Axel R. Sauter

Electrical Nerve Stimulation or Ultrasound Guidance for Lateral Sagittal Infraclavicular Blocks : A Randomized, Controlled, Observer-Blinded, Comparative Study

BACKGROUND:Ultrasound guidance is frequently used to perform infraclavicular brachial plexus blocks. In this study, we compared electrical nerve stimulation and ultrasound guidance for the lateral sagittal infraclavicular block. METHODS:Eighty patients, ASA 1–2, were randomized for either nerve stimulation (group NS) or ultrasound-guided blocks (group US). The brachial plexus was anesthetized with 0.6 mL/kg mepivacaine (15 mg/mL) with epinephrine (2.5 &mgr;g/mL) in both groups. For ultrasound-guided blocks, local anesthetic was injected cranioposterior to the axillary artery. An observer who was blinded for the method assessed the blocks and questioned the patients. Successful block was defined as analgesia or anesthesia of all five nerves distal to the elbow. The main outcome variables were the time until readiness for surgery, quantified discomfort during the block, and pain related to tourniquet ischemia on a numeric rating scale (0–10). RESULTS:Block performance time was 4.3 min (sd 1.3) and 4.1 min (sd 1.3) (P = 0.64) in group NS and group US, respectively. Onset time for sensory block was 13.7 min (sd 6.6) and 13.9 min (sd 5.8), (P = 0.99). The time until readiness for surgery was 18.1 min in both groups (sd 6.6 and 6.0) (P = 0.99). Median discomfort related to the block procedure was 1 in both groups (P = 0.92), and median tourniquet pain was 0.5 in group NS and 1 in group US (P = 32). Differences in success rates, between 85% in group NS and 95% in group US, were not significant (P = 0.26). CONCLUSIONS:We conclude that favorable results can be obtained when either nerve stimulation or ultrasound guidance is used for lateral sagittal infraclavicular block. Using ultrasound, local anesthetic injection cranioposterior to the artery appears feasible.

Current Threshold for Nerve Stimulation Depends on Electrical Impedance of the Tissue: A Study of Ultrasound-Guided Electrical Nerve Stimulation of the Median Nerve

BACKGROUND: Understanding the mechanisms causing variation in current thresholds for electrical nerve stimulation may improve the safety and success rate of peripheral nerve blocks. Electrical impedance of the tissue surrounding a nerve may affect the response to nerve stimulation. In this volunteer study, we investigated the relationship between impedance and current threshold needed to obtain a neuromuscular response. METHODS: Electrical nerve stimulation and impedance measurements were performed for the median nerve in the axilla and at the elbow in 29 volunteers. The needletip was positioned at a distance of 5, 2.5, and 0 mm from the nerve as judged by ultrasound. Impulse widths of 0.1 and 0.3 ms were used for nerve stimulation. RESULTS: A significant inverse relationship between impedance and current threshold was found at the elbow, at nerve-to-needle distances of 5 and 2.5 mm (P = 0.001 and P = 0.036). Impedance values were significantly lower in the axilla (mean 21.1, sd 9.7 kohm) than at the elbow (mean 36.6, sd 13.4 kohm) (P < 0.001). Conversely, current thresholds for nerve stimulation were significantly higher in the axilla than at the elbow (P < 0.001, P < 0.001, P = 0.024). A mean ratio of 1.82 was found for the measurements of current thresholds with 0.1 versus 0.3 ms impulse duration. CONCLUSIONS: Our results demonstrate an inverse relationship between impedance measurements and current thresholds and suggest that current settings used for nerve stimulation may require adjustment based on the tissue type. Further studies should be performed to investigate the clinical impact of our findings.

Brachial plexus block with or without ultrasound guidance.

Purpose of review Should ultrasound or nerve stimulation be used for brachial plexus blocks? We investigated last years literature to help answer this question. Recent findings Many of the reports concluded that ultrasound guidance may provide a higher success rate for brachial plexus blocks than guidance by nerve stimulator. However, the studies were not large enough to conclude that ultrasound will reduce the risk of nerve injury, local anesthetic toxicity or pneumothorax. Ultrasound may reveal anatomical variations of importance for performing brachial plexus blocks. For postoperative analgesia, 5 ml of ropivacaine 0.5% has been sufficient for an ultrasound-guided interscalene block. For peroperative anesthesia, as much as 42 ml of a local anesthetic mixture was calculated to be appropriate for an ultrasound-guided supraclavicular method. For the future, we notice that three-dimensional and four-dimensional ultrasound technology may facilitate visualizing the needle, the nerves and the local anesthetic distribution. Impedance measurements may be helpful for nerve blocks not guided by ultrasound. Summary We think that the literature gives a sufficient basis to recommend the use of ultrasound for guidance of brachial plexus blocks. The potential for ultrasound to improve efficacy and reduce complications of brachial plexus blocks requires larger scaled studies.

The Shamrock lumbar plexus block: A dose-finding study

BACKGROUND The Shamrock technique is a new method for ultrasound-guided lumbar plexus blockade. Data on the optimal local anaesthetic dose are not available. OBJECTIVE The objective of this study is to estimate the effective dose of ropivacaine 0.5% for a Shamrock lumbar plexus block. DESIGN A prospective dose-finding study using Dixons up-and-down sequential method. SETTING University Hospital Orthopaedic Anaesthesia Unit. INTERVENTION Shamrock lumbar plexus block performance and block assessment were scheduled preoperatively. Ropivacaine 0.5% was titrated with the Dixon and Massey up-and-down method using a stepwise change of 5 ml in each consecutive patient. Combined blocks of the femoral, the lateral femoral cutaneous and the obturator nerve were prerequisite for a successful lumbar plexus block. PATIENTS Thirty patients scheduled for lower limb orthopaedic surgery completed the study. MAIN OUTCOME MEASURES The minimum effective anaesthetic volume of ropivacaine 0.5% (ED50) to achieve a successful Shamrock lumbar plexus block in 50% of the patients. Further analysis of the data was performed with a logistic regression model to calculate ED95 and to estimate the effective doses for a sensory lumbar plexus block not requiring a motor block of the femoral nerve. RESULTS The Dixon and Massay estimate of the ED50 was 20.4 [95% confidence interval (95% CI) 13.9 to 30.0] ml ropivacaine 0.5%. The logistic regression estimate of the ED95 was 36.0 (95% CI 19.7 to 52.2) ml ropivacaine 0.5%. For a sensory lumbar plexus block, the ED50 was 17.1 (95% CI 12.3 to 21.9) ml and the ED95 was 25.8 (95% CI 18.6 to 33.1) ml. CONCLUSION A volume of 20.4 ml ropivacaine 0.5% provided a successful Shamrock lumbar plexus block in 50% of the patients. A volume of 36.0 ml would be successful in 95% of the patients. TRIAL REGISTRATION ClinicalTrials.gov identifier NCT01956617.

Lateral sagittal infraclavicular block (LSIB).

o the Editor: We congratulate Koscielniak-Nielsen et al.1 on their ery interesting clinical study of the lateral sagittal infralavicular block (LSIB).2 Data from our first 500 patients ay supplement the clinical impression of the method. In 374 patients (75%), the block was aided by a peipheral nerve stimulator (NS) alone, whereas ultrasound US) was used in the remaining 126 patients (25%). In he NS group, we sought distal responses (from the finers and wrist) and used a single-injection technique, as n the study by Koscielniak-Nielsen et al.1 In the US roup, we used one or more deposits, depending on the bserved spread of local anesthetic. Overall, the blocks ere sufficient for surgery in 89.5% of patients. An aditional 5.8% of patients’ blocks were sufficient for surery after supplementary peripheral blocks, and 4.7% equired general anesthesia. There was no significant diference in the success rate between the NS and US roups. These results are comparable to those of Kocielniak-Nielsen et al.1 No clinical signs of pneumothorax were evident either n the 160 patients of Koscielniak-Nielsen et al.1 or in our 00 patients. No reports of neuropathy related to the lock were made. Koscielniak-Nielsen et al.1 reported ascular puncture in only 2% of the patients. This low umber may, as they suggest, be related to the fact that hey did not have continuous suction on the needle durng its insertion. Among 371 patients with continuous eedle suction and reliable documentation, we observed enous aspiration in 13.7%, arterial blood in 5.7%, and nclassified blood in 0.8%. We have included patients ith just traces of blood in the extension tube or aspiated blood from the thin needle used for subcutaneous nesthesia at the insertion site. Despite a total of 20% ascular punctures, no hematomas were reported. Could our success rates be improved? A needle position n the center of the plexus will provide a short distribuion distance to all 3 cords. To achieve this, we now use he following procedure: The first insertion is in the fronal plane, at 0°. If required, the needle is redirected poseriorly in steps of 10° until an NS response is obtained, arely to more than 60°. After we made the first contact usually the lateral cord), we do not inject, even with a istal response from the wrist or the fingers (previously e redirected only after a biceps response). The needle is edirected further posteriorly, in even smaller steps, to btain a distal response from a second cord (usually the edial or posterior cord). We then inject the single deosit. The benefit of this new algorithm has to be confirmed n a clinical study. However, we feel justified in informing sers of the LSIB about this possible improvement. fi

The Analgesic Effect of Ultrasound-guided Quadratus Lumborum Block After Cesarean Delivery: A Randomized Clinical Trial

BACKGROUND: Landmark and ultrasound-guided transversus abdominis plane blocks have demonstrated an opioid-sparing effect postoperatively after cesarean delivery. The more posterior quadratus lumborum (QL) might provide superior local anesthetic spread to the thoracolumbar fascia and paravertebral space. The aim of our study was to evaluate the efficacy of the QL block after cesarean delivery. METHODS: A randomized, double-blind, controlled trial was performed. Forty parturients undergoing cesarean delivery received bilateral ultrasound-guided QL blocks with either 2 mg/mL ropivacaine or saline postoperatively. All patients received spinal anesthesia with bupivacaine and sufentanil and a postoperative analgesic regimen of paracetamol, ibuprofen, and ketobemidone administered by a patient-controlled analgesic pump. The ketobemidone consumption and time of each dose administered were recorded. The primary outcome was ketobemidone consumption during the first 24 hours postoperatively. Secondary and exploratory analyses compared repeated measures of pain scores, nausea, and fatigue, and total differences in time until patients were able to stand and able to walk 5 m, and the interaction between the effective analgesic score and time. RESULTS: All 40 patients completed the trial, 20 in each group. The cumulative ketobemidone consumption in 24 hours was reduced in the active group compared with the control group (P = .04; ratio of means = 0.60; 95% confidence interval, 0.37–0.97). The effective analgesic scores were significantly better in the treatment group compared with the placebo group both at rest (P < .01) and during coughing (P < .01). CONCLUSIONS: QL block with ropivacaine reduces the postoperative ketobemidone consumption and pain intensity as a part of a multimodal analgesic regimen that excludes neuraxial morphine.

Local infiltration analgesia (LIA) and repeated bolus or continuous infusion peripheral nerve blocks for acute postoperative pain: Be ware of local anaesthetic toxicity, especially in elderly patients with cardiac co-morbidities!

Peripheral nerve blocks for postoperative pain, repeated bolus njections or continuous infusion through catheters placed near a lexus or peripheral nerves is an effective way of relieving localzed acute pain after surgery, e.g. femoral nerve block after total nee replacement [1]. Electrical nerve stimulation and ultrasound uided localization of peripheral nerves make this technique more ffective [2]. Local infiltration of a large dose of a local anaesthetic rug during major joint surgery and subsequent bolus injection hrough a catheter left in situ is a recently popularized technique. otal knee replacement is the operation in which such local infilration analgesia (LIA) is documented to be effective [3,4]. LIA is ess effective for pain after hip arthroplasty [4]. In addition to the ocal anaesthetic, adrenaline and an NSAID are added in the LIA echnique. Adrenaline is usually not added for intermittent or coninuous femoral nerve block [1,3,4].

Subacute Pain After Total Knee Arthroplasty

ABSTRACT Acute pain during and immediately after total knee arthroplasty (TKA) can be well controlled by spinal anesthesia, local infiltration analgesia, and peripheral nerve blocks; this enables early or fast-track rehabilitation. However, about half of patients have clinically significant pain in the following weeks. Active movements and rehabilitation of joint function, muscle strength, and ability to maintain balance and prevent falls all become more difficult when the joint is painful on movement. Intensive analgesic and antihyperalgesic treatment during the first few weeks after TKA surgery may reduce the risk of chronic pain after this operation, which is itself intended to remove the patients chronic osteoarthritis pain. Spinal cord stimulation may be an effective option for patients with mainly neuropathic pain after TKA surgery. This report is adapted from paineurope 2013; Issue 4, ©Haymarket Medical Publications Ltd., and is presented with permission. paineurope is provided as a service to pain management by Mundipharma International, Ltd., and is distributed free of charge to health care professionals in Europe. Archival issues can be accessed via the Web site: http://www.paineurope.com, at which European health professionals can register online to receive copies of the quarterly publication.

Reply to: importance of half-the-air pressure test in Shamrock lumbar plexus block

I would like to congratulate Dr Sauter and colleagues who have found the adequate volume of the Shamrock method to achieve an effective sensory block with the lumbar plexus. However, there could be room for discussion in terms of some descriptions and techniques used in this study. As the authors stated, ‘the Shamrock method might improve, but not eliminate, all challenges related to a deep ultrasound-guided nerve block’. Therefore, lumbar plexus block should be performed in combination with additional monitors besides Shamrock ultrasound and nerve stimulation. Complications encountered in their study included epidural spread and local anaesthetic systemic toxicity. It is the opening injection pressure, but not the injection volume mentioned in their introduction, that mainly determines whether epidural spread occurs during lumbar plexus block. Furthermore, the authors claimed that systemic toxicity might result from a needle tip partially placed inside a blood vessel, although local anaesthetic spread was observed during the injection. Probably before the spread is visible, significant amounts of the local anaesthetic have already been injected into the vessels, therefore resulting in systemic toxicity. I thus recommend monitoring opening injection pressure as a routine practice, which prevents epidural spread by keeping opening injection pressure less than 15 psi. It also decreases the risk of intravascular injection because the solution used to hydrolocate the needle tip and visualise the hypoechoic spread is 5% dextrose instead of local anaesthetic. The surrounding tissues, including the vessels, are usually pushed away from the needle tip after visualising the dextrose spread, permitting safer timing of local anaesthetic injection for lumbar plexus block. Compared with about 25 to 35 ml of effective volume to achieve sensory or complete block for lumbar plexus, emptying the dextrose in this low-dead space (1.4 ml) extension tube before the injection of the local anaesthetic will not result in a significant dilutional effect.

Detection of needle to nerve contact based on electric bioimpedance and machine learning methods

In an ongoing project for electrical impedance-based needle guidance we have previously showed in an animal model that intraneural needle positions can be detected with bioimpedance measurement. To enhance the power of this method we in this study have investigated whether an early detection of the needle only touching the nerve also is feasible. Measurement of complex impedance during needle to nerve contact was compared with needle positions in surrounding tissues in a volunteer study on 32 subjects. Classification analysis using Support-Vector Machines demonstrated that discrimination is possible, but that the sensitivity and specificity for the nerve touch algorithm not is at the same level of performance as for intra-neuralintraneural detection.