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The Disposition of Radiocontrast in the Interscalene Space in Healthy Volunteers

Gautier, Philippe MD*; Vandepitte, Catherine MD; Schaub, Isabelle MD*; Fourneau, Kristof MD; Kuroda, Maxine M. PhD, MPH§; De Merlier, Yvan MD; Hadzic, Admir MD, PhD†¶

doi: 10.1213/ANE.0000000000000649
Regional Anesthesia: Brief Report

BACKGROUND: We measured the spread of radiocontrast in the interscalene space after injection under low (<15 psi) and high (>20 psi) pressures.

METHODS: Nine healthy volunteers received ultrasound-guided injections of 10 mL radio-opaque NaCl 0.9% in both interscalene spaces. Spread of injectate as assessed by computed tomography scan and discomfort on injection were recorded.

RESULTS: Under both opening pressure conditions, injectate contacted 3 brachial plexus roots and spilled over the surface of the anterior and/or middle scalene muscles underneath the cervical fascia.

CONCLUSIONS: Regardless of injection pressure, the interscalene space was filled with 10 mL of radiocontrast injectate.

Published ahead of print March 4, 2015

From the *Department of Anesthesiology, Clinique Ste Anne-St Remi, Brussels, Belgium; Ziekenhuis Oost-Limburg (ZOL), Genk, Belgium; Sint Jozefskliniek, Izegem, Belgium; §NAICE (North American Institute for Continuous Education), New York, New York; Department of Radiology, Clinique Ste Anne-St Remi, Brussels, Belgium; and New York School of Regional Anesthesia, New York, New York.

Accepted for publication November 25, 2014.

Published ahead of print March 4, 2015

Funding: Department of Anesthesiology, Clinique Ste Anne-St Remi.

Conflict of Interest: See Disclosures at the end of the article.

Reprints will not be available from the authors.

Address correspondence to Admir Hadzic, MD, PhD, NYSORA, 2753 Broadway, Suite 183, New York, NY 10025. Address e-mail to admir@nysora.com

We simulated the effect of opening injection pressure on the spread of local anesthetic by injecting 10 mL of a radiocontrast medium into the interscalene space under low (<15 psi)- and high (>20 psi)-pressure conditions. Selection of the low pressure range was based on published data where opening injection pressure >15 psi detected all needle-nerve contacts in patients having interscalene brachial plexus block, whereas perineural injections away from the root were consistently possible with <15 psi.1 Selection of high pressure (>20 psi) was based on the more extensive spread of local anesthetic into the epidural space observed with high injection pressures.2 Our primary outcome was the spread of radiocontrast in the interscalene space as detected by computed tomography (CT) scan.

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METHODS

After obtaining IRB approval from the Catholic University of Louvain (national registration no. B403201317719), written, informed consent was obtained from 9 healthy volunteers (ASA physical status I, body mass index < 35). All injections were 10 mL of radiocontrast solution (1 mL of 10% Iohexol solution, Omnipaque 240R; GE Healthcare) mixed with 9 mL NaCl 0.9%. No premedication was administered. Injections were made into the right and left interscalene spaces outside the connective tissue stroma.3 A 22-G stimulating needle (0.5 mA, 0.1 ms; SonoPlex, Pajunk) was placed under ultrasound guidance between the C5 and C6 roots of the brachial plexus as in actual clinical practice.3 Absence of needle-nerve contact as seen on ultrasound, absence of motor response at 0.5 mA, and opening injection pressure <15 psi were confirmed before injection to decrease the risk of inadvertent needle-nerve contact or intraneural needle insertion.1,2

Opening injection pressure was defined as the pressure at which the flow of injectate was first detected by ultrasound.1 Injection pressures are equal throughout the syringe-tubing-needle system regardless of the length or diameter of the tubing (Pascal’s law).1 An in-line disposable manometer (BSmart; BBraun Medical, Bethlehem, PA) measured injection pressure ranges where <15 psi is indicated on a piston as white, 15 to 20 psi as yellow, and >20 psi as orange, with precision ±15%.1 Injections were adjusted to keep the manometer indicator <15 psi for low injection pressure and >20 psi for high injection pressure.1,2 The first 1 mL of radiocontrast was injected to assure opening injection pressure was <15 psi to avoid the risk of nerve injury or epidural spread of injectate.1 The remaining 9 mL of injectate was administered under low injection pressure (<15 psi) into the right interscalene space or under greater injection pressure (>20 psi) into the left interscalene space. The order of injection was randomized, and one side was completed before the other side was started. The volunteers were blinded to injection pressure. Injection flow rates were maintained between 10 and 20 mL/min, commensurate with clinical practice. During injection, the volunteers were asked to report their pain on an 11-point Numeric Rating Scale score (from 0 being no pain to 10 being the worst imaginable pain). Injections were halted on the volunteer’s request or with a report of pain (Numeric Rating Scale >5). Both injection procedures were completed within 30 minutes via the use of in-plane, lateral-to-medial needle insertions. A radiologist blinded to injection pressure completed the CT assessments of injectate spread within 15 minutes after completion of both injection procedures.

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Statistical Methods

Continuous variables are presented as mean ± SD, and ordinal and nominal (categorical) variables as n (%). This preliminary study neither intended to test specific hypotheses nor was it powered for such tests; thus, the findings are presented descriptively.

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RESULTS

Nine healthy volunteers participated in this study (Table 1). Injections were completed within 100 seconds unless the volunteer requested that the injection be halted. When paused, the injections were resumed after cessation of pain. The full volume of injectate (10 mL) was administered in all volunteers. CT imaging confirmed the spread of injectate in the interscalene space (Table 2). Bilaterally, 10 mL of the injectate filled the entire interscalene space between the anterior and middle scalene muscles and underneath the cervical fascia. The amount of injectate detected at the C5, C6, and C7 levels on CT imaging suggested increasing capacity from higher to lower levels of the interscalene space (Table 2; Figs. 1 and 2). Injectate surrounded the C5, C6, and C7 roots at all levels.

Table 1

Table 1

Table 2

Table 2

Figure 1

Figure 1

Figure 2

Figure 2

With all injections, contrast medium spilled outside the interscalene space, beneath the cervical fascia, both laterally and medially over the anterior and middle scalene muscles (Table 3).

Table 3

Table 3

Epidural spread of injectate occurred in 1 volunteer with injection pressure >20 psi (Fig. 3). All volunteers requested that injection be halted because of discomfort with high injection pressure (>20 psi) but not with low injection pressure (<15 psi). Injections were halted twice during high pressure injection in 3 volunteers

Figure 3

Figure 3

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DISCUSSION

Several recent studies in which investigators used ultrasonography have established that the volume of local anesthetic required to accomplish interscalene brachial plexus block is lower than that commonly used without ultrasound.4–6 We found that 10 mL of radiocontrast injectate filled the interscalene space and surrounded the neural elements of the brachial plexus. Moreover, a portion of the injectate consistently leaked outside the interscalene space beneath the cervical fascia over the anterior and middle scalene muscles with all injections. This finding may have clinical relevance because the superficial cervical plexus and the phrenic nerve are both located beneath the cervical fascia, on the surface of the middle and anterior scalene muscles, and outside the interscalene space.

Because the sample size for this descriptive study was small, further study is warranted to determine whether limiting injection pressure results in less discomfort in unpremedicated patients. Moreover, because we did not inject local anesthetic, we do not have data on the sensory-motor characteristics of the blocks, nor can we compare the distributional characteristics of local anesthetics with saline or radiocontrast.

In summary, the spread of radiocontrast in the interscalene brachial plexus was measured by CT scan after injection under low (<15 psi) and high (>20 psi) pressure. Regardless of injection pressure, the interscalene space was filled by the relatively small volume (10 mL) of injectate used in our study.

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DISCLOSURES

Name: Philippe Gautier, MD.

Contribution: This author helped design the study, conduct the study, collect study data, analyze data, and prepare the manuscript.

Attestation: Philippe Gautier approved the final manuscript.

Conflicts of Interest: This author has no conflicts of interest to declare.

Name: Catherine Vandepitte, MD.

Contribution: This author helped design the study, conduct the study, collect study data, analyze data, and prepare the manuscript.

Attestation: Catherine Vandepitte attests to the integrity of the original data and the analysis reported in this manuscript.

Conflicts of Interest: This author has no conflicts of interest to declare.

Name: Isabelle Schaub, MD.

Contribution: This author helped conduct the study and collect study data.

Attestation: Isabelle Schaub attests to the integrity of the original data and the analysis reported in this manuscript.

Conflicts of Interest: This author has no conflicts of interest to declare.

Name: Kristof Fourneau, MD.

Contribution: This author helped conduct the study, collect study data, analyze data, and prepare the manuscript.

Attestation: Kristof Fourneau is the archival author.

Conflicts of Interest: This author has no conflicts of interest to declare.

Name: Maxine M. Kuroda, PhD, MPH.

Contribution: This author analyzed the study data, and helped to prepare the manuscript.

Attestation: Maxine M. Kuroda attests to the integrity of the data analysis and preparation of this manuscript.

Conflicts of Interest: This author has no conflicts of interest to declare.

Name: Yvan De Merlier, MD.

Contribution: This author helped conduct the study, collect study data, and analyze data.

Attestation: Yvan De Merlier attests to the integrity of the original data and the analysis reported in this manuscript.

Conflicts of Interest: This author has no conflicts of interest to declare.

Name: Admir Hadzic, MD, PhD.

Contribution: This author helped interpret the study data and prepare the manuscript.

Attestation: Admir Hadzic attests to the integrity of the original data and the analysis reported in this manuscript.

Conflicts of Interest: Admir Hadzic has consulted and advised for Skypharma, GE, Sonosite, Codman & Shrutleff, Inc. (Johnson and Johnson), Cadence, Pacira, Baxter, and B. Braun Medical. His recent industry-sponsored research includes Glaxo Smith-Kline Industries, Pacira, and Baxter. Dr. Hadzic receives royalty income from B. Braun Medical.

This manuscript was handled by: Terese T. Horlocker, MD.

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REFERENCES

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3. Gadsden JC, Choi JJ, Lin E, Robinson A. Opening injection pressure consistently detects needle-nerve contact during ultrasound-guided interscalene brachial plexus block. Anesthesiology. 2014;120:1246–53
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