Michael S. Dodgson

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.

Additive analgesic effect of codeine and paracetamol can be detected in strong, but not moderate, pain after Caesarean section

Background: A randomized, double‐blind, placebo‐controlled single oral dose study was done in order to examine whether codeine has an additive analgesic effect to that of paracetamol for moderate and strong postoperative pain after abdominal surgery. The maximum recommended single dose of paracetamol 1000 mg (Paracet®) was compared with a combination of a submnximal dose of paracetamol 800 mg plus codeine 60 mg (Paralgin forte®) and placebo for pain relief after Caesarean section in 125 patients.

Use of magnetic resonance imaging to define the anatomical location closest to all three cords of the infraclavicular brachial plexus.

Infraclavicular techniques are often used to perform brachial plexus blocks. In our volunteer study we used magnetic resonance imaging to identify the brachial plexus and axillary vessels in a sagittal plane corresponding to the lateral sagittal infraclavicular block. In 20 volunteers, all cords were positioned within 2 cm from the artery approximately within 2/3 of a circle. We derived an injection site that was closest to all cords, cranio-posterior and adjacent to the axillary artery. We conclude that this knowledge may be useful for the performance of infraclavicular blocks aided by ultrasound. However, our proposals should be tested by clinical studies.

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.

Effect of chronic bupivacaine infusion on seizure threshold to bupivacaine

Thirty rats were pretreated with a continuous infusion of bupivacaine or placebo. On the fourth day the acute seizure threshold to bupivacaine was determined for both groups. The seizure dose, blood and brain concentration of bupivacaine showed no difference between the groups. The tachyphylaxis seen clinically when bupivacaine is used for a regional nerve blockade does not seem to evolve for the CNS‐effects.

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.

Ultrasound controlled nerve stimulation in the elbow region: high currents and short distances needed to obtain motor responses

Background:  Electrical nerve stimulation is commonly used to perform peripheral nerve blocks. The purpose of this study was to investigate the relation between stimulating currents and the distance between the needle‐tip and stimulated nerves.

Antagonism of flunitrazepam-induced sedative effects by flumazenil in patients after surgery under general anaesthesia. A double-blind placebo-controlled investigation of efficacy and safety.

This study aimed to assess the efficacy and safety of flumazenil and a placebo in reversing the residual effects of flunitrazepam used to induce anaesthesia for elective laparoscopy in 49 female patients aged 16 to 52 years. In contrast to the placebo, flumazenil gave reductions in amnesia, sedation score, mood rating for mental sedation and physical sedation, and time taken to complete a psychomotor performance test which lasted throughout the study. There were no significant changes in pulse rate, respiration rate or blood pressure, and no unwanted effects were attributed to flumazenil.

Antagonism of diazepam-induced sedative effects by Ro 15–1788 in patients after surgery under lumbar epidural block

The aim of this study was to assess the efficacy of Ro 15–1788 and a placebo in reversing diazepam‐induced effects after surgery under epidural block, and to evaluate the local tolerance and general safety of Ro15‐1788. Fifty‐seven patients were sedated with diazepam for surgery under epidural anaesthesia. Antagonism of diazepam‐induced effects by Ro15‐1788 was investigated postoperatively in a double‐blind placebo‐controlled trial. The patients subjective assessment of mood rating, an objective test of performance, a test for amnesia, and vital signs were recorded for up to 300 min after administration of the trial drug. No significant differences between the two groups were observed for mood rating, amnesia, or vital signs. The Ro15‐1788 group showed a significant improvement in the performance test up to 120 min after administration of the drug. There was no evidence of reaction at the injection site.

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