Functional Deficits After Intraneural Injection During Interscalene Block:

Efficacy and safety of extrafascial injection versus intrafascial injection for interscalene brachial plexus block: a systematic review and meta-analysis

INTRODUCTION

This systematic review and meta-analysis aimed to assess the efficacy and safety of interscalene brachial plexus block (ISB) techniques in upper limb and shoulder surgeries.

EVIDENCE ACQUISITION

We conducted a comprehensive search of PubMed, Web of Science, Cochrane Central Register of Controlled Trials, Embase, Medline, and Scopus databases up to May 14th, 2023. We employed a search strategy involving keywords such as "brachial plexus block," "interscalene brachial plexus block," "ISB," "extrafascial," and "intrafascial," without applying search restrictions or filters. Eligible studies consisted of randomised controlled trials (RCTs) that compared extrafascial and intrafascial ISB techniques in adult patients undergoing upper limb and shoulder surgeries.

EVIDENCE SYNTHESIS

Our analysis included six RCTs encompassing 485 participants. Extrafascial injection demonstrated superiority over intrafascial injection in reducing the incidence of hemidiaphragmatic paresis (RR 0.33, 95% CI 0.124 to 0.47, P<0.00001) and preserving respiratory function (MS 0.31, 95% CI 0.1 to 0. 52, P=0.003 FEV1 in liters). Additionally, extrafascial ISB exhibited a lower risk of block-related complications (RR 0.35, 95% CI 0.25 to 0.50, P<0.00001). However, the intrafascial technique offered a faster sensory and motor block onset. The duration of sensory block did not significantly differ. The incidence of Horner syndrome showed no statistically significant difference.

CONCLUSIONS

Our findings favor extrafascial ISB techniques because they reduce hemidiaphragmatic paresis, preserve respiratory function, and lower block-related complications. However, further research is necessary to establish their safety and efficacy in specific patient populations.

Sciatic Nerve Intrafascicular Injection Induces Neuropathy by Activating the Matrix Modulators MMP-9 and TIMP-1

Background: Peripheral nerve block (PNB) under echo guidance may not prevent intrafascicular anesthetic injection-induced nerve injury. This study investigated whether unintended needle piercing alone, or the intrafascicular nerve injectant could induce neuropathy.

Methods: 120 adult male Sprague-Dawley rats were divided into four groups: 1) group S, only the left sciatic nerve was exposed; 2) group InF-P, the left sciatic nerve was exposed and pierced with a 30 G needle; 3) group InF-S, left sciatic nerve was exposed and injected with saline (0.9% NaCl 30 µL); 4) group InF-R, left sciatic nerve was exposed and injected with 0.5% (5 mg/mL, 30 µL) ropivacaine. Behaviors of thermal and mechanical stimuli responses from hindpaws, sciatic nerve vascular permeability and tight junction protein expression, and macrophage infiltration were assessed. Pro-inflammatory cytokine expression and TIMP-1 and MMP-9 activation at the injection site and the swollen, and distal sites of the sciatic nerve were measured by cytokine array, western blotting, and immunofluorescence of POh14 and POD3.

Results: Intrafascicular saline and ropivacaine into the sciatic nerve, but not needle piercing alone, significantly induced mechanical allodynia that lasted for seven days. In addition, the prior groups increased vascular permeability and macrophage infiltration, especially in the swollen site of the sciatic nerve. Thermal hypersensitivity was induced and lasted for only 3 days after intrafascicular saline injection. Obvious upregulation of TIMP-1 and MMP-9 on POh6 and POh14 occurred regardless of intrafascicular injection or needle piercing. Compared to the needle piercing group, the ratio of MMP-9/TIMP-1 was significantly higher in the intrafascicular injectant groups at the injected and swollen sites of the sciatic nerve. Although no gross changes in the expressions of tight junction proteins (TJPs) claudin-5 and ZO-1, the TJPs turned to apparent fragmentation and fenestration-like degenerative change in swollen endothelial cells and thickened microvessels.

Conclusion: Intrafascicular nerve injection is a distinct mechanism that induces neuropathy. It is likely that the InF nerve injection-induced neuropathy was largely due to dramatic, but transient, increases in enzymatic activities of MMP-9 and activating TIMP-1 in the operated nerves. The changes in enzymatic activities then contributed to certain levels of extracellular matrix degradation, which leads to increases in endoneurial vascular permeability.

The effects of shoulder arthroscopy on ultrasound image quality of the interscalene brachial plexus: a pre-procedure vs post-procedure comparative study

BACKGROUND

Fluid extravasation from the shoulder compartment and subsequent absorption into adjacent soft tissue is a well-documented phenomenon in arthroscopic shoulder surgery. We aimed to determine if a qualitative difference in ultrasound imaging of the interscalene brachial plexus exists in relation to the timing of performing an interscalene nerve block (preoperative or postoperative).

METHODS

This single-center, prospective observational study compared pre- and postoperative interscalene brachial plexus ultrasound images of 29 patients undergoing shoulder arthroscopy using a pretest-posttest methodology where individual patients served as their own controls. Three fellowship-trained regional anesthesiologists evaluated image quality and confidence in performing a block for each ultrasound scan using a five-point Likert scale. The association of image quality with age, gender, BMI, duration of surgery, obstructive sleep apnea, and volume of arthroscopic irrigation fluid were analyzed as secondary outcomes.

RESULTS

Aggregate preoperative mean scores in quality of ultrasound visualization were higher than postoperative scores (preoperative 4.5 vs postoperative 3.8; p < .001), as was confidence in performing blockade based upon the imaging (preoperative 4.8 vs postoperative 4.2; p < .001). Larger BMI negatively affected visualization of the brachial plexus in the preoperative period (p < 0.05 for both weight categories). Patients with intermediate-high risk or confirmed obstructive sleep apnea had lower aggregate postoperative mean scores compared to the low-risk group for both ultrasound visualization (3.4 vs 4.0; p < .05) and confidence in block performance (3.8 vs 4.4; p < .05).

CONCLUSION

Due to the potential reduction of ultrasound visualization of the interscalene brachial plexus after shoulder arthroscopy, we advocate for a preoperative interscalene nerve block when feasible.

TRIAL REGISTRATION

ClinicalTrials.gov ( NCT03657173 ; September 4, 2018).

Ultrasound-Guided Peripheral Nerve Blocks Performed by Orthopedic Surgeons: A Retrospective, Multicenter Study in Akita Prefecture, Japan

The shortage of doctors is a societal problem, especially in rural areas such as Akita Prefecture, Japan. Therefore, it is not unusual in Akita for orthopedic surgeons to perform upper and lower limb surgeries under ultrasound-guided peripheral nerve blocks managed by the operators themselves. Multicenter studies of ultrasound-guided peripheral nerve blocks performed by orthopedic surgeons have not been reported. The purpose of this study was to clarify the safety and reliability of ultrasound-guided peripheral nerve blocks performed by orthopedic surgeons in Akita. A total of 1,674 upper extremity surgery cases operated under ultrasound-guided peripheral nerve blocks at 8 hospitals in Akita prefecture from April 2016 to April 2018 were investigated retrospectively. These blocks were performed by a total of 37 orthopedic surgeons, including senior surgeons and residents. In 321 of the 1,674 cases (19%), local anesthetics were added to the surgical field. Two cases with special factors were converted to general anesthesia. There were 2 cases of complications associated with the nerve block, but they were all transient and recovered promptly. The block site and the hospital where the block was performed showed a significant relationship with the addition of local anesthetics to the surgical site (P < 0.001). Surgery time, age at surgery, and surgical site showed no significant relationships with the addition of local anesthetics. The volume of the anesthetic used for the nerve block showed a significant inverse relationship with the addition of local anesthetics (P=0.040). Many orthopedic surgeons in Akita prefecture began to perform ultrasound-guided peripheral nerve blocks, which had a reliable anesthesia effect with no noticeable complications, whether performed by residents or senior orthopedic surgeons, and this is a useful anesthetic technique for orthopedic surgeons.

Extraplexus versus intraplexus ultrasound-guided interscalene brachial plexus block for ambulatory arthroscopic shoulder surgery: A randomized controlled trial

Background

This randomized study compared the efficacy and safety of extraplexus and intraplexus injection of local anesthetic for interscalene brachial plexus block.

Methods

208 ASA I-II patients scheduled for elective shoulder arthroscopy under general anesthesia and ultrasound-guided interscalene brachial plexus block were randomly allocated to receive an injection of 25mL ropivacaine 0.5% either between C5-C6 nerve roots (intraplexus), or anterior and posterior to the brachial plexus into the plane between the perineural sheath and scalene muscles (extraplexus). The primary outcome was time to loss of shoulder abduction. Secondary outcomes included block duration, perioperative opioid consumption, pain scores, block performance time, number of needle passes, onset of sensory blockade, paresthesia, recovery room length of stay, patient satisfaction, incidence of Horner’s syndrome, dyspnea, hoarseness, and post-operative nausea and vomiting.

Results

Time to loss of shoulder abduction was faster in the intraplexus group (log-rank p-value<0.0005; median [interquartile range]: 4 min [2–6] vs. 6 min [4–10]; p-value <0.0005). Although the intraplexus group required fewer needle passes (2 vs. 3, p<0.0005), it resulted in more transient paresthesia (35.9% vs. 14.5%, p = 0.0004) with no difference in any other secondary outcome.

Conclusion

The intraplexus approach to the interscalene brachial plexus block results in a faster onset of motor block, as well as sensory block. Both intraplexus and extraplexus approaches to interscalene brachial plexus block provide effective analgesia. Given the increased incidence of paresthesia with an intraplexus approach, an extraplexus approach to interscalene brachial plexus block is likely a more appropriate choice.

Real-Time Injection Pressure Sensing and Minimal Intensity Stimulation Combination During Ultrasound-Guided Peripheral Nerve Blocks: An Exploratory Observational Trial

BACKGROUND

Nerve damage can occur after peripheral nerve block (PNB). Ultrasound guidance does not eliminate the risk of intraneural injection or nerve injury. Combining nerve stimulation and injection pressure (IP) monitoring with ultrasound guidance has been suggested to optimize needle tip location in PNB. In this prospective observational study, we hypothesized that measured pairs of IP and minimum intensity of stimulation (MIS) might differentiate successive needle tip locations established by high-resolution ultrasound during PNB.

METHODS

For this exploratory study, 240 observations for 40 ultrasound-guided PNBs were studied in 28 patients scheduled for orthopedic surgery. During the progression of the needle to the nerve observed by ultrasonography, the IP was measured continuously using a computerized pressure-sensing device with a low flow rate of solution. Stimulation thresholds and electrical impedance were obtained by an impedance analyzer coupled to the nerve stimulator at 6 successive needle positions. The median (quartile) or mean (95% confidence interval [CI]) was reported. A mixed model analysis was used, and the sample was also explored using a classification and regression tree (CART) algorithm.

RESULTS

Specific combinations of IP and MIS were measured for subcutaneous, epimysium contact, intramuscular, nerve contact (231 mm Hg [203-259 mm Hg] and 1.70 mA [1.38-2.02 mA]), intraneural location (188 mm Hg [152-224 mm Hg] and 0.58 mA [0.46-0.70 mA]), and subparaneural location (47 mm Hg [41-53 mm Hg] and 1.35 mA [1.09-1.61 mA]). The CART algorithm shows that the optimal subparaneural needle tip position might be defined by the lowest pressure (<81.3 mm Hg) and MIS (<1.5 mA) cutoffs.

CONCLUSIONS

Our exploratory study evaluated concepts to generate hypotheses. The combinations of IP and MIS might help the physician during a PNB procedure. A low IP and low MIS might confirm a subparaneural location, and a high IP and a low MIS might be an alert for the intraneural location of the needle tip.

Comparison of Single-Agent Versus 3-Additive Regional Anesthesia for Foot and Ankle Surgery

BACKGROUND

This study compared the results of regional blocks containing a single anesthetic, bupivacaine, with those containing bupivacaine and 3 additives (buprenorphine, clonidine, and dexamethasone) in patients undergoing foot and ankle surgery.

METHODS

Eighty patients undergoing foot and ankle surgery over a 9-month period were prospectively enrolled and randomized to receive a peripheral nerve block containing either a single anesthetic (SA) or one with 3 additives (TA). Patients, surgeons, and anesthesiologists were blinded to the groups. Patients maintained pain diaries and were evaluated at 1 and 12 weeks postoperatively. Fifty-six patients completed the study.

RESULTS

The TA group had a longer duration of analgesic effect than the SA group (average 82 vs 34 hours, P < .05). Forty-eight hours after surgery, 93% of SA blocks, compared with 34% of TA blocks, had completely worn off. The TA group had a longer duration of sensory effects. At 3 months, 10 of 26 (38.5%) TA patients, compared with 3 of 30 (10%) SA patients, reported postoperative neurologic symptoms. Pain scores in both groups were not statistically different at 1 week or 3 months after surgery. Patients in both groups were similarly satisfied with their blocks.

CONCLUSION

Both types of nerve blocks provided equivalent pain control and patient satisfaction in patients undergoing foot and ankle surgery. The 3-additive agent blocks were associated with a longer duration of pain relief and a longer duration of numbness, as well as higher rates of postoperative neurologic symptoms. Longer pain relief may be obtained at the cost of prolonged sensory deficits.

LEVEL OF EVIDENCE

Level II, prospective comparative study.

Complications After Multiple-Site Peripheral Nerve Blocks for Foot and Ankle Surgery Compared With Popliteal Sciatic Nerve Block Alone

BACKGROUND

Single or combined multiple-site peripheral nerve blocks (PNBs) are becoming popular for patients undergoing surgery on their feet or ankles. These procedures are known to be generally safe in surgical settings compared with other forms of anesthesia, such as spinal block. The purposes of this study were to assess the incidence of complications after the administration of multiple PNBs for foot and ankle surgery and to compare the rates of complications between patients who received a single PNB and those who received multiple blocks.

METHODS

Charts were reviewed retrospectively to assess peri- and postoperative complications possibly related to the PNBs. The records of 827 patients who had received sciatic nerve blocks, femoral nerve blocks adductor canal blocks, or combinations of these for foot and/or ankle surgery were analyzed for complications. The collected data consisted of age, sex, body mass index, presence of diabetes mellitus, smoking history, tourniquet time, and complications both immediately postoperatively and 1 year later.

RESULTS

Of these 827 patients, 92 (11.1%) developed neurologic symptoms after surgery; 22 (2.7%) of these likely resulted from the nerve blocks, and 7 (0.8%) of these were unresolved after the patients' last follow-up visits. There were no differences in complication rates between combined blocks and single sciatic nerve blocks.

CONCLUSION

There were more complications, both transient and long term, after anesthetic PNBs than previous literature has reported. Combined multiple-site blocks did not increase the rate of neurologic complications.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

High Opening Injection Pressure Is Associated With Needle-Nerve and Needle-Fascia Contact During Femoral Nerve Block

BACKGROUND AND OBJECTIVES

High opening injection pressures (OIPs) have been shown to predict sustained needle tip contact with the roots of the brachial plexus. Such roots have a uniquely high ratio of fascicular versus connective tissue. It is unknown if this relationship is preserved during multifascicular nerve blockade. We hypothesized that OIP can predict needle-nerve contact during femoral nerve block, as well as detect needle contact with the fascia iliaca.

METHODS

Twenty adults scheduled for femoral block were recruited. Using ultrasound, a 22-gauge needle was sequentially placed in 4 locations: indenting the fascia iliaca, advanced through the fascia iliaca while lateral to the nerve, slightly indenting the femoral nerve, and withdrawn from the nerve 1 mm. At each location, the OIP required to initiate an injection of 1 mL D5W (5% dextrose in water) at 10 mL/min was recorded. Blinded investigators performed evaluations and aborted injections when an OIP of 15 psi was reached.

RESULTS

Opening injection pressure was 15 psi or greater for 90% and 100% of cases when the needle indented the femoral nerve and fascia iliaca, respectively. Opening injection pressure was less than 15 psi for all 20 patients when the needle was withdrawn 1 mm from the nerve as well as at the subfascial position (McNemar χ2 P < 0.001).

CONCLUSIONS

Opening injection pressure greater than 15 psi was associated with a block needle tip position slightly indenting the epineurium of the femoral nerve (90%) and the fascia iliaca (100%). Needle tip positions not indenting these structures were associated with OIP of less than 15 psi (100%).

Comparison Between Ultrasound-Guided Supraclavicular and Interscalene Brachial Plexus Blocks in Patients Undergoing Arthroscopic Shoulder Surgery: A Prospective, Randomized, Parallel Study

Although supraclavicular brachial plexus block (SCBPB) was repopularized by the introduction of ultrasound, its usefulness in shoulder surgery has not been widely reported. The objective of this study was to compare motor and sensory blockades, the incidence of side effects, and intraoperative opioid analgesic requirements between SCBPB and interscalene brachial plexus block (ISBPB) in patients undergoing arthroscopic shoulder surgery. Patients were randomly assigned to 1 of 2 groups (ISBPB group: n = 47; SCBPB group: n = 46). The side effects of the brachial plexus block (Horner's syndrome, hoarseness, and subjective dyspnea), the sensory block score (graded from 0 [no cold sensation] to 100 [intact sensation] using an alcohol swab) for each of the 5 dermatomes (C5-C8 and T1), and the motor block score (graded from 0 [complete paralysis] to 6 [normal muscle force]) for muscle forces corresponding to the radial, ulnar, median, and musculocutaneous nerves were evaluated 20 min after the brachial plexus block. Fentanyl was administered in 50 μg increments when the patients complained of pain that was not relieved by the brachial plexus block. There were no conversions to general anesthesia due to a failed brachial plexus block. The sensory block scores for the C5 to C8 dermatomes were significantly lower in the ISBPB group. However, the percentage of patients who received fentanyl was comparable between the 2 groups (27.7% [ISBPB group] and 30.4% [SCBPB group], P = 0.77). SCBPB produced significantly lower motor block scores for the radial, ulnar, and median nerves than did ISBPB. A significantly higher incidence of Horner's syndrome was observed in the ISBPB group (59.6% [ISBPB group] and 19.6% [SCBPB group], P < 0.001). No patient complained of subjective dyspnea. Despite the weaker degree of sensory blockade provided by SCBPB in comparison to ISBPB, opioid analgesic requirements are similar during arthroscopic shoulder surgery under both brachial plexus blocks. However, SCBPB produces a better motor blockade and a lower incidence of Horner's syndrome than ISBPB.

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.

A Randomized Controlled Trial Evaluating the See, Tilt, Align, and Rotate (STAR) Maneuver on Skill Acquisition for Simulated Ultrasound-Guided Interventional Procedures

OBJECTIVES

Achieving the best view of the needle and target anatomy when performing ultrasound-guided interventional procedures requires technical skill, which novices may find difficult to learn. We hypothesized that teaching novice performers to use 4 sequential steps (see, tilt, align, and rotate [STAR] method) to identify the needle under ultrasound guidance is more efficient than training with the commonly described probe movements of align, rotate, and tilt (ART).

METHODS

This study compared 2 instructional methods for transducer manipulation including alignment of a probe and needle by novices during a simulated ultrasound-guided nerve block. Right-handed volunteers between the ages of 18 and 55 years who had no previous ultrasound experience were recruited and randomized to 1 of 2 groups; one group was trained to troubleshoot misalignment with the ART method, and the other was trained with the new STAR maneuver. Participants performed the task, consisting of directing a needle in plane to 3 targets in a standardized gelatin phantom 3 times. The performance assessor and data analyst were blinded to group assignment.

RESULTS

Thirty-five participants were recruited. The STAR group was able to complete the task more quickly (P < .001) and visualized the needle in a greater proportion of the procedure time (P = .004) compared to the ART group. All STAR participants were able to complete the task, whereas 41% of ART participants abandoned the task (P = .003).

CONCLUSIONS

Novices are able to complete a simulated ultrasound-guided nerve block more quickly and efficiently when trained with the 4-step STAR maneuver compared to the ART method.

Evaluation of the eZono 4000 with eZGuide for ultrasound-guided procedures

Ultrasound-guided procedures are increasingly common in a variety of acute care settings, such as the operating room, critical care unit and emergency room. However, accurate judgment of needle tip position using traditional ultrasound technology is frequently difficult, and serious injury can result from inadvertently advancing beyond or through the target. Needle navigation is a recent innovation that allows the clinician to visualize the needle position and trajectory in real time as it approaches the target. A novel ultrasound machine has recently been introduced that is portable and designed for procedural guidance. The eZono 4000™ features an innovative needle navigation technology that is simple to use and permits the use of a wide range of commercially available needles, avoiding the inconvenience and cost of proprietary equipment. This article discusses this new ultrasound machine in the context of other currently available ultrasound machines featuring needle navigation.

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.

The effect of needle dimensions and infusion rates on injection pressures in regional anaesthesia needles: a bench-top study

Animal studies have shown that injection pressures > 75 kPa indicate probable intrafascicular needle tip position. This study describes the flow/pressure characteristics of seven common needle systems. A syringe pump delivered flow rates of 5, 6.67, 10, 13.3, 15 and 20 ml.min(-1) through these needle systems, while keeping the needle tips open to atmosphere. A pressure transducer connected between the syringe and needle provided a real-time graphical display for analysis. Mean plateau pressures increased linearly with flow and with decreasing needle diameter (2.7-92 kPa). Flow rates > 17 ml.min(-1) and needle sizes 22 G and smaller produced mean plateau pressures > 75 kPa. Pressure monitors upstream from the needle may produce false-positive alarms at high flow rates due to needle resistance, and unreliable readings due to non-laminar flow. We recommend injection rates ≤ 15 ml.min(-1) (0.25 ml.s(-1) ) to reduce the effect of factors upstream from the needle tip as a cause of high pressure readings.

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.

Ultrasound-guided peripheral nerve blockade of the upper extremity

PURPOSE OF REVIEW

Is ultrasound guidance changing the practice of upper extremity regional anesthesia? This review will aim to describe the findings published in the literature during the previous 18 months.

RECENT FINDINGS

In some approaches to brachial plexus blockade, local anesthetic volumes may be reduced without deterioration of analgesic effect. However, even 10 ml of local injected into the interscalene space may result in diaphragmatic paresis. High-resolution ultrasonography has revealed anatomical variations of C5, C6 and C7 nerve roots in almost half of the patients examined, without negative block effectiveness. The addition of dexamethasone may prolong analgesia after single-shot interscalene and supraclavicular blocks. Insertion of brachial plexus perineural catheters using ultrasound guidance can be successful and provides better postoperative analgesia than single-shot blocks for up to 24 h postoperatively. Infraclavicular catheters provide superior analgesia when compared with supraclavicular catheters. Multiple-site injections of local offer no advantage over a single-site injection during an infraclavicular block. Ultrasound guidance compared with neurostimulation may reduce patient discomfort during axillary blocks compared with neurostimulation. Intra-epineural injections are common during an interscalene blockade, but the incidence of neurological injury remains low. There is an ongoing debate on the effectiveness and safety of ultrasound-guided intra-epineurial injections.

SUMMARY

Current literature suggests a reduction of the volume of local anesthetics used for ultrasound-guided upper extremity blockades. Dexamethasone may prolong duration of brachial plexus blocks and more frequent use of perineural catheters is encouraged. Controversy over intra-epineurial injections exists and requires additional large-scale studies.

The role of continuous peripheral nerve blocks

A continuous peripheral nerve block (cPNB) is provided in the hospital and ambulatory setting. The most common use of CPNBs is in the peri- and postoperative period but different indications have been described like the treatment of chronic pain such as cancer-induced pain, complex regional pain syndrome or phantom limb pain. The documented benefits strongly depend on the analgesia quality and include decreasing baseline/dynamic pain, reducing additional analgesic requirements, decrease of postoperative joint inflammation and inflammatory markers, sleep disturbances and opioid-related side effects, increase of patient satisfaction and ambulation/functioning improvement, an accelerated resumption of passive joint range-of-motion, reducing time until discharge readiness, decrease in blood loss/blood transfusions, potential reduction of the incidence of postsurgical chronic pain and reduction of costs. Evidence deriving from randomized controlled trials suggests that in some situations there are also prolonged benefits of regional anesthesia after catheter removal in addition to the immediate postoperative effects. Unfortunately, there are only few data demonstrating benefits after catheter removal and the evidence of medium- or long-term improvements in health-related quality of life measures is still lacking. This review will give an overview of the advantages and adverse effects of cPNBs.