Functional anatomy of the nerve and optimal placement of the needle for successful (and) safe nerve blocks.

PURPOSE OF REVIEW: Summarize the current thinking concerning the clinically relevant aspects of nerve anatomy and best injection sites for nerve blocks. RECENT FINDINGS: The widespread use of ultrasound in regional anesthesia has changed the practice of regional anesthesia and created new possibilities. Among them is the ability to identify fascial planes, and this has become the basis for a new group of blocks, the fascial plane blocks. In this kind of blocks, the target for injection is the plane itself and not a nerve in particular. transversus abdominis plane, pectoralis muscles, erector spinae plane blocks are some examples of fascial blocks. Because injecting into a fascial plane is not controversial, these blocks are not included in our discussion of optimal placement of the needle.To determine optimal needle placement, it is important to have a clear definition of what constitutes intraneural. Although, there is almost universal agreement that the violation of the epineurium defines the intraneural concept, the literature include several studies where this assessment is erroneous.Although intentional intraneural injection is still considered objectionable, some literature suggests that injecting intraneurally, especially if extrafascicular, may be benign. This evidence is limited and anecdotal. SUMMARY: It is necessary to have a better understanding of what intraneural injection is when dealing with any type of nerve blocks, be that single nerve, plexuses, or the sciatic nerve. Perineural injections provide successful anesthesia without putting the nerve integrity at risk. That practice is supported by years of experience and common sense. Currently, there is no evidence to support any kind of intraneural injections, intrafascicular or extrafascicular.

Standardizing nomenclature in regional anesthesia: an ASRA-ESRA Delphi consensus study of upper and lower limb nerve blocks.

BACKGROUND: Inconsistent nomenclature and anatomical descriptions of regional anesthetic techniques hinder scientific communication and engender confusion; this in turn has implications for research, education and clinical implementation of regional anesthesia. Having produced standardized nomenclature for abdominal wall, paraspinal and chest wall regional anesthetic techniques, we aimed to similarly do so for upper and lower limb peripheral nerve blocks. METHODS: We performed a three-round Delphi international consensus study to generate standardized names and anatomical descriptions of upper and lower limb regional anesthetic techniques. A long list of names and anatomical description of blocks of upper and lower extremities was produced by the members of the steering committee. Subsequently, two rounds of anonymized voting and commenting were followed by a third virtual round table to secure consensus for items that remained outstanding after the first and second rounds. As with previous methodology, strong consensus was defined as ≥75% agreement and weak consensus as 50%-74% agreement. RESULTS: A total of 94, 91 and 65 collaborators participated in the first, second and third rounds, respectively. We achieved strong consensus for 38 names and 33 anatomical descriptions, and weak consensus for five anatomical descriptions. We agreed on a template for naming peripheral nerve blocks based on the name of the nerve and the anatomical location of the blockade and identified several areas for future research. CONCLUSIONS: We achieved consensus on nomenclature and anatomical descriptions of regional anesthetic techniques for upper and lower limb nerve blocks, and recommend using this framework in clinical and academic practice. This should improve research, teaching and learning of regional anesthesia to eventually improve patient care.

Paravertebral block: anatomy and relevant safety issues.

Paravertebral block, especially thoracic paravertebral block, is an effective regional anesthetic technique that can provide significant analgesia for numerous surgical procedures, including breast surgery, pulmonary surgery, and herniorrhaphy. The technique, although straightforward, is not devoid of potential adverse effects. Proper anatomic knowledge and adequate technique may help decrease the risk of these effects. In this brief discourse, we discuss the anatomy and technical aspects of paravertebral blocks and emphasize the importance of appropriate needle manipulation in order to minimize the risk of complications. We propose that, when using a landmark-based approach, limiting medial and lateral needle orientation and implementing caudal (rather than cephalad) needle redirection may provide an extra margin of safety when performing this technique. Likewise, recognizing a target that is not in close proximity to the neurovascular bundle when using ultrasound guidance may be beneficial.

Real-time three-dimensional ultrasound-assisted axillary plexus block defines soft tissue planes.

Two-dimensional (2D) ultrasound is commonly used for regional block of the axillary brachial plexus. In this technical case report, we described a real-time three-dimensional (3D) ultrasound-guided axillary block. The difference between 2D and 3D ultrasound is similar to the difference between plain radiograph and computer tomography. Unlike 2D ultrasound that captures a planar image, 3D ultrasound technology acquires a 3D volume of information that enables multiple planes of view by manipulating the image without movement of the ultrasound probe. Observation of the brachial plexus in cross-section demonstrated distinct linear hyperechoic tissue structures (loose connective tissue) that initially inhibited the flow of the local anesthesia. After completion of the injection, we were able to visualize the influence of arterial pulsation on the spread of the local anesthesia. Possible advantages of this novel technology over current 2D methods are wider image volume and the capability to manipulate the planes of the image without moving the probe.

Refining a great idea: the consolidation of PECS I, PECS II and serratus blocks into a single thoracic fascial plane block, the SAP block.

The popularity of ultrasound-guided nerve blocks has impacted the practice of regional anesthesia in profound ways, improving some techniques and introducing new ones. Some of these new nerve blocks are based on the concept of fascial plane blocks, in which the local anesthetic is injected into a plane instead of around a specific nerve. Pectoralis muscles (PECS) and serratus blocks, most commonly used for post op analgesia after breast surgery, are good examples. Among the nerves targeted by PECS/serratus blocks are different branches of the brachial plexus that traditionally have been considered purely motor nerves. This unsubstantiated claim is a departure from accepted anatomical knowledge and challenges our understanding of the sensory innervation of the chest wall. The objective of this Daring Discourse is to look beyond the ability of PECS/serratus blocks to provide analgesia/anesthesia of the chest wall, to concentrate instead on understanding the mechanism of action of these blocks and, in the process, test the veracity of the claim. After a comprehensive review of the evidence we have concluded that (1) the traditional model of sensory innervation of the chest wall, which derives from the lateral branches of the upper intercostal nerves and does not include branches of the brachial plexus, is correct. (2) PECS/serratus blocks share the same mechanism of action, blocking the lateral branches of the upper intercostal nerves, and so their varied success is tied to their ability to reach them. This common mechanism agrees with the traditional innervation model. (3) A common mechanism of action supports the consolidation of PECS/serratus blocks into a single thoracic fascial plane block with a point of injection closer to the effector site. In a nod to transversus abdominus plane block, the original inspiration for PECS blocks, we propose naming this modified block, the serratus anterior plane block.

Gross anatomy of the brachial plexus sheath in human cadavers.

BACKGROUND AND OBJECTIVES: Major nerves and vessels run alongside each other in a "neurovascular bundle" kept together by connective tissue that is often referred to by anatomists, surgeons, and anesthesiologists as the "sheath." Our goal was to macroscopically demonstrate the brachial plexus sheath in embalmed and fresh cadaver dissections. METHODS: Systematic dissections were performed on 11 embalmed cadavers (6 females and 5 males), plus one fresh, unembalmed male cadaver. Dissections were started in the arm, and progressed proximally to the axilla and the supraclavicular area. Notes and photographic documentation were obtained. RESULTS: A sheath around the neurovascular bundle of the brachial plexus was visible to the naked eye in every dissection. The sheath had a fibrous external appearance, and was filled with loose connective tissue. No evidence of septa was found. CONCLUSIONS: We observed a macroscopic fibrous structure surrounding the plexus, which was filled with loose connective tissue lacking any apparent organization.

Supraclavicular block in the obese population: an analysis of 2020 blocks.

Regional anesthesia in the obese patient can be challenging and possibly carries a greater failure rate as compared with that in the non-obese patient. We retrospectively reviewed our prospectively gathered peripheral block data to determine the influence of body weight on success rate of the supraclavicular block. Obesity was defined as body mass index > or =30. The overall success rate was 97.3% in nonobese and 94.3% in obese patients (P < 0.01). Residents completed 80% of the blocks in nonobese patients and 73% in obese patients (P < 0.01). No difference in acute complications was observed. Obesity is associated with a slight decrease in success rate of supraclavicular block and an increase in its relative difficulty without apparent effect on acute complications.

A subgluteal approach to the sciatic nerve in adults at 10 cm from the midline.

BACKGROUND AND OBJECTIVES: In 2003 we introduced the concept of a sciatic nerve block performed in the midgluteal area at a fixed distance from the midline in all adults regardless of gender and/or body size. The anatomic basis for that study suggested that a subgluteal block could also be accomplished in a similar fashion. METHODS: After informed consent, 20 patients were prospectively recruited. Patients were positioned in lateral decubitus. The needle insertion site was located in the subgluteal fold at 10 cm from the midline. The needle was advanced parallel to the midline until a sciatic nerve response was elicited. With a visible response at 0.5 mA, 30 mL 1.5% mepivacaine plus 1:200,000 epinephrine was slowly injected. Sensory anesthesia was tested on the plantar and dorsal aspects of the foot as well as the posterior thigh. RESULTS: Residents performed all blocks. The approach was 100% successful in locating the sciatic nerve with 3 attempts or less from a site located 10 cm from the midline. The block provided successful surgical anesthesia in 90% of the cases; 2 cases required local anesthetic supplementation. Only 3 patients developed anesthesia of the posterior thigh within 30 minutes of injection. CONCLUSIONS: This report shows that a sciatic nerve block can be performed in the subgluteal area at 10 cm from the midline in adult patients of both sexes and various sizes. Anesthesia of the posterior thigh is not consistently accomplished with this approach.

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.

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.

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.

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.

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.

Upper extremity regional anesthesia: essentials of our current understanding, 2008.

Brachial plexus blockade is the cornerstone of the peripheral nerve regional anesthesia practice of most anesthesiologists. As part of the American Society of Regional Anesthesia and Pain Medicine's commitment to providing intensive evidence-based education related to regional anesthesia and analgesia, this article is a complete update of our 2002 comprehensive review of upper extremity anesthesia. The text of the review focuses on (1) pertinent anatomy, (2) approaches to the brachial plexus and techniques that optimize block quality, (4) local anesthetic and adjuvant pharmacology, (5) complications, (6) perioperative issues, and (6) challenges for future research.