Carlo D. Franco

1,001 subclavian perivascular brachial plexus blocks: Success with a nerve stimulator

Background and Objectives: Among the supraclavicular approaches to the brachial plexus, the subclavian perivascular technique is a well‐established method of anesthesia of the upper extremity. Ever since Kulenkampf described his technique, eliciting a paresthesia has been almost mandatory (“no paresthesia, no anesthesia”). Lately, nerve stimulators have become more popular. However, up to the present time, clinical studies involving the nerve stimulator have failed to show success rates comparable to paresthesia techniques. Methods: Data from 1,001 consecutive, subclavian perivascular blocks were prospectively gathered over 2.5 years. All blocks were performed according to Winnies technique, but using a nerve stimulator instead of a paresthesia. When an adequate response was obtained, 35 to 40 mL of local anesthetic solution was injected. Results: Nine hundred seventy‐three blocks (97.2%) were completely successful; 16 blocks (1.6%) were incomplete and needed supplementation; and 12 blocks (1.2%) failed and required general anesthesia, giving a success rate for regional anesthesia of 98.8%. Conclusions: The subclavian perivascular block consistently provides an effective block for surgery on the upper extremity. At the site of injection with this technique, the plexus is reduced to its smallest components and the sheath is reduced to its smallest volume, which explains in great part the success obtained with this block. We believe that we have demonstrated a nerve stimulator technique that is both highly successful and safe; no clinical pneumothorax was found nor did any other major complications develop.

Buprenorphine added to the local anesthetic for axillary brachial plexus block prolongs postoperative analgesia

Background and Objectives Buprenorphine added to local anesthetic solutions for supraclavicular block was found to triple postoperative analgesia duration in a previous study when compared with local anesthetic block alone. That study, however, did not control for potentially confounding factors, such as the possibility that buprenorphine was affecting analgesia through intramuscular absorption or via a spinal mechanism. To specifically delineate the role of buprenorphine in peripherally mediated opioid analgesia, the present study controlled for these 2 factors. Methods Sixty American Society of Anesthesiologists (ASA) P.S. I and II, consenting adults for upper extremity surgery, were prospectively assigned randomly in double-blind fashion to 1 of 3 groups. Group I received local anesthetic (1% mepivacaine, 0.2% tetracaine, epinephrine 1:200,000), 40 mL, plus buprenorphine, 0.3 mg, for axillary block, and intramuscular (IM) saline. Group II received local anesthetic-only axillary block, and IM buprenorphine 0.3 mg. Group III received local anesthetic-only axillary block and IM saline. Postoperative pain onset and intensity were compared, as was analgesic medication use. Results The mean duration of postoperative analgesia was 22.3 hours in Group I; 12.5 hours in group II, and 6.6 hours in group III. Differences between groups I and II were statistically significant (P = .0012). Differences both between groups I and III and II and III were also statistically significant (P < .001). Conclusions Buprenorphine-local anesthetic axillary perivascular brachial plexus block provided postoperative analgesia lasting 3 times longer than local anesthetic block alone and twice as long as buprenorphine given by IM injection plus local anesthetic-only block. This supports the concept of peripherally mediated opioid analgesia by buprenorphine.

Buprenorphine added to the local anesthetic for brachial plexus block to provide postoperative analgesia in outpatients

Background and Objectives Over the past 10 years, several studies have suggested that the addition of certain opiates to the local anesthetic used for brachial block may provide effective, long-lasting postoperative analgesia. One of these studies indicated that the agonist-antagonist, buprenorphine, added to bupivacaine provided a longer period of postoperative analgesia than the traditional opiates, but in this study, it is impossible to determine the relative contributions of the local anesthetic and the opiate to the postoperative analgesia because of the extremely long duration of the anesthesia provided by the local anesthetic, bupivacaine. By repeating the study using a local anesthetic of a shorter duration, the present study delineates more clearly the contribution of the buprenorphine to postoperative analgesia when added to a shorter-acting local anesthetic. Methods Forty, healthy, consenting adult patients scheduled for upper extremity surgery were enrolled in the study. Premedication was provided by intravenous midazolam 2 mg/70 kg and anesthesia by a subclavian perivascular brachial plexus block. The patients were assigned randomly to 1 of 2 equal groups based on the agents used for the blocks. The patients in group I received 40 mL of a local anesthetic alone, while those in group II received the same local anesthetic plus buprenorphine 0.3 mg. The study was kept double-blind by having 1 anesthesiologist prepare the solutions, a second anesthesiologist perform the blocks, and a third anesthesiologist monitor the anesthesia and analgesia thereafter, up to and including the time of the first request for an analgesic medication. The data were reported as means (± SEM), and differences between groups were determined using repeated measures of analysis of variance (ANOVA) and Χ2, followed by the Fisher exact test for post hoc comparison. A P value of less than .05 was considered to be statistically significant. Results The mean duration of postoperative pain relief following the injection of the local anesthetic alone was 5.3 (± 0.15) hours as compared with 17.4 (± 1.26) hours when buprenorphine was added, a difference that was statistically (and clinically) significant (P < .0001). Conclusions The addition of buprenorphine to the local anesthetic used for brachial plexus block in the present study provided a 3-fold increase in the duration of postoperative analgesia, with complete analgesia persisting 30 hours beyond the duration provided by the local anesthetic alone in 75% of the patients. This practice can be of particular benefit to patients undergoing ambulatory upper extremity surgery by providing prolonged analgesia after discharge from the hospital.

Connective tissues associated with peripheral nerves.

A s the popularity and acceptance of ultrasound-guided nerve block techniques increase, also does the need to define with better precision the planes into which the local anesthetic is deposited and the relationship of these deposits with the target nerves. Significant confusion exists in our literature regarding the nature and nomenclature of the various layers of connective tissue that are associated with peripheral nerves and their trajectories. This problem goes beyond pure semantics because it prevents us from agreeing on what exactly constitutes intraneural and what is definitely outside the nerve. In this issue of Regional Anesthesia and Pain Medicine, Andersen et al report their study of connective tissues associated with the sciatic nerve in the popliteal fossa, with the main goal of determining whether some of this connective tissue is indeed extraneural. To accomplish their goal, they studied 28 unembalmed cadaver legs by performing anatomic dissections, ultrasound imaging, dye injections, and even some histologic analysis on a few specimens. Their results led them to conclude that, outside the epineurium of the sciatic nerve, there are some layers of connective tissue that are associated with the nerve but do not form part of its structure. They have called this connective tissue ‘‘paraneural sheath.’’ The presence of connective tissue around the sciatic nerve beyond what seems to be the epineurium of the nerve has already been described in our literature, although its nature remains controversial. Reviewing the existing literature on peripheral nerves, it is rather surprising to realize that most of our questions regarding peripheral nerves and their surrounding tissue structures could be answered by putting together various pieces of already existing information. Some of these accepted facts are as follows: & Peripheral nerves are composed both of neural (reunion of axons into 1 or more fascicles) and nonneural (connective tissue) components, both forming a unitary complex. & The non-neural connective tissue component of a nerve is an intrinsic part of the nerve architecture (it ‘‘belongs’’ to it). It is arranged into 3 different layers, called from the inside out, endoneurium, perineurium, and epineurium.6,8 & The endoneurium is composed mainly of fine collagen fibers. The perineurium is highly specialized, consisting of flat squamous cells that share tight junctions and are arranged into 1 or more layers along with some collagen fibers. Functionally, the perineurium is, in effect, the nerve-blood barrier. The epineurium has 2 components, the interfascicular component or ‘‘internal’’ epineurium, made of loose connective tissue that fills the space among the fascicles and a denser ‘‘external’’ epineurium that forms the ‘‘skin’’ of the nerve. & The epineurium, perineurium, and endoneurium are intimately connected to one another. & Connective tissue, in general, is ubiquitous in the body, and as such, it is commonly found alongside nerves (extraneural) and vascular structures (neurovascular bundles). & The intraneural, connective tissue forming the epineurium of a nerve blends insensibly with the extraneural connective tissue of the regions that the nerve travels through. It is at this plane of transition that the nerve maintains a degree of mobility throughout life. & Peripheral nerves can be either cranial or spinal. The 31 pairs of spinal nerves give origin to the intercostal nerves and the roots of the plexuses (cervical, brachial, lumbar, and sacral). They originate by the reunion of ventral (motor) and dorsal (sensory) roots around the proximal end of an intervertebral foramen. As they emerge through it, they evaginate the dura and arachnoid maters giving origin to the dural cuffs or nerve sleeves. & At the distal end of the intervertebral foramen, the dura layer of the nerve sleeve becomes continuous with the epineurium of each of the 31 pairs of spinal nerves. & The sciatic nerve is formed by 2 nerves: tibial and common peroneal. They are independent nerve structures that do not mix their fibers, but they happen to share a long trajectory in the gluteal region and posterior thigh until they diverge from each other in the popliteal fossa. EDITORIAL

The Supraclavicular Block with a Nerve Stimulator: To Decrease or Not to Decrease, That Is the Question

Portable nerve stimulators for nerve blocks have been available for more than 40 yr. It is generally accepted that seeking a motor response at low outputs increases the chances of success. It is customary to start the procedure at a higher current with the goal of finding the nerve. After an adequate response is elicited, the current is decreased before the local anesthetic is injected. However, how low is low enough and, for that matter, how high is too high have not been adequately determined. Our experience seems to indicate that, in the supraclavicular block, the type of response obtained is as important as the output at which it is elicited, provided that this current is not higher than 1 mA. In this context, it is theoretically possible that our initial seeking current of 0.9 mA could be an adequate injection current if it is combined with an appropriate response. We designed this study to test the hypothesis that a response of the fingers in flexion or extension, elicited at 0.9 mA, could be followed immediately by the local anesthetic injection. We did not intend to compare 0.5 and 0.9 mA as minimum stimulating currents but rather as currents able to elicit an unmistakable motor twitch. Sixty patients were randomly assigned to one of two groups. Group 1 (n = 30) was injected with a motor twitch in the fingers that was still visible at 0.5 mA. Group 2 (n = 30) was injected after a similar response to that in Group 1 was elicited, but at the initial output of 0.9 mA, without any further decrease. The blocks were injected with 40 mL of local anesthetic solution. One patient was excluded from the study for failing to meet protocol criteria. The success rate in the remaining 59 patients was 100%; success was defined as complete sensory blockade at the median, ulnar, and radial nerve territories of the hand that was accomplished in ≤30 min from the time of injection and that did not require supplementation or general anesthesia. In fact, all blocks became complete within 22 min of the injection. The onset of anesthesia occurred in 10.9 ± 5.4 min in the 0.5-mA group and 11.4 ± 4.8 min in the 0.9-mA group; this difference was not statistically different. The onset of analgesia and the duration of anesthesia were also similar in both groups. There were no complications, and the respondents in both groups graded their experience at a similar level of satisfaction. We conclude that during the performance of a supraclavicular block eliciting a clearly visible response of the fingers at 0.9 mA can be immediately followed by the injection of local anesthetic, because decreasing the output to 0.5 mA does not seem to improve the overall quality of the block as measured by the onset and duration of anesthesia or patient satisfaction.

Innervation of the Anterior Capsule of the Human Knee: Implications for Radiofrequency Ablation.

Background and Objectives Chronic knee pain is common in all age groups. Some patients who fail conservative therapy benefit from radiofrequency neurotomy. Knowledge of the anatomy is critical to ensure a successful outcome. The purpose of this study was to reanalyze the innervation to the anterior knee capsule from the perspective of the interventional pain practitioner. Methods The study included a comprehensive literature review followed by dissection of 8 human knees to identify the primary capsular innervation of the anterior knee joint. Photographs and measurements were obtained for each relevant nerve branch. Stainless-steel wires were placed along the course of each primary innervation, and radiographs were obtained. Results Literature review revealed a lack of consensus on the number and origin of nerve branches innervating the anterior knee capsule. All dissections revealed the following 6 nerves: superolateral branch from the vastus lateralis, superomedial branch from the vastus medialis, middle branch from the vastus intermedius, inferolateral (recurrent) branch from the common peroneal nerve, inferomedial branch from the saphenous nerve, and a lateral articular nerve branch from the common peroneal nerve. Nerve branches showed variable proximal trajectories but constant distal points of contact with femur and tibia. The inferolateral peroneal nerve branch was found to be too close to the common peroneal nerve, making it inappropriate for radiofrequency neurotomy. Conclusions The innervation of the anterior capsule of the knee joint seems to follow a constant pattern making at least 3 of these nerves accessible to percutaneous ablation. To optimize clinical outcome, well-aligned radiographs are critical to guide lesion placement.

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.

Ultrasound-Guided Interscalene Block: Reevaluation of the "Stoplight" Sign and Clinical Implications.

Background and Objectives The “stoplight” sign is a frequently described image during ultrasound-guided interscalene block, referring to 3 hypoechoic structures found between the anterior and middle scalene muscles. This study was designed to establish the ultrasound-anatomy correlation of this sign and to find any other anatomical features within the roots that could help with the interpretation of the ultrasound images obtained at the interscalene level. Methods We performed 20 dissections of the brachial plexus in 10 embalmed human cadavers and systematically analyzed and measured the roots of C5 to C7 and then correlated these findings with ultrasonographic images on file. Results We found that the C5 root is significantly smaller than either C6 or C7 (P < 0.0001). We also found that C6 and C7, but not C5, frequently present macroscopic evidence of intraroot splitting visible to the naked eye. We also found that the roots of C5 and C6, but not of C7, present frequent variations in their relationship with the scalene muscles. Conclusions Our results provide the anatomic basis to define the stoplight sign as one made of, from cephalad to caudal, the root of C5, the upper fascicle(s) of C6, and the lower fascicle(s) of C6 without contribution from C7. The important clinical implication is that an injection attempted between what is commonly perceived as the gap between C6 and C7 would indeed be an intraneural injection at C6, which could potentially spread toward the neuraxial space.

The subclavian perivascular block

The subclavian perivascular technique, introduced by Winnie and Collins in 1964, is one of the most popular supraclavicular approaches to the brachial plexus. It is based on an anatomical concept, the existence of a fibrous tissue sheath surrounding the neurovascular bundle. This sheath acts as a barrier, limiting the diffusion of the local anesthetic away from the nerves. Thus, a single injection of an adequate volume of local anesthetic within this space is able to reach the components of the plexus, consistently producing good results. Different methods are employed to identify the presence of the needle inside the sheath. A fascial “click”, used by some, is a subjective sensation felt by the operator when the needle pierces the fascia. More popular is the technique of eliciting paresthesias. It requires physical contact between needle and nerve, as well as the patients cooperation to qualify and locate the response. The possibility of increased risk of nerve damage has been raised with this technique. Lately, nerve stimulators have enjoyed increased popularity. They have the theoretical advantage of helping to bring the needle close enough to the nerve to ensure intrafascial injection, without the need for physical contact. The subclavian perivascular block, performed with a nerve stimulator, makes an already good technique even better.

The sensory territory of the lateral cutaneous nerve of the thigh as determined by anatomic dissections and ultrasound-guided blocks.

Background and Objectives A femoral block sometimes fails to provide complete sensory anesthesia of the anterior aspect of middle and distal thigh, and a block of the lateral cutaneous nerve of the thigh (LCN) is often necessary to supplement it. The goal of this study was to demonstrate, both in the anatomy laboratory and in the clinical setting, a possible contribution of the LCN to the innervation of the anterior thigh. Methods This was a prospective, observational study, including anatomic dissections and a clinical section in which 22 patients received an ultrasound-guided block of the LCN. The resulting area of anesthesia was determined 15 minutes later using pinprick examination. Results In 1 of 3 thigh dissections, we found a dominant LCN innervating most of the anterior aspect of the middle and distal thigh, areas that are usually attributed to the femoral nerve. In the clinical part of the study, 10 patients (45.5%) developed an area of anesthesia that extended to the medial aspect of the thigh and distally to the patella. Conclusions Our results, coming from a small sample, seem to indicate that the LCN may contribute to the innervation of the anterior thigh in some cases. A block of the LCN could be considered when a femoral block has failed to produce the expected area of anesthesia.