Anesth Analg 2008; 106:1910-1915
© 2008 International Anesthesia Research Society
doi: 10.1213/ane.0b013e318173280f
ANALGESIA
Section Editor:
Terese T. Horlocker
Electrical Nerve Stimulation or Ultrasound Guidance for Lateral Sagittal Infraclavicular Blocks: A Randomized, Controlled, Observer-Blinded, Comparative Study
Axel R. Sauter, MD*,
Michael S. Dodgson, FRCA ,
Audun Stubhaug, DMSc,
Anne Marie Halstensen, CRNA, and
Øivind Klaastad, DMSc
*Faculty of Medicine, University of Oslo and Division of Anaesthesiology and Intensive Care Medicine, Rikshospitalet University Hospital, Oslo, Norway.
Address correspondence and reprint requests to Axel R. Sauter, MD, Department of Anesthesiology, Rikshospitalet, 0027 Oslo, Norway. Address e-mail to sauter{at}start.no.
Abstract
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 µg/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.
The lateral sagittal infraclavicular block (LSIB) was developed by a magnetic resonance imaging (MRI) study.1 It was introduced in 2004 as a nerve stimulator-guided, single-injection technique. Clinical studies involving LSIB have shown satisfactory block efficacy and onset time.2,3 In recent years, ultrasound guidance has frequently been used to perform infraclavicular brachial plexus blocks.4–6 For the LSIB, ultrasound guidance has not been clinically investigated. On the basis of an analysis of MRIs, we suggested an injection site for ultrasound-guided blocks cranioposterior to the axillary artery.7 The aim of our present study was to compare electrical nerve stimulation and ultrasound guidance for LSIB. The main outcome variables were the time until readiness for surgery, discomfort associated with the block procedure, and pain related to tourniquet ischemia on a numeric rating scale (NRS). In addition, we evaluated the feasibility of ultrasound-guided local anesthetic injections cranioposterior to the axillary artery.
METHODS
Having obtained approval of the protocol from the Committee for Medical Research Ethics, Region South, Norway, 80 adult patients scheduled for elective ambulatory surgery of the hand or forearm gave written, informed consent to participate in the study. Patients aged 18–70 yr, with ASA I or II and weight 50–100 kg, normal neurological status and who could cooperate, were included. Two anesthesiologists (A.R.S., Ø.K.), with substantial experience in nerve stimulation and ultrasound-guided techniques, performed the blocks. The study was a randomized, observer-blinded comparison of LSIB with use of electrical nerve stimulation (group NS, n = 40) or ultrasound (group US, n = 40). To secure an equal number of both techniques to the two anesthesiologists, randomization was stratified for anesthesiologist. Block randomization was performed by using a list of random numbers, with varying block sizes of six or eight patients. Sealed envelopes revealing group allocation were opened immediately before the block was performed.
Routine monitoring included electrocardiogram, pulse oximetry and noninvasive arterial blood pressure. Before the block procedure, the patients received oral paracetamol 1.5 g, and IV alfentanil 0.5 mg and midazolam 1 mg. The patients were supine with the arm adducted and the hand on the abdomen. Aseptic preparation included a skin scrub with Chlorhexidine 0.5% and, in group US, the use of sterile transducer covers (D-4570, Swemed Lab, Kungsbacka, Sweden) and sterile ultrasound gel (Aquasonic, Parker Laboratories, Fairfield, NJ). Mepivacaine (15 mg/mL) with epinephrine (2.5 µg/mL) was used for subcutaneous infiltration (1–2 mL) and nerve blocks (0.6 mL/kg). In both groups, an 80 mm, 22-gauge insulated needle with a 15 degrees bevel (Stimuplex® D; B. Braun, Melsungen, Germany) was used. Injection speed was approximately 1 mL/s interrupted by aspiration after each 5 mL.
Nerve Stimulation
We followed our earlier algorithms.1,8 The nerve stimulator (Stimuplex® HNS 12; B. Braun) was connected with the cathode to the insulated needle and with the anode to a solid gel skin electrode 15 cm proximal to the elbow. Motor responses were initially sought with a current of 1.5 mA, and 0.1 ms impulse duration at a frequency of 2 Hz. The point of needle insertion was at the intersection between the clavicle and the coracoid process. The needle was directed strictly in the sagittal plane to a maximum of 6.5 cm, initially caudally at 0 degrees and then posteriorly in steps of 10 degrees until a motor response was obtained. If the first response was from the lateral cord (musculocutaneous or median nerve), the needle was redirected further posteriorly in smaller steps until a distal nerve response (fingers or wrist) from either the posterior or medial cord (radial or ulnar nerve) was elicited. When thresholds for nerve stimulation were between 0.2 and 0.5 mA, the local anesthetic was injected as a single injection.
Ultrasound
A Titan ultrasound unit (SonoSite, Bothell, WA) with a C11, 5–8 MHz, broadband curved array probe (SonoSite) was used. A prescan was performed to adjust the settings of the ultrasound unit and to provide an overview of the infraclavicular anatomy. We recorded if the lateral, medial, or posterior cord could be visualized. The needle was directed in-plane with the ultrasound probe towards the cranioposterior part of the axillary artery. The needle tip was positioned close to the recognizable cords if at least two were identified. If none, or only one of the cords was identified, the needle was placed in 9 o’clock position (in reference to a clock face: 12 o’clock–0 degrees—anterior, 3 o’clock–90 degrees—caudal, 6 o’clock–180 degrees—posterior, 9 o’clock–270 degrees—cranial). The visualized local anesthetic distribution was considered sufficient when it reached all identified cords or surrounded the artery from 3 to 11 o’clock. If spread was estimated as insufficient after injecting approximately one-third of the local anesthetic, additional injections were performed with the remaining dose. All patients, independent of the number of injections, received a total dose of 0.6 mL/kg.
Performance time was measured by stopwatch by the anesthesiologist performing the block from needle insertion until finishing local anesthetic injection. In group US, the prescan time was included in the performance time. The number of needle passes was counted by the same anesthesiologist. An additional needle pass was defined as withdrawal and a subsequent reinsertion of at least 2 cm. A continuous slight suction was applied to the needle by aspirating and subsequently closing the needle set with a 3-way stopcock. Backflow of blood, including just traces of blood, was registered as arterial, venous, or unspecified. For each local anesthetic injection, the needle depth and the needle angle were measured. In group US, the position of the needle tip was additionally recorded in relation to the center of the axillary artery. In both groups, patients were asked to report paresthesia (not synchronous to the 2 Hz impulse).
An observer, blinded for the block technique, assessed the blocks 5, 10, 15, 20, 25, and 30 min after injection was completed. Sensory testing included the axillary, musculocutaneous, radial, median, ulnar, medial antebrachial cutaneous, medial brachial cutaneous, and intercostobrachial nerve. Blocks were assessed by temperature test, using an ice bag, repeatedly touching the skin on predefined marked positions in the sensory area of the nerves. The following scale was used: 0 = normal, 1 = hypalgesia, patient felt coldness but less than on the contralateral side, 2 = analgesia, patient felt touch but not coldness, 3 = anesthesia, no feeling at all. Motor blocks were also examined but are not reported.
A block was defined as successful when all five nerves distal to the elbow (musculocutaneous, radial, median, ulnar, and antebrachial cutaneous nerve) had sensory test scores of 2 or 3. Test scores of 0 or 1 for one or more nerves were recorded as block failure. The time between the end of the injection and development of successful block was defined as onset time. Readiness for surgery was defined as performance time plus onset time. When the last block assessment was completed, the patients were asked about discomfort during the block procedure and the IV cannulation using a NRS (0 = no discomfort, 10 = worst discomfort imaginable). Patients were also asked if the most unpleasant sensation was needle advancement, electrical nerve stimulation, or local anesthetic injection. Need for local anesthetic block supplementation, sedatives/analgesics, or general anesthesia was documented. Adverse events, the surgical procedures, surgery times, and tourniquet times were recorded.
Before leaving the day care unit, the patients were asked if they would choose the same peripheral nerve block again, or choose general anesthesia for later surgical procedures (patient acceptance). At this time, the patients also scored their degree of tourniquet pain, using a NRS-scale (0 = no pain, 10 = worst imaginable pain).
Statistics and Power Analysis
All the statistical analyses were performed using STATA for MAC, version 9.2. Continuous data are presented as mean and standard deviation. Needle positions are additionally presented by range. Student’s t-test was used for continuous data. Categorical and ordinal data were presented as median and range. For comparison of such data, the Mann–Whitney– Wilcoxon test was used; 95% confidence intervals (CI) for percentile difference were calculated by Hodges-Lehman’s method. For differences in proportions, Fisher’s exact test was applied. P values smaller than 0.05 were considered statistically significant.
Predefined main outcome variables were the time until readiness for surgery, quantified discomfort during the block, and pain related to tourniquet ischemia on a NRS 0–10. Pilot results using electrical nerve stimulation gave a mean of 21 min with sd 7 for the time until readiness for surgery. We considered a difference in time until readiness for surgery of 5 min clinically significant. Based on this, it was calculated that a sample size of 37 in each group would have 80% power to detect a difference in means of 5 min assuming a common sd of 7.5 min, using a two-group t-test with  0.05. For NRS-registration of discomfort, we calculated that a sample size of 33 per group would have 80% power to detect a probability of 0.7 that an observation in group 1 is less than an observation in group 2 using Wilcoxon (Mann–Whitney) rank sum test with a 0.05 two-sided significance level (nQuery Advisor, Statistical Solutions, MA). To allow for missing data or dropouts, 40 patients were included in each group.
RESULTS
There was no statistically significant difference between the two groups regarding demographical data, surgery time, or tourniquet time (Table 1). In group NS, the blocks were completed in 39 patients. No satisfactory nerve stimulator response was obtained in the remaining patient. He received an ultrasound-guided block that was successful, and was excluded from further study. In group US, all blocks were completed. During the prescan, the lateral cord was assumed to be identified in 40 (100%), the posterior cord in 38 (97.5%), and the medial cord in 19 (47.5%) patients.
A single local anesthetic injection was used for all patients in group NS. In group US, a single injection was used in 10 (25%), 2 injections in 26 (65%), and 3 injections in 4 (10%) of the patients (P < 0.001). In group US, the median needle position in relation to the axillary artery (with reference to a clock face) was 8 (range, 6–9) for the first, 7 (range, 6–11) for the second, and 9 (range, 7–9) for the third injections. The median number of needle passes was 3 (range, 2–10) in group NS and 1 (range, 1–3) in group US (P < 0.001). The mean needle depths were 5.4 (sd 0.9, range, 3.5–7.5) cm and 5.1 (sd 0.8, range, 3–7) cm (P = 0.13), whereas the needle angles posterior to the frontal plane were 24 (sd 12, range, 0–60) degrees and 27 (sd 16, range, 0–60) degrees (P = 0.44), in group NS and group US, respectively.
Aspiration of blood was noted in 13 (33%) patients (7 times venous, 6 times unspecific) in group NS, but only in 2 (5%) patients (unspecific) in group US (P = 0.001). One patient in group NS (2.5%) and 8 patients in group US (20%) experienced paresthesia (P = 0.029). No hematoma was observed in any group.
Sensory test scores are shown for both groups in Figure 1. Block success, block failures, need for peripheral nerve block supplementation, and general anesthesia are shown in Table 2. In group NS, block failures included one (n = 1), two (n = 2), and four (n = 2) of the nerves. Two patients had peripheral block supplementation at the elbow level of one and two nerves. General anesthesia was given to two patients who had deficient blocks of two and four nerves, respectively. One of the patients with block failure obtained a sufficient block after 45 min latency without supplementation. In group US, the block failures (n = 2) were limited to a single (ulnar) nerve. In both patients all three cords had been identified by ultrasound and two local anesthetic injections had been used. Ulnar nerve supplementations were performed at the elbow level.
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Figure 1. Sensory block assessment 5, 10, 15, 20, 25, and 30 min after local anesthetic injection. The bars represent the frequencies for the sensory test scores: 1 = hypalgesia (light-gray), 2 = analgesia (gray), 3 = anesthesia (dark-gray). Sensory testing included the axillary (ax), musculocutaneous (mc), radial (rad), median (med), ulnar (uln), medial antebrachial cutaneous (mac), medial brachial cutaneous (mbc), and intercostobrachial (icb) nerve.
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Performance time did not show a statistically significant difference (mean difference (MD) = 0.14, 95% CI: –0.45 to 0.73, P = 0.64). However, when prescan time was not included, the performance time was significantly shorter in group US (MD = 0.83, 95% CI: 0.29–1.37, P = 0.003). Also block onset time (MD: 0.02, 95% CI: –2.90 to 2.95, P = 0.99) and readiness for surgery (MD = –0.01, 95% CI: –2.98 to 2.95, P = 0.99) were similar between the groups (Fig. 2).
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Figure 2. The bars represent performance time, onset time, and time until readiness for surgery (means, sd in parentheses). No significant differences were found for these measurements.
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On a NRS-scale from 0 to 10, the median discomfort associated with the block procedure was 1 (range, 0–9) in group NS and 1 (range, 0–5) in group US (CI: –1 to 1, P = 0.92). Median discomfort because of venous cannulation was 0 (range, 0–7) in all patients. The frequency patterns for most unpleasant sensations associated with the block procedure are shown in Figure 3. Median tourniquet pain during surgery was 0.5 (range, 0–8) in group NS and 1 (range, 0–9) in group US (CI: –1 to 0, P = 0.32).
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Figure 3. Patients communicated whether needle advancement, electrical nerve stimulation, or local anesthetic injection was the most unpleasant sensation during block procedure. Twenty-two patients could not indicate which was the most unpleasant sensation.
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One patient in group US developed hypotension after block placement and received IV ephedrine. In group NS one patient became nauseous and was given ondansetron. No other adverse effects were observed.
Seventy-seven patients who underwent surgery with regional anesthesia would choose the same peripheral nerve block again. The two patients who received general anesthesia (group NS) and one patient with uncompleted block (group NS) were not asked this question.
DISCUSSION
In the present study, nerve stimulation or ultrasound guidance was used to perform LSIB. Data from 80 randomized patients showed no statistically significant differences in the time required to perform the block, its onset or the patients’ readiness for surgery. Discomfort related to the block procedure and to tourniquet pain was low and similar. Correspondingly, the patient acceptance of the block was high in both groups.
The success rates for blocks aided by nerve stimulation was 85% in the present study and similar to those published in previous studies on LSIB,2,3 whereas the success rate was 95% in group US. Such a difference might be of clinical importance, but our study was not designed or sized to prove a difference in success rate. A sample size of 320 patients would have been necessary to demonstrate a statistically significant difference of this magnitude.9 In other prospective, randomized studies comparing ultrasound-guided and electrical stimulating techniques, success rates and time consumption were often improved with ultrasound guidance.10–14 In contrast, in a recent study on axillary blocks, Casati et al. concluded that there were no clinically relevant differences between nerve stimulation and ultrasound guidance.15
Aspiration of blood during the block procedure was significantly less frequent when ultrasound was used. Ultrasound visualization of the cephalic vein and the axillary vessels may diminish the incidence of vessel punctures and associated risks such as intravascular injections, local anesthetic intoxication, or hematoma. No such adverse events were found in either of our study groups. Conversely, only one of the patients experienced paresthesia when nerve stimulation was used, whereas eight patients noticed paresthesia under ultrasound guidance.
Ultrasound visualization of an adequate local anesthetic distribution to the nerves often predicts a successful block.16 Therefore, additional injections were used in some of the patients with ultrasound-guided blocks. Corrections of the needle position of only a few millimeters in the needle axis were sufficient to improve local anesthetic distribution by a second injection in most of the cases.
In our previous MRI study, we suggested an injection site for ultrasound-guided blocks close to the axillary artery in the cranioposterior quadrant.7 Injecting at the 8 o’clock position should theoretically give efficient local anesthetic distribution to all three cords. In the present study, the lateral and posterior cords were identified in almost all of the patients. Therefore, the needle was primarily placed in a central position close to the visualized cords, regularly dorsal to the lateral cord. The needle positions were almost exclusively in the cranioposterior quadrant (6–9 o’clock). The satisfactory success rate in group US supports our suggested injection site.
Visualization of the infraclavicular cords may be difficult because of a larger skin to nerve distance than in other parts of the brachial plexus.17 Certainly, discrimination between the lateral, posterior, and medial cord can be challenging. As we did not use nerve stimulation to confirm ultrasound findings, our identification of cords must be taken as a subjective estimation.
Needle depths and needle angles to the frontal plane were similar for nerve stimulation and ultrasound guidance. The needle angles were steeper than those primarily suggested for LSIB.1 Similar steeper angles to the plexus were also found in a prospective multicenter clinical study of LSIB guided by nerve stimulation.3 Compared with the MRI study1 a slightly more medial3 and caudal insertion of the needle is chosen in clinical practice to avoid painful needle contact with the coracoid process or clavicle. This may explain the steeper angles in clinical practice.
In conclusion, in experienced hands, favorable results can be obtained when either nerve stimulation or ultrasound guidance is used for LSIB. When ultrasound guidance is used, local anesthetic injection cranioposterior to the artery can provide sufficient local anesthetic distribution and block effect.
Footnotes
Accepted for publication February 20, 2008.
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- Klaastad O, Smith HJ, Smedby O, Winther-Larssen EH, Brodal P, Breivik H, Fosse ET. A novel infraclavicular brachial plexus block: the lateral and sagittal technique, developed by magnetic resonance imaging studies. Anesth Analg 2004;98:252–6[Abstract/Free Full Text]
- Koscielniak-Nielsen ZJ, Rasmussen H, Hesselbjerg L, Nielsen TP, Gurkan Y. Infraclavicular block causes less discomfort than axillary block in ambulatory patients. Acta Anaesthesiol Scand 2005;49:1030–4[Web of Science][Medline]
- Koscielniak-Nielsen ZJ, Rasmussen H, Hesselbjerg L, Gurkan Y, Belhage B. Clinical evaluation of the lateral sagittal infraclavicular block developed by MRI studies. Reg Anesth Pain Med 2005;30:329–34[Web of Science][Medline]
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- Sauter AR, Smith HJ, Stubhaug A, Dodgson MS, Klaastad O. Use of magnetic resonance imaging to define the anatomical location closest to all three cords of the infraclavicular brachial plexus. Anesth Analg 2006;103:1574–6[Abstract/Free Full Text]
- Klaastad O, Dodgson MS, Stubhaug A, Sauter AR. Lateral sagittal infraclavicular block (LSIB). Reg Anesth Pain Med 2006;31:86; author reply 7
- Altman DG. Practical statistics for medical research. London: Chapman & Hall, 1999:455–60
- Marhofer P, Schrogendorfer K, Koinig H, Kapral S, Weinstabl C, Mayer N. Ultrasonographic guidance improves sensory block and onset time of three-in-one blocks. Anesth Analg 1997; 85:854–7[Abstract]
- Williams SR, Chouinard P, Arcand G, Harris P, Ruel M, Boudreault D, Girard F. Ultrasound guidance speeds execution and improves the quality of supraclavicular block. Anesth Analg 2003;97:1518–23[Abstract/Free Full Text]
- Soeding PE, Sha S, Royse CE, Marks P, Hoy G, Royse AG. A randomized trial of ultrasound-guided brachial plexus anaesthesia in upper limb surgery. Anaesth Intensive Care 2005; 33:719–25[Web of Science][Medline]
- Sites BD, Beach ML, Spence BC, Wiley CW, Shiffrin J, Hartman GS, Gallagher JD. Ultrasound guidance improves the success rate of a perivascular axillary plexus block. Acta Anaesthesiol Scand 2006;50:678–84[Web of Science][Medline]
- Chan VW, Perlas A, McCartney CJ, Brull R, Xu D, Abbas S. Ultrasound guidance improves success rate of axillary brachial plexus block. Can J Anaesth 2007;54:176–82[Web of Science][Medline]
- Casati A, Danelli G, Baciarello M, Corradi M, Leone S, Di Cianni S, Fanelli G. A prospective, randomized comparison between ultrasound and nerve stimulation guidance for multiple injection axillary brachial plexus block. Anesthesiology 2007; 106:992–6[Web of Science][Medline]
- Gray AT. Ultrasound-guided regional anesthesia: current state of the art. Anesthesiology 2006;104:368–73[Web of Science][Medline]
- Perlas A, Chan VW, Simons M. Brachial plexus examination and localization using ultrasound and electrical stimulation: a volunteer study. Anesthesiology 2003;99:429–35[Web of Science][Medline]
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