A Randomized Comparison Between Subepineural and Conventional Ultrasound-Guided Popliteal Sciatic Nerve Block:

Selective RNAi silencing of Schwann cell Piezo1 alleviates mechanical hypersensitization following peripheral nerve injury

The present study was designed to investigate the role of Schwann cell (SC) Piezo1 in peripheral nociception. We first developed an AAV vector that has primary SC tropism after delivery into the sciatic (or tibial) nerve. This was achieved by packing AAV-GFP transcribed by a CBA promoter using a capsid AAVolig001 to generate AAVolig001-CBA-GFP. Six weeks after intraneural injection of AAVolig001-CBA-GFP in naive rats, GFP expression was detected selectively in both myelinating SCs (mSCs) and non-myelinating SCs (nmSCs). A dual promoter and bidirectional AAV encoding a U6-driven short hairpin RNA against rat Piezo1 (PZ1shRNA) and CBA-transcribed GFP was packed with capsid olig001 (AAVolig001-PZ1shRNA), and AAV was injected into unilateral sciatic (or tibial) nerve immediately after induction of common peroneal nerve injury (CPNI). Results showed that the development of mechanical hypersensitivity in the CPNI rats injected with AAVolig001-PZ1shRNA was mitigated compared to rats subjected to AAVolig001-scramble. Selective in vivo SC transduction and functional block of Piezo1 channel activity of primary cultured SCs was confirmed. These data demonstrate that (1) AAVolig001 has unique and selective primary tropism to SCs via intraneural delivery, and (2) SC Piezo1 contributes to mechanical hypersensitivity following nerve injury.

Evaluating the impact of ultrasound-guided subsheath versus extrasheath sciatic nerve block on postoperative wound pain in tibial and foot surgeries: A systematic review and meta-analysis

This systematic review and meta-analysis evaluate the impact of ultrasound-guided subsheath versus extrasheath sciatic nerve blocks on postoperative wound pain in tibial and foot surgeries, crucial for effective pain management and patient recovery. Adhering to PRISMA guidelines, this study used a PICO framework, focusing on patients undergoing tibial and foot surgeries and comparing the efficacy and safety of subsheath and extrasheath sciatic nerve blocks. The literature search spanned four databases without time restrictions, assessing various outcomes like success rate, onset time, duration of analgesia and complication rates. Quality assessment employed the Cochrane Collaboration's risk of bias tool, and statistical analyses included heterogeneity assessment, fixed-effect and random-effects models, sensitivity analysis and publication bias evaluation using funnel plots and Egger's linear regression test. From an initial pool of 1213 articles, six met the inclusion criteria. The subsheath group showed a significantly higher success rate of complete sensory blockade within 30 min compared with the extrasheath group (OR = 5.39; 95% CI: 2.82-10.28; p < 0.01). No significant differences were found in procedure duration or incidence of nerve-related complications between the two techniques. The subsheath approach also demonstrated a quicker onset time of sensory blockade (MD = -8.57; 95% CI: -11.27 to -5.88; p < 0.01). Sensitivity analysis confirmed the stability of the results, and no significant publication bias was detected. Ultrasound-guided subsheath sciatic nerve blocks are more effective than extrasheath blocks in achieving rapid and complete sensory blockade for tibial and foot surgeries, with a quicker onset time and comparable safety profile. Subsheath injections are thus recommended as a preferred method for anaesthesia and postoperative pain management in these surgical procedures, enhancing overall patient outcomes.

Neurological injury following peripheral nerve blocks: a narrative review of estimates of risks and the influence of ultrasound guidance

BACKGROUND

Peripheral nerve injury or post-block neurological dysfunction (PBND) are uncommon but a recognized complications of peripheral nerve blocks (PNB). A broad range of its incidence is noted in the literature and hence a critical appraisal of its occurrence is needed.

OBJECTIVE

In this review, we wanted to know the pooled estimates of PBND and further, determine its pooled estimates following various PNB over time. Additionally, we also sought to estimate the incidence of PBND with or without US guidance.

EVIDENCE REVIEW

A literature search was conducted in six databases. For the purposes of the review, we defined PBND as any new-onset sensorimotor disturbances in the distribution of the performed PNB either attributable to the PNB (when reported) or reported in the context of the PNB (when association with a PNB was not mentioned). Both prospective and retrospective studies which provided incidence of PBND at timepoints of interest (>48 hours to <2 weeks; >2 weeks to 6 weeks, 7 weeks to 5 months, 6 months to 1 year and >1 year durations) were included for review. Incidence data were used to provide pooled estimates (with 95% CI) of PBND at these time periods. Similar estimates were obtained to know the incidence of PBND with or without the use of US guidance. Additionally, PBND associated with individual PNB were obtained in a similar fashion with upper and lower limb PNB classified based on the anatomical location of needle insertion.

FINDINGS

The overall incidence of PBND decreased with time, with the incidence being approximately 1% at <2 weeks' time (Incidence per thousand (95% CI)= 9 (8; to 11)) to approximately 3/10 000 at 1 year (Incidence per thousand (95% CI)= 0. 3 (0.1; to 0.5)). Incidence of PBND differed for individual PNB with the highest incidence noted for interscalene block.

CONCLUSIONS

Our review adds information to existing literature that the neurological complications are rarer but seem to display a higher incidence for some blocks more than others. Use of US guidance may be associated with a lower incidence of PBND especially in those PNBs reporting a higher pooled estimates. Future studies need to standardize the reporting of PBND at various timepoints and its association to PNB.

Selective RNAi-silencing of Schwann cell Piezo1 alleviates mechanical hypersensitization following peripheral nerve injury

We previously reported functional Piezo1 expression in Schwann cells of the peripheral nervous system. This study is designed to further investigate the role of Schwann cell Piezo1 in peripheral nociception. We first developed an adeno-associated viral (AAV) vector that has primary Schwann cell tropism after delivery into the sciatic nerve. This was achieved by packing AAV-GFP transcribed by a hybrid CMV enhancer/chicken β-actin (CBA) promoter using a capsid AAVolig001 to generate AAVolig001-CBA-GFP. Five weeks after intrasciatic injection of AAVolig001-CBA-GFP in naïve rats, GFP expression was detected selectively in the Schwann cells of the sciatic nerve. A short hairpin RNA against rat Piezo1 (PZ1shRNA) was designed that showed efficient physical and functional knockdown of Piezo1 in NG108 neuronal cells. A dual promoter and bidirectional AAV encoding a U6-driven PZ1shRNA and CBA-transcribed GFP was packed with capsid olig001 (AAVolig001-PZ1shRNA), and AAV was injected into unilateral sciatic nerve immediately after induction of common peroneal nerve injury (CPNI). Results showed that the development of mechanical hypersensitivity in the CPNI rats injected with AAVolig001-PZ1shRNA was mitigated, compared to rats subjected with AAVolig001-scramble. Selective in vivo Schwann cell transduction and functional block of Piezo1 channel activity of primary cultured Schwann cells was confirmed. Together, our data demonstrate that 1) AAVolig001 has unique and selective primary tropism to Schwann cells via intrasciatic delivery and 2) Schwann cell Piezo1 contributes to mechanical hypersensitivity following nerve injury.

Ultrasound-Guided Popliteal Sciatic Nerve Block: A Minimally Invasive Method for Pain Control During Endovascular Treatment of Critical Limb Ischemia

PURPOSE

To evaluate the safety and effectiveness of ultrasound-guided popliteal sciatic nerve block (PSNB) for pain control in endovascular treatment of critical limb ischemia (CLI).

MATERIALS AND METHODS

This retrospective study included 252 patients who underwent endovascular treatment for CLI between January 2020 and August 2022. Of these, 69 patients underwent PSNB, whereas moderate procedural sedation and analgesia was delivered in 183 patients. Pain scores were assessed using the visual analog scale (VAS) before and during the intervention. Technical and clinical success of PSNB, duration of the procedure, time to onset of nerve block, time for block resolution, and adverse events were recorded. Patient and operator satisfaction were assessed using the Likert scale.

RESULTS

All PSNB procedures were technically and clinically successful, and the mean procedural duration of PSNB was 5.0 minutes ± 0.8 (range, 4-7 minutes). Prolonged effect of PSNB was observed in 3 patients, which resolved within 24 hours. No adverse events were encountered. Median VAS score was significantly lower in the PSNB group than in the moderate procedural sedation and analgesia group during endovascular treatment (0 [range, 0-2] vs 3 [range, 0-7]; P < .001). Patient satisfaction was comparable ("very satisfied" in 66 [95.7%] vs 161 [88.0%]; P = .069). However, operator satisfaction was significantly higher in the PSNB group ("very satisfied" in 69 [100%] vs 161 [88.0%]; P = .003).

CONCLUSIONS

PSNB is safe and effective for pain control during endovascular treatment of CLI. Low adverse event rates with high patient and operator satisfaction make PSNB a reasonable alternative for high-risk patients.

Impact of an extrafascial versus intrafascial injection for supraclavicular brachial plexus block on respiratory function: a randomized, controlled, double-blind trial

Introduction

Hemidiaphragmatic paresis after ultrasound-guided supraclavicular brachial plexus block is reported to occur in up to 67% of patients. We tested the hypothesis that an injection outside the brachial plexus sheath reduces the incidence of hemidiaphragmatic paresis compared with an intrafascial injection while providing similar analgesia.

Methods

Fifty American Society of Anesthesiologists I–III patients scheduled for elective upper limb surgery received a supraclavicular brachial plexus block using 30 mL of 1:1 mixture of mepivacaine 1% and ropivacaine 0.5%. The block procedures were randomized to position the needle tip either within the brachial plexus after piercing the sheath (intrafascial injection) or outside the brachial plexus sheath (extrafascial injection). The primary outcome was the incidence of hemidiaphragmatic paresis 30 min after the injection, measured by M-mode ultrasonography. Additional outcomes included time to surgery readiness, and resting and dynamic pain scores at 24 hours postoperatively (Numeric Rating Scale, 0–10).

Results

The incidence of hemidiaphragmatic paresis 30 min after the injection was 9% (95% CI 1% to 29%) and 0% (95% CI 0% to 15%) in the intrafascial and extrafascial groups respectively (p=0.14). Extrafascial injection was associated with a longer time to surgery readiness (intrafascial: 18 min (95% CI: 16 to 21 min); extrafascial: 37 min (95% CI: 31 to 42 min); p<0.001). At 24 hours, resting and dynamic pain scores were similar between groups.

Discussion

Ultrasound-guided supraclavicular brachial plexus block with an extrafascial injection does not reduce the incidence of hemidiaphragmatic paresis although it provides similar analgesia, when compared with an intrafascial injection. The longer time to surgery readiness is less compatible with contemporary operating theater efficiency requirements.

Trial registration number

NCT03957772.

Regional haemodynamic variables and perfusion index in the evaluation of sciatic nerve block: a prospective observational trial

OBJECTIVE

We determined whether regional haemodynamics and perfusion index (PI) could be reliable indicators of a successful sciatic nerve block (SNB).

DESIGN

Prospective observational trial.

SETTING

A tertiary teaching hospital in China from April 2020 to August 2020.

PARTICIPANTS

We assessed 79 patients for eligibility to participate in this study. Nine patients were excluded for not meeting our inclusion criteria, and three patients were excluded due to missing measurements at all time points.

INTERVENTIONS

The patients underwent SNB. Pulsed-wave Doppler and PI measurements were performed.

PRIMARY AND SECONDARY OUTCOME MEASURES

The primary outcome measure was the diagnostic power of regional haemodynamic change and PI to predict successful SNB. The secondary outcome measure was the effect of SNB on the regional haemodynamics and PI in the lower extremity.

RESULTS

We assessed 79 patients in this study and 67 patients available for the final analysis. The SNB was successful in 59 patients and failed in eight patients. There were no significant differences in demographic characteristics between the patients with successful and failed SNB. Starting from 10 min after SNB, the peak systolic velocity (PSV), end-diastolic velocity, time-averaged maximum velocity and time-averaged mean velocity of the anterior tibial artery and posterior tibial artery of patients in the successful SNB group were significantly higher than those in the failed SNB group (p<0.05). The PSV percentage increase at 10 min after SNB has great potential to predict the block success. The area under the receiver operating characteristic curve (AUC) values were 0.893 (95% CI 0.7809 to 1.000) and 0.880 (95% CI 0.7901 to 0.9699). The corresponding cut-off values were 19.22 and 35.88, respectively. The PI increased during 5-45 min intervals in patients with successful SNB. The AUC for the PI percentage increases at 10 min after SNB was 0.853 (95% CI 0.7035 to 1.000), with a cut-off value of 93.09.

CONCLUSION

The regional haemodynamic variables, PSV and PI in particular, can be used as alternative indicators for clinicians to evaluate the success of SNB objectively and early.

TRIAL REGISTRATION NUMBER

ChiCTR2000030772.

Ultrasound-guided single popliteal sciatic nerve block is an effective postoperative analgesia strategy for calcaneal fracture: a randomized clinical trial

OBJECTIVES

The aim of this study was to evaluate the postoperative analgesia effect of ultrasound-guided single popliteal sciatic nerve block for calcaneal fracture.

METHODS

A total of 120 patients scheduled for unilateral open reduction and internal fixation of calcaneal fracture were enrolled in this prospective randomized study. Patients in group B received ultrasound-guided single popliteal sciatic nerve block after operation, but Patients in group A did not. All patients received patient-controlled intravenous analgesia (PCIA) after operation. The time to initiation of PCIA, the time of first pressing the analgesia pump, duration of analgesia pump use and the total number of times the patient pressed the analgesia pump were recorded. The time of rescue analgesia and the adverse reactions were recorded. Pain magnitude of the patients immediately after discharge from operating room (T1), and at 4th (T2), 8th (T3), 12th (T4), 16th (T5), 24th (T6) and 48th (T7) h after the operation were assessed with visual analog scale (VAS). In addition, patient, surgeon and nurse satisfaction were recorded.

RESULTS

The VAS scores at T2 ~ T5, the time of rescue analgesia and the adverse reactions, the total number of times the patient pressed the analgesia pump were significantly declined in group B (p < 0.001). The time to initiation of PCIA, the time of first pressing the analgesia pump, duration of analgesia pump use were prolonged and patient surgeon and nurse satisfaction were improved in group B (p < 0.05).

CONCLUSION

Ultrasound-guided single popliteal sciatic nerve block is an effective postoperative analgesia strategy for calcaneal fracture.

TRIAL REGISTRATION

ChiCTR, ChiCTR2100042340. Registered 19 January 2021, URL of trial registry record: http://www.chictr.org.cn/showproj.aspx?proj=66526 .

Ultrasound-Guided Popliteal Nerve Block with Short-Acting Lidocaine in the Surgical Treatment of Ingrown Toenails

Background: Digital nerve block (DB) is a commonly utilized anesthetic procedure in ingrown toenail surgery. However, severe procedure-related pain has been reported. Although the popliteal sciatic nerve block (PB) is widely accepted in foot and ankle surgery, its use in ingrown toenail surgery has not been reported. Therefore, this study aimed to investigate the safety and effectiveness of PB in the surgical treatment of ingrown toenails. Methods: One-hundred-ten patients surgically treated for an ingrown toenail were enrolled. Sixty-six patients underwent DB, and 44 underwent PB. PB was performed under ultrasound-guidance via a 22-gauge needle with 15 mL of 1% lidocaine in the popliteal region. The visual analogue scale was used to assess pain at two-time points: pain with skin penetration and pain with the solution injection. Time to sensory block, duration of sensory block, need for additional injections, and adverse events were recorded. Results: PB group demonstrated significantly lower procedure-related pain than the DB group. Time to sensory block was significantly longer in the PB group (20.8 ± 4.6 versus 6.5 ± 1.6 minutes). The sensory block duration was significantly longer in the PB group (187.9 ± 22.0 versus 106.5 ± 19.1 minutes). Additional injections were required in 16 (24.2%) DB cases, while no additional injections were required in PB cases. Four adverse events occurred in the DB group and two in the PB group. Conclusion: PB was a less painful anesthetic procedure associated with a longer sensory block duration and fewer repeat injections compared with DB. The result of this study implicates that PB can be an alternative anesthetic option in the surgical treatment of ingrown toenails.

Does subepineural injection damage the nerve integrity? A technical report from four amputated limbs

Local anesthetic (LA) injection outside the sheath in epineural or paraneural connective tissue is considered safe practice among regional anesthesiologists. There is limited evidence as to whether neurological complications occur if LA is injected inside the sheath (subepineural - intraneural). We performed ultrasound guided injections at the level of undivided sciatic nerve in four amputated lower limbs. In two specimens, LA was injected in epineural connective tissue (paraneural tissue) and in another two specimens by penetrating the outer nerve sheath (hyperechoic epineurium). Ultrasonography demonstrated an increase in the size of nerve and macroscopic findings revealed fascicular tracings with sub-epineural injections. Limbs were sent for histological analysis in formalin containers. Pathologist performed the analysis which demonstrated an intact perineurium and a breach in the epineurium. We conclude that sub-epineural injections are unsafe and injection should be done in paraneural tissue to ensure safety and avoid unwanted neurological sequelae after the block.

An ultrasound-guided subparaneural approach to the sciatic nerve in the dog: a cadaver study

OBJECTIVE

To describe the gross and microscopic anatomy of the sciatic nerve paraneural sheath and to report an ultrasound (US)-guided subparaneural approach to the sciatic nerve in dogs, comparing two different volumes of injectate.

STUDY DESIGN

Prospective, randomized, anatomical study.

ANIMALS

A group of nine middle-sized adult Mongrel canine cadavers (18 limbs).

METHODS

The sciatic nerves of three pelvic limbs of two canine cadavers were identified, exposed and isolated between the greater trochanter and the popliteal fossa for gross anatomical and microscopic examination. An additional three pelvic limbs were surgically dissected on the lateral surface of the limb; the sciatic nerves were isolated, and a 26 gauge over-the-needle catheter was inserted through the paraneural sheath under direct visualization. A methylene blue solution was then slowly injected into the subparaneural compartment through the catheter under US visualization using an 8-13 MHz linear-array transducer. Subsequently, 12 pelvic limbs (six cadavers) were randomly allocated to one of two groups; using US-guided percutaneous subparaneural approach, either 0.1 or 0.05 mL kg^-1of a 1:1 solution of methylene blue and 0.5% bupivacaine was injected. The spread of the dye solution and the amount of nerve staining were macroscopically scored. The stained sciatic nerves with their sheaths were then harvested for microscopic examination.

RESULTS

The paraneural sciatic nerve sheath was easily identified distinct from the nerve trunk both macroscopically and with US visualization, and microscopically. Complete staining was achieved in five of six (83.3%) sciatic nerves in each group; no difference was found in the amount of staining between the two groups. Microscopically, no signs of sciatic nerve intraneural injection were observed.

CONCLUSIONS AND CLINICAL RELEVANCE

The US-guided subparaneural injection of 0.05 mL kg^-1 of a dye injectate resulted in satisfactory nerve staining without evidence of sciatic nerve intraneural injection.

Ultrasound-guided subparaneural popliteal sciatic nerve block: there is more to it than meets the eyes

The popliteal sciatic nerve block is routinely used for anesthesia and analgesia during foot and ankle surgery. This article reviews our current understanding of the anatomy of the sciatic nerve and discusses how fascial tissue layers associated with the nerve may affect block outcomes . The anatomy of the sciatic nerve is more complex than previously described. The tibial and common peroneal nerves within the sciatic nerve trunk appear to be centrally separated by the Compton-Cruveilhier septum and encompassed by their own paraneural sheaths. This unique internal architecture of the sciatic nerve appears to promote proximal spread of local anesthetic to the internal aspect of the sciatic nerve trunk after a subparaneural injection at or below the divergence of the tibial and common peroneal nerves.

Gradient local anesthesia for percutaneous endoscopic interlaminar discectomy at the L5/S1 level: a feasibility study

BACKGROUND

During the process of shearing the ligamentum flavum, rotating the working channel, and manipulating the annulus fibrosis, the sinuvertebral nerve and the spinal nerve root can be irritated, inducing intolerable back and leg pain. Thus, general anesthesia is recommended and well accepted by most surgeons when performing percutaneous endoscopic lumbar discectomy (PELD) via the interlaminar approach. The aim of our study was to explore the efficacy and safety of percutaneous endoscopy interlaminar lumbar discectomy with gradient local anesthesia (LA) in patients with L5/S1 disc herniation.

METHODS

This retrospective study was conducted between December 2017 and June 2018. The study included 50 consecutive patients who met the study criteria, had single-level L5/S1 disc herniation, and underwent PELD via the interlaminar approach under gradient LA. Different concentrations of local anesthetic compound (LAC) were injected into different tissues inside and outside the ligamentum flavum to complete gradient LA. The evaluation criteria included the intraoperative satisfaction score, visual analog scale (VAS) score, Oswestry Disability Index (ODI), complications, and adverse reactions.

RESULTS

The intraoperative satisfaction score was consistently over 7, with an average score of 9.3 ± 0.7, indicating that LAC can achieve satisfactory pain control throughout the PELD operation without additional anesthesia. The postoperative VAS score and ODI were dramatically improved at each follow-up interval (P < 0.001, respectively). There was no serious complication such as dural rupture caused by puncture, dural laceration caused by manipulation under endoscopy, total spinal anesthesia, iatrogenic nerve root injury, epidural hematoma, infections, or local anesthetic-related adverse reactions. Three patients experienced transient postoperative dysesthesia of the lower limbs that gradually recovered within 24 h.

CONCLUSIONS

Gradient local anesthesia can satisfactorily and safely control intraoperative pain during the PELD via the interlaminar approach. It can not only improve intraoperative satisfaction, but also reduce local anesthesia-related adverse reactions and surgery-related complications.

Ultrasound and Anatomical Study of Accessing the Nerves in the Knee by Fascial Planes

The fascia is an undifferentiated mesenchymal tissue related to the peripheral nerves. Both can be identified by ultrasound, which is useful when performing peripheral nerve blocks. However, there is no unanimity about the approaching point of each nerve, nor is there a consensus on how to name the appropriate infiltration zone, although the paraneural zone is frequently mentioned. The aims of this study were to determine if ultrasound is accurate for identifying the fascial planes and the paraneural space of the nerves in the knee, infiltrating them, and achieving a correct anatomical diffusion, as well as for establishing access routes to avoid intraneural infiltration. The study was performed in 16 cryopreserved lower extremities of the dissection room of the Faculty of Medicine and Health Sciences, University of Barcelona. Nerves of the knee were injected with colorant guided by ultrasound after they were visualized. Correct location of the nerves by ultrasound was achieved in 98.75% of the cases, correct visualization of the needle by ultrasound in 82.5%, the hypoechogenic image around the nerve after infiltration in 82.5%, and a correct paraneural infiltration in 76.25% of cases. With these results, we can conclude that high-definition ultrasound enables location of the peripheral nerves and adjacent structures as well as the fasciae that surround them, and therefore allows performance of infiltrations in the paraneural spaces.

Suture-method versus Through-the-needle Catheters for Continuous Popliteal-sciatic Nerve Blocks

Background

The basic perineural catheter design has changed minimally since inception, with the catheter introduced through or over a straight needle. The U.S. Food and Drug Administration recently cleared a novel perineural catheter design comprising a catheter attached to the back of a suture-shaped needle that is inserted, advanced along the arc of its curvature pulling the catheter past the target nerve, and then exited through the skin in a second location. The authors hypothesized that analgesia would be noninferior using the new versus traditional catheter design in the first two days after painful foot/ankle surgery with a primary outcome of average pain measured with the Numeric Rating Scale.

Methods

Subjects undergoing painful foot or ankle surgery with a continuous supraparaneural popliteal-sciatic nerve block 5 cm proximal to the bifurcation were randomized to either a suture-type or through-the-needle catheter and subsequent 3-day 0.2% ropivacaine infusion (basal 6 ml/h, bolus 4 ml, lockout 30 min). Subjects received daily follow-up for the first four days after surgery, including assessment for evidence of malfunction or dislodgement of the catheters.

Results

During the first two postoperative days the mean ± SD average pain scores were lower in subjects with the suture-catheter (n = 35) compared with the through-the-needle (n = 35) group (2.7 ± 2.4 vs. 3.4 ± 2.4) and found to be statistically noninferior (95% CI, −1.9 to 0.6; P &lt; 0.001). No suture-style catheter was completely dislodged (0%), whereas the tips of three (9%) traditional catheters were found outside of the skin before purposeful removal on postoperative day 3 (P = 0.239).

Conclusions

Suture-type perineural catheters provided noninferior analgesia compared with traditional catheters for continuous popliteal-sciatic blocks after painful foot and ankle surgery. The new catheter design appears to be a viable alternative to traditional designs used for the past seven decades.

Editor’s Perspective

What We Already Know about This Topic

What This Article Tells Us That Is New

Factors Associated With Minimum Effective Volume of Lidocaine 1.5% for Sciatic Nerve Blocks

OBJECTIVES

The objectives of this study were to investigate the correlations between the minimum effective volume (MEV) of lidocaine 1.5% for an ultrasound-guided popliteal sciatic nerve block and individual factors including the cross-sectional nerve area, sex, age, body mass index, and the depth of the sciatic nerve and to evaluate the safety of combined femoral and sciatic nerve blocks by monitoring the plasma concentration of local anesthetics.

METHODS

Forty patients received combined single-shot femoral and continuous sciatic nerve blocks. The femoral nerve block was performed with an in-plane technique and 15 mL of lidocaine 1.5%. A continuous peripheral nerve block annular tube was positioned between the tibial and peroneal nerves inside the paraneural sheath. Thirty minutes after the femoral nerve block, a loading dose of 5 mL of lidocaine 1.5% was given to block the sciatic nerve after obtaining the maximum compound muscle action potential (CMAP) amplitude using nerve conduction studies. Additional lidocaine 1.5% was pumped at a rate of 30 mL/h through the indwelling annular tube if, after 8 minutes, the CMAP amplitude was still present. The CMAP amplitude monitored by the nerve conduction studies and pinprick tests were recorded every 2 minutes after the administration of lidocaine 1.5%. When the CMAP amplitude decreased to nearly 0 mV, this MEV was recorded. The influences of the cross-sectional area of the sciatic nerve, sex, age, body mass index, and the depth of the sciatic nerve on the MEV were analyzed using stepwise multiple linear regression. Blood samples were collected from 10 patients to evaluate the safety of combined femoral and sciatic nerve blocks by ultra-performance liquid chromatography-tandem mass spectrometry. Blood was drawn at 0 minutes before femoral nerve injection; 0 minutes before sciatic nerve injection; 8 minutes after sciatic nerve injection; and 0, 10, 20, 30, 45, 60, 75, 90, and 120 minutes after the pumping of lidocaine 1.5% stopped.

RESULTS

A significant correlation was found between the MEV of lidocaine 1.5% and the cross-sectional area of the sciatic nerve (r=0.459), with a regression equation of the MEV (mL)=5.969+0.095×(the cross-sectional area of the sciatic nerve). The coefficient of determination was 0.211 (P<0.05). The MEV of lidocaine 1.5% for complete sciatic nerve blocks ranged from 7 to 15 mL. The maximum concentrations of lidocaine, monoethylglycinexylidide, and glycinexylidide were 1672.9 (227.6), 265.7 (32.7), and 42.2 (22.4) ng/mL, respectively.

CONCLUSIONS

There is a positive correlation between the cross-sectional area of the sciatic nerve and the MEV. The regression equation can help to predict the MEV of lidocaine 1.5% for popliteal sciatic nerve blocks. The maximum concentrations of lidocaine and its metabolites did not approach toxic threshold limits in this study.

Stepwise Local Anesthesia for Percutaneous Endoscopic Interlaminar Discectomy: Technique Strategy and Clinical Outcomes

BACKGROUND

Due to suboptimal pain control under conventional local anesthesia, percutaneous endoscopic interlaminar discectomy is typically performed under general anesthesia. The purpose of this study was to develop a stepwise approach of local anesthesia for endoscopic interlaminar discectomy and evaluate its efficacy.

METHODS

A stepwise local anesthesia was developed, which mainly includes 3 steps: conventional local anesthesia from skin to laminae, epidural injection, and nerve root block. From June 2015 to May 2017, consecutive patients who underwent endoscopic interlaminar discectomy were included. Local anesthesia or general anesthesia was used based on patients' preference. Anesthetic effectiveness was evaluated as excellent, good, or poor, and adverse events were recorded. Hospitalization expense was compared between the 2 groups. Clinical outcomes were assessed using the Visual Analog Scale and the Oswestry Disability Index.

RESULTS

There were 98 patients included in the study. Among them, 48 received stepwise local anesthesia and the other 50 received general anesthesia. In the stepwise local anesthesia group, 40 (83.3%) patients rated anesthetic effectiveness as excellent, 7 (14.6%) as good, and 1 (2.1%) as poor. Nine patients had complications that may be associated with local anesthesia, including dyspnea, temporary paresis of legs, and temporary worsened dysesthesia or numbness in legs. After surgery, the patients' leg pain and Oswestry Disability Index significantly improved in both groups. On average, hospitalization expense was approximately 20% less when local anesthesia was used, as compared with using general anesthesia.

CONCLUSIONS

The stepwise local anesthesia can achieve satisfactory pain control and seems to be a good choice for endoscopic interlaminar discectomy.

Subparaneural Injection in Popliteal Sciatic Nerve Blocks Evaluated by MRI

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

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

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

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

Continuous Popliteal-Sciatic Blocks for Postoperative Analgesia: Traditional Proximal Catheter Insertion Superficial to the Paraneural Sheath Versus a New Distal Insertion Site Deep to the Paraneural Sheath

We tested the hypothesis that during a continuous popliteal-sciatic nerve block, postoperative analgesia is improved with the catheter insertion point "deep" to the paraneural sheath immediately distal to the bifurcation between the tibial and common peroneal branches, compared with the traditional approach "superficial" to the paraneural sheath proximal to the bifurcation. The needle tip location was determined to be accurately located with a fluid bolus visualized with ultrasound; however, catheters were subsequently inserted without a similar fluid injection and visualization protocol (visualized air injection was permitted and usually implemented, but not required per protocol). The average pain (0-10 scale) the morning after surgery for subjects with a catheter inserted at the proximal subparaneural location (n = 31) was a median (interquartile) of 1.5 (0.0-3.5) vs 1.5 (0.0-4.0) for subjects with a catheter inserted at the distal supraparaneural location (n = 32; P = .927). Secondary outcomes were similarly negative.

Lower extremity regional anesthesia: essentials of our current understanding

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

Mechanics of anesthetic needle penetration into human sciatic nerve

Nerve blocks are frequently performed by anesthesiologists to control pain. For sciatic nerve blocks, the optimal placement of the needle tip between its paraneural sheath and epineurial covering is challenging, even under ultrasound guidance, and frequently results in nerve puncture. We performed needle penetration tests on cadaveric isolated paraneural sheath (IPS), isolated nerve (IN), and the nerve with overlying paraneural sheath (NPS), and quantified puncture force requirement and fracture toughness of these specimens to assess their role in determining the clinical risk of nerve puncture. We found that puncture force (123 ± 17 mN) and fracture toughness (45.48 ± 9.72 J m^-2) of IPS was significantly lower than those for NPS (1440 ± 161 mN and 1317.46 ± 212.45 Jm^-2, respectively), suggesting that it is not possible to push the tip of the block needle through the paraneural sheath only, without pushing it into the nerve directly, when the sheath is lying directly over the nerve. Results of this study provide a physical basis for tangential placement of the needle as the ideal situation for local anesthetic deposition, as it allows for the penetration of the sheath along the edge of the nerve without entering the epineurium.

Which Ultrasound-Guided Sciatic Nerve Block Strategy Works Faster? Prebifurcation or Separate Tibial-Peroneal Nerve Block? A Randomized Clinical Trial

BACKGROUND

Peripheral nerve block is an accepted method in lower limb surgeries regarding its convenience and good tolerance by the patients. Quick performance and fast sensory and motor block are highly demanded in this method. The aim of the present study was to compare 2 different methods of sciatic and tibial-peroneal nerve block in lower limb surgeries in terms of block onset.

METHODS

In this clinical trial, 52 candidates for elective lower limb surgery were randomly divided into 2 groups: sciatic nerve block before bifurcation (SG; n = 27) and separate tibial-peroneal nerve block (TPG; n = 25) under ultrasound plus nerve stimulator guidance. The mean duration of block performance, as well as complete sensory and motor block, was recorded and compared between the groups.

RESULTS

The mean duration of complete sensory block in the SG and TPG groups was 35.4 ± 4.1 and 24.9 ± 4.2 minutes, respectively, which was significantly lower in the TPG group (P = 0.001). The mean duration of complete motor block in the SG and TPG groups was 63.3 ± 4.4 and 48.4 ± 4.6 minutes, respectively, which was significantly lower in the TPG group (P = 0.001). No nerve injuries, paresthesia, or other possible side effects were reported in patients.

CONCLUSIONS

According to the present study, it seems that TPG shows a faster sensory and motor block than SG.

3D ultrasound estimation of the effective volume for popliteal block at the level of division

Local anaesthetic injection between the tibial and commmon peroneal nerves within connective tissue sheath results in a predictable diffusion and allows for a reduction in the volume needed to achieve a consistent sciatic popliteal block. Using 3D ultrasound volumetric acquisition, we quantified the visible volume in contact with the nerve along a 5cm segment.

METHODS

We included 20 consecutive patients scheduled for bunion surgery. Ultrasound guided popliteal block was performed using a posterior, out of plane approach at the level of división of the sciatic nerve. Thirty ml of mepivacaine 1.5% and levobupivacaine 0.5% were slowly injected while assessing the injection pressure and the diffusion of the local anaesthetic. Volumetric acquisition was performed before and after the block to quantify the the volume of the sciatic nerve and the volume of the surrounding hypoechoic halo contained inside the connective tissue in a 5cm segment.

RESULTS

All blocks were successful within 20min after the injection. The total estimated volume contained inside the common connective tissue sheath was 6.8±2.6cm³. Of this, the volume of the halo sorrounding the nerve was 4.4±1.7cm³ and the volume inside the sciatic nerve was 2.4±1.7cm³.

CONCLUSIONS

The volume of local anaesthetic in close contact with the sciatic nerve can be estimated by volumetric acquisition. Our results suggest that the effective volume of local anaesthetic needed for a successful sciatic popliteal block could be reduced to less than 7ml.

[Sciatic nerve block "out-of-plane" distal to the bifurcation: effective and safe]

BACKGROUND

Ultrasound guided distal sciatic nerve block (DSB) at bifurcation level shows fast onset and provides excellent success rates. However, its safe performance might be difficult for the unexperienced physician. Just slightly distal to the bifurcation, the tibial nerve (TN) and common fibular nerve (CFN) can be shown clearly separated from each other. Therefore, we investigated if a block done here would provide similar quality results compared to the DSB proximally to the division, with a potentially lower risk of nerve damage.

METHODS

In this randomized, prospective trial, 56 patients per group received either a DSB distal to the bifurcation "out-of-plane" (dist.) or proximally "in-plane" (prox.) with 30 ml of Mepivacaine 1% each. Success was tested by a blinded examiner after 15 and 30 min respectively (sensory and motor block of TN and CFN: 0 = none, 2 = complete, change of skin temperature). Videos of the blocks were inspected by an independent expert retrospectively with regard to the spread of the local anesthetic (LA) and accidental intraneural injection.

RESULTS

Cumulative single nerve measurements and temperature changes revealed significant shorter onset and better efficacy (dist/prox: 15 min: 3.13 ± 1.86/1.82 ± 1.62; 30 min: 5.73 ± 1.92/3.21 ± 1.88; T_{15 min}: 30.3 ± 3.48/28.0 ± 3.67, T_{30 min}. 33.0 ± 2.46/30.6 ± 3.86; MV/SD; ANOVA; p < 0.01) combined with a higher rate of subparaneural spread in the dist. group (41/51 vs.12/53; χ2; p < 0,01). Procedure times were similar. There were no complications in either group.

DISCUSSION

The subparaneural spread of the LA turned out to be crucial for better results in the distal group. The steep angle using the out-of-plane approach favors needle penetration through the paraneural sheath. The distance between the branches allows the safe application of the LA, so an effective block can be done with just one injection.

CONCLUSION

DSB slightly distal to the bifurcation, in an out-of-plane technique between the TN and CFN, can be done fast, effectively and safe.

Continuous Popliteal Sciatic Blocks: Does Varying Perineural Catheter Location Relative to the Sciatic Bifurcation Influence Block Effects? A Dual-Center, Randomized, Subject-Masked, Controlled Clinical Trial

BACKGROUND

Multiple studies have demonstrated that, for single-injection popliteal sciatic nerve blocks, block characteristics are dependent upon local anesthetic injection relative to the sciatic nerve bifurcation. In contrast, this relation remains unexamined for continuous popliteal sciatic nerve blocks. We, therefore, tested the hypothesis that postoperative analgesia is improved with the perineural catheter tip at the level of the bifurcation compared with 5 cm proximal to the bifurcation.

METHODS

Preoperatively, subjects having moderately painful foot or ankle surgery were randomly assigned to receive an ultrasound-guided subepimyseal perineural catheter inserted either at or 5 cm proximal to the sciatic nerve bifurcation. Subjects received a single injection of mepivacaine 1.5% either via the insertion needle preoperatively or the perineural catheter postoperatively, followed by an infusion of ropivacaine 0.2% (6 mL/h basal, 4 mL bolus, and 30-min lockout) for the study duration. The primary end point was the average pain measured on a numeric rating scale (0-10) in the 3 hours before a data collection telephone call the morning after surgery.

RESULTS

The average numeric rating scale of subjects with a catheter inserted at the sciatic nerve bifurcation (n = 64) was a median (10th, 25th to 75th, and 90th quartiles) of 3.0 (0.0, 2.4-5.0, and 7.0) vs 2.0 (0.0, 1.0-4.0, and 5.0) for subjects with a catheter inserted proximal to the bifurcation (n = 64; P = 0.008). Similarly, maximum pain scores were greater in the group at the bifurcation: 6.0 (3.0, 4.4-8.0, and 9.0) vs 5.0 (0.0, 3.0-8.0, and 10.0) (P = 0.019). Differences between the groups for catheter insertion time, opioid rescue dose, degree of numbness in the foot/toes, catheter dislodgement, and fluid leakage did not reach statistical significance.

CONCLUSIONS

For continuous popliteal sciatic nerve blocks, a catheter inserted 5 cm proximal to the sciatic nerve bifurcation provides superior postoperative analgesia in subjects having moderately painful foot or ankle surgery compared with catheters located at the bifurcation. This is in marked contrast with single-injection popliteal sciatic nerve blocks for which benefits are afforded to local anesthetic injection distal, rather than proximal, to the bifurcation.

Efficacy of ultrasound-guided fascia iliaca compartment block after hip hemiarthroplasty: A prospective, randomized trial

BACKGROUND

The fascia iliaca compartment block (FICB) provides an analgesic effect in patients with femur fractures. However, the postoperative pain after hip surgery is different from that after femur fracture, because of the difference in the degree and location of tissue trauma. Whether FICB provides effective postoperative analgesia in patients undergoing total hip arthroplasty is not well understood. Moreover, there is no prospective randomized study to evaluate FICB as a postoperative analgesia in hemiarthroplasty. Therefore, we performed a randomized and prospective study to determine the effect of FICB after hemiarthroplasty. The objective of this study was to compare the opioid consumption between patients who received intravenous patient-controlled analgesia (PCA) with and without FICB.

METHODS

Twenty-two patients aged 70 to 90 years who underwent bipolar hemiarthroplasty for femoral neck fracture were recruited and allocated randomly into 2 groups: FICB group (n = 11) and Non-FICB group (n = 11). All patients received spinal anesthesia with 10 mg of 0.5% hyperbaric bupivacaine. After surgery, the FICB was conducted using a modified technique with 0.2% ropivacaine (40 mL) under ultrasonographic guidance, and the intravenous PCA was administered to patients in both groups in the separate block room. The PCA was set up in the only bolus mode with no continuous infusion. The visual analog scale (VAS) and the opioid consumption were noted at 4, 8, 12, 24, and 48 hours postoperatively.

RESULTS

The VAS was similar in both groups. The fentanyl requirement at 4, 8, and 12 hours was low in the FICB group. The total amount of fentanyl required in the first 24 hours was 246.3 μg in the FICB group and 351.4 μg in the Non-FICB group. No patient developed any residual sensory-motor deficit during the postoperative period. Patients in the Non-FICB group had nausea (n = 2), and pruritus (n = 1), and 1 patient had nausea in the FICB group during postoperative 2 days.

CONCLUSION

The FICB has a significant opioid-sparing effect in first 24 hours after hemiarthroplasty. This suggests that FICB is an effective way for multimodal analgesia in hip surgery.

Minimum effective local anesthetic volume for surgical anesthesia by subparaneural, ultrasound-guided popliteal sciatic nerve block: A prospective dose-finding study

Because of its rapid onset time, recent years have seen an increase in the use of ultrasound (US)-guided popliteal sciatic nerve block (PSNB) via subparaneural injection for induction of surgical anesthesia. Moreover, in below-knee surgery, combined blocks, as opposed to sciatic nerve block alone, have become more common. These combined blocks often require a large volume of local anesthetic (LA), thus increasing the risk of local-anesthetic systemic toxicity (LAST). Thus, to decrease the risk of LAST, it is important to know the minimum effective volume (MEV) required for an adequate block. We, therefore, aimed to determine the MEV of ropivacaine 0.75% for induction of surgical anesthesia by the method of US-guided popliteal sciatic nerve block via subparaneural injection.Thirty patients underwent a US-guided PSNB with ropivacaine 0.75% at a 20-mL starting volume. Using a step-up/step-down method, we determined injection volumes for consecutive patients from the preceding patient's outcome. When an effective block was achieved within 40 minutes after injection, the next patient's volume was decreased by 2 mL. If the block failed, the next patient's volume was increased by 2 mL. The sensory and motor blockade was graded according to a 4-point scale. The block was considered a success if a combination of anesthesia and paresis (a score of 3 for both the sensory and motor nerves) was achieved within 40 minutes. The primary outcome measure was the MEV resulting in a successful subparaneural block of the sciatic nerve in 50% of patients (MEV50). Additionally, the data were processed with a probit regression analysis to determine the volume required to produce a complete sciatic nerve block in 90% of subjects (ED90).The MEV50 of 0.75% ropivacaine is 6.14 mL (95% confidence interval, 4.33-7.94 mL). The ED90 by probit analysis for a subparaneural injection was 8.9 mL (95% CI, 7.09-21.75 mL).The 6.14-mL MEV50 of ropivacaine 0.75% represents a 71% reduction in volume compared with neurostimulation techniques and a 14.7% reduction in volume compared with US-guided PSNB using the alternative perineural injection technique.

A double-blind randomized controlled trial comparing dexamethasone and clonidine as adjuvants to a ropivacaine sciatic popliteal block for foot surgery

Background and aims

A popliteal block is effective in managing postoperative pain for foot surgery, but since the duration of analgesia is limited following a single-shot popliteal fossa block technique, methods to prolong effective postoperative analgesia are mandatory. The aim of this study was to assess the effect of adjuvants to ropivacaine on the duration of sensory and motor block.

Methods

In this double-blind randomized placebo-controlled study, we evaluated the analgesic effect of clonidine or dexamethasone (DXM) when added to ropivacaine for hallux valgus surgery. After obtaining institutional ethics research board approval and written informed consent, a total of 72 patients were randomly allocated. Fifty-seven of these patients were statistically analyzed. All patients received an ultrasound-guided single-shot popliteal fossa block with 30 mL of ropivacaine 0.75%, supplemented with saline, clonidine 100 µg, or DXM 5 mg. The primary end point was time to first pain sensation. Secondary end points were time to complete sensory and motor block regression.

Results

Compared to saline, duration to first pain sensation was prolonged by 9 hours (mean ± standard deviation: 31±9 hours) (42%) in the DXM group (P=0.024) and by 6 hours (28±10 hours) (27%) in the clonidine group (P=0.024). Compared to saline, DXM prolonged both complete sensory and motor blockade by 12 hours (25±7 hours) (46%) and 13 hours (36±6 hours) (55%), respectively, while clonidine prolonged complete sensory and motor blockade by 7 hours (30±7 hours) (27%) and 2 hours (22±5 hours) (10%), respectively. DXM prolonged sensory block regression time by 6 hours (21±7 hours) (41%) and clonidine by 2 hours (17±6 hours) (13%) compared to the control group (P=0.006). Similarly, DXM prolonged motor block regression by 7 hours (25±7 hours) (46%) and clonidine by 4 hours (21±4 hours) (19%) (P<0.0001).

Conclusion

Addition of DXM and clonidine to ropivacaine significantly prolonged the duration of postoperative sensory and motor block.

The Requisites of Needle-to-Nerve Proximity for Ultrasound-Guided Regional Anesthesia: A Scoping Review of the Evidence

This scoping review examines the literature to determine whether the position of the needle tip relative to the target nerve is accurately and reliably detected during ultrasound (US)-guided regional anesthesia. The requisites for successful and safe needle tip positioning relative to the target nerve include accurate and reliable needle presentation by the machine, needle interpretation by the operator, nerve presentation by the machine, and nerve interpretation by the operator. Failure to visualize the needle tip is a common occurrence, frequently prompting operators to use needle and probe maneuvers, which are not necessarily based on evidence. Needle tip interpretation often relies on surrogate indicators that have not been validated. The acoustic resolution of modern portable US machines limits the extent to which nerve microanatomy can be reliably presented. Finally, our interpretation of the sonographic end points for local anesthetic injection that best balance success and safety for US-guided regional anesthesia continues to evolve.

WHAT'S NEW

In order to determine whether or not the position of the needle tip relative to the target nerve is accurately and reliably detected during US-guided regional anesthesia, the available literature is reviewed and interpreted to address the following 4 questions.

0.5% levobupivacaine versus 0.5% ropivacaine: Are they different in ultrasound-guided sciatic block?

Context and Aims:

Little is known about onset and duration of sciatic block after 0.5% levobupivacaine (Levo) versus 0.5% ropivacaine (Ropi) for ultrasound-guided technique. We assessed these parameters in the ultrasound-guided block, to know for the practice.

Setting and Design:

A comparative randomized double-blind study was conducted in the University Hospital.

Materials and Methods:

Were included 35 adults of ASA I-II, scheduled for foot surgery, presenting clear imaging of their sciatic nerve at mid-thigh. A volume of 20 mL of either 0.5% Levo or 0.5% Ropi were injected around the sciatic nerve at mid-thigh using ultrasound guidance (out of the plane) followed by placement of a catheter to use, if necessary, for perioperative analgesia. A femoral single shot block was systematically performed to block the saphenous nerve. The onset times until complete foot block (primary outcome) and the sensory and motor block duration (secondary outcome) were assessed using Wilcoxon test. Values were expressed as medians (1^st-3^rd quartile).

Results:

Except for two delayed sciatic blocks in each group, the onset time otherwise was 35 min (20-60) in Ropi versus 40 min (30-60) in Levo, P = 0.5. Sensory block lasted longer in Levo, 17 h (14-27) compared with 15 h (10-17) in Ropi, P = 0.04. No significant between-group difference was found with motor block durations, 15 h (12-18) in Levo and 15 h (12-16) in Ropi, P = 0.3.

Conclusion:

No difference of onset times was found in ultrasound-guided sciatic block whether using Levo or Ropi. Levo induced a longer-lasting sensory block.

Minimum Effective Anaesthetic Volume of 0.5% Ropivacaine for Ultrasound-Guided Popliteal Sciatic Nerve Block in Patients Undergoing Foot and Ankle Surgery: Determination of ED50 and ED95

Compared to nerve stimulation or classic paraesthesia techniques, ultrasound (US)-guided popliteal sciatic nerve block requires a smaller volume of local anaesthetic. The up-and-down method was used to determine the minimum effective anaesthetic volume of 0.5% ropivacaine necessary for US-guided popliteal sciatic nerve block to achieve successful surgical anaesthesia for foot and ankle surgery. The study included 32 patients receiving an US-guided popliteal sciatic nerve bock. The starting dose of 0.5% ropivacaine was set at 30 ml, which was decreased by 3 ml if the block succeeded and increased by 3 ml if the block failed. After the injection of local anaesthetic, the degree of sensory and motor blockade of the tibial and common peroneal nerves was assessed every 5 minutes for 30 minutes. The ED50 and ED95 volumes of local anaesthetic were 6 ml and 16 ml, respectively. The success rates of sensory blockade of the tibial nerve and common peroneal nerve were 69% and 88%, respectively. The success rates of motor blockade of these nerves were 75% and 90%, respectively. The ED50 and ED95 of 0.5% ropivacaine for US-guided popliteal sciatic nerve block were 6 ml and 16 ml, respectively.

Evidence-based medicine for ultrasound-guided regional anesthesia

Available evidence favoring the use of ultrasound for regional anesthesia is reviewed, updated, and critically assessed. Important outcome advantages include decreased time to block onset; decreased risk of local anesthetic systemic toxicity; and, depending on the outcome definition, increased block success rates. Ultrasound guidance, peripheral nerve blocks, and central neuraxial blocks are discussed.

Peripheral nerve blocks for ambulatory surgery

Peripheral nerve blocks (PNBs) provide significant improvement in postoperative analgesia and quality of recovery for ambulatory surgery. Use of continuous PNB techniques extend these benefits beyond the limited duration of single-injection PNBs. The use of ultrasound guidance has significantly improved the overall success, efficiency, and has contributed to the increased use of PNBs in the ambulatory setting. More recently, the use of ultrasound guidance has been demonstrated to decrease the risk of local anesthetic systemic toxicity. This article provides a broad overview of the indications and clinically useful aspects of the most commonly used upper and lower extremity PNBs in the ambulatory setting. Emphasis is placed on approaches that can be used for single-injection PNBs and continuous PNB techniques.

Ultrasound guided injection inside the common sheath of the sciatic nerve at division level has a higher success rate than an injection outside the sheath

BACKGROUND AND OBJECTIVE

The recommendations for the level of injection and ideal placement of the needle tip required for successful ultrasound-guided sciatic popliteal block vary among authors. A hypothesis was made that, when the local anesthetic is injected at the division of the sciatic nerve within the common connective tissue sheath, the block has a higher success rate than an injection outside the sheath.

METHODS

Thirty-four patients scheduled for hallux valgus repair surgery were randomized to receive either a sub-sheath block (n=16) or a peri-sheath block (n=18) at the level of the division of the sciatic nerve at the popliteal fossa. For the sub-sheath block, the needle was advanced out of plane until the tip was positioned between the tibial and peroneal nerves, and local anesthetic was then injected without moving the needle. For the peri-sheath block, the needle was advanced out of plane both sides of the sciatic nerve, to surround the sheath. Mepivacaine 1.5% and levobupivacaine 0.5% 30mL were used in both groups. The progression of motor and sensory block was assessed at 5min intervals. Duration of block was recorded.

RESULTS

Adequate surgical block was achieved in all patients in the subsheath group (100%) compared to 12 patients (67%) in the peri-sheath group at 30min. Sensory block was achieved faster in the subsheath than peri-sheath (9.1±7.4min vs. 19.0±4.0; p<.001).

CONCLUSIONS

Our study suggests that for successful sciatic popliteal block in less than 30min, local anesthetic should be injected within the sheath.

Ultrasound-guided popliteal block through a common paraneural sheath versus conventional injection: a prospective, randomized, double-blind study

BACKGROUND AND OBJECTIVES

The macroscopic anatomy of a common paraneural sheath that surrounds the sciatic nerve in the popliteal fossa has been studied recently in a human cadaveric study. It has been suggested that an injection through this sheath could be an ideal location for local anesthetic administration for popliteal block. The aim of the present study was to evaluate the hypothesis that popliteal sciatic nerve blockade through a common paraneural sheath results in shorter onset time when compared with conventional postbifurcation injection external to the paraneural tissue. To illustrate the microscopic anatomy of the paraneural tissues, we performed histological examinations of a human leg specimen.

METHODS

Following institutional review board approval and written informed consent, 89 patients undergoing an ultrasound-guided popliteal block for foot or ankle surgery were included in the study. They were prospectively randomized to receive a single injection of local anesthetic at the site of bifurcation through a common paraneural sheath (group 1) or 2 separate circumferential injections of the tibial and common peroneal nerves distally to sciatic nerve bifurcation (group 2).

RESULTS

Patients in group 1 had a 30% shorter onset time of both sensory and motor block. This was associated with a more extensive proximal and distal longitudinal spread of local anesthetic in this group. Nerve diameter and cross-sectional area remained unchanged in both groups after injection, which is consistent with extraneural injection. A greater proportion of patients in group 1 required a single needle pass for block performance.

DISCUSSION

An ultrasound-guided popliteal sciatic nerve block through a common paraneural sheath at the site of sciatic nerve bifurcation is a simple, safe, and highly effective block technique. It results in consistently short onset time, while respecting the integrity of the epineurium and intraneural structures.

Anatomical comparison of sciatic nerves between adults and newborns: clinical implications for ultrasound guided block

The sciatic nerve (SN) is easily blocked under ultrasound guidance by identifying either the SN common trunk or its two components: the tibial nerve (TN) and the common peroneal nerve (CPN). The authors investigate whether there are anatomical differences between newborns and adults. The SN, TN and CPN of both lower extremities in 24 (11 neonatal and 13 adults) formolized cadavers were dissected. Distances were measured from the origin of the SN (passing under the piriformis muscle) to its division into TN and CPN, and from there to the popliteal crease. The sciatic/thigh coefficient (proportion relating SN length to thigh length) and the variation coefficient for the SN were calculated. The distance from the popliteal crease to the SN division was significantly shorter in neonates than in adults (1.04 ± 0.9 cm vs. 5.6 ± 5.1 cm, P = 0.0003). In addition, the neonatal SN divided at a proportionally more distal position in the thigh than it did in adults (86 ± 13 vs. 74 ± 15%, P = 0.0059). However, the coefficient of variation between the SN-division distances was not statistically different in infants and adults (12.8 vs. 18.2%, P = 0.4345). The variations in the point of SN division seen in the adult SN are already seen in the neonatal period, but in newborns the SN divided in a more distal position in relation to the thigh than in adults, so this finding of anatomical variability in neonates suggests that ultrasound guidance can be useful when performing a SN block in these small patients.