Xavier Sala-Blanch

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

BACKGROUND: Prevention of an intraneural injection of a local anesthetic during peripheral nerve blockade is considered important to avoid neurologic injury. However, the needle-nerve relationship during low-current electrical nerve localization is not well understood. METHODS: We postulated that intraneural needletip location is common during low-current stimulation popliteal sciatic nerve blockade. Twenty-four consecutive ASA class I-III patients scheduled for foot or ankle surgery under popliteal sciatic nerve block using a combined ultrasound and nerve stimulator-guided technique were prospectively studied. The end point for needle advancement was predetermined to be either an elicited motor response between 0.2 and 0.5 mA (100 &mgr;s/2 Hz) or an apparent intraneural location of the needletip as seen on ultrasound, whichever came first. The injection occurred at either end points provided the injection pressure was <20 psi. The injection was considered intraneural when injectate resulted in both the swelling and compartmentalization of the nerve within the epineurium. RESULTS: Elicited motor response could be obtained only upon entry of the needle into the intraneural space in 20 patients (83.3%). In the remaining four patients (16.7%), a motor response with a stimulating current of 1.5 mA could not be obtained even after the needle entry into the intraneural space. An injection in the intraneural space occurred in all patients who had motor-evoked response at current 0.2–0.4 mA. All 24 blocks resulted in adequate anesthesia for foot surgery. No patient developed postoperative neurologic dysfunction. CONCLUSION: The absence of motor response to nerve stimulation during popliteal sciatic nerve block does not exclude intraneural needle placement and may lead to additional unnecessary attempts at nerve localization. Additionally, low-current stimulation was associated with a high frequency of intraneural needle placement.

peripheral Nerve Stimulation in the Practice of Brachial Plexus Anesthesia : a Review

Success of plexus nerve block is dependent on the correct positioning of the local anesthetic solution near the desired nerves.1,2 Throughout the history of regional anesthesia, elicitation of paresthesia has been a classical method to locate nerves, while mechanical aids, including radioscopy3 and peripheral nerve stimulation (PNS),4,5 have been promoted to facilitate close approximation of needle and nerve, theoretically increasing the corresponding success rate.2 Experience with electrical stimulation for locating nerves suggests it is beneficial in teaching regional anesthetic techniques to residents in training, performing difficult nerve blocks, or using novel approaches and smaller doses of local anesthetic.1,2,6 Further, nerve stimulation can be used effectively for less cooperative patients and in anesthetized patients,7 though the risk of neural injury remains present.8 Electrical stimulation facilitates the localization of nerves, and its use does not eliminate the need for basic technical knowledge: in effect, knowledge of the anatomy of the area to be blocked, the muscle innervation scheme, applied neurophysiology, and the pharmacology of the local anesthetic used. Consideration of these factors is important to evaluate the conflicting results in the PNS literature—results that in some cases are reportedly inferior to those of more classical methods, having only 2 series effectively confirm that nerve stimulation affords an increased success rate with plexus block.9,10 For these reasons, the objective of our article is to review the applied neurophysiology and the principal features of the use of PNS in regional anesthesia.

Ultrasound in the Practice of Brachial Plexus Anesthesia

However, the costsof the US devices continue to limit widespread ap-plication of this approach. Gradual cost reductionas a result of technological advancement, togetherwith a reduction in the block complications will, webelieve, make the US technique increasingly attrac-tive for anesthesiologists in their practices.The present review provides some basic details ofultrasonographic technique, with emphasis on an-atomical knowledge important for US of the bra-chial plexus. Finally, a brief analysis of the literatureabout regional block and US is provided.

Structural injury to the human sciatic nerve after intraneural needle insertion.

Background: Recent clinical reports suggest that intraneural needle placement may not always lead to neurologic injury. To explain the absence of neurologic complications in these reports, we studied the risk and extent of nerve injury after intentional needle-nerve placement in a cryopreserved human sciatic nerve. Methods: The sciatic nerve was dissected from a cryopreserved cadaver through partial exposure. Needles were inserted through the nerve, using blunt-tip (30 degrees beveled) (group A) and sharp-tip (15 degrees beveled) (group D) needles. Five needle insertions were made for each needle type. Subsequently, transverse nerve sections at 10 needle trajectories were processed. Nerve samples were stained with hematoxylin-eosin, Masson trichromic, and immunohistochemical stains. In each section, the following variables were quantified: total number of fascicles and vessels in the immediate vicinity of the needle trajectories and the number of injured fascicles and vessels. Results: A total of 520 fascicles were quantified, of which 134 were in contact with the needle trajectories. The numbers of fascicles and vessels per section were 65 ± 8 and 14 ± 7, respectively. A mean of 16 ± 5 fascicles were found in contact with the needle trajectory (group A: 17± 3, group D: 15 ± 6). Of these, 4 fascicles (3.2%) and 1 intraneural vessel were found damaged in group D. No fascicular or vascular injuries were found in group A. Conclusions: Our findings suggest that intraneural needle insertion may more commonly result in interfascicular rather than intrafascicular needle placement.

No Clinical or Electrophysiologic Evidence of Nerve Injury after Intraneural Injection during Sciatic Popliteal Block

Background: Intraneural injection during nerve-stimulator–guided sciatic block at the popliteal fossa may be a common occurrence. Although intraneural injections have not resulted in clinically detectable neurologic injury in small studies in human subjects, intraneural injections result in postinjection inflammation in animal models. This study used clinical, imaging, and electrophysiologic measures to evaluate the occurrence of any subclinical neurologic injury in patients with intraneural injection during sciatic popliteal block. Methods: Twenty patients undergoing popliteal block were enrolled; 17 patients completed the study protocol. After tibial nerve response was achieved by nerve stimulation (0.3–0.5 mA; 2 Hz; 0.1 ms), 20 ml mixture of mepivacaine (1.25%) and radiopaque contrast (2 ml) were injected. Location and spread of the injectant were assessed by ultrasound measurements of the sciatic nerve area before and after injection, and by computed tomography. In addition to clinical neurologic evaluations, serial electrophysiologic studies (nerve conduction and late response studies using predefined criteria) were performed at baseline and at 1 week and 3 weeks after the block for signs of subclinical neurologic dysfunction. Results: Sixteen injections (94%, 95% CI: 71–100%) met criteria for an intraneural injection. Postinjection nerve area on ultrasound increased by 45% (95% CI: 29–58%), P < 0.001. Computed tomography demonstrated fascicular separation in 70% (95% CI: 44–90%), air within the nerve in 29% (95% CI: 10–56%), contrast along bifurcations in 65% (95% CI: 38–86%), and concentric contrast layers in 100% (95% CI: 84–100%). Neither clinical nor electrophysiologic studies detected neurologic dysfunction indicating injury to the nerve. Conclusions: Nerve-stimulator–guided sciatic block at the popliteal fossa often results in intraneural injection that may not lead to clinical or electrophysiologic nerve injury.

Ultrasound guidance may reduce but not eliminate complications of peripheral nerve blocks.

THE relatively recent technological advances and clinical research are continuously facilitating the metamorphosis of ultrasound-guided regional anesthesia from an experimental technique into a standard procedure in clinical care. The intense enthusiasm from its most vocal proponents led to almost religious belief that the ability to continuously monitor needle placement and administration of local anesthetic is a bulletproof technique to accomplish safe and successful regional anesthesia. However, evidence is mounting that such radical views are not only overly optimistic, but may prove counterproductive. Recent reports suggest that expert ultrasound guidance may reduce but not eliminate the most common complications of regional anesthesia, such as blood vessel puncture or inadvertent intraneural or intravascular injections. Sites et al. analyzed videos of some 60 ultrasound-guided blocks performed by trainees. They concluded that the most common errors are failure to recognize the maldistribution of local anesthetic, failure to recognize the needle tip before injection, and poor choice of needle-insertion site and angle, preventing needle visualization. This report alone serves as a reminder of the main limitation of ultrasound technology: dependence on the operator. The reputation of clinical excellence of the authors of the two reports in the current issue of ANESTHESIOLOGY suggests limitation in the technology, rather than a lack of expertise, as the additional obstacle in reliably detecting an intravascular injection during ultrasound-guided nerve blocks. This is of no surprise, given that multiple technical factors may also influence the ability to monitor the path of the needle, disposition of the local anesthetic, and visualization of the relevant anatomy. One of the main advantages of ultrasound guidance during peripheral nerve blocks is the ability to deliver multiple smaller aliquots of local anesthetics at different locations. It would be logical to expect that such a strategy should result in less risk of block failure and less risk of intravascular injection of a large dose of local anesthetic, particularly in a highly vascular area such as the axilla. However, despite the research suggesting that ultrasound guidance during nerve block procedures allows for reduction of total dose/volume of local anesthetic, the doses and volumes used for reliable blockade by many clinicians are still capable of producing significant systemic toxicity. Therefore, similar precautions during a nerve blockade and in the choice of local anesthetics should be adhered to, regardless of whether ultrasound guidance is used. Results of a recent survey of practice strategies to reduce and treat local anesthetic–induced toxicity among practitioners in academic anesthesiology departments pointed out a surprising variability in safety precautions and preparedness for local anesthetic toxicity. Lessons learned from reports of malignant hyperthermia unambiguously indicate that well-established treatment protocols allow for lifesaving, timely intervention. Local anesthetic toxicity during peripheral nerve blockade is likely more common than malignant hyperthermia, but similar guidelines for its prevention and treatment have not been well established or widely adopted. This finding is disappointing because both laboratory evidence and clinical case reports suggest that timely treatment may be lifesaving. Ultrasound guidance is without a doubt one of the most significant developments in regional anesthesia. It would be a collective judgment error, however, to lean on this technology as a replacement for all existing practice strategies or as a panacea for all safety considerations. An approach more likely to improve the safety of regional anesthesia is evidence-based integration of ultrasound technology into the existing and emerging monitoring and practice protocols during the administration of regional anesthesia. This task should be incumbent upon the leadership of organized anesthesia societies to secure the future of regional anesthesia.

Intraneural Injection during Anterior Approach for Sciatic Nerve Block

To the Editor:—We read with interest the case report by Sala-Blanch et al. The authors describe an unorthodox but interesting treatment for patients undergoing continuous sciatic nerve block that raises several concerns. In short, using computed tomographic imaging without clear clinical indication, the authors documented that nerve stimulator–guided needle placement during sciatic nerve block through the anterior approach resulted in an intraneural needle placement. The authors then inserted the catheter and administered local anesthetics. Conventional wisdom suggests that intraneural needle placement and catheter insertion should be avoided because intraneural application of local anesthetics has been shown to result in neurologic injury in animal models. However, despite the documented intraneural needle and catheter placement—although it is not clear whether the stimulating needle lies between fascia and epineurium or between epineurium and perineurium—the patients did not have neurologic injury. Therefore, this case report suggests that not all intraneural injections lead to neurologic injury. It also suggests that nerve stimulators may not be reliable in avoiding intraneural needle or catheter placement. Finally, a better definition of what constitutes an intraneural versus an intraepineural sheath injection during blockade of peripheral nerves and plexuses is needed for more meaningful discussion of this matter. Some experts may view the patient treatment in report by Sala-Blanch et al. unusual or even potentially hazardous. However, their findings should be welcomed because they clearly pose some important questions. At the least, they suggest that future research should continue to focus on developing more reliable and objective tools of nerve localization and injection monitoring techniques to help avoid intraneural injection and reduce the risk of consequent neurologic injury. In any case, it is recommended to withdraw the needle or the catheter if one has any doubt that its position is too close to the nerve, for the safety of regional anesthesia.

Ultrasound-guided popliteal sciatic block with a single injection at the sciatic division results in faster block onset than the classical nerve stimulator technique.

BACKGROUND: For successful, fast-onset sciatic popliteal block (SPB), either a single injection above the division of the sciatic nerve, or 2 injections to block the tibial nerve (TN) and common peroneal nerve (CPN) separately have been recommended. In this study, we compared the traditional nerve stimulator (NS)-guided SPB above the division of the sciatic nerve with the ultrasound (US)-guided block with single injection of local anesthetic (LA) between the TN and CPN at the level of their division. We hypothesized that US-SPB with a single injection between TN and CPN would result in faster block onset than a single-injection NS-SPB. METHODS: Fifty-two patients were randomized to receive either an NS-SPB or a US-SPB. For both blocks, a single injection of 20 mL mepivacaine 1.5% was given using an automated injection pump while controlling for injection force. For NS-SPB, a TN response below 0.5 mA was sought 7 cm above the popliteal fossa crease (and proximal to the divergence of the TN and peroneal nerves). For US-SPB, the injection was made after a US-guided needle was inserted between the TN and CPN at the level of their separation. Motor response was not actively sought but registered if present. The location and spread of LA were evaluated by US in both groups. Onset of motor and sensory blocks was serially assessed in 5-minute intervals in the TN and CPN divisions and compared between the groups. RESULTS: All patients in both groups had successful block at 30 minutes after the injection, defined as sensory block to allow surgery without supplementation. A higher proportion of patients in the US-SPB group had a complete sensory (80% vs 4%, P < 0.001) and motor block (60% vs 8%, P < 0.001), defined as anesthesia and paralysis in all nerve territories, at 15 minutes after injection. US signs of intraepineural injection were present in 19 patients (73%) in the NS-SPB group and 25 patients (100%) in the US-SPB group (P < 0.001). CONCLUSIONS: A single injection of LA in US-SPB with needle insertion at the separation of the TN and CPN results in a similar success rate at 30 minutes; however, more patients in the US-SPB group than in the NS-SPB group had complete block at 15 minutes.

Ultrasound-guided ankle block for forefoot surgery: the contribution of the saphenous nerve.

Background Ankle blocks typically include the block of 5 nerves, the 4 branches that trace their origin back to the sciatic nerve plus the saphenous nerve (SaN). The sensory area of the SaN in the foot is variable. Based on our clinical experience, we decided to study the sensory distribution of the SaN in the foot and determine whether the block of this nerve is necessary as a component of an ultrasound-guided ankle block for bunion surgery. Methods One hundred patients scheduled for bunion surgery under ankle block were prospectively studied. We performed ultrasound-guided individual blocks of the tibial, deep peroneal, superficial peroneal, and sural nerves. After obtaining complete sensory block of these nerves, we mapped the SaN sensory territory as such area without anesthesia on the medial side of the foot. Results Every nerve block was successful within 10 minutes of injection. The saphenous territory extended into the foot to 57 ± 13 mm distal to the medial malleolus. This distal margin was 22 ± 11 mm proximal to the first tarsometatarsal joint. The proximal end of the surgical incision was located 1 cm distal to the first tarsometatarsal joint. In only 3 patients (3%), the area of SaN innervation reached the proximal end of the planned incision. Conclusions Ultrasound-guided ankle block is a highly effective technique for bunion surgery. The sensory territory of the SaN in the foot seems to extend only to the midfoot. According to our sample, 97% of the patients undergoing bunion surgery under an ankle block would not benefit from having a SaN block.

Three-dimensional/four-dimensional volumetric ultrasound imaging of the sciatic nerve.

Introduction Currently, there are limited data on the use of 3-dimensional ultrasound to image peripheral nerves. We undertook this imaging study to determine the feasibility of using 3-dimensional ultrasound imaging to delineate the anatomy of the sciatic nerve. Methods After research ethics committee approval and written informed consent, 4 healthy young adult male volunteers underwent 3-dimensional ultrasound scan of the sciatic nerve. A Voluson 730 Expert (GE Healthcare, Austria) with a broadband convex volume transducer (4–8.5 MHz) was used to scan the sciatic nerves at 3 levels: the subgluteal space, posterior aspect of the midthigh, and at the apex of the popliteal fossa. Three-dimensional volumetric ultrasound scan of the sciatic nerve was performed with the transverse plane as the data acquisition plane. The acquired 3-dimensional volumes were also rendered using a 3-dimensional volume-rendering software and displayed as a multiplanar image or as a “niche” display. Results The right sciatic nerve was successfully scanned using the broadband convex volume transducer in all 4 volunteers. A distinct perineural space was identified around the sciatic nerve from the subgluteal space to the level of the popliteal fossa. Proximally, the sciatic nerve was visualized in a hypoechoic “subgluteal space” between the epimysium of the gluteus maximus and the quadratus femoris muscle. More distally, a hypoechoic “perineural” space was identifiable between the sciatic nerve and the hamstrings muscles. The niche view demonstrated the cranial extension of the subgluteal space, as an intermuscular tunnel or as a conduit for the sciatic nerve. Conclusions We have demonstrated that it is feasible to perform 3-dimensional ultrasound imaging of the sciatic nerve. The anatomic information obtained is more detailed than that with a 2-dimensional scan, which provides better insight into the spatial relationship of the sciatic nerve with its surrounding structures. A distinct “perineural space” was also identified alongside the course of the sciatic nerve, which may play a significant role in sciatic nerve blockade.