Comparison of peripheral nerve stimulator versus ultrasonography guided axillary block using multiple injection technique

A prospective, randomised, single-blinded controlled trial comparing ultrasound versus nerve stimulator guidance for interscalene block for ambulatory upper limb surgeries

Background

Interscalene block is usually performed using either ultrasound (US) or nerve stimulator (NS) guidance. This single-blinded, prospective, randomised study was performed to find out whether US was able to offer distinct advantages over conventional NS guidance.

Methods

100 patients in the American Society of Anaesthesiology (ASA) physical status I to III, aged 18-70 years were randomised into US guided or NS guided group for interscalene block with 15 ml 0.5% bupivacaine and 5 ml 2% lignocaine. Patients were premedicated with midazolam 0.03 mg/kg (maximum 2 mg) and fentanyl 2 mcg/kg (max 100 mcg) was used as rescue analgesia.

Result

Mean time of onset of sensory block in the NS group was 6.2 min (3.1), the US group 4.7 min (1.1), p value (<0.001). Mean duration of post-operative analgesia in NS group 323.6 min (98.6), US group 558.6 min (144.3), (p < 0.001). Mean time for performance of block NS Group 7.3 min (2.0), and in the US group 4.9 min (1.3), (p < 0.001). Number of needle passes NS group 1.7(0.9), US group 1.3 (1.0), (p < 0.005). Total cost per surgery with NS was Rs 363.10 less than in the US-guided block. Incremental cost effectiveness ratio for ultrasound group for onset of block was Rs -242.07, Rs 92.0 for duration of block and Rs -151.29 for time for performance of block. No incident of post-operative neurological complications seen in either group.

Conclusion

Ultrasound use offers faster onset, longer duration of block, reduces time for performance of blocks with comparable complication rates. For most of the measured parameters it was superior but more costly than nerve stimulator for directly measured costs.

What Is the Risk of Postoperative Neurologic Symptoms After Regional Anesthesia in Upper Extremity Surgery? A Systematic Review and Meta-analysis of Randomized Trials

BACKGROUND

The risk of neurologic symptoms after regional anesthesia in orthopaedic surgery is estimated to approach 3%, with long-term deficits affecting 2 to 4 per 10,000 patients. However, current estimates are derived from large retrospective or observational studies that are subject to important systemic biases. Therefore, to harness the highest quality data and overcome the challenge of small numbers of participants in individual randomized trials, we undertook this systematic review and meta-analysis of contemporary randomized trials.

QUESTIONS/PURPOSES

In this systematic review and meta-analysis of randomized trials we asked: (1) What is the aggregate pessimistic and optimistic risk of postoperative neurologic symptoms after regional anesthesia in upper extremity surgery? (2) What block locations have the highest and lowest risk of postoperative neurologic symptoms? (3) What is the timing of occurrence of postoperative neurologic symptoms (in days) after surgery?

METHODS

We searched Ovid MEDLINE, Embase, Cochrane Central Register of Controlled Trials and Cochrane Database of Systematic Reviews, Web of Science, Scopus, and PubMed for randomized controlled trials (RCTs) published between 2008 and 2019 that prospectively evaluated postoperative neurologic symptoms after peripheral nerve blocks in operative procedures. Based on the Grading of Recommendations, Assessment, Development, and Evaluation guidance for using the Risk of Bias in Non-Randomized Studies of Interventions tool, most trials registered a global rating of a low-to-intermediate risk of bias. A total of 12,532 participants in 143 trials were analyzed. Data were pooled and interpreted using two approaches to calculate the aggregate risk of postoperative neurologic symptoms: first according to the occurrence of each neurologic symptom, such that all reported symptoms were considered mutually exclusive (pessimistic estimate), and second according to the occurrence of any neurologic symptom for each participant, such that all reported symptoms were considered mutually inclusive (optimistic estimate).

RESULTS

At any time postoperatively, the aggregate pessimistic and optimistic risks of postoperative neurologic symptoms were 7% (915 of 12,532 [95% CI 7% to 8%]) and 6% (775 of 12,532 [95% CI 6% to 7%]), respectively. Interscalene block was associated with the highest risk (13% [661 of 5101] [95% CI 12% to 14%]) and axillary block the lowest (3% [88 of 3026] [95% CI 2% to 4%]). Of all symptom occurrences, 73% (724 of 998) were reported between 0 and 7 days, 24% (243 of 998) between 7 and 90 days, and 3% (30 of 998) between 90 and 180 days. Among the 31 occurrences reported at 90 days or beyond, all involved sensory deficits and four involved motor deficits, three of which ultimately resolved.

CONCLUSION

When assessed prospectively in randomized trials, the aggregate risk of postoperative neurologic symptoms associated with peripheral nerve block in upper extremity surgery was approximately 7%, which is greater than previous estimates described in large retrospective and observational trials. Most occurrences were reported within the first week and were associated with an interscalene block. Few occurrences were reported after 90 days, and they primarily involved sensory deficits. Although these findings cannot inform causation, they can help inform risk discussions and clinical decisions, as well as bolster our understanding of the evolution of postoperative neurologic symptoms after regional anesthesia in upper extremity surgery. Future prospective trials examining the risks of neurologic symptoms should aim to standardize descriptions of symptoms, timing of evaluation, classification of severity, and diagnostic methods.

LEVEL OF EVIDENCE

Level I, therapeutic study.

Peripheral Nerve Stimulator Versus Ultrasound-Guided Femoral Nerve Block for Knee Arthroscopy Procedures: A Randomized Controlled Trial

Background

Femoral nerve block (FNB) provides effective analgesia and is a widely used technique for postoperative pain relief for orthopedic procedures on lower limbs. This study aims to compare the efficacy of ultrasonography (USG) versus peripheral nerve stimulator (PNS)-guided FNB in knee arthroscopic procedures.

Methodology

This randomized comparative study included two study groups with 30 participants in each group who were given FNB with either PNS or USG for knee arthroscopic procedures following spinal anesthesia. The study evaluated the number of needle repositioning, the time taken for performing the block, the efficacy of postoperative analgesia based on the duration of the block, and patient satisfaction.

Results

The number of needle repositioning and time taken to finish the procedure using USG was lower compared to the group using PNS (p < 0.001). The duration of the block was comparable in both groups (p = 0.584). Patients were satisfied with both techniques and responded as either very good or outstanding and chose neither as inferior (p = 0.310).

Conclusions

Both techniques have equal efficacy concerning the duration of the effect of the block and patient satisfaction. However, the procedural time and number of needle repositioning were significantly less in the group where USG was used for the block.

New composite scale for evaluating peripheral nerve block quality in upper limb orthopaedics surgery

INTRODUCTION

Developments in ultrasound guided (UG) peripheral nerve block (PNB) techniques have significant advantages for patients undergoing trauma surgery. Brachial plexus blockade (BPB) for upper extremity surgery provide superior analgesia, improve recovery and patient satisfaction. To the best of our knowledge there is no tool for evaluation of the quality of UG PNB which concerns the quality of PNB, the tolerance of the patient towards the anaesthetic approach, and postoperative analgesia as well.

PATIENTS AND METHODS

Standardized UG BPB anaesthesia - was performed; interscalene-supraclavicular (ISC-SC) and axillary-supraclavicular (AX-SC) approach for upper limb surgery. A GCS like tool was developed with which the Sensory, Motor, Coping of patient and Postoperative (SMCP) pain qualities were measured. The quality of PNBs were evaluated by a quality of anaesthesia graded by anaesthesiologist (QAGA) and the SMCP scale as well, the means of midazolam and opioid consumption during surgery, vital parameters, postoperative pain intensity (VNRS) were compared between the two groups.

RESULTS

Ninety three unpremedicated adult patients with ASA I-III were scheduled for unilateral upper limb surgery. Nearly the same mean volumes of local anaesthetic solution were used in the AX-SC and ISC-SC groups (28.3-31.0 ml). There were no significant difference in the quality of PNB measured by QAGA or SMCP scale between the AX-SC and the ISC-SC groups, however 75 patients were assessed as Excellent with the SMCP scale vs. 39 with the QAGA. 97.8% of the patients were in the Excellent and Good category evaluated with SMPC vs. 86% with QAGA (p < 0.001). There was no surgery abandoned due to failed PNB and no tourniquet pain was detected. There was no evidence of side effects or complications of PNB during the follow-up period.

DISCUSSION

This composite tool is designed for evaluating the loss of sensory and motor function; the coping of the patient and the postoperative pain as well. Our novel SMCP evaluation tool focuses on the overall condition of the patient during surgery and in the postoperative period. This more precise outcome evaluating scale is significantly superior to the formerly used QAGA in representing the high success rate of UG PNB.

Onset times and duration of analgesic effect of various concentrations of local anesthetic solutions in standardized volume used for brachial plexus blocks

Visualization of the nerve structures of brachial plexus allows anesthesiologists to use a lower dose of local anesthetics. The content of this low dose is not unequivocal, consequently, the pharmacokinetics of local anesthetics used by various authors are difficult to compare. In this study, the onset times and duration of the analgesic effect of local anesthetic mixture solutions used for brachial plexus blocks are investigated and the quality of anesthesia is compared. 85 unpremedicated American Society of Anesthesiologist physical status I-III, 19-83-year-old patients scheduled for upper limb trauma surgery are assigned to four groups for the axillary-supraclavicular block with lidocaine 1% and bupivacaine 0,5% 1:1 mixture (Group LB) or bupivacaine 0.33% (Group BS) or lidocaine 0,66% (Group LS) or bupivacaine 0.5% and lidocaine 1% 2:1 mixture (Group BL). 0.4 ml/kg was administered to the four groups. The onset time was significantly shorter in the lidocaine group (LS 13.0 ± 1.02) than in the other study groups (LB 16.64 ± 0.89; BS 17.21 ± 0.74; BL 16.92 ± 0.51 min ±SEM, p = 0.002). No differences were observed in the onset times between LB, BS, and BL groups (p > 0.05). Statistical differences were found in the duration of local anesthetics between LB (392.9 ± 20.4), BS (546.4 ± 14.9), LS (172.85 ± 7.8), and BL (458.7 ± 11.9 min ±SEM, p = 0.001). Lidocaine does not shorten the onset times, but significantly decreases the duration of action of bupivacaine when used in mixture solutions. Lidocaine exhibits a good quality of block in the applied dose, while other solutions have excellent quality. Bupivacaine without lidocaine has the longest duration of action to achieve the longest postoperative analgesia.

A Comparative Clinical Study of Ultrasonography-Guided Perivascular and Perineural Axillary Brachial Plexus Block for Upper Limb Surgeries

Background:

Axillary brachial plexus block (ABPB) is safest among other methods of brachial plexus block because of its ease and reliability. The two approaches of ultrasonography-guided ABPB are perivascular (PV) and perineural (PN).

Aims:

This study was conducted to compare primary outcomes such as performance time, onset of the block, number of needle passes, block success rate, duration of sensory and motor block, and complications between ultrasound-guided PV and PN ABPB in patients posted for upper limb surgeries.

Settings and Design:

This prospective randomized study was conducted on 106 patients American Society of Anesthesiologists Class I and II posted for forearm, wrist, and hand surgeries, who were allotted into Group PV and Group PN 53 each.

Materials and Methods:

In both methods, 20 mL of the drug was used. To start with, musculocutaneous nerve was blocked with 5 mL of the drug. In the PV technique, remaining 15 mL of the drug was deposited anterior and posterior to axillary artery, and in PN technique, 5 mL of the drug was injected around radial, ulnar, and median nerve.

Statistical Analysis:

Mann–Whitney and Chi-square test were used for statistical analysis.

Results:

Significant difference was observed between the two groups in performance time (PV – 8.647 ± 0.54 min and PN – 14.53 ± 0.20 min), onset time (PV – 19.48 ± 2.83 min and PN – 13.86 ± 1.81 min), and number of needle passes (PV – 2.30 ± 0.50 and PN – 4.91 ± 0.66). Other parameters were comparable in both the groups.

Conclusions:

Ultrasound-guided PV axillary plexus block is better than PN axillary plexus block with respect to performance time and number of needle passes; but onset time was shorter in PN block, with precaution eliminating the risk of complications.

A rat model of nerve stimulator-guided brachial plexus blockade

It is important to develop a feasible animal model of regional anesthesia other than sciatic nerve blockade for pharmacokinetic investigations of new local anesthetics or analgesia in upper extremity surgery. Herein, we explored a nerve stimulator (NS)-guided brachial plexus block (BPB) in a rat model. The anatomy of the brachial plexus in rats was delineated in cadavers, and various BPBs were examined. The puncture point was located 0.5-1.0 cm below the lateral one-third of the clavicle. The efficacy and safety of the NS-guided BPB were evaluated using an injection of 2% lidocaine or 0.5% bupivacaine in 16 live animals; saline injection was used as a control. Both sides of the brachial plexus were located successfully using the NS-guided technique. Sensory blockade (nociception assessment) and motor blockade (grasping and straightening tests) appeared after application of the two classical local anesthetics, but not normal saline. The motor and sensory blockade induced by bupivacaine exhibited a longer duration than that induced by lidocaine ( p < 0.05). All rats recovered uneventfully from general anesthesia and BPB. No abnormal results were found in pathological studies or behavioral observations. Thus, a rat model of NS-guided BPB was established, and BPB induced an overall reversible sensory and motor blockade in the thoracic limbs. Evaluation of the efficacy and safety demonstrated that this rat BPB model was feasible, reproducible, and safe.

Comparison of Nerve Stimulation-guided Axillary Brachial Plexus Block, Single Injection versus Four Injections: A Prospective Randomized Double-blind Study

BACKGROUND

A variety of techniques have been described for the axillary block using nerve stimulator, either with single injection, two, three, or four separate injections. Identification of all the four nerves is more difficult and time-consuming than other methods.

AIMS

Aim of the present study is to compare success rate, onset, and duration of sensory and motor anesthesia of axillary block using nerve stimulator, either with single injection after identification of any one of the four nerves or four separate injections following identification of each of nerve.

SETTING AND DESIGN

Prospective, randomized, double-blind study. Patients undergoing forearm and hand surgeries under axillary block.

METHODOLOGY

One hundred patients, aged 18-75 years, were randomly allocated into two groups of 50 each. Axillary block was performed under the guidance of nerve stimulator with a mixture of 18 ml of 1.5% lignocaine and 18 ml of 0.5% bupivacaine. In the first group (n = 50), all 36 ml of local anesthetic was injected after the identification of motor response to any one of the nerves and in Group 2, all the four nerves were identified by the motor response, and 9 ml of local anesthetic was injected at each of the nerves. The success rate of the block, onset, and duration of sensory and motor block was assessed.

STATISTICAL ANALYSIS

Categorical variables were compared using the Chi-square test, and continuous variables were compared using independent t-test.

RESULTS

The success rate of the block with four injection technique was higher compared to single-injection technique (84% vs. 56%, P = 0.02). Four injection groups had a faster onset of sensory and motor block and prolonged duration of analgesia compared to single-injection group (P < 0.001). There were no significant differences in the incidence of accidental arterial puncture and hemodynamic parameter between the groups.

CONCLUSION

Identification of all the four nerves produced higher success rate and better quality of the block when compared to single-injection technique.

Nerve Stimulator versus Ultrasound-Guided Femoral Nerve Block; a Randomized Clinical Trial

INTRODUCTION

Pain control is the most important issue in emergency department management of patients with femoral bone fractures. The present study aimed to compare the procedural features of ultrasonography and nerve stimulator guided femoral nerve block in this regard.

METHOD

In this randomized clinical trial, patients with proximal femoral fractures presenting to emergency department were randomly divided into two groups of ultrasonography or nerve stimulator guided femoral block and compared regarding success rate, procedural time, block time, and need for rescue doses of morphine sulfate, using SPSS 20.

RESULTS

50 patients were randomly divided into two groups of 25 (60% male). The mean age of studied patients was 35.14 ± 12.95 years (19 - 69). The two groups were similar regarding age (p= 0.788), sex (p = 0.564), and initial pain severity (p = 0.513). In 2 cases of nerve stimulator guided block, loss of pinprick sensation did not happen within 30 minutes of injection (success rate: 92%; p = 0.490). Ultrasonography guided nerve block cases had significantly lower procedural time (8.06 ± 1.92 vs 13.60 ± 4.56 minutes; p < 0.001) and lower need for rescue doses of opioid (2.68 ± 0.74 vs 5.28 ± 1.88 minutes; p < 0.001).

CONCLUSION

Ultrasonography and nerve stimulator guided femoral block had the same success rate and block duration. However, the ultrasonography guided group had lower procedure time and lower need for rescue doses of morphine sulfate. Therefore, ultrasonography guided femoral block could be considered as an available, safe, rapid, and efficient method for pain management of femoral fracture in emergency department.

Upper extremity nerve block: how can benefit, duration, and safety be improved? An update

Upper extremity blocks are useful as both sole anaesthesia and/or a supplement to general anaesthesia and they further provide effective postoperative analgesia, reducing the need for opioid analgesics. There is without doubt a renewed interest among anaesthesiologists in the interscalene, supraclavicular, infraclavicular, and axillary plexus blocks with the increasing use of ultrasound guidance. The ultrasound-guided technique visualising the needle tip and solution injected reduces the risk of side effects, accidental intravascular injection, and possibly also trauma to surrounding tissues. The ultrasound technique has also reduced the volume needed in order to gain effective block. Still, single-shot plexus block, although it produces effective anaesthesia, has a limited duration of postoperative analgesia and a number of adjuncts have been tested in order to prolong analgesia duration. The addition of steroids, midazolam, clonidine, dexmedetomidine, and buprenorphine has been studied, all being off-label when administered by perineural injection, and the potential neurotoxicity needs further study. The use of perineural catheters is an effective option to improve and prolong the postoperative analgesic effect.

Upper extremity plexus blocks have an obvious place as a sole anaesthetic technique or as a powerful complement to general anaesthesia, reducing the need for analgesics and hypnotics intraoperatively, and provide effective early postoperative pain relief. Continuous perineural infusion is an effective option to prolong the effects and improve postoperative quality.

Ultrasound guidance for upper and lower limb blocks

BACKGROUND

Peripheral nerve blocks can be performed using ultrasound guidance. It is not yet clear whether this method of nerve location has benefits over other existing methods. This review was originally published in 2009 and was updated in 2014.

OBJECTIVES

The objective of this review was to assess whether the use of ultrasound to guide peripheral nerve blockade has any advantages over other methods of peripheral nerve location. Specifically, we have asked whether the use of ultrasound guidance:1. improves success rates and effectiveness of regional anaesthetic blocks, by increasing the number of blocks that are assessed as adequate2. reduces the complications, such as cardiorespiratory arrest, pneumothorax or vascular puncture, associated with the performance of regional anaesthetic blocks

SEARCH METHODS

In the 2014 update we searched the Cochrane Central Register of Controlled Trials (CENTRAL; 2014, Issue 8); MEDLINE (July 2008 to August 2014); EMBASE (July 2008 to August 2014); ISI Web of Science (2008 to April 2013); CINAHL (July 2014); and LILACS (July 2008 to August 2014). We completed forward and backward citation and clinical trials register searches.The original search was to July 2008. We reran the search in May 2015. We have added 11 potential new studies of interest to the list of 'Studies awaiting classification' and will incorporate them into the formal review findings during future review updates.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) comparing ultrasound-guided peripheral nerve block of the upper and lower limbs, alone or combined, with at least one other method of nerve location. In the 2014 update, we excluded studies that had given general anaesthetic, spinal, epidural or other nerve blocks to all participants, as well as those measuring the minimum effective dose of anaesthetic drug. This resulted in the exclusion of five studies from the original review.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trial quality and extracted data. We used standard Cochrane methodological procedures, including an assessment of risk of bias and degree of practitioner experience for all studies.

MAIN RESULTS

We included 32 RCTs with 2844 adult participants. Twenty-six assessed upper-limb and six assessed lower-limb blocks. Seventeen compared ultrasound with peripheral nerve stimulation (PNS), and nine compared ultrasound combined with nerve stimulation (US + NS) against PNS alone. Two studies compared ultrasound with anatomical landmark technique, one with a transarterial approach, and three were three-arm designs that included US, US + PNS and PNS.There were variations in the quality of evidence, with a lack of detail in many of the studies to judge whether randomization, allocation concealment and blinding of outcome assessors was sufficient. It was not possible to blind practitioners and there was therefore a high risk of performance bias across all studies, leading us to downgrade the evidence for study limitations using GRADE. There was insufficient detail on the experience and expertise of practitioners and whether experience was equivalent between intervention and control.We performed meta-analysis for our main outcomes. We found that ultrasound guidance produces superior peripheral nerve block success rates, with more blocks being assessed as sufficient for surgery following sensory or motor testing (Mantel-Haenszel (M-H) odds ratio (OR), fixed-effect 2.94 (95% confidence interval (CI) 2.14 to 4.04); 1346 participants), and fewer blocks requiring supplementation or conversion to general anaesthetic (M-H OR, fixed-effect 0.28 (95% CI 0.20 to 0.39); 1807 participants) compared with the use of PNS, anatomical landmark techniques or a transarterial approach. We were not concerned by risks of indirectness, imprecision or inconsistency for these outcomes and used GRADE to assess these outcomes as being of moderate quality. Results were similarly advantageous for studies comparing US + PNS with NS alone for the above outcomes (M-H OR, fixed-effect 3.33 (95% CI 2.13 to 5.20); 719 participants, and M-H OR, fixed-effect 0.34 (95% CI 0.21 to 0.56); 712 participants respectively). There were lower incidences of paraesthesia in both the ultrasound comparison groups (M-H OR, fixed-effect 0.42 (95% CI 0.23 to 0.76); 471 participants, and M-H OR, fixed-effect 0.97 (95% CI 0.30 to 3.12); 178 participants respectively) and lower incidences of vascular puncture in both groups (M-H OR, fixed-effect 0.19 (95% CI 0.07 to 0.57); 387 participants, and M-H OR, fixed-effect 0.22 (95% CI 0.05 to 0.90); 143 participants). There were fewer studies for these outcomes and we therefore downgraded both for imprecision and paraesthesia for potential publication bias. This gave an overall GRADE assessment of very low and low for these two outcomes respectively. Our analysis showed that it took less time to perform nerve blocks in the ultrasound group (mean difference (MD), IV, fixed-effect -1.06 (95% CI -1.41 to -0.72); 690 participants) but more time to perform the block when ultrasound was combined with a PNS technique (MD, IV, fixed-effect 0.76 (95% CI 0.55 to 0.98); 587 participants). With high levels of unexplained statistical heterogeneity, we graded this outcome as very low quality. We did not combine data for other outcomes as study results had been reported using differing scales or with a combination of mean and median data, but our interpretation of individual study data favoured ultrasound for a reduction in other minor complications and reduction in onset time of block and number of attempts to perform block.

AUTHORS' CONCLUSIONS

There is evidence that peripheral nerve blocks performed by ultrasound guidance alone, or in combination with PNS, are superior in terms of improved sensory and motor block, reduced need for supplementation and fewer minor complications reported. Using ultrasound alone shortens performance time when compared with nerve stimulation, but when used in combination with PNS it increases performance time.We were unable to determine whether these findings reflect the use of ultrasound in experienced hands and it was beyond the scope of this review to consider the learning curve associated with peripheral nerve blocks by ultrasound technique compared with other methods.

Ultrasound guidance for upper and lower limb blocks

BACKGROUND

Peripheral nerve blocks can be performed using ultrasound guidance. It is not yet clear whether this method of nerve location has benefits over other existing methods. This review was originally published in 2009 and was updated in 2014.

OBJECTIVES

The objective of this review was to assess whether the use of ultrasound to guide peripheral nerve blockade has any advantages over other methods of peripheral nerve location. Specifically, we have asked whether the use of ultrasound guidance:1. improves success rates and effectiveness of regional anaesthetic blocks, by increasing the number of blocks that are assessed as adequate2. reduces the complications, such as cardiorespiratory arrest, pneumothorax or vascular puncture, associated with the performance of regional anaesthetic blocks

SEARCH METHODS

In the 2014 update we searched the Cochrane Central Register of Controlled Trials (CENTRAL; 2014, Issue 8); MEDLINE (July 2008 to August 2014); EMBASE (July 2008 to August 2014); ISI Web of Science (2008 to April 2013); CINAHL (July 2014); and LILACS (July 2008 to August 2014). We completed forward and backward citation and clinical trials register searches.The original search was to July 2008. We reran the search in May 2015. We have added 11 potential new studies of interest to the list of 'Studies awaiting classification' and will incorporate them into the formal review findings during future review updates.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) comparing ultrasound-guided peripheral nerve block of the upper and lower limbs, alone or combined, with at least one other method of nerve location. In the 2014 update, we excluded studies that had given general anaesthetic, spinal, epidural or other nerve blocks to all participants, as well as those measuring the minimum effective dose of anaesthetic drug. This resulted in the exclusion of five studies from the original review.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trial quality and extracted data. We used standard Cochrane methodological procedures, including an assessment of risk of bias and degree of practitioner experience for all studies.

MAIN RESULTS

We included 32 RCTs with 2844 adult participants. Twenty-six assessed upper-limb and six assessed lower-limb blocks. Seventeen compared ultrasound with peripheral nerve stimulation (PNS), and nine compared ultrasound combined with nerve stimulation (US + NS) against PNS alone. Two studies compared ultrasound with anatomical landmark technique, one with a transarterial approach, and three were three-arm designs that included US, US + PNS and PNS.There were variations in the quality of evidence, with a lack of detail in many of the studies to judge whether randomization, allocation concealment and blinding of outcome assessors was sufficient. It was not possible to blind practitioners and there was therefore a high risk of performance bias across all studies, leading us to downgrade the evidence for study limitations using GRADE. There was insufficient detail on the experience and expertise of practitioners and whether experience was equivalent between intervention and control.We performed meta-analysis for our main outcomes. We found that ultrasound guidance produces superior peripheral nerve block success rates, with more blocks being assessed as sufficient for surgery following sensory or motor testing (Mantel-Haenszel (M-H) odds ratio (OR), fixed-effect 2.94 (95% confidence interval (CI) 2.14 to 4.04); 1346 participants), and fewer blocks requiring supplementation or conversion to general anaesthetic (M-H OR, fixed-effect 0.28 (95% CI 0.20 to 0.39); 1807 participants) compared with the use of PNS, anatomical landmark techniques or a transarterial approach. We were not concerned by risks of indirectness, imprecision or inconsistency for these outcomes and used GRADE to assess these outcomes as being of moderate quality. Results were similarly advantageous for studies comparing US + PNS with NS alone for the above outcomes (M-H OR, fixed-effect 3.33 (95% CI 2.13 to 5.20); 719 participants, and M-H OR, fixed-effect 0.34 (95% CI 0.21 to 0.56); 712 participants respectively). There were lower incidences of paraesthesia in both the ultrasound comparison groups (M-H OR, fixed-effect 0.42 (95% CI 0.23 to 0.76); 471 participants, and M-H OR, fixed-effect 0.97 (95% CI 0.30 to 3.12); 178 participants respectively) and lower incidences of vascular puncture in both groups (M-H OR, fixed-effect 0.19 (95% CI 0.07 to 0.57); 387 participants, and M-H OR, fixed-effect 0.22 (95% CI 0.05 to 0.90); 143 participants). There were fewer studies for these outcomes and we therefore downgraded both for imprecision and paraesthesia for potential publication bias. This gave an overall GRADE assessment of very low and low for these two outcomes respectively. Our analysis showed that it took less time to perform nerve blocks in the ultrasound group (mean difference (MD), IV, fixed-effect -1.06 (95% CI -1.41 to -0.72); 690 participants) but more time to perform the block when ultrasound was combined with a PNS technique (MD, IV, fixed-effect 0.76 (95% CI 0.55 to 0.98); 587 participants). With high levels of unexplained statistical heterogeneity, we graded this outcome as very low quality. We did not combine data for other outcomes as study results had been reported using differing scales or with a combination of mean and median data, but our interpretation of individual study data favoured ultrasound for a reduction in other minor complications and reduction in onset time of block and number of attempts to perform block.

AUTHORS' CONCLUSIONS

There is evidence that peripheral nerve blocks performed by ultrasound guidance alone, or in combination with PNS, are superior in terms of improved sensory and motor block, reduced need for supplementation and fewer minor complications reported. Using ultrasound alone shortens performance time when compared with nerve stimulation, but when used in combination with PNS it increases performance time.We were unable to determine whether these findings reflect the use of ultrasound in experienced hands and it was beyond the scope of this review to consider the learning curve associated with peripheral nerve blocks by ultrasound technique compared with other methods.