Title

That which we call a rose by any other name would smell as sweet - and its thorns would hurt as much

Authors

Boezaart AP

Journal

Regional Anesthesia and Pain Medicine 2009 Jan-Feb; 34(1): 3-7.

Study Summary

Study design

Editorial

Comments on the study

• This is an extremely informative editorial that should be read in conjunction with the case reports by Mariano1 and Antonakakis2 in the same journal on the posterior interscalene block.
• Dr Borgeat highlights the similarity of this US-guided posterior interscalene block to the cervical paravertebral block3. He also puts forward the tantalizing prospect that targeting the posterior aspect of the nerve root may be able to result in preferential blockade of pain / sensation versus motor function.
• The second half of his article provides an informative discussion of the anatomical and functional difference between root, plexus and peripheral nerve and the implications for regional anesthesia. It is recommended reading for all regional practitioners seeking to refine or improve their technique.

References

• Mariano ER, Loland VJ, Ilfeld BM. Interscalene perineural catheter placement using an ultrasound-guided posterior approach. Reg Anesth Pain Med 2009;34:60-63.
• Antonakakis JG, Sites BD, Shiffrin J. Ultrasound-guided posterior approach for the placement of a continuous interscalene catheter. Reg Anesth Pain Med 2009;34:64-68.
• Boezaart AP, Koorn R, Rosenquist RW. Paravertebral approach to the brachial plexus: an anatomic improvement in technique. Reg Anesth Pain Med 2003;28:241-244.

Title

Ultrasound-guided paravertebral puncture and placement of catheters in human cadavers: an imaging study

Authors

Luyet C, Eichenberger U, Greif R, et al.

Journal

British Journal of Anaesthesia 2009 Apr;102(4):534-9. (Advance Access)

Study Summary

Study design

Observational, descriptive study in cadavers

Patient population

10 embalmed adult cadavers; bilateral punctures performed (total 20 cases)

Intervention

• The pleura and the superior costotransverse ligament, representing the anterior and posterior boundaries of the paravertebral space respectively, were visualized with a curved array 2-5MHz transducer
• An 18 G Tuohy needle was inserted in-plane with the transducer in a lateral-to-medial direction into the paravertebral space and the space was dilated with 15mL of normal saline
• A catheter was introduced 5cm beyond the needle tip and 10mL of contrast dye was injected
• A CT scan was performed to assess the spread of contrast

Comparator(s)

None

Main findings

• The thoracic paravertebral space, and subsequent needle insertion into the space, was easily visualized using the approach described
• The authors found it difficult to insert a catheter in the majority of patients. The distribution of contrast was mainly epidural in 6/20 cases, and in the posterior mediastinum in 2/20 cases

Comments on the study

• This is an important paper for practitioners of thoracic paravertebral block. It describes a simple approach to ultrasonographic visualization and guided needle puncture of the thoracic paravertebral space.
• It should be noted though that they found it difficult to advance a catheter into the space; the reason for this difficulty is not clear. The precise location of the catheter tip was not evident from the CT scan and the authors did not attempt to determine this by subsequent dissection.
• Contrast injection suggests that there is a high probability of migration of the catheter tip out of the paravertebral space.
• We therefore concur with the authors' opinion that their described technique is best suited at present to a single-shot thoracic paravertebral block. Clinical studies confirming its feasibility and utility in patients are eagerly awaited. However, the optimal technique for insertion of paravertebral catheters, as well as their risk-benefit ratio, remains to be determined.

Title

Ultrasound-guided anterior approach to sciatic nerve block: a comparison with the posterior approach

Authors

Ota J, Sakura S, Hara K, Saito Y et al.

Journal

Anesthesia and Analgesia 2009 Feb; 108(2): 660-665.

Study Summary

Study design

Randomized controlled clinical study

Patient population

• 100 adult patients undergoing minor knee surgery
• Patients received a femoral + lateral femoral cutaneous nerve block, + sciatic nerve block, and sedation during surgery

Intervention

• Ultrasound-guided anterior sciatic nerve block
• Curved array 2-5MHz transducer
• In-plane approach with a 100mm 21G block needle
• End-point for needle insertion was proximity to the nerve as visualized on ultrasound, and a minimum threshold current for motor response of 0.7mA or less
• End-point for injection was circumferential spread of local anesthetic solution: 20mL of 1.5% mepivacaine with 1:400,000 epinephrine

Comparator(s)

• Ultrasound-guided posterior subgluteal sciatic nerve block
• Curved array 2-5MHz transducer
• In-plane approach with a 100mm 21G block needle
• Endpoints for needle insertion and injection as above

Main findings

• The sciatic nerve could not be identified in 5 patients (2 anterior, 3 posterior approach)
• Recognition time and block execution time were similar for both techniques (31-36 seconds and 5-6 min respectively)
• The average depth of the nerve was 5.9cm and 3.4cm for the anterior and posterior approach respectively
• Incidence of complete sensory block was similar at 30 minutes between the 2 groups, except in the distribution of the posterior femoral cutaneous nerve (68.1% vs 14.9% in posterior and anterior groups respectively)
• Of note, the incidence of complete sensory block of the tibial nerve at 30 minutes was only 51.1% in both groups
• Onset and duration of block was similar between groups

Comments on the study

• This study nicely illustrates the ultrasonographic anatomy of the anterior and posterior subgluteal approaches to the sciatic nerve.
• It should be noted that this study was performed in Asian patients with an average BMI of 23 kg/m2. Our experience with patients with BMI >30 kg/m2 is that identification of the sciatic nerve in the posterior gluteal region can be difficult. The depth to the nerve is also greater in these patients.
• An out-of-plane approach to the nerve may be preferable in patients with deeper and less-easily visualized nerves. Needle visibility is difficult at steep angles and increased depth. In addition, the sciatic nerve is anisotropic; the manipulation of the transducer required to maintain needle-beam alignment in the in-plane approach can result in decreased visibility of the target nerve.
• The low rate of complete sensory block of the tibial nerve at 30 minutes is disconcerting. One explanation may be the use of only 20 ml of local anesthetic. Further studies are needed to determine the minimum effective volume for ultrasound-guided sciatic nerve blockade.
• We agree that the ultrasound-guided anterior sciatic approach is feasible and useful, especially if turning the patient into the lateral position is to be avoided. However the authors' finding that the posterior femoral cutaneous nerve is usually missed in this approach indicates that this is not a useful block for operations above the knee.

Title

Ultrasound-guided anterior approach to sciatic nerve block: a comparison with the posterior approach

Authors

van Geffen GJ, van den Broek E, Braak GJJ et al.

Journal

Anaesthesia and Intensive Care 2009 Jan; 37(1): 32-37.

Study Summary

Study design

Randomized controlled clinical study

Patient population

• 40 adult patients undergoing foot or ankle surgery under regional anesthesia
• Patients received only a popliteal fossa sciatic nerve block

Intervention

• Ultrasound (US)-guided popliteal fossa sciatic nerve block in Sims' position
• Linear array 7-13 MHz transducer
• Out-of-plane approach with a 50mm 22G block needle
• Neurostimulation was not used
• End-point for injection was circumferential spread of local anesthetic solution: up to 40mL of 1.5% lidocaine with 1:200,000 epinephrine no minimum volume specified)

Comparator(s)

• Neurostimulation (NS)-guided posterior popliteal fossa sciatic nerve block in Sims' position
• 50mm 22 g block needle inserted 8-10cm above the popliteal skin crease at midpoint between tendons of biceps femoris and semitendinosus muscle
• Endpoints for needle insertion was a minimum current threshold of 0.2-0.5mA that elicited plantar or dorsiflexion of foot / toes
• 25-40mL of 1.5% lidocaine with 1:200,000 epinephrine (actual volume left to anesthesiologist's discretion)

Main findings

• The block success rate (defined as no need for intraoperative supplementation or conversion to general or spinal anesthesia) was 100% in the US-guided group and 75% in the NS-guided group
• Of the NS-guided group, the nerve could not be located in 2 patients and the block was not performed. Success rate in the patients who did receive a block was 83%
• The median local anesthetic volume used was 17 vs 37 mL in the US-guided and NS-guided groups respectively
• Block performance time, onset and duration were similar between the two groups
• Significantly fewer needle insertion attempts were required in the US-guided group

Comments on the study

• This well-designed randomized controlled trial adds to the growing literature that suggests the minimum effective local anesthetic volume is reduced when US-guidance is used instead of NS-guidance. Both block onset and duration were similar despite a twofold difference in the volume of local anesthetic used.
• One of the strengths of this study is the lack of operator bias, as the NS-guided blocks were performed only by experienced anesthesiologists who had never used the US-guided approach.
• In this study the success rate was also significantly higher in the US-guided approach to the sciatic nerve in the popliteal fossa; however as the authors acknowledge, the study was not powered to detect this outcome and the difference may not have been apparent in a larger study.
• Although block performance time was similar between groups, significantly fewer needle insertion attempts were required in the US-guided group. This resulted in lower block-associated pain scores (2.5 vs 4), although the difference was not statistically significant. These findings are in keeping with other comparative trials of US-guidance versus NS-guidance.

Title

Ultrasound guidance compared with electrical neurostimulation for peripheral nerve block: a systematic review and meta-analysis of randomized controlled trials

Authors

Abrahams MS, Aziz MF, Fu RF, Horn JL

Journal

British Journal of Anaesthesia 2009 Apr; 102(3): 408-17.

Study Summary

Study design

Systematic review of the literature

Patient population

Randomized controlled trials comparing ultrasound-guided and neurostimulation-guided peripheral nerve blocks.

Intervention

Ultrasound-guided peripheral nerve block (US-PNB)

Comparator(s)

Neurostimulation-guided peripheral nerve block (NS-PNB)

Main findings

• They identified 13 studies involving 946 patients that met the inclusion criteria
• The relative risk of block failure in US-PNB was 0.41 (95% CI 0.26-0.66, 9 studies)
• The relative risk for complete sensory block in all nerve territories covered by US-PNB was 1.23 (95%CI 1.07-1.41,5 studies)
• Block performance time was 1 minute shorter (95% CI 0.4-1.7, 7 studies) in US-PNB
• Onset time was 29% faster (95% CI 12-45%, 8 studies) in US-PNB
• Duration was 25% longer (95% CI 12-38%, 5 studies) in US-PNB
• The relative risk for vascular puncture in US-PNB was 0.16 (95% 0.05-0.47, 4 studies)
• No other significant differences were observed

Comments on the study

• This is one of the earliest systematic reviews / meta-analyses examining the question of whether ultrasound-guided peripheral nerve blockade is superior to neurostimulation-guided techniques. As such it is an important paper to be aware of when following the literature on ultrasound-guided regional anesthesia.
• Nevertheless, although the results of the meta-analyses suggest benefit of ultrasound-guidance with respect to block success, onset, duration and the risk of vascular puncture, it is important to bear in mind that there are methodological limitations. Firstly, only a small number of studies were included, especially for the individual outcomes that were considered. Secondly, there was significant clinical heterogeneity amongst the studies included (children vs adults, anatomical site of block, type and volume of local anesthetic used, neurostimulation technique, etc) and this limits the extent to which the findings can be generalized.
• Further randomized controlled trials are still needed to establish the efficacy and safety of ultrasound-guidance compared to neurostimulation in peripheral nerve blockade. Future systematic reviews and meta-analyses should also seek to subgroup outcomes by the anatomical area / nerve being blocked.

Title

Current threshold for nerve stimulation depends on electrical impedance of the tissue: a study of ultrasound-guided electrical nerve stimulation of the median nerve

Authors

Sauter AR, Dodgson MS, Kalvey H et al.

Journal

Anesthesia and Analgesia 2009 Apr; 108(4): 1338-43.

Study Summary

Study design

Prospective volunteer study

Patient population

29 healthy adult volunteers

Intervention

• Insertion of a 25G insulated needle, primed with normal saline, to a distance of 0, 2.5, and 5 mm from the median nerve in the axilla and at the elbow
• Impedance was measured using specialized equipment
• The minimum current threshold to produce a motor response was sought

Comparator(s)

None

Main findings

• A significant inverse relationship between impedance and current threshold was found for the median nerve at the elbow when the needle was 2.5 or 5 mm from the nerve
• This was not seen in the axilla, nor with the needle in contact with the epineurium of the nerve (0mm distance)
• Impedance was lower when the needle tip was in muscle, compared to fat / connective tissue
• Failure to obtain a motor response was frequently observed despite a current of 5 mA and impulse duration of 0.1 msec when the needle was 2.5-5mm away from the nerve. This was improved by use of 0.3 msec impulse duration

Comments on the study

• This is an important study to be aware of when using a combined ultrasound and neurostimulation-guided peripheral block technique.
• It offers one possible explanation for why motor response may not be seen despite needle-nerve contact visualized on ultrasound. One area where we have frequently observed this is in the subgluteal sciatic region. Here the nerve is surrounded by muscle, which tends to have lower impedance according to this study, and hence may have a higher current threshold.
• The findings validate our current practice of using neurostimulation only to confirm the identity of a motor nerve. We do not seek a minimum current threshold as the endpoint for needle insertion, but rather look for needle-nerve contact.
• The results of this study also suggest that if a motor response is not obtained at high currents, one should try increasing the impulse duration from 0.1 to 0.3 msec. The authors reported a mean ratio of 1.82 for current thresholds obtained using 0.1 vs 0.3 msec impulse duration.

Title

Preliminary results of the Australasian Regional Anaesthesia Collaboration: A prospective audit of more than 7000 peripheral nerve and plexus blocks for neurologic and other complications

Authors

Barrington MJ, Watts, SA, Gledhill SR, et al.

Journal

Regional Anesthesia and Pain Medicine 2009; 34: 534-541.

Study Summary

This article describes the structure, and results of a large, web-based, prospective database designed to capture quality and safety data on peripheral nerve blockade (PNB). It also contains details on the clinical pathway used for followup and assessment of suspected neurologic injury. A structured form was provided on the website for data entry and capture, as well as recommended pathways for patient followup, and assessment in the case of suspected complications. The database is maintained by the Australasian Regional Anaesthesia Collaboration and can be accessed at www.regional.anaesthesia.org.au.

Between January 2006 and January 2007, data was collected from 2 hospitals; from January 2007 onwards, a web-based database was established that allowed collection of data from an additional 7 hospitals. Of 6950 patients entered into the database, 6069 were successfully followed up. These 6069 patients received a total of 7156 blocks. Thirty patient (0.5%) had clinical features prompting assessment for neurologic injury. Three of these met the criteria for PNB-related injury, giving an incidence of 0.04% for nerve injury due to PNB. Local anesthetic toxicity occurred in 8 patients; in 4 of these patients, ultrasound was used, and all patients received axillary block. The results are consistent with previous reports of the incidence of complications following PNB. Given that these complications are rare, a database such as this is a valuable resource. We look forward to further reporting of results from the ARAC, and we encourage all block practitioners to participate in the project.

Title

Extraneural versus intraneural stimulation thresholds during ultrasound-guided supraclavicular block

Authors

Bigeleisen PE, Moayeri N, Groen GJ

Journal

Anesthesiology 2009;110:1235-43.

Study Summary

This study highlights the fact that intraneural needle placement cannot be excluded by a minimum current threshold during neurostimulation. On the other hand, a minimum current threshold of 0.2mA or less strongly suggests that the needle tip may be intraneural. Further work is needed to determine if this is applicable to all peripheral nerves or only to the supraclavicular brachial plexus. There appears to be no single wholly reliable indicator of intraneural needle placement. Instead, practitioners should look at a combination of factors including paresthesia or pain, reistance to local anesthetic injection, nerve distension on ultrasound, and the minimum threshold current for neurostimulation.

Title

A comparison of a single or triple injection technique for ultrasound-guided infraclavicular block: a prospective randomized controlled study

Authors

Desgagnes MC et al.

Journal

Anesthesia and Analgesia 2009; 109: 668-72.

Study Summary

The authors enrolled 100 patients undergoing surgery of the distal upper arm under regional anesthesia alone. Blocks were performed under ultrasound-guidance without neurostimulation, using a 20G Tuohy needle and a 5-12 MHz linear high-frequency ultrasound probe. The needle was inserted in-plane in a cephalad to caudad direction, and patients were randomized to one of two groups. In group S, the needle was positioned at the posterior aspect of the axillary artery (with elicitation of a fascial click) and 30 mls of 1.5% mepivacaine was injected in a single bolus. In group T, 10 mls of 1.5% mepivacaine was injected at each of three locations: lateral, posterior and medial aspects of the axillary artery. Patients were subsequently assessed at 5 minute intervals for complete loss of cold sensation in the ulnar, median, radial and musculocutaneous dermatomes.

The primary outcome was complete loss of cold sensation in all 4 dermatomes at 15 minutes post-block. The incidence of this was similar between groups S and T (84% vs 78%), and remained similar up to 30 minutes post block. Block performance time was shorter in group S, and this difference was statistically but not clinically significant (2 vs 3 minutes). There were no other significant differences between the two groups.

It is important to note though, that because the block success rate at 15 minutes was higher than that assumed in their power analysis, the study is actually underpowered to detect any difference in the primary outcome between the two techniques. Detection of a 15% difference, given the observed success rate of 78% in group T, would require at least 150 patients per group.

Notwithstanding this, the findings are consistent with our clinical observation that U-shaped local anesthetic spread posterior to the axillary artery is an appropriate endpoint for an ultrasound-guided infraclavicular block is; visualization and targeting of individual cords is not necessary for block success. The study further suggests that there is no benefit with regards to rapidity of onset, and that the single-injection technique is easier to perform (as reflected by the shorter block performance time). At this time therefore, we support the authors' conclusion that the single-injection technique described is the preferred approach to ultrasound-guided infraclavicular block.

Title

Analgesic effectiveness of ropivacaine 0.2% vs 0.4% via an ultrasound-guided C5-6 root/superior trunk perineural ambulatory catheter

Authors

Frederickson MJ, Price DJ

Journal

British Journal of Anaesthesia 2009; 103: 434-9.

Study Summary

The study looked at 65 adult patients undergoing total shoulder replacement or rotator cuff repair (arthroscopic or open). One of two experienced operators placed a perineural catheter under ultrasound guidance next to the C5-6 nerve roots in the interscalene region. An initial bolus of 30ml of 0.5% ropivacaine was administered preoperatively, and the patients subsequently also received a general anesthetic. Postoperatively, the patients were started on a continuous perineural infusion of ropivacaine at 2ml/h with patient-controlled boluses of 5ml. They were randomized to receive either a 0.2% or 0.4% concentration of ropivacaine. All patients also received round-the clock acetaminophen and diclofenac.

There was no difference between the groups for all indices of postoperative analgesia (pain scores at rest and movement on postoperative days 1 and 2, supplemental opioid, ropivacaine boluses, night awakenings). There were, however, significantly fewer episodes of an insensate arm (0 vs 5) in the 0.2% ropivacaine group, as well as greater patient satisfaction (95% CI 8.6-9.6 vs 6.8-8.7).

The specifics of the technique used in this study should be noted when attempting to generalize the results to one's clinical practice. In particular, experienced operators performed all the blocks, and the catheter tip was placed adjacent to the C5-6 nerve roots using ultrasound-guidance. This may account for the effectiveness of an infusion at only 2 ml/h.

Other studies of varying local anaesthetic concentration in continuous interscalene (1) and infraclavicular block (2) have also found that 0.2% ropivacaine solution at 8ml/h provides better postoperative analgesia than 0.4% ropivacaine at 4ml/h. As the authors of this paper point out, these findings indicate that volume, rather than concentration, may be the important factor in determining analgesic efficacy of continuous peripheral nerve blockade of the upper limb.

References

• Le LT et al. Effects of local anesthetic concentration and dose on continous interscalene nerve blocks: a dual-center, randomized, observed-masked, controlled study. Reg Anesth Pain Med 2008;33:518-25.
• Ilfeld BM et al. The effects of local anesthetic concentration and dose on continuous infraclavicular nerve blocks: a multicenter, randomized, observer-masked, controlled study. Anesth Analg 2009;108:345-50.

Title

A prospective randomized comparison of ultrasound and neurostimulation as needle end points for interscalene catheter placement

Authors

Frederickson MJ, Ball CM, Dalgleish AJ et al.

Journal

Anesthesia and Analgesia 2009; 108: 1695-700.

Study Summary

The study enrolled 81 patients undergoing shoulder surgery with a interscalene nerve block catheter placed for postoperative analgesia. Patients were randomized to one of two groups: 1) appropriate needle tip position confirmed by ultrasonographic visualization, or 2) by an appropriate motor response to neurostimulation. All the blocks were performed by a single experienced operator, who set himself a maximum time limit of 5 minutes for obtaining either a satisfactory ultrasound image or appropriate motor response upon needle insertion. The catheter itself was advanced blindly 2-3 cm beyond the needle tip and 30 mls of 0.5% ropivacaine was delivered through the catheter. All patients received a general anesthetic in addition to the block.

The US-guided technique was associated with statistically significant (but clinically insignificant) decreases in needle-under-skin time (30 seconds) and block associated pain scores. Measures of postoperative analgesic quality were equivalent between groups. Three patients in the US-guided group and 6 patients in the NS-guided group had transient neurological symptoms (overall incidence 11%).

This study demonstrates that both techniques are equally effective in experienced hands. It should be noted that the operator failed to obtain an adequate ultrasound image within the stipulated time limit in one patient, who subsequently had a successful neurostimulation-guided block. Ultrasound is clearly not infallible, and operator experience and expertise are definitely factors that affect the success of the techqniue. We agree with the authors when they recommend that neurostimulation should always be available for use if necessary. At the same time, there are multiple studies indicating that the sensitivity and specificity neurostimulation is also not ideal. In our practice, we commonly combine both ultrasound and neurostimulation as endpoints for needle placement; we view both techniques as complementary and not mutually exclusive.

Title

Ultrasound or nerve stimulation-guided wrist blocks for carpal tunnel release: a randomized prospective comparative study

Authors

Macaire P et al.

Journal

Regional Anesthesia and Pain Medicine2008;33: 363-8.

Study Summary

This article nicely illustrates the utility of ultrasound-guidance in performing forearm blocks of the median and ulnar nerve. The authors studied 60 adult patients undergoing carpal tunnel surgery and randomized them to either ultrasound-guided or neurostimulation-guided median and ulnar nerve blocks in the forearm. The endpoint of the ultrasound-guided technique was adequate local anesthetic spread, and the endpoint of the neurostimulation technique was motor or sensory response to a minimum current threshold of 0.5mA. The authors looked at individual as well as total block performance time, which included scanning and injection time.

The nerves were located very quickly; scanning time for nerve location took an average of 12 seconds (10-20 seconds). Block performance time was shorter in the ultrasound-guided group for the median nerve (55 vs. 100 sec) and the ulnar nerve (58 vs. 80 sec). Interestingly, onset time was longer in the ultrasound-guided group (370vs 254 sec for median nerve, 367 vs. 241sec for ulnar nerve). The authors observed a high incidence of intraneural injection (evidenced by nerve expansion on ultrasound) in the neurostimulation group and postulated that this might account for the faster onset. This is in keeping with other reports by Bigeleisen and Rodriguez, which suggest that rapid onset may be a consequence of intraneural injection.

Given that the difference in onset was not clinically significant, and the success rates were equivalent, ultrasound-guidance appears to be preferable, especially if intraneural injection is to be avoided.

References

• Bigeleisen, P. E. (2006). "Nerve puncture and apparent intraneural injection during ultrasound-guided axillary block does not invariably result in neurologic injury." Anesthesiology 105(4): 779-83.
• Rodriguez J, Taboada M, Blanco M, Oliveira J, Barcena M, Alvarez J. Intraneural catheterization of the sciatic nerve in humans: a pilot study. Reg Anesth Pain Med. 2008 Jul-Aug;33(4):285-90.

Title

Electrical stimulation versus ultrasound guidance for popliteal-sciatic perineural catheter insertion: a randomized controlled trial

Authors

Mariano ER et al.

Journal

Regional Anesthesia and Pain Medicine 2009; 34: 480-5.

Study Summary

40 patients undergoing foot and ankle surgery were randomized to undergo insertion of a popliteal perineural catheter by one of two methods: ultrasound guided (USG) or neurostimulation guided (NSG).

In the NSG group, the needle was inserted in the long axis of the nerve with the patient prone. The endpoint for needle insertion was plantarflexion of the foot or toes at a current threshold of 0.3-0.6mA. The catheter was then inserted 5 cm beyond the tip; the endpoint for successful catheter insertion was plantarflexion of the foot or toes at a current threshold of 0.8 mA or less. Following insertion, a bolus of 40 ml of 1.5% mepivacaine with epinephrine was injected through the catheter.

In the USG group, the sciatic nerve was identified in a short-axis view in the mid-thigh region, and the needle was inserted in-plane with the US beam in the short axis of the nerve. A bolus of 40 ml of 1.5% mepivacaine with epinephrine was injected through the needle to achieve circumferential spread around the nerve. The catheter was then threaded 5cm beyond the tip of the needle and the needle was withdrawn.

The primary outcome, for which the study was powered, was the time required for catheter placement; this was defined as the time the patient was first touched, to the time that the needle was removed after catheter placement. Placement failure was defined as failure to obtain a motor evoked response with the needle or to identify the sciatic nerve within 15 minutes, and failure to place the catheter per protocol within 30 minutes. Secondary outcomes included procedure-related pain scores, and pain scores on the first postoperative day (POD).

4 out of 20 patients in the NSG group failed to have a catheter successfully placed - 3 of these because an appropriate motor response could not be obtained with the needle within 15 minutes, and 1 because an appropriate motor response could not be obtained with the catheter within 30 minutes. Time to placement of the catheter was significantly shorter in the USG group (median 5 min versus 10 min, P = 00.034), and there was less procedure-related pain (0 vs 2, P = 0.005, on a 0-10 scale). All but one of the catheters were placed by trainee anesthesiologists (residents or fellows).

There was no significant difference observed in pain scores on the first POD, but again as the authors point out, the study was not powered to detect a difference. In fact there is a trend to higher pain scores in the USG group. An unanswered question with perineural catheters is: does catheter tip position influence the quality of postoperative analgesia? The authors mention that catheter tip position in the USG was checked by injecting 1 ml of air and withdrawing the catheter as necessary, however no further details are given. It is possible that the stringent current threshold endpoint required in the NSG group may have resulted in the catheter tip being positioned closer to the nerve, which in turn may explain the trend observed.

In conclusion, the longer block performance time and the 20% failure rate in the NSG group observed in this study are consistent with our belief that USG does facilitate perineural catheter insertion, especially for novice practitioners. Larger studies looking specifically at efficacy and safety outcomes are warranted to establish if one technique is clearly superior over the other.

Title

A prospective, randomized comparison between ultrasound-guided supraclavicular, infraclavicular, and axillary brachial plexus blocks

Authors

Tran DQH, Russo G, Munoz L et al.

Journal

Regional Anesthesia and Pain Medicine 2009; 34: 366-71.

Study Summary

This study shows that the time to readiness for surgery (or anesthesia-related time) was similar for three commonly-used, ultrasound (US)-guided, approaches to the brachial plexus: the supraclavicular (SCB), infraclavicular (ICB), and axillary (AXB) blocks. Success rates were also equivalent between the three groups. The fact that over 80% of the blocks were done by inexperienced operators increases the generalizability of the results.

Methods

120 patients were recruited and randomized to one of 3 groups, to receive either an US-guided supraclavicular (SCB), infraclavicular (ICB), or axillary (AXB) block. A multi-frequency (5-10 MHz) linear probe and portable ultrasound unit with compound imaging capability (Sonosite Micromaxx) were used for all blocks. A 17G Tuohy needle was used for all blocks, and a perineural catheter was inserted after injection of 35 mL of lidocaine 1.5%; however the effectiveness of the catheter was not examined in this study. In the SCB approach, local anesthetic (LA) injection was performed at the junction of the first rib and axillary artery. In the ICB approach, LA injection was performed posterior to the axillary artery. In the AXB approach, LA was injected separately around the musculocutaneous nerve, and then in a perivascular distribution around the axillary artery.

Results

Anesthesia-related time (block performance time + onset time of surgical anesthesia) was the primary outcome. There was no difference between groups (SCB 23.1 ± 8.6 min, ICB 23.9 ± 9.2 min, AXB 25.5 ± 7.7 min). The AXB was associated with a (statistically) significantly longer needling and performance time, but this difference was not clinically significant (needling time: SCB 294 ± 114 sec, ICB 331 ± 251 sec, AXB 442 ± 131 sec; performance time: SCB 6.0 ± 2.1 min, 6.2 ± 4.5 min, AXB 8.5 ± 2.3 min). Block success was defined in terms of a composite score of sensory and motor blockade at 30 minutes, and required at least 14 out of a possible 16 points. There was no significant difference between groups (SCB 92.5%, ICB 92.5%, AXB 90.0%). Block-related pain scores, the incidence of vascular puncture and paresthesia were similar between groups; however significantly more patients receiving a SCB developed a Horner's syndrome (SCB 37.5%, ICB 5%, AXB 0%).

Comments

This is a useful study because it involved multiple operators, the majority of whom were inexperienced (defined as less than 60 blocks performed), and also because it utilized relatively simple US-guided techniques with easily reproducible endpoints. The similar success rates suggests that any of these three techniques are a suitable choice for anesthesia of the distal upper limb; although it should be noted that the study was not powered to detect a difference in this outcome. The AXB was associated with more needle passes, and a longer needling and performance time; this is not unexpected given the technique itself. What is notable is that it did not significantly prolong the time to readiness for surgery, nor did it increase the block-associated pain scores.

In our opinion, the main considerations for choosing one of these blocks over the other two relates to other factors that may hinder ease of block performance, and the adverse effects that may accompany the block. It can be difficult to visualize the brachial plexus in the SCB approach in individuals who have short necks, pronounced concavity of the supraclavicular fossa, or both. The ICB approach is relatively difficult in individuals with a thick chest wall (although the use of a curved low-frequency probe may help). In these instances, the AXB approach may be the best choice. The AXB is also the best choice if the risks of phrenic nerve palsy and Horner's syndrome are to be avoided. It is possible that the ICB and SCB approaches may provide better anaesthesia for surgery on the elbow, compared to the AXB, although this has not been formally studied.

Title

A comparison of ultrasound-guided supraclavicular and infraclavicular blocks for upper extremity surgery

Authors

Koscielnak-Nielsen ZJ, Frederiksen BS, Rasmussen H, Hesselbjerg L.

Journal

Acta Anaesthesiologica Scandinavica 2009; 53: 620-626.

Study Summary

This article attempts to answer the important question of which ultrasound (US)-guided block to choose for surgery of the elbow / forearm / hand by comparing two popular techniques: supraclavicular (SCB) versus infraclavicular block (ICB). The strengths of this study include diversity of operator experience (residents as well as staff anesthesiologists), and a detailed assessment of both efficacy and adverse outcomes. It is important to interpret the results (better success and faster onset of sensory block with ICB) in the context of the details of the block techniques used. It is possible that the efficacy of the SCB may have been different if a variant of the technique (e.g. the "corner pocket" technique) had been used.

Methods

The authors recruited 120 patients having surgery of the elbow /forearm/hand and randomized them to receive either an US-guided supraclavicular (SCB) or infraclavicular block (ICB). A 0.5ml/kg volume of a local anesthetic (LA) mixture of 50:50 ropivacaine 0.75% and mepivacaine 2% was injected in all patients.

The supraclavicular block was performed as follows: coronal oblique probe orientation, in-plane needle advancement, and injection of the first half of the LA mixture superficial to the plexus, and the remainder injected so as to achieve circumferential spread around visible nerves.

The infraclavicular block was performed as follows: parasagittal probe orientation, in-plane needle advancement, and injection of the first half of the LA mixture posterior to the axillary artery, and the remainder injected to achieve a U-shaped LA spread. The nerves themselves were not specifically targeted.

Surgical readiness or block success was defined as analgesia or anesthesia to pinch in all 5 nerves distal to the elbow (median, ulnar, radial, musculocutaneous, medial brachial cutaneous nerves).

Results

ICB resulted in significantly greater block success (93% vs 78%, p = 0.017). There was also a statistically significant difference in block onset time (ICB 19.0 min vs SCB 22.7 min, p = 0.003) although this is not clinically significant. Block performance times were similar (ICB 5.0 min vs SCB 5.7 min).

There were more adverse effects in the SCB group: paraesthesiae/pain on injection (37% vs 13%, p = 0.003), Horner's syndrome (29% vs 0%, p less than 0.0001), suspected diaphragmatic palsy (12% vs 0%, p less than 0.0001).

Comments

The authors are to be commended for producing a study that involved operators with a range of experience, including supervised residents (although it would have been helpful to know the number and distribution of operators involved). This makes the results more applicable to a non-expert practitioner trying to decide between one block or another.

However the relatively low success rates observed with the supraclavicular block are not congruent with results reported in other studies (1,2,3). Reasons for this include operator bias in favor of the ICB (this was discussed by the authors), and the fact that the technique used here may not have been the optimal one. Our experience indicates that it can be difficult to visualize the inferior trunk of the brachial plexus in the supraclavicular approach, and this leads to the ulnar nerve being missed in a disproportionate number of patients, as it was in this study. Our solution to this is to perform a "corner pocket" technique, in which the majority of the local anesthetic solution is injected deep to the plexus at the "corner" between the subclavian artery and the first rib (3). We postulate that this may produce better block success than the technique described in this study, in which the initial injection was performed superficial to the plexus. This has also been observed by other authors (4), and may explain why a similar study comparing US-guided SCB, ICB and axillary block failed to show any significant difference in block success (5).

The higher incidence of adverse outcomes is worthy of note, and of further study in a large number of patients. Given the high incidence of block success that is achievable with most US-guided approaches, the risk of adverse effects may prove to be the deciding factor in choosing which block to perform.

References

• Perlas A, Lobo G, Lo N et al. Ultrasound-guided supraclavicular block - outcome of 510 consecutive cases. Reg Anesth Pain Med 2009;34:171-176.
• Arcand G, Williams SR, Chouinard P, et al. Ultrasound-guided infraclavicular versus supraclavicular block. Anesth Analg 2005;101:886-90.
• Soares LG, Brull R, Lai J, Chan VW. Eight ball, corner pocket: the optimal needle position for ultrasound-guided supraclavicular block. Reg Anesth Pain Med 2007;32:94-5.
• Tran de QH, Munoz L, Russo G, Finlayson RJ. A trick shot to the corner pocket. Reg Anesth Pain Med 2008; 33: 503-4.
• Tran de QH, Russo G, Munoz L, Zaouter C, Finlayson RJ. A prospective, randomized comparison between ultrasound-guided supraclavicular, infraclavicular, and axillary brachial plexus blocks. Reg Anesth Pain Med 2009; 34: 366-71.