement | baseline, after 30 minutes | 
| EtCO2 changes before and after interscalene nerve block | Will be measured before/during/after interscalene nerve block placement | baseline, after 30 minutes | 
| SpO2 changes before and after interscalene nerve block | Will be measured before/during/after interscalene nerve block placement | baseline, after 30 minutes | 
| Type of local anesthetic | Local anesthetic characteristics will be collected after interscalene block placement. | 30 minutes after the nerve block | 
| Position of the needle on the cervical trunk for interscalene nerve block | Needle position for interscalene nerve block insertion will be assessed at the time of interscalene block placement | Baseline | 
| Volume of of local anesthetic | Local anesthetic characteristics will be collected after interscalene block placement. | 30 minutes after the nerve block | 
| Concentration of local anesthetic | Local anesthetic characteristics will be collected after interscalene block placement. | 30 minutes after the nerve block |