Paul E. Bigeleisen

Nerve Puncture and Apparent Intraneural Injection during Ultrasound-guided Axillary Block Does Not Invariably Result in Neurologic Injury

Background: Nerve puncture by the block needle and intraneural injection of local anesthetic are thought to be major risk factors leading to neurologic injury after peripheral nerve blocks. In this study, the author sought to determine the needle–nerve relation and location of the injectate during ultrasound-guided axillary plexus block. Methods: Using ultrasound-guided axillary plexus block (10-MHz linear transducer, SonoSite, Bothel, WA; 22-gauge B-bevel needle, Becton Dickinson, Franklin Parks, NJ), the incidence of apparent nerve puncture and intraneural injection of local anesthetic was prospectively studied in 26 patients. To determine the onset, success rate, and any residual neurologic deficit, qualitative sensory and quantitative motor testing were performed before and 5 and 20 min after block placement. At a follow-up 6 months after the blocks, the patients were examined for any neurologic deficit. Results: Twenty-two of 26 patients had nerve puncture of at least one nerve, and 21 of 26 patients had intraneural injection of at least one nerve. In the entire cohort, 72 of a total of 104 nerves had intraneural injection. Sensory and motor testing before and 6 months after the nerve injections were unchanged. Conclusions: Under the conditions of this study, puncturing of the peripheral nerves and apparent intraneural injection during axillary plexus block did not lead to a neurologic injury.

Extraneural versus Intraneural Stimulation Thresholds during Ultrasound-guided Supraclavicular Block

Background:A stimulation current of no more than 0.5mA is regarded as safe in avoiding nerve injury and delivering adequate stimulus to provoke a motor response. However, there is no consistent level of stimulating threshold that reliably indicates intraneural placement of the needle. The authors determined the minimally required stimulation threshold to elicit a motor response outside and inside the most superficial part of the brachial plexus during high-resolution, ultrasound-guided, supraclavicular block. Methods:After institutional review board approval, ultrasound-guided, supraclavicular block was performed on 55 patients. Patients with neurologic dysfunction were excluded. Criteria for extraneural and intraneural stimulation were defined and assessed by independent experts. To determine success rate and any residual neurologic deficit, qualitative sensory and motor examinations were performed before and after block placement. At 6 month follow-up, the patients were examined for any neurologic deficit. Results:Thirty-nine patients met all set stimulation criteria. Median ± SD (interquartile range) minimum stimulation threshold outside was 0.60 ± 0.37 mA (0.40, 1.0) and inside 0.30 ± 0.19 mA (0.20, 0.40). The difference of 0.30 mA was statistically significant (P < 0.0001). Stimulation currents of 0.2 mA or less were not observed outside the trunk in any patient. Significantly higher thresholds were observed in diabetic patients. Success rate was 100% after 20 min. Thirty-four patients had normal sensory and motor examination at 6 months. Five patients were lost to follow-up. Conclusion:Within the limitations of this study and the use of ultrasound, a stimulation current of 0.2 mA or less is reliable to detect intraneural placement of the needle. Furthermore, stimulation currents of more than 0.2 and no more than 0.5 mA could not rule out intraneural position.

Quantitative Architecture of the Brachial Plexus and Surrounding Compartments, and Their Possible Significance for Plexus Blocks

Background:Nerve injury after regional anesthesia of the brachial plexus (BP) is a relatively rare and feared complication that is partly attributed to intraneural injection. However, recent studies have shown that intraneural injection does not invariably cause neural injury, which may be related to the architecture within the epineurium. A quantitative study of the neural components and the compartment outside BP was made. Methods:From four frozen shoulders, high-resolution images of sagittal cross-sections with an interval of 0.078 mm were obtained using a cryomicrotome to maintain a relatively undisturbed anatomy. From this data set, cross-sections perpendicular to the axis of the BP were reconstructed in the interscalene, supraclavicular, midinfraclavicular, and subcoracoid regions. Surface areas of both intraepineurial and connective tissue compartments outside the BP were delineated and measured. Results:The nonneural tissue (stroma and connective tissue) inside and outside the BP increased from proximal to distal, being significant between interscalene/supraclavicular and midinfraclavicular/subcoracoid regions (P < 0.001 for tissue inside BP, P < 0.02 for tissue outside BP). The median amount of neural tissue remained approximately the same in the four measured regions (41.1 ± 6.3 mm2; range, 30–60 mm2). The ratio of neural to nonneural tissue inside the epineurium increased from 1:1 in the interscalene/supraclavicular to 1:2 in the midinfraclavicular/subcoracoid regions. Conclusion:Marked differences in neural architecture and size of surrounding adipose tissue compartments are demonstrated between proximal and distal parts of the brachial plexus. These differences may explain why some injections within the epineurium do not result in neural injury and affect onset times of BP blocks.

Different Approaches to Ultrasound-guided Thoracic Paravertebral Block An Illustrated Review

Given the fast development and increasing clinical relevance of ultrasound guidance for thoracic paravertebral blockade, this review article strives (1) to provide comprehensive information on thoracic paravertebral space anatomy, tailored to the needs of a regional anesthesia practitioner, (2) to interpret ultrasound images of the thoracic paravertebral space using cross-sectional anatomical images that are matched in location and plane, and (3) to briefly describe and discuss different ultrasound-guided approaches to thoracic paravertebral blockade. To illustrate the pertinent anatomy, high-resolution photographs of anatomical cross-sections are used. By using voxel anatomy, it is possible to visualize the needle pathway of different approaches in the same human specimen. This offers a unique presentation of this complex anatomical region and is inherently more realistic than anatomical drawings.

Ultrasound-guided approach to the paravertebral space for catheter insertion in infants and children

Paravertebral perineural blocks are used to prevent pain in the thoracoabdominal dermatomes. Traditionally, a landmark‐based technique is used in children, while ultrasound‐guided (UG) techniques are being employed in adult patients.

Coherence-gated Doppler: a fiber sensor for precise localization of blood flow.

Miniature optical sensors that can detect blood vessels in front of advancing instruments will significantly benefit many interventional procedures. Towards this end, we developed a thin and flexible coherence-gated Doppler (CGD) fiber probe (O.D. = 0.125 mm) that can be integrated with minimally-invasive tools to provide real-time audio feedback of blood flow at precise locations in front of the probe. Coherence-gated Doppler (CGD) is a hybrid technology with features of laser Doppler flowmetry (LDF) and Doppler optical coherence tomography (DOCT). Because of its confocal optical design and coherence-gating capabilities, CGD provides higher spatial resolution than LDF. And compared to DOCT imaging systems, CGD is simpler and less costly to produce. In vivo studies of rat femoral vessels using CGD demonstrate its ability to distinguish between artery, vein and bulk movement of the surrounding soft tissue. Finally, by placing the CGD probe inside a 30-gauge needle and advancing it into the brain of an anesthetized sheep, we demonstrate that it is capable of detecting vessels in front of advancing probes during simulated stereotactic neurosurgical procedures. Using simultaneous ultrasound (US) monitoring from the surface of the brain we show that CGD can detect at-risk blood vessels up to 3 mm in front of the advancing probe. The improved spatial resolution afforded by coherence gating combined with the simplicity, minute size and robustness of the CGD probe suggest it may benefit many minimally invasive procedures and enable it to be embedded into a variety of surgical instruments.

Nerve Roots, Trunks, and the Vagaries of Ultrasound

To the Editor: We thank Dr Hebbard for his interest in and comments regarding our work. We used the approach originally described by Dr Hebbard et al in our study because it is widely used, and there is some confusion and debate on the best way to block the nerves in the transversus abdominis plane (TAP). As Dr Hebbard mentions, our point of injection might have been too far from the location of the anterior branches of the L1 nerves, the ilioinguinal and iliohypogastric nerves, to anesthetize them. Studies of the cutaneous innervation after TAP blocks indicate that the TAP is not a space where correctly placed local anesthetic will spread unhindered but rather a virtual space with unpredictable adhesions and individual variations. We believe that the unpredictable spread in the TAP might be an important limitation to single point injection. The oblique subcostal TAP block described by Hebbard et al is a promising approach that facilitates a more extensive spread in the TAP because the plane is hydrodissected. The pain mechanism is another important issue.We tend to focus on the innervation of the skin, but it is likely to be more important that nociception from deeper tissues than the skin is blocked. Muscle relaxation and immobilization of the abdominal wall caused by the TAP block may also be important factors. Our study was conducted in healthy volunteers to avoid confounding factors and demonstrates only the effect on the

Safety and Subepineural Injections

To the Editor: In their recent editorial, Short et al 1 express concern regarding the safety of intraneural injections. Their citation concerning nerve injury after intraneural injection omits the fact that the needle used for the block considered in this study was a biopsy needle. Using a needle designed to cause damage to tissue shows little knowledge of the history of regional anesthesia and/or little attention to detail. Short et al also cite a study reporting nerve damage after the injection of local anesthetic outside and inside the epineurium of the sciatic nerve in rats. In some animals, the toxicity just inside the epineurium was 8 times that outside the epineurium. The editorial authors call for a cessation on outcome studies of subepineural injections unless safety is included in the study. They suggest that the size of future studies be based on the number needed to treat to find a difference in safety, yet they supply no suggestions on how large such a study would need to be. Suppose the adverse outcomes from nerve blocks of extraepineurial and subepineural nerve blocks are as follows:

Cervical paravertebral block for forearm and hand anesthesia: the jury is still out.

mates them. This has also occasionally i tified the supraclavicular nerve runn subcutaneously at the point of needle in tion, and an aberrant course of a su scapular nerve. For a sensory nerve block, the sti lating current is returned to zero. The id tified nerve is approximated. The p width is set to 0.3 milliseconds. The rent is slowly increased to elicit a 2-Hz esthesia in the intended territory. In context of a supraclavicular nerve bl this allows confirmation of the struct and whether this structure is the medial termediate, or lateral component, and a location can be performed as necessary An additional use for intersca blockade is during approximation of brachial plexus. As soon as the ne leaves middle scalene (or the preverte fascia if steep in-plane or out-of-pla usually a noticeable “pop” is felt, acc panied by the commencement of m stimulation. Manipulation of the hub of needle should alter the needle-tip locat If this results in loss of motor stimula then the needle tip cannot be physic connected to such a structure; howeve motor stimulation continues despite manipulation of the hub, then the ne tip may be in continuity with a motor fa cle and should be relocated. It is impossible to say whether the of a nerve stimulator would have chan the outcome of the case described by Tho et al, but as regional anesthesia enthus and believers in making anesthesia as for patients as possible, we strongly that the appropriate use of a nerve stim tor (in conjunction with imaging mod ties) should be encouraged and passed to the next generation, or until such t as nerve location using pure imaging t niques has become a more definitively cessful tool.

A novel marker for identifying and studying the membranes, barriers, and compartments surrounding peripheral nerves microscopically: A Novel Marker for Studying Nerves

Recent anatomical discoveries indicate the importance of identifying membranes and compartments surrounding peripheral nerves into which local anesthetic agents can be injected and continuous nerve block catheters placed during regional anesthetic procedures. However, current markers used in anatomical studies have multiple drawbacks, specifically extravasation into noninjected locations, which can result in inadequate treatment. We studied a readily‐available new marker, heparinized blood solution (HBS), which is easy to identify by microscopy and can remain in the nerve compartment into which it is deposited without distorting the tissue. We collected blood from 22 patients and prepared it as HBS. This was then injected into four fresh cadavers as in routine clinical practice for ultrasound‐guided nerve blocks to form a so‐called “doughnut” by “hydro‐dissecting” at 32 sites. All samples, including nerves and neighboring tissues, were then prepared and examined by light microscopy. Although no deliberate intraneural injection was attempted, the marker was identified inside all the nerve compartments except the fascicles. Apart from leaking through the needle entry site in some instances, there was no extravasation of the HBS into neighboring nerve compartments in either direction. The tissues were not distorted and the erythrocytes did not form a thrombus. Nerve membranes and compartments could be clearly identified with routine staining. This technique enabled us to study the longitudinal and circumferential spread in all nerve compartments and to collect data for better interpretation of factors influencing an anesthetic nerve block and situations in which complications could possibly arise. HBS seemed superior to other markers because it did not leave the compartments into which it had been injected, did not distort the tissue, and was easily visible under the light microscope. Clin. Anat., 31:1050–1057, 2018.