Incidence of sub-perineural injection using a targeted intracluster supraclavicular ultrasound-guided approach in cadavers.

BACKGROUND: Multi-injection targeted intracluster injection ultrasound-guided supraclavicular brachial plexus block has been advocated to provide a faster onset of anaesthesia compared with a double injection technique. By placing the needle within clusters of hypoechoic structures, corresponding to neural tissue, this technique may increase needle trauma and the incidence of nerve injury. This study assessed the rate of sub-perineural needle placement with a single intracluster brachial plexus injection in the supraclavicular fossa of human cadavers. METHODS: A single ultrasound-guided intracluster brachial plexus injection was performed bilaterally at the supraclavicular fossa on 21 lightly embalmed clinical grade cadavers. Using an in-plane technique, an echogenic needle was positioned to target the middle or lower trunk 'cluster', where 0.2 ml black India ink was injected. An effort was taken to avoid the hypoechoic structures with the needle tip. Tissue samples were assessed histologically by two experienced reviewers. RESULTS: All 42 injections were sonographically assessed to be within the 'main cluster'. Ink was extra-epineural in 13/41 (32%), sub-epineural but outside perineurium in 18/41 (44%), and sub-perineural in 10/41 sections (24%; 95% confidence interval, 13-41%). The histology from one injection was uninterpretable. Of the 10 sub-perineural deposits, the ink was intrafascicular in nine sections. CONCLUSIONS: We observed a high rate of sub-perineural injection with a single intracluster injection. Thus the targeted intracluster injection supraclavicular block cannot be recommended until further evidence is available regarding the safety of this technique.

Histological confirmation of needle tip position during ultrasound-guided interscalene block: a randomized comparison between the intraplexus and the periplexus approach.

PURPOSE: Ultrasound-guided interscalene block can be performed using either periplexus or intraplexus needle placement. In this novel study, we histologically examined the needle tip position in relation to the neural tissues with the two techniques. Our objective was to investigate the variable risk of subepineurial needle tip placement resulting from the two ultrasound-guided techniques. METHODS: In an embalmed cadaveric model, periplexus or intraplexus interscalene injections were performed with the side, order, and technique assigned randomly. Under real-time ultrasound guidance, the block needle was placed next to the hyperechoic layer of the plexus (periplexus) or between the hypoechoic nerve roots (intraplexus). Once positioned, 0.1 mL of black acrylic ink was injected. The brachial plexus tissues were then removed and histology sections were prepared and then coded in order to blind two reviewers to group allocation. The area of ink staining was used to determine needle tip location, and the groups were compared for the presence of subepineurial ink. RESULTS: Twenty-six cadavers had each of the blocks performed on either brachial plexus (i.e., 52 injections). No subepineurial ink deposits were observed in the periplexus group (0%), but subepineurial ink deposition was observed in 3/26 (11.5%) intraplexus injections (odds ratio, 0; 95% confidence interval, 0 to 2.362; P = 0.235). Furthermore, in the intraplexus group, two (of the three) subepineurial ink deposits were observed under the perineurium. CONCLUSION: Although our study was somewhat underpowered due to a lower than previously reported rate of subepineurial needle tip positioning, our results suggest that there may be an increased likelihood of subepineurial needle tip position with the intraplexus approach. The periplexus technique resulted in no subepineurial spread of ink, suggesting that this approach may be less likely to result in mechanical trauma to nerves from direct needle injury.

A Cadaver Study Investigating Structures Encountered by the Needle During a Retroclavicular Approach to Infraclavicular Brachial Plexus Block.

BACKGROUND AND OBJECTIVES: Retroclavicular block is designed to overcome the negative aspects of the commonly utilized ultrasound-guided parasagittal approach to the infraclavicular block. However, this approach necessitates the needle traversing an area posterior to the clavicle inaccessible to ultrasound wave conduction. This study sought to document the structures vulnerable to needle injury during a retroclavicular block. METHODS: A Tuohy needle was inserted using a retroclavicular approach to the infraclavicular block in 3 lightly embalmed cadavers followed by a catheter insertion 4 cm beyond the needle tip. The process was repeated on the contralateral side. With the needle and catheter in position, the cadavers were dissected and photographed. RESULTS: In 4 of the 6 dissections, the needle was directly touching the suprascapular nerve deep to the clavicle. In the remaining 2 dissections, the suprascapular nerve was within 2 cm of the needle. In 1 dissection, the suprascapular vein was indented, behind the clavicle. The trapezius was the only muscle layer traversed by the needle in all dissections. In 3 of the 6 dissections, the catheter penetrated the posterior cord. In the remaining 3, the catheter threaded along the neurovascular bundle. CONCLUSIONS: The suprascapular nerve is consistently in the path of the block needle posterior to the clavicle. This raises the possibility of risk of injury to the suprascapular nerve when using this approach to the brachial plexus. Vascular injury is also possible deep to the clavicle, and because of the noncompressible location, caution is advised in patients with disordered coagulation.

Long current impulses may be required for nerve stimulation in patients with ischemic pain.

PURPOSE: To report on the efficacy of peripheral plexus catheters in the treatment of ischemic pain in spite of nerve stimulation with long current impulses. CLINICAL FEATURES: Two patients with severe neuropathic ischemic foot pain are described. A 56-yr-old man with diabetes, renal failure, and autonomic neuropathy presented with severe ischemic foot pain. Opioids produced excess sedation and hypotension. A 62-yr-old woman was admitted after femoral-popliteal bypass and developed a reperfusion pain syndrome not relieved with opioids, gabapentin, amitryptiline, and clonidine. In both patients, a sciatic plexus catheter was placed with resolution of pain. Conventional nerve stimulation, which uses a pulse duration of 0.1 msec, did not result in muscle contraction. However, by using a nerve stimulator capable of delivering a 1.0 msec impulse duration, a muscle twitch or paresthesia endpoint ensued allowing for successful catheter placement. CONCLUSION: Peripheral plexus catheters provide a safe alter-native to systemic analgesics for pain relief in patients with ischemic foot pain. However, conventional nerve stimulation techniques may not elicit a motor response in patients with underlying neuropathy, and the use of nerve stimulators capable of delivering long current impulses is recommended.