Intraneural Injection with Low-Current Stimulation During Popliteal Sciatic Nerve Block

Enhancing Safety in Regional Anesthesia: Guidelines from the Italian Society of Anesthesia, Analgesia, Resuscitation and Intensive Care (SIAARTI)

BACKGROUND

Regional anesthesia techniques have become integral to modern perioperative care, offering enhanced pain management and recovery outcomes. However, their application in patients with specific conditions, such as anticoagulation therapy or preexisting comorbidities, raises concerns regarding safety and efficacy. Current guidelines addressing these issues are fragmented, necessitating comprehensive, evidence-based recommendations.

METHODS

A multidisciplinary panel of experts in anesthesiology and pain management was convened under the auspices of the Italian Society of Anesthesia, Analgesia, Resuscitation, and Intensive Care (SIAARTI). The guidelines presented herein were developed according to the GRADE system (Grading of Recommendations of Assessment Development and Evaluations), in compliance with the methodological manual for the production of clinical practice guidelines published by the National Center for Clinical Excellence, Quality, and Safety of Care, Italian National Institute of Health.

RESULTS

The guidelines encompass recommendations on neuraxial blocks in anticoagulated patients, the dual guidance use in peripheral nerve blocks, the role of sterile field preparation, and post-procedural monitoring. Evidence from meta-analyses and large-scale observational studies supported most recommendations, though limitations in study heterogeneity were noted.

CONCLUSIONS

These guidelines provide a structured framework for clinicians to enhance patient safety and procedural efficacy in regional anesthesia. Further research is encouraged to address identified gaps, particularly regarding specific patient subgroups and novel regional anesthesia techniques.

Regional Anesthesia in the Elite Athlete

Elite athletes are exposed to an elevated risk of musculoskeletal injury which may present a significant threat to an athlete's livelihood. The perioperative anesthetic plan of care for these injuries in the general population often incorporates regional anesthesia procedures due to several benefits. However, some concern exists regarding the potential for regional anesthesia to adversely impact functional recovery in an elite athlete who may have a lower tolerance for this risk. This article aims to review the data behind this concern, discuss strategies to improve the safety of these procedures and explore the features of consent in this patient population.

The Safety of Peripheral Nerve Blocks: The Role of Triple Monitoring in Regional Anaesthesia, a Comprehensive Review

Regional anaesthesia, referred to as regional blocks, is one of the most frequently used methods of anaesthesia for surgery and for pain management. Local anaesthetic drug should be administered as close to the nerve as possible. If administered too far away, this may result in insufficient block. If it is administrated too close, severe nerve damage can occur. Neurostimulation techniques and ultrasound imaging have improved the effectiveness and safety of blockade, but the risk of nerve injury with permanent nerve disfunction has not been eliminated. Intraneural administration of a local anaesthetic damages the nerve mechanically by the needle and the high pressure generated by the drug inside the nerve. In many studies, injection pressure is described as significantly higher for unintended intraneural injections than for perineural ones. In recent years, the concept of combining techniques (neurostimulation + USG imaging + injection pressure monitoring) has emerged as a method increasing safety and efficiency in regional anaesthesia. This study focuses on the contribution of nerve identification methods to improve the safety of peripheral nerve blocks by reducing the risk of neural damage.

The effect of warming ropivacaine on ultrasound-guided subgluteal sciatic nerve block: a randomized controlled trial

BACKGROUND

There is a long latent period for the sciatic nerve block before a satisfactory block is attained. Changes in the temperature of local anesthetics may influence the characters of the peripheral nerve block. This study was designed to evaluate the effect of warming ropivacaine on the ultrasound-guided subgluteal sciatic nerve block.

METHODS

Fifty-four patients for distal lower limbs surgery were randomly allocated into warming group (group W, n = 27) or room tempeture group (group R, n = 27) with the ultrasound-guided subgluteal sciatic nerve block. The group W received 30 ml of ropivacaine 0.5% at 30℃ and the group R received 30 ml of ropivacaine 0.5% at 23℃. The sensory and motor blockade were assessed every 2 min for 30 min after injection. The primary outcome was the onset time of limb sensory blockade.

RESULTS

The onset time of sensory blockade was shorter in group W than in group R (16 (16,18) min vs 22 (20,23) min, p < 0.001), and the onset time of motor blockade was also shorter in group W than in group R (22 (20,24) min vs 26 (24,28) min, p < 0.001). The onset time of sensory blockade for each nerve was shorter in group W than in group R (p < 0.001). No obvious differences for the duration of sensory and motor blockade and the patient satisfaction were discovered between both groups. No complications associated with nerve block were observed 2 days after surgery.

CONCLUSIONS

Warming ropivacaine 0.5% to 30℃ accelerates the onset time of sensory and motor blockade in the ultrasound-guided subgluteal sciatic nerve block and it has no influence on the duration of sensory and motor blockade.

TRIAL REGISTRATION

The trial was registered on October 3, 2022 in the Chinese Clinical Trial Registry ( https://www.chictr.org.cn/bin/project/edit?pid=181104 ), registration number ChiCTR2200064350 (03/10/2022).

"Knowing It Before Blocking It," the ABCD of the Peripheral Nerves: Part B (Nerve Injury Types, Mechanisms, and Pathogenesis)

Selander emphatically said, "Handle these nerves with care," and those words still echo, conveying a loud and clear message that, however rare, peripheral nerve injury (PNI) remains a perturbing possibility that cannot be ignored. The unprecedented nerve injuries associated with peripheral nerve blocks (PNBs) can be most tormenting for the unfortunate patient and a nightmare for the anesthetist. Possible justifications for the seemingly infrequent occurrences of PNB-related PNIs include a lack of documentation/reporting, improper aftercare, or associated legal implications. Although they make up only a small portion of medicolegal claims, they are sometimes difficult to defend. The most common allegations are attributed to insufficient informed consent; preventable damage to a nerve(s); delay in diagnosis, referral, or treatment; misdiagnosis, and inappropriate treatment and follow-up care. Also, sufficient prospective studies or randomized trials have not been conducted, as exploring such nerve injuries (PNB-related) in living patients or volunteers may be impractical or unethical. Understanding the pathophysiology of various types of nerve injury is vital to dealing with them further. Processes like degeneration, regeneration, remyelination, and reinnervation can influence the findings of electrophysiological studies. Events occurring in such a process and their impact during the assessment determine the prognosis and the need for further interventions. This educational review describes various types of PNB-related nerve injuries and their associated pathophysiology.

Ultrasound-Guided Block of the Sciatic and the Femoral Nerves in Rabbits-A Descriptive Anatomical Study

The rabbit is a popular animal model for human biomechanical research involving surgery on the hind limb. Mortality is higher in rabbits when undergoing general anesthesia compared to dogs and cats. Moreover, due to their nature as prey animals, rabbits have a tendency to hide signs of pain, making it challenging to detect discomfort at an early stage. Incorporating regional anesthesia into an anesthetic protocol can greatly reduce the requirements for systemic anesthetic and analgesic drugs, thereby minimizing associated side effects. In other species, a block of the sciatic (ScN) and the femoral nerves (FN) is usually applied in patients undergoing hind limb surgery. In phase 1 of this study, the ScN and the FN have been localized and an appropriate approach has been evaluated under sonographic guidance. In phase 2, a mixture of new methylene blue and lidocaine have been administered to the ScN and the FN in 10 cadavers (20 hind limbs). Staining of the nerves was evaluated by dissection. Ultrasonographically, the ScN appeared as a binocular structure surrounded by a hyperechoic rim. The FN appeared as a hypoechoic structure in the dorsal part of the iliopsoas muscle (IPM), becoming hyperechoic/honey-comb-like in the ventral part. Both nerves could be successfully stained in all animals over a median length of 2.3 cm which was considered effective. This technique allows feasible and accurate access to block the ScN and the FN and may lead to successful analgesia in rabbits undergoing hind limb surgery.

FactFinders for patient safety: Motor stimulation testing in lumbar radiofrequency neurotomy and radiofrequency neurotomy in patients with posterior hardware

This series of FactFinders presents a brief summary of the evidence and outlines recommendations regarding the use of motor stimulation testing in lumbar radiofrequency neurotomy and performance of radiofrequency neurotomy in patients with posterior spinal hardware. The evidence in support of the following facts is presented: (1) Motor stimulation does not inherently protect against unwanted damage to the spinal nerve, exiting spinal nerve root or its ventral ramus due to a lack of sensitivity of this test for identification of electrode contact or close proximity to sensorimotor nerves. Even when motor stimulation is performed, verification of correct electrode placement with multiplanar imaging including a minimum of true anterior-posterior and lateral fluoroscopic views is a recommended safeguard. (2) The existence of posterior spinal hardware is not an absolute contraindication to radiofrequency neurotomy, but direct contact with hardware should be avoided.

Regional Anesthesia in the Elite Athlete

Elite athletes are exposed to an elevated risk of musculoskeletal injury which may present a significant threat to an athlete's livelihood. The perioperative anesthetic plan of care for these injuries in the general population often incorporates regional anesthesia procedures due to several benefits. However, some concern exists regarding the potential for regional anesthesia to adversely impact functional recovery in an elite athlete who may have a lower tolerance for this risk. This article aims to review the data behind this concern, discuss strategies to improve the safety of these procedures and explore the features of consent in this patient population.

Development of Guidance Techniques for Regional Anesthesia: Past, Present and Future

Regional anesthesia has been widely used in clinical practice. Over the past 30 years, various guidance techniques have been developed for regional anesthesia ranging from paresthesia progressing to neurostimulation and currently ultrasound guidance. Especially, the use of point-of-care ultrasound greatly enhances the success rate of regional anesthesia. However, the poor imaging quality of ultrasound in patients with obesity, fat infiltration, etc., limits the use of ultrasound. The combined use of ultrasound with neurostimulator, electromyography, pressure monitoring, etc. is advocated in order to facilitate regional anesthesia in this cohort of patients. The accumulated evidence has shown that the ultrasound combined with other techniques (UCOT) can help to solve the difficulties of puncture location caused by obesity, anatomical variation, and other factors when using ultrasound guidance alone. In recent years, with the development of medical image fusion and medical image artificial intelligence identification technology, guidance techniques for regional anesthesia have advanced considerably. To understand the advantages and disadvantages of the various guidance techniques for regional anesthesia developed in recent years and to guide their rational clinical application, this paper reviews these techniques, describing the progression from the early use of paresthesia to the latest UCOT, as well as the latest research on UCOT, and the prospects for the development of new guidance techniques for regional anesthesia.

Short-Term Effects of Deliberate Subparaneural or Subepineural Injections With Saline Solution or Bupivacaine 0.75% in the Sciatic Nerve of Rabbits

Background: Ultrasound (US)-guided techniques for peripheral nerve blockade have revealed that intraneural injections are relatively frequent and not necessarily associated with neurological deficits. Objectives: To evaluate the short-term effects of deliberate injections performed under direct vision in two different sites of the sciatic nerve (ScN). Material and Methods: Seventy-two New Zealand white rabbits randomly assigned to one of four experimental groups (n = 18) were employed. All procedures were conducted at a proximal femoral level where the ScN incorporates the common peroneal nerve and the tibial nerve (TN). Fixed volumes of 0.5 ml of saline solution (ES group) or bupivacaine 0.75% (EB group) were administered extrafascicularly inside the paraneurium of the ScN or intrafascicularly (IS and IB groups) under the epineurium of the TN. Cross-sectional area (CSA) and relative echogenicity (RE) of the entire ScN were determined by US before injections, after injections, and at 3 and 7 days. ScN samples were obtained for structural and ultrastructural histopathological studies. Proprioceptive, sensorial, and motor function were clinically evaluated on a daily basis. Results: The CSA of the ScN increased significantly immediately after injections when compared with pre-injection values in all groups (p < 0.05). The RE of the ScN decreased in relation to pre-injection values in all groups (p < 0.05). The CSA and RE of the ScN returned to normal values 7 days after injections in almost all groups. Injected nerves showed histological signs of mild perineural inflammation. Histopathological scores were not significantly different between groups (p > 0.05). The architecture of the ScN was preserved in all rabbits at 3 days and in 31/32 rabbits at 7 days. A focal area of damaged nerve fibers with degeneration of the axons and myelin sheath affecting the TN was observed in one rabbit of the IB group. Nerve function was not clinically impaired in any case. Conclusion: Despite the lack of severe nerve disruption observed in most rabbits, the evidence of a focal area of damaged nerve fibers in one rabbit injected intrafascicularly with bupivacaine confirms that intrafascicular injections should be avoided as they may increase the risk of nerve damage.

Arsenal of regional blocks of urgent anesthetist in pediatric anesthesiology

The main methods of regional analgesia in the practice of pediatric anesthesiologist are discussed in this article. Description of these methods is presented, including anatomy, sonoanatomy, and techniques for performing these regional blocks. The main indications for the use of different methods of regional anesthesia in the arsenal of pediatric anesthetist are considered. The main local anesthetics and their dosage are presented depending on the regional method.

Subparaneural Injection in Popliteal Sciatic Nerve Blocks Evaluated by MRI

Intraneural injection of a local anesthetic can damage the nerve, yet it occurs frequently during distal sciatic block with no neurological sequelae. This has led to a controversy about the optimal needle tip placement that results from the particular anatomy of the sciatic nerve with its paraneural sheath.

The study population included patients undergoing lower extremity surgery under popliteal sciatic nerve block. Ultrasound-guidance was used to position the needle tip subparaneurally and to monitor the injection of the local anesthetic. Sonography and magnetic resonance imaging were used to assess the extent of the subparaneural injection.

Twenty-two patients participated. The median sciatic cross-sectional area increased from 57.8 mm2 pre-block to 110.8 mm² immediately post-block. An intraneural injection according to the current definition was seen in 21 patients. Two patients had sonographic evidence of an intrafascicular injection, which was confirmed by MRI in one patient (the other patient refused further examinations). No patient reported any neurological symptoms.

A subparaneural injection in the popliteal segment of the distal sciatic nerve is actually rarely intraneural, i.e. intrafascicular. This may explain the discrepancy between the conventional sonographic evidence of an intraneural injection and the lack of neurological sequelae.

Lower extremity regional anesthesia: essentials of our current understanding

The advent of ultrasound guidance has led to a renewed interest in regional anesthesia of the lower limb. In keeping with the American Society of Regional Anesthesia and Pain Medicine's ongoing commitment to provide intensive evidence-based education, this article presents a complete update of the 2005 comprehensive review on lower extremity peripheral nerve blocks. The current review article strives to (1) summarize the pertinent anatomy of the lumbar and sacral plexuses, (2) discuss the optimal approaches and techniques for lower limb regional anesthesia, (3) present evidence to guide the selection of pharmacological agents and adjuvants, (4) describe potential complications associated with lower extremity nerve blocks, and (5) identify informational gaps pertaining to outcomes, which warrant further investigation.

Intraneural Ultrasound-guided Sciatic Nerve Block

What We Already Know about This Topic

What This Article Tells Us That Is New

Background

Both extra- and intraneural sciatic injection resulted in significant axonal nerve damage. This study aimed to establish the minimum effective volume of intraneural ropivacaine 1% for complete sensory-motor sciatic nerve block in 90% of patients, and related electrophysiologic variations.

Methods

Forty-seven consecutive American Society of Anesthesiologists physical status I-II patients received an ultrasound-guided popliteal intraneural nerve block following the up-and-down biased coin design. The starting volume was 15 ml. Baseline, 5-week, and 6-month electrophysiologic tests were performed. Amplitude, latency, and velocity were evaluated. A follow-up telephone call at 6 months was also performed.

Results

The minimum effective volume of ropivacaine 1% in 90% of patients for complete sensory-motor sciatic nerve block resulted in 6.6 ml (95% CI, 6.4 to 6.7) with an onset time of 19 ± 12 min. Success rate was 98%. Baseline amplitude of action potential (mV) at ankle, fibula, malleolus, and popliteus were 8.4 ± 2.3, 7.1 ± 2.0, 15.4 ± 6.5, and 11.7 ± 5.1 respectively. They were significantly reduced at the fifth week (4.3 ± 2.1, 3.5 ± 1.8, 6.9 ± 3.7, and 5.2 ± 3.0) and at the sixth month (5.9 ± 2.3, 5.1 ± 2.1, 10.3 ± 4.0, and 7.5 ± 2.7) (P &lt; 0.001 in all cases). Latency and velocity did not change from the baseline. No patient reported neurologic symptoms at 6-month follow-up.

Conclusions

The intraneural ultrasound-guided popliteal local anesthetic injection significantly reduces the local anesthetic dose to achieve an effective sensory-motor block, decreasing the risk of systemic toxicity. Persistent electrophysiologic changes suggest possible axonal damage that will require further investigation.

Peripheral nerve blocks of the pelvic limb in dogs: A retrospective clinical study

Objective: To evaluate the success rate and complications of lumbar plexus (LP) and femoral nerve (FN) blocks, each combined with a sciatic nerve (SN) block, in dogs undergoing pelvic limb orthopaedic surgery.

Design: Retrospective clinical study.

Procedure: The intra-operative and postoperative clinical records of dogs that underwent orthopaedic surgery of the pelvic limb were reviewed. Dogs were divided into two groups according to the analgesic technique used during surgery: dogs that received a peripheral nerve block (group PNB) and dogs in which opioid analgesia alone was used (group C).

Results: The PNB and C groups included 265 and 31 dogs, respectively. Complete statistical analysis was performed in 115/265 dogs of PNB group. The overall success rate of the PNB performed was 77% (89/115): 76% (72/95) and 85% (17/20) for LP-SN and FN-SN blocks, respectively. In group PNB, the prevalence of intra-operative hypotension was 7.8% (9/115). Only one (out of 95 [1.05%]) LP-SN block manifested transient postoperative bilateral pelvic limb paralysis. None of the 265 dogs in group PNB manifested neurological complications at six weeks postoperatively.

Conclusion: The success rate and the absence of neurological complications obtained support the use of LP-SN and FN-SN for loco-regional anaesthesia and analgesia in dogs undergoing orthopaedic surgery of the pelvic limb.

Intraneural injection of a test dose of local anesthetic in peripheral nerves - does it induce histological changes in nerve tissue?

BACKGROUND & OBJECTIVES

Most anesthesiologists use the injection of a test dose of local anesthetic in order to evaluate the final needle tip position. Thus, the intraneural injection of a full dose can be avoided. The aim of this study was to analyze whether an intraneural injection of a test dose of bupivacaine could trigger histological changes.

METHODS

Intraneural injections under direct vision were performed in 40 brachial plexus nerves in seven anesthetized pigs. Tibial nerves served as positive and negative controls. Two milliliter of bupivacaine 0.5% was injected in three nerves on the left brachial plexus. For control of local anesthetic's toxicity Ringer's solution was applied intraneurally on the right side. After maintaining 48 h of general anesthesia, the nerves were resected. The specimens were processed for histological examination and assessed for inflammation (hematoxylin and eosin stain, CD68-immunohistochemistry) and myelin damage (Kluver-Barrera stain). The degree of nerve injury was rated on a scale from 0 (no injury) to 4 (severe injury).

RESULTS

Statistical analysis showed no significant differences between the bupivacaine group [median (interquartile range) 1 (1-1.5)] and the Ringer's solution group [1 (0.5-2) P = 0.772]. Mild myelin alteration was found in 12.5% of all specimens following intraneural injection, irrespective of the applied substance.

CONCLUSIONS

"In our experimental study, intraneural injection of 2 ml of bupivacaine or Ringer's solution showed comparable mild inflammation. Nevertheless, inflammation can only be prevented by strictly avoiding nerve perforation followed by intraneural injection, as mechanical nerve perforation is a key factor for evolving inflammation.

Diabetic neuropathy increases stimulation threshold during popliteal sciatic nerve block

BACKGROUND

Peripheral nerve stimulation is commonly used for nerve localization in regional anaesthesia, but recommended stimulation currents of 0.3-0.5 mA do not reliably produce motor activity in the absence of intraneural needle placement. As this may be particularly true in patients with diabetic neuropathy, we examined the stimulation threshold in patients with and without diabetes.

METHODS

Preoperative evaluation included a neurological exam and electroneurography. During ultrasound-guided popliteal sciatic nerve block, we measured the current required to produce motor activity for the tibial and common peroneal nerve in diabetic and non-diabetic patients. Proximity to the nerve was evaluated post-hoc using ultrasound imaging.

RESULTS

Average stimulation currents did not differ between diabetic (n=55) and non-diabetic patients (n=52). Although the planned number of patients was not reached, the power goal for the mean stimulation current was met. Subjects with diminished pressure perception showed increased thresholds for the common peroneal nerve (median 1.30 vs. 0.57 mA in subjects with normal perception, P=0.042), as did subjects with decreased pain sensation (1.60 vs. 0.50 mA in subjects with normal sensation, P=0.038). Slowed ulnar nerve conduction velocity predicted elevated mean stimulation current (r=-0.35, P=0.002). Finally, 15 diabetic patients required more than 0.5 mA to evoke a motor response, despite intraneural needle placement (n=4), or required currents ≥2 mA despite needle-nerve contact, vs three such patients (1 intraneural, 2 with ≥2 mA) among non-diabetic patients (P=0.003).

CONCLUSIONS

These findings suggest that stimulation thresholds of 0.3-0.5 mA may not reliably determine close needle-nerve contact during popliteal sciatic nerve block, particularly in patients with diabetic neuropathy.

CLINICAL TRIAL REGISTRATION

NCT01488474.

Postoperative sciatic and femoral or saphenous nerve blockade for lower extremity surgery in anesthetized adults

Background:

Guidelines warn of increased risks of injury when placing regional nerve blocks in the anesthetized adult but complications occurred in patients that received neither sedation nor local anesthetic. This restriction of nerve block administration places vulnerable categories of patients at risk of severe opioid induced side effects. Patient and operative technical factors can preclude use of preoperative regional anesthesia. The purpose of this study was to assess complications following sciatic popliteal and femoral or saphenous nerve blockade administered to anesthetized adult patients following foot and ankle surgery.

Materials and Methods:

Postoperative patients administered general anesthesia received popliteal sciatic nerve blockade and either femoral or saphenous nerve blockade if operative procedures included medial incisions. Nerve blocks were placed with nerve stimulator or ultrasound guidance. A continuous nerve catheter was inserted if hospital admission was over 24 hours. Opioid analgesic supplementation was administered for inadequate pain relief. Postoperative pain scores and total analgesic requirements for 24 hours were recorded. Nerve block related complications were monitored for during the hospital admission and at follow up surgical clinic evaluation.

Results:

190 anesthetized adult patients were administered 357 nerve blocks. No major nerve injury or deficit was reported. One patient had numbness in the toes not ascribed to a specific nerve of the lower extremity. Perioperative opioid dose differences were noted between male and female and between opioid naïve and tolerant patients.

Neurotoxicity of perineural vs intraneural-extrafascicular injection of liposomal bupivacaine in the porcine model of sciatic nerve block

Liposomal bupivacaine is a prolonged-release local anaesthetic, the neurotoxicity of which has not yet been determined. We used quantitative histomorphometric and immunohistochemical analyses to evaluate the neurotoxic effect of liposomal bupivacaine after perineural and intraneural (extrafascicular) injection of the sciatic nerve in pigs. In this double-blind prospective randomised trial, 4 ml liposomal bupivacaine 1.3% was injected either perineurally (n = 5) or intraneurally extrafascicularly (n = 5). Intraneural-extrafascicular injection of saline (n = 5) was used as a control. After emergence from anaesthesia, neurological examinations were conducted over two weeks. After harvesting the sciatic nerves, no changes in nerve fibre density or myelin width indicative of nerve injury were observed in any of the groups. Intraneural injections resulted in longer sensory blockade than perineural (p < 0.003) without persistent motor or sensory deficit. Sciatic nerve block with liposomal bupivacaine in pigs did not result in histological evidence of nerve injury.

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.

Pathophysiology and Etiology of Nerve Injury Following Peripheral Nerve Blockade

This review synthesizes anatomical, anesthetic, surgical, and patient factors that may contribute to neurologic complications associated with peripheral nerve blockade. Peripheral nerves have anatomical features unique to a given location that may influence risk of injury. Peripheral nerve blockade-related peripheral nerve injury (PNI) is most severe with intrafascicular injection. Surgery and its associated requirements such as positioning and tourniquet have specific risks. Patients with preexisting neuropathy may be at an increased risk of postoperative neurologic dysfunction. Distinguishing potential causes of PNI require clinical assessment and investigation; a definitive diagnosis, however, is not always possible. Fortunately, most postoperative neurologic dysfunction appears to resolve with time, and the incidence of serious long-term nerve injury directly attributable to peripheral nerve blockade is relatively uncommon. Nonetheless, despite the use of ultrasound guidance, the risk of block-related PNI remains unchanged.

WHAT'S NEW

Since the 2008 Practice Advisory, new information has been published, furthering our understanding of the microanatomy of peripheral nerves, mechanisms of peripheral nerve injection injury, toxicity of local anesthetics, the etiology of and monitoring methods, and technologies that may decrease the risk of nerve block-related peripheral nerve injury.

Nerve localization techniques for peripheral nerve block and possible future directions

BACKGROUND

Ultrasound guidance is now a standard nerve localization technique for peripheral nerve block (PNB). Ultrasonography allows simultaneous visualization of the target nerve, needle, local anesthetic injectate, and surrounding anatomical structures. Accurate deposition of local anesthetic next to the nerve is essential to the success of the nerve block procedure. Due to limitations in the visibility of both needle tip and nerve surface, the precise relationship between needle tip and target nerve is unknown at the moment of injection. Importantly, nerve injury may result both from an inappropriately placed needle tip and inappropriately placed local anesthetic. The relationship between the block needle tip and target nerve is of paramount importance to the safe conduct of peripheral nerve block.

METHODS

This review summarizes the evolution of nerve localization in regional anesthesia, characterizes a problem faced by clinicians in performing ultrasound-guided nerve block, and explores the potential technological solutions to this problem.

RESULTS

To date, technology newly applied to PNB includes real-time 3D imaging, multi-planar magnetic needle guidance, and in-line injection pressure monitoring. This review postulates that optical reflectance spectroscopy and bioimpedance may allow for accurate identification of the relationship between needle tip and target nerve, currently a high priority deficit in PNB techniques.

CONCLUSIONS

Until it is known how best to define the relationship between needle and nerve at the moment of injection, some common sense principles are suggested.

Anesthesia for Vascular access Surgery

The type of anesthesia chosen is an integral part of the decision-making process for arteriovenous access construction. We discuss the different types of anesthesia used, with emphasis on brachial plexus block, which is potentially safer than general anesthesia in this fragile patient population with end-stage renal disease. Brachial plexus block is superior to local anesthesia and enables the use of a tourniquet to minimize potential damage to the blood vessels during anastomosis using microsurgery techniques, and does not lead to the vasospasm that may be seen with local anesthesia. Regional anesthesia has a beneficial sympathectomy-like effect that causes vasodilation with increased blood flow during surgery and in the fistula postoperatively that may prevent early thrombosis and potentially improve outcome.

Intraneural or extraneural: diagnostic accuracy of ultrasound assessment for localizing low-volume injection

BACKGROUND AND OBJECTIVES

When one is performing ultrasound-guided peripheral nerve blocks, it is common to inject a small amount of fluid to confirm correct placement of the needle tip. If an intraneural needle tip position is detected, the needle can then be repositioned to prevent injection of a large amount of local anesthetic into the nerve. However, it is unknown if anesthesiologists can accurately discriminate intraneural and extraneural injection of small volumes. Therefore, this study was conducted to determine the diagnostic accuracy of ultrasound assessment using a criterion standard and to compare experts and novices in ultrasound-guided regional anesthesia.

METHODS

A total of 32 ultrasound-guided infragluteal sciatic nerve blocks were performed on 21 cadaver legs. The injections were targeted to be intraneural (n = 18) or extraneural (n = 14), and 0.5 mL of methylene blue 1% was injected. Cryosections of the nerve and surrounding tissue were assessed by a blinded investigator as "extraneural" or "intraneural." Ultrasound video clips of the injections were reviewed by 10 blinded observers (5 experts, 5 novices) independently who scored each injection as either "intraneural," "extraneural," or "undetermined."

RESULTS

The mean sensitivity of experts and novices was measured to be 0.84 (0.80-0.88) and 0.65 (0.60-0.71), respectively (P = 0.006), whereas mean specificity was 0.97 (0.94-0.98) and 0.98 (0.96-0.99) (P = 0.53).

CONCLUSIONS

Discrimination of intraneural or extraneural needle tip position based on an injection of 0.5mL is possible, but even experts missed 1 of 6 intraneural injections. In novices, the sensitivity of assessment was significantly lower, highlighting the need for focused education.

Opening Injection Pressure Consistently Detects Needle–Nerve Contact during Ultrasound-guided Interscalene Brachial Plexus Block

Background:

Needle trauma may cause neuropathy after nerve blockade. Even without injection, nerve injury can result from forceful needle–nerve contact (NNC). High opening injection pressures (OIPs) have been associated with intrafascicular needle tip placement and nerve damage; however, the relationship between OIP and NNC is unclear. The authors conducted a prospective, observational study to define this relationship.

Methods:

Sixteen patients scheduled for shoulder surgery under interscalene block were enrolled if they had clear ultrasound images of the brachial plexus roots. A 22-gauge stimulating needle was inserted within 1 mm of the root, and 1-ml D5W injected at 10 ml/min by using an automated pump. OIP was monitored using an in-line pressure manometer and injections aborted if 15 psi or greater. The needle was advanced to displace the nerve slightly (NNC), and the procedure repeated. Occurrence of evoked motor response and paresthesia were recorded.

Results:

Fifteen patients had at least one clearly visible root. OIP at 1 mm distance from the nerve was less than 15 psi (mean peak pressure 8.2 ± 2.4 psi) and the 1-ml injection could be completed in all but two cases (3%). In contrast, OIP during NNC was 15 psi or greater (mean peak pressure 20.9 ± 3.7 psi) in 35 of 36 injections. Aborting the injection when OIP reached 15 psi prevented commencement of injection in all cases of NNC except one.

Conclusion:

High OIP (≥15 psi) consistently detected NNC, suggesting that injection pressure monitoring may be useful in preventing injection against nerve roots during interscalene block.

No correlation between minimal electrical charge at the tip of the stimulating catheter and the efficacy of the peripheral nerve block catheter for brachial plexus block: a prospective blinded cohort study

Background

Stimulating catheters offer the possibility of delivering an electrical charge via the tip of the catheter. This may be advantageous as it allows verifying if the catheter tip is in close proximity to the target nerve, thereby increasing catheter performance. This prospective blinded cohort study was designed to investigate whether there is a correlation between the minimal electrical charge at the tip of the stimulating catheter, and the efficacy of the peripheral nerve block (PNB) catheter as determined by 24 h postoperative morphine consumption.

Methods

Forty adult patients with ASA physical health classification I-III scheduled for upper extremity surgery under combined continuous interscalene block and general anesthesia were studied. Six patients were excluded from analysis.

After inserting a stimulating catheter as if it were a non-stimulating catheter for 2–5 cm through the needle, the minimal electrical charge necessary to obtain an appropriate motor response was determined. A loading dose of 20 mL ropivacaine 0.75% ropivacaine was then administered, and postoperative analgesia was provided by a continuous infusion of ropivacaine 0.2% 8 mL.h^-1 via the brachial plexus catheter, and an intravenous morphine patient-controlled analgesia (PCA) device.

Main outcome measures include the minimal electrical charge (MEC) at the tip of the stimulating catheter necessary to elicit an appropriate motor response, and the efficacy of the PNB catheter as determined by 24 h postoperative PCA morphine consumption.

Results

Mean (SD) [range] MEC at the tip of the stimulating catheter was 589 (1414) [30 – 5000] nC. Mean (SD) [range] 24 h morphine consumption was 8.9 (9.9) [0–29] mg. The correlation between the MEC and 24 h postoperative morphine consumption was Spearman’s Rho r_s = -0.26, 95% CI -0.56 to 0.09.

Conclusion

We conclude that there is no proportional relation between MEC at the tip of the blindly inserted stimulating catheter and 24 h postoperative morphine consumption.

Trial registration

Trialregister.nl identifier: NTR2328

[Localization of peripheral nerves. Success and safety with electrical nerve stimulation]

Peripheral electrical nerve stimulation is one of the standard applications in peripheral regional anesthesia in addition to the ultrasound technique. Among other findings, the visualization of needle and nerve during ultrasound-guided blockade caused a change in clinical practice of peripheral nerve stimulation in the last decade. In the present article old and new aspects of principles and clinical practice of the nerve stimulation technique are presented and summarized in a total clinical concept in order to achieve safe and successful peripheral regional anesthesia using electrical peripheral nerve stimulation.

Electron microscopy of human peripheral nerves of clinical relevance to the practice of nerve blocks. A structural and ultrastructural review based on original experimental and laboratory data

AIM

The goal is to describe the ultrastructure of normal human peripheral nerves, and to highlight key aspects that are relevant to the practice of peripheral nerve block anaesthesia.

METHOD

Using samples of sciatic nerve obtained from patients, and dural sac, nerve root cuff and brachial plexus dissected from fresh human cadavers, an analysis of the structure of peripheral nerve axons and distribution of fascicles and topographic composition of the layers that cover the nerve is presented. Myelinated and unmyelinated axons, fascicles, epineurium, perineurium and endoneurium obtained from patients and fresh cadavers were studied by light microscopy using immunohistochemical techniques, and transmission and scanning electron microscopy. Structure of perineurium and intrafascicular capillaries, and its implications in blood-nerve barrier were revised.

RESULTS

Each of the anatomical elements is analyzed individually with regard to its relevance to clinical practice to regional anaesthesia.

CONCLUSIONS

Routine practice of regional anaesthetic techniques and ultrasound identification of nerve structures has led to conceptions, which repercussions may be relevant in future applications of these techniques. In this regard, the ultrastructural and histological perspective accomplished through findings of this study aims at enlightening arising questions within the field of regional anaesthesia.