Ultrasound examination and localization of the sciatic nerve: a volunteer study

BACKGROUND: Few studies have examined the use of ultrasound for sciatic nerve localization. The authors evaluated the usefulness of low-frequency ultrasound in identifying the sciatic nerve at three locations in the lower extremity and in guiding needle advancement to target before nerve stimulation. METHODS: In this prospective observational study, 15 volunteers underwent sciatic nerve examination using a curved ultrasound probe in the range of 2-5 MHz and a Philips-ATL 5000 unit (ATL Ultrasound, Bothell, WA) in the gluteal, infragluteal, and proximal thigh regions. Thereafter, an insulated block needle was advanced inline with the ultrasound beam to reach the nerve target, which was further confirmed by electrical stimulation. The quality of sciatic nerve images, ease of needle to nerve contact, threshold stimulating current, and resultant motor response were recorded. RESULTS: The sciatic nerve was successfully identified in the transverse view as a solitary predominantly hyperechoic structure on ultrasound in all of the three regions examined. The target nerve was visualized easily in 87% and localized within two needle attempts in all patients. Nerve stimulation was successful in 100% after two attempts with a threshold current of 0.42 +/- 0.12 (mean +/- SD) eliciting foot plantarflexion or dorsiflexion. CONCLUSIONS: These preliminary data show that a curved 2- to 5-MHz ultrasound probe provides good quality sciatic nerve imaging in the gluteal, infragluteal, and proximal thigh locations. Ultrasound-assisted sciatic nerve localization is potentially valuable for clinical sciatic nerve blocks.     

Guidance of Block Needle Insertion by Electrical Nerve Stimulation: A Pilot Study of the Resulting Distribution of Injected Solution in Dogs

Background: Little is known regarding the final needle tip location when various intensities of nerve stimulation are used to guide block needle insertion. Therefore, in control and hyperglycemic dogs, the authors examined whether lower-intensity stimulation results in injection closer to the sciatic nerve than higher-threshold stimulation.

Methods: During anesthesia, the sciatic nerve was approached with an insulated nerve block needle emitting either 1 mA (high-current group, n = 9) or 0.5 mA (low-current group, n = 9 in control dogs and n = 6 in hyperglycemic dogs). After positioning to obtain a distal motor response, the lowest current producing a response was identified, and ink (0.5 ml) was injected. Frozen sections of the tissue revealed whether the ink was in contact with the epineurium of the nerve, distant to it, or within it.

Results: In control dogs, the patterns of distribution using high-threshold (final current 0.99 +/- 0.03 mA, mean +/- SD) and low-threshold (final current 0.33 +/- 0.08 mA) stimulation equally showed ink that was in contact with the epineurium or distant to it. One needle placement in the high-threshold group resulted in intraneural injection. In hyperglycemic dogs, all needle insertions used a low-threshold technique (n = 6, final threshold 0.35 +/- 0.08 mA), and all resulted in intraneural injections.     

Locating the target nerve and injectate spread in rabbit sciatic nerve block

BACKGROUND AND OBJECTIVES: The purpose of this study is to determine how close the needle tip is placed to the target nerve using a nerve stimulator and to determine how far the injectate spreads in percutaneous nerve blocks. METHODS: Twenty-four sciatic nerves of New Zealand white rabbits were located with a 2-dimensional needle manipulator and a nerve stimulator (pulse width: 100 micros for group I, 250 micros for group II). The stimulation current required to elicit a motor response for each insertion depth of the needle and the nerve-needle distance at which the required current reached the minimum were measured. Another 10 sciatic nerves were located manually using a nerve stimulator and neurolyzed with a mixed solution of 5% phenol and Indian ink (100 microL). RESULTS: The nerve-needle distance was in the range of -1.2 mm to +2.8 mm in group I (1.1 +/- 0.9 mm [mean +/- standard error] in absolute value) and -0.2 mm to +4.8 mm (2.2 +/- 1.7 mm [mean +/- standard error] in absolute value) in group II (positive values signify the center of the beveled surface is past the nerve), when the stimulation current reached the minimum (average minimum current: 0.47 mA in group I, 0.37 mA in group II). Indian ink spread over a significant distance (25.4 +/- 0.5 mm [mean +/- standard error]; range, 19-31 mm) longitudinally within the perineural tissue, and axonal degeneration was observed linearly at the peripheral portion of the nerve fascicle in a similar pattern as Indian ink spread. CONCLUSIONS: The target nerve was located within 5 mm from the needle with less than 0.5-mA stimulation current. The injectate spread to more than 20 mm on average even when a small volume (100 microL) of the injectate was injected in rabbit sciatic nerves.     

Brachial Plexus Examination and Localization Using Ultrasound and Electrical Stimulation: A Volunteer Study

Background: Current techniques of brachial plexus block are "blind," and nerve localization can be frustrating and time consuming. Previous studies on ultrasound-assisted brachial plexus blocks are mostly performed with scanning probes of 10 MHz or less. The authors tested the usefulness of a state-of-the-art, high-resolution ultrasound probe (up to 12 MHz) in identifying the brachial plexus in five locations of the upper extremity and in guiding needle advancement to target before nerve stimulation.

Methods: In this prospective observational study, 15 volunteers underwent brachial plexus examination using an L12-L5 MHz probe and a Philips-ATL 5000 ultrasound unit in the interscalene, supraclavicular, infraclavicular, axillary, and midhumeral regions. Thereafter, an insulated block needle was advanced under direct ultrasound guidance to target nerves before confirmation by electrical nerve stimulation in five volunteers in each of the interscalene, supraclavicular, and axillary regions. The quality of brachial plexus images, anatomic variations, and the technique of needle advancement for nerve localization were recorded.

Results: The brachial plexus components were successfully identified in the transverse view as round to oval hypoechoic structures with small internal punctuate echos in all regions examined except the infraclavicular area (visualized in 27% of the cases). The authors' technique of advancing the needle in-line with the ultrasound beam allowed moment-by-moment observation of the needle shaft and tip movement at the time of nerve localization. Hypoechoic structures were stimulated electrically and confirmed to be nerves.     

Posterior subgluteal approach to block the sciatic nerve: description of the technique and initial clinical experiences

BACKGROUND AND OBJECTIVE: A new posterior approach to the sciatic nerve in the subgluteal region was developed. We describe our clinical experiences on 135 consecutive patients. METHODS: All blocks were performed with a nerve stimulator (stimulation frequency 2 Hz; intensity from 1 reduced to < or = 0.5 mA before application). A line was drawn from the greater trochanter to the ischial tuberosity of the femur; then, from the mid-point of this line, a second line was drawn perpendicularly and extended caudally for 4 cm: the end of this line represented the entry point of the needle. Sciatic stimulation was elicited at < or = 0.5 mA; then ropivacaine 0.75% 20 mL was injected. An independent observer recorded the time from needle insertion to successful sciatic nerve stimulation (performance time), the depth of appropriate sciatic stimulation and the number of needle redirections, as well as the quality of nerve block, the discomfort during the procedure and patient acceptance. RESULTS: The performance time was 41 +/- 25 s (mean +/- SD) and the mean (SD) depth at which the sciatic nerve stimulation was found was 45 +/- 10 mm. The median (range) number of needle redirections required to find the proper sciatic stimulation was 2 (1-5). The tibial response was observed in 77 patients (57%), while the common peroneal response was observed in 58 patients (43%). The degree of discomfort reported was very low and only 16 patients (12%) reported severe pain during placement of the block. The onset time (mean +/- SD) of sensory and motor block was 7 +/- 4 and 17 +/- 13 min respectively, and the surgical procedure was completed with only the peripheral nerve block in 127 patients (94%). The same anaesthesia procedure was acceptable by 127 patients (94%) and only eight patients (6%) would prefer a different anaesthesia technique in the future. CONCLUSIONS: The study demonstrated that the sciatic nerve can be easily blocked using this new posterior subgluteal approach, suggesting that it represents a safe and effective alternative to block the sciatic nerve at a proximal level, with the potential for reducing the discomfort experienced by the patient during block placement.     

Piriformis Syndrome: Anatomic Considerations, a New Injection Technique, and a Review of the Literature

Background: Piriformis syndrome can be caused by anatomic abnormalities. The treatments of piriformis syndrome include the injection of steroid into the piriformis muscle and near the area of the sciatic nerve. These techniques use either fluoroscopy and muscle electromyography to identify the piriformis muscle or a nerve stimulator to stimulate the sciatic nerve.

Methods: The authors performed a cadaver study and noted anatomic variations of the piriformis muscle and sciatic nerve. To standardize their technique of injection, they also noted the distance from the lower border of the sacroiliac joint (SIJ) to the sciatic nerve. They retrospectively reviewed the charts of 19 patients who had received piriformis muscle injections, noting the site of needle insertion in terms of the distance from the lower border of the SIJ and the depth of needle insertion at which the motor response of the foot was elicited. The authors tabulated the response of the patients to the injection, any associated diagnoses, and previous treatments that these patients had before the injection. Finally, they reviewed the literature on piriformis syndrome, a rare cause of buttock pain and sciatica.

Results: In the cadavers, the distance from the lower border of the SIJ to the sciatic nerve was 2.9 +/- 0.6 (1.8-3.7) cm laterally and 0.7 +/- 0.7 (0.0-2.5) cm caudally. In 65 specimens, the sciatic nerve passed anterior and inferior to the piriformis. In one specimen, the muscle was bipartite and the two components of the sciatic nerve were separate, with the tibial nerve passing below the piriformis and the peroneal nerve passing between the two components of the muscle. In the patients who received the injections, the site of needle insertion was 1.5 +/- 0.8 (0.4-3.0) cm lateral and 1.2 +/- 0.6 (0.5-2.0) cm caudal to the lower border of the SIJ as seen on fluoroscopy. The needle was inserted at a depth of 9.2 +/- 1.5 (7.5-13.0) cm to stimulate the sciatic nerve. Patients had comorbid etiologies including herniated disc, failed back surgery syndrome, spinal stenosis, facet syndrome, SIJ dysfunction, and complex regional pain syndrome. Sixteen of the 19 patients responded to the injection, their improvements ranged from a few hours to 3 months.     

Ultrasound guidance for lateral midfemoral sciatic nerve block: a prospective, comparative, randomized study

Block of the sciatic nerve at the midfemoral level is usually performed using nerve stimulation techniques. We investigated the efficacy of ultrasound, combined with nerve stimulation, to locate and block the sciatic nerve at the lateral midfemoral level compared to nerve stimulation alone. Sixty-one patients scheduled for foot and ankle surgery were enrolled in this prospective, randomized study. Thirty patients underwent a lateral block of the sciatic nerve at the midfemoral level guided by ultrasound (group US) and 31 patients received the block without ultrasound (group ES). Once an adequate motor response was obtained using nerve stimulation, 35 mL of ropivacaine 0.5% was administered. The main end-points of the study were: number of attempts to obtain an adequate motor response, success rate of nerve location at the first attempt, quality and duration of both sensory and motor blocks, and anesthetic distribution. The success of sciatic nerve location at the first attempt was significantly more frequent in the US group than in the ES group (76.6% versus 41.9%; P < 0.001). The quality of the sensory block and the tolerance to the pneumatic tourniquet were also significantly better in the US group (P < 0.01). We conclude that ultrasound combined with nerve stimulation improved the quality of the sensory block and the tolerance to the pneumatic tourniquet, reducing the number of attempts to perform sciatic nerve block at the midfemoral level.     

Electrical Impedance to Distinguish Intraneural from Extraneural Needle Placement in Porcine Nerves during Direct Exposure and Ultrasound Guidance

Background: Intraneural injection during peripheral nerve blockade can cause neurologic injury. Current approaches to prevent or detect intraneural injection lack reliability and consistency, or only signal intraneural injection upon the event. A change in electrical impedance (EI) could be indicative of intraneural needle placement before injection.

Methods: After animal care committee approval, eight pigs were anesthetized and kept spontaneously breathing. In four pigs (part 1), the sciatic nerves were exposed bilaterally for direct needle placement; in a further four pigs (part 2), the tissue was kept intact for ultrasound-guided needle placement. An insulated needle (Sprotte 24 gauge; Pajunk GmbH Medizintechnologie, Geisingen, Germany), attached to a nerve stimulator displaying EI (Braun Stimuplex HNS 12; B. Braun Medical, Bethlehem, PA), was placed extraneurally and then advanced to puncture the nerve sheath. Five punctures within approximately a 1-cm length of each nerve were performed. For each Part, overall EI at each compartment and EI after individual punctures were compared using a general linear model, with post hoc analysis using the Duncan multiple range test.

Results: The EI was lower extraneurally compared with intraneurally during open dissection (12.1 +/- 1.8 vs. 23.2 +/- 4.4 k[OMEGA]; P < 0.0001; n = 8) and when using ultrasound guidance (10.8 +/- 2.9 vs. 18.2 +/- 6.1 k[OMEGA]; P < 0.0001; n = 7 nerves were visualized adequately). The EI difference was maintained despite performing five sequential punctures.     

Brachial plexus examination and localization using ultrasound and electrical stimulation: a volunteer study

BACKGROUND: Current techniques of brachial plexus block are "blind," and nerve localization can be frustrating and time consuming. Previous studies on ultrasound-assisted brachial plexus blocks are mostly performed with scanning probes of 10 MHz or less. The authors tested the usefulness of a state-of-the-art, high-resolution ultrasound probe (up to 12 MHz) in identifying the brachial plexus in five locations of the upper extremity and in guiding needle advancement to target before nerve stimulation. METHODS: In this prospective observational study, 15 volunteers underwent brachial plexus examination using an L12-L5 MHz probe and a Philips-ATL 5000 ultrasound unit in the interscalene, supraclavicular, infraclavicular, axillary, and midhumeral regions. Thereafter, an insulated block needle was advanced under direct ultrasound guidance to target nerves before confirmation by electrical nerve stimulation in five volunteers in each of the interscalene, supraclavicular, and axillary regions. The quality of brachial plexus images, anatomic variations, and the technique of needle advancement for nerve localization were recorded. RESULTS: The brachial plexus components were successfully identified in the transverse view as round to oval hypoechoic structures with small internal punctuate echos in all regions examined except the infraclavicular area (visualized in 27% of the cases). The authors' technique of advancing the needle in-line with the ultrasound beam allowed moment-by-moment observation of the needle shaft and tip movement at the time of nerve localization. Hypoechoic structures were stimulated electrically and confirmed to be nerves. CONCLUSIONS: These preliminary data show that the high-resolution L12-L5 probe provides good quality brachial plexus ultrasound images in the superficial locations i.e., the interscalene, supraclavicular, axillary, and midhumeral regions. The needle technique described here for ultrasound-assisted nerve localization provides real-time guidance and is potentially valuable for brachial plexus blocks.     

Ultrasound-guided posterior approach to block the sciatic nerve at the popliteal fossa

The recent introduction of ultrasound guidance for locating peripheral nerves and nerve plexi has allowed injection of anesthetic agents to block the sciatic nerve at the popliteal fossa proximal to division, thus preventing damage to adjacent structures, repeated punctures, and multiple nerve stimulations to verify anesthetic diffusion around the nerve. We report the case of a 23-year-old man, ASA I, who underwent reduction and osteosynthesis of a fractured right fibula. Ultrasound was used to guide the needle after identification of the sciatic nerve 10 cm from the knee fold and 3.5 cm deep. When the point of the needle was near the nerve, the nerve stimulator was switched on to 0.5 mA, and when no response was obtained the current was increased to 1.5 mA. The needle was moved slightly (1-2 mm) to produce a plantar flexion (tibial component) that persisted until stimulation had been reduced to 0.4 mA, at which time 30 mL of 1.5% mepivacaine was injected. The sonographic image during injection showed that the anesthetic had surrounded the nerve (donut sign). The motor and sensory block of the sciatic nerve was complete and no adverse events occurred during or after surgery. We conclude that the combination of ultrasound guidance and nerve stimulation allows the sciatic nerve to be located easily. The approach to the point before division of the sciatic nerve can be guaranteed so that puncture of neighboring vessels can be avoided and optimal anesthesia provided.     

Ultrasound imaging for popliteal sciatic nerve block

BACKGROUND AND OBJECTIVES: Ultrasound is a novel method of nerve localization but its use for lower extremity blocks appears limited with only reports for femoral 3-in-1 blocks. We report a case series of popliteal sciatic nerve blocks using ultrasound guidance to illustrate the clinical usefulness of this technology. CASE REPORT: The sciatic nerve was localized in the popliteal fossa by ultrasound imaging in 10 patients using a 4- to 7-MHz probe and the Philips ATL HDI 5000 unit. Ultrasound imaging showed the sciatic nerve anatomy, the point at which it divides, and the spatial relationship between the peroneal and tibial nerves distally. Needle contact with the nerve(s) was further confirmed with nerve stimulation. Circumferential local anesthetic spread within the fascial sheath after injection appears to correlate with rapid onset and completeness of sciatic nerve block. CONCLUSIONS: Our preliminary experience suggests that ultrasound localization of the sciatic nerve in the popliteal fossa is a simple and reliable procedure. It helps guide block needle placement and assess local anesthetic spread pattern at the time of injection.     

Distale Blockaden des N. ischiadicus

Background and objectives

The design of this study is related to an important current issue: should local anesthetics be intentionally injected into peripheral nerves? Answering this question is not possible without better knowledge regarding classical methods of nerve localization (e.g. cause of paresthesias and nerve stimulation technique). Have intraneural injections ever been avoided? This prospective, randomized comparison of distal sciatic nerve block with ultrasound guidance tested the hypothesis that intraneural injection of local anesthetics using the nerve stimulation technique is common and associated with a higher success rate.

Material and methods

In this study 250 adult patients were randomly allocated either to the nerve stimulation group (group NS, n?=?125) or to the ultrasound guidance group (group US, n?=?125). The sciatic nerve was anesthetized with 20 ml prilocaine 1% and 10 ml ropivacaine 0.75%. In the US group the goal was an intraepineural needle position. In the NS group progress of the block was observed by a second physician using ultrasound imaging but blinded for the investigator performing the nerve stimulation. The main outcome variables were time until readiness for surgery (performance time and onset time), success rate and frequency of paresthesias. In the NS group needle positions and corresponding stimulation thresholds were recorded.

Results

In both groups seven patients were excluded from further analysis because of protocol violation. In the NS group (n?=?118) the following needle positions were estimated: intraepineural (NS 1, n?=?51), extraparaneural (NS 2, n?=?33), needle tip dislocation from intraepineural to extraparaneural while injecting local anesthetic (NS 3, n?=?19) and other or not determined needle positions (n?=?15). Paresthesias indicated an intraneural needle position with an odds ratio of 27.4 (specificity 98.8%, sensitivity 45.9%). The success rate without supplementation was significantly higher in the US group (94.9% vs. 61.9%, p?<?0.001) and the time until readiness for surgery was significantly (p?<?0.001) shorter for successful blocks: 15.1 min (95% confidence interval CI 13.6–16.5 min) vs. 28 min (95% CI 24.9–31.1 min). In the NS subgroups the results were as follows (95% CI in brackets): NS1 88.2% and 22.7 min (19.5–25.9 min), NS2 24.2% and 43.3 min (35.5–51.1 min) and NS3 36.8% and 35.3 min (22.1–48.4 min).

Conclusions

For distal sciatic nerve blocks using the nerve stimulation technique, intraepineural injection of local anesthetics is common and associated with significant and clinically important higher success rates as well as shorter times until readiness for surgery. In both groups no block-related nerve damage was observed. The results indicate that for some blocks (e.g. sciatic, supraclavicular) perforation of the outer layers of connective tissue was always an important prerequisite for success using classical methods of nerve localization (cause of paresthesias and nerve stimulation technique). Additional nerve stimulation with an ultrasound-guided distal sciatic nerve block cannot make any additional contribution to the safety or success of the block. New insights concerning the architecture of the sciatic nerve are discussed and associated implications for the performance of distal ultrasound-guided sciatic nerve block are addressed.     

Correlation between Evoked Motor Response of the Sciatic Nerve and Sensory Blockade

Background: Incomplete sensory blockade of the foot after sciatic nerve block in the popliteal fossa may be related to the motor response that was elicited when the block was performed. We investigated the appropriate motor response when a nerve stimulator is used in sciatic nerve block at the popliteal fossa.

Methods: Six volunteers classified as American Society of Anesthesiologists' physical status I underwent 24 sciatic nerve blocks. Each volunteer had four sciatic nerve blocks. During each block, the needle was placed to evoke one of the following motor responses of the foot: eversion, inversion, plantar flexion, or dorsiflexion. Forty milliliters 1.5% lidocaine was injected after the motor response was elicited at < 1 mA intensity. Sensory blockade of the areas of the foot innervated by the posterior tibial, deep peroneal, superficial peroneal, and sural nerves was checked in a blinded manner. Motor blockade was graded on a three-point scale. The width of the sciatic nerve and the orientation of the tibial and common peroneal nerves were also examined in 10 cadavers.

Results: A significantly greater number of posterior tibial, deep peroneal, superficial peroneal, and sural nerves were blocked when inversion or dorsiflexion was seen before injection than after eversion or plantar flexion (P < 0.05). Motor blockade of the foot was significantly greater after inversion. Anatomically, the tibial and common peroneal nerves may be separate from each other throughout their course. The sciatic nerve ranged from 0.9-1.5 cm in width and was divided into the tibial and common peroneal nerves at 8 +/- 3 (range, 4-13) cm above the popliteal crease.     

Piriformis syndrome: anatomic considerations,a new injection technique,and a review of the literature

BACKGROUND: Piriformis syndrome can be caused by anatomic abnormalities. The treatments of piriformis syndrome include the injection of steroid into the piriformis muscle and near the area of the sciatic nerve. These techniques use either fluoroscopy and muscle electromyography to identify the piriformis muscle or a nerve stimulator to stimulate the sciatic nerve. METHODS: The authors performed a cadaver study and noted anatomic variations of the piriformis muscle and sciatic nerve. To standardize their technique of injection, they also noted the distance from the lower border of the sacroiliac joint (SIJ) to the sciatic nerve. They retrospectively reviewed the charts of 19 patients who had received piriformis muscle injections, noting the site of needle insertion in terms of the distance from the lower border of the SIJ and the depth of needle insertion at which the motor response of the foot was elicited. The authors tabulated the response of the patients to the injection, any associated diagnoses, and previous treatments that these patients had before the injection. Finally, they reviewed the literature on piriformis syndrome, a rare cause of buttock pain and sciatica. RESULTS: In the cadavers, the distance from the lower border of the SIJ to the sciatic nerve was 2.9 +/- 0.6 (1.8-3.7) cm laterally and 0.7 +/- 0.7 (0.0-2.5) cm caudally. In 65 specimens, the sciatic nerve passed anterior and inferior to the piriformis. In one specimen, the muscle was bipartite and the two components of the sciatic nerve were separate, with the tibial nerve passing below the piriformis and the peroneal nerve passing between the two components of the muscle. In the patients who received the injections, the site of needle insertion was 1.5 +/- 0.8 (0.4-3.0) cm lateral and 1.2 +/- 0.6 (0.5-2.0) cm caudal to the lower border of the SIJ as seen on fluoroscopy. The needle was inserted at a depth of 9.2 +/- 1.5 (7.5-13.0) cm to stimulate the sciatic nerve. Patients had comorbid etiologies including herniated disc, failed back surgery syndrome, spinal stenosis, facet syndrome, SIJ dysfunction, and complex regional pain syndrome. Sixteen of the 19 patients responded to the injection, their improvements ranged from a few hours to 3 months. CONCLUSIONS: Anatomic abnormalities causing piriformis syndrome are rare. The technique used in the current study was successful in injecting the medications near the area of the sciatic nerve and into the piriformis muscle.     

Three‐dimensional ultrasound‐assisted popliteal catheter placement revealing aberrant anatomy: implications for block failure

Background: The current means of introducing continuous sciatic catheters include nerve stimulation, with or without catheter stimulation techniques. More recently, ultrasound has been utilized to facilitate catheter placement. Methods: This case represents a stimulating catheter‐guided continuous block facilitated by three‐dimensional ultrasound, which revealed aberrant anatomy with proximal and wide bifurcation of the sciatic nerve with implications for block failure. Results: Before ultrasound imaging secondary failures were attributed to catheter misplacement or dislodgement. Conclusion: Because of this case observation, our current practice is to use ultrasound confirmation of the bifurcation of the nerve of all popliteal catheter placements, particularly catheters placed in patients having ambulatory procedures to prevent secondary failure of catheters at home.     

Stereospecific Effect of Pregabalin on Ectopic Afferent Discharges and Neuropathic Pain Induced by Sciatic Nerve Ligation in Rats

Background : The new anticonvulsants, gabapentin and pregabalin, are effective in the treatment of neuropathic pain. The sites and mechanisms of their analgesic action are not fully known. The authors have previously demonstrated that systemic gabapentin suppresses ectopic afferent discharges recorded from injured sciatic nerves in rats. In the current study, they further examined the stereospecific effect of pregabalin on neuropathic pain and afferent ectopic discharges in a rodent model of neuropathic pain.

Methods : Tactile allodynia and thermal hyperalgesia were induced by partial ligation of the left sciatic nerve in rats. Single-unit activity of afferent ectopic discharges was recorded from the sciatic nerve proximal to the site of ligation.

Results : Intravenous injection of 10-30 mg/kg pregabalin dose-dependently attenuated tactile allodynia (n = 10) and thermal hyperalgesia (n = 8). The stereoisomer of pregabalin, R-3-isobutylgaba, had no analgesic effect in this dose range. Furthermore, intravenous injection of pregabalin, but not R-3-isobutylgaba, significantly inhibited the ectopic discharges from injured afferents in a dose-dependent manner (from 20.8 +/- 2.4 impulses/s during control to 2.3 +/- 0.7 impulses/s after treatment with 30 mg/kg pregabalin, n = 15). Pregabalin did not affect the conduction velocity of afferent fibers and the response of normal afferent nerves to mechanical stimulation.     

Ultrasound-guided subgluteal sciatic nerve blocks with stimulating catheters in children: a descriptive study

We describe our clinical experience of combining ultrasound guidance and nerve stimulation for the insertion of subgluteal sciatic catheters in children. Ten children scheduled for lower limb surgery with a combined general anesthetic and a subgluteal sciatic catheter placement for both operative anesthesia and postoperative pain relief were studied. Under ultrasonographic guidance the sciatic catheter was placed using an 17-gauge 50-mm Arrow continuous peripheral nerve block needle and a 19-gauge stimulating catheter (Stimucath). The minimal electrical current required for muscle contraction on the stimulating needle and catheter differed widely among patients. Based on the visualization of the spread of local anesthetic during injection through the catheter, a successful prediction for the sciatic block was made in all patients. All catheters were successfully placed and provided excellent postoperative pain relief without complications.     

Ultrasound-guided Lumbar Facet Nerve Block: A Sonoanatomic Study of a New Methodologic Approach

Background: Lumbar facet nerve (medial branch) block for pain relief in facet syndrome is currently performed under fluoroscopic or computed tomography scan guidance. In this three-part study, the authors developed a new ultrasound-guided methodology, described the necessary landmarks and views, assessed ultrasound-derived distances, and tested the clinical feasibility.

Methods: (1) A paravertebral cross-axis view and long-axis view were defined under high-resolution ultrasound (15 MHz). Three needles were guided to the target point at L3-L5 in a fresh, nonembalmed cadaver under ultrasound (2-6 MHz) and were subsequently traced by means of dissection. (2) The lumbar regions of 20 volunteers (9 women, 11 men; median age, 36 yr [23-67 yr]; median body mass index, 23 kg/m2 [19-36 kg/m2]) were studied with ultrasound (3.5 MHz) to assess visibility of landmarks and relevant distances at L3-L5 in a total of 240 views. (3) Twenty-eight ultrasound-guided blocks were performed in five patients (two women, three men; median age, 51 yr [31-68 yr]) and controlled under fluoroscopy.

Results: In the cadaver, needle positions were correct as revealed by dissection at all three levels. In the volunteers, ultrasound landmarks were delineated as good in 19 and of sufficient quality in one (body mass index, 36 kg/m2). Skin-target distances increased from L3 to L5, reaching statistical significance (*, **P < 0.05) between these levels on both sides: L3r, 45 +/- 6 mm*; L4r, 48 +/- 7 mm; L5r, 50 +/- 6 mm*; L3l, 44 +/- 5 mm**; L4l, 47 +/- 6 mm; L5l, 50 +/- 6 mm**. In patients, 25 of 28 ultrasound-guided needles were placed accurately, with the remaining three closer than 5 mm to the radiologically defined target point.     

The effects of three different approaches on the onset time of sciatic nerve blocks with 0.75% ropivacaine

We studied three different injection techniques of sciatic nerve block in terms of block onset time and efficacy with 0.75% ropivacaine. A total of 75 patients undergoing foot surgery were randomly allocated to receive sciatic nerve blockade by means of the classic posterior approach (group classic; n = 25), a modified subgluteus posterior approach (group subgluteus; n = 25), or a lateral popliteal approach (group popliteal; n = 25). All blocks were performed with the use of a nerve stimulator (stimulation frequency, 2 Hz; intensity, 2-0.5 mA) and 30 mL of 0.75% ropivacaine. Onset of nerve block was defined as complete loss of pinprick sensation in the sciatic nerve distribution with concomitant inability to perform plantar or dorsal flexion of the foot. In the three groups, an appropriate sciatic stimulation was elicited at <0.5 mA. The failure rate was similar in the three groups (group popliteal: 4% versus group classic: 4% versus group subgluteus: 8%). The onset of nerve block was slower in group popliteal (25 +/- 5 min) compared with group classic (16 +/- 4 min) and group subgluteus (17 +/- 4 min; P < 0.001). There was no significant difference in the onset of nerve block between group classic and group subgluteus. No differences in the degree of pain measured at the first postoperative administration of pain medication were observed among the three groups. We conclude that the three approaches resulted in clinically acceptable anesthesia in the distribution of the sciatic nerve. The subgluteus and classic posterior approaches generated a significantly faster onset of anesthesia than the lateral popliteal approach. IMPLICATIONS: Comparing three different approaches to the sciatic nerve with 0.75% ropivacaine, the classic and subgluteal approaches exhibited a faster onset time of sensory and motor blockade than the lateral popliteal approach.