Ultrasound (US) guidance for nerve localization during peripheral nerve blockade has gained considerable popularity worldwide. Much of this popularity is attributable to several important advantages of real-time sonographic visualization compared with traditional nerve localization techniques. The benefits largely apply to procedural and technical block-related outcomes and stem from comparative studies focusing primarily on the impact of US guidance on “block success” in the immediate operative setting.1,2 Although peripheral nerve blocks are often inserted for the purposes of postoperative analgesia and not necessarily surgical anesthesia, acute pain–related outcomes are featured far less prominently in the regional anesthesia and pain literature. The use of nerve blocks specifically for the treatment of acute pain is intrinsic to the practice of regional anesthesia and increasingly emphasized in subspecialty training.3,4 The importance of interventional acute pain management is underscored by the popularity of perineural catheters, which have become the cornerstone of inpatient, and even outpatient, surgical and nonsurgical multimodal analgesic protocols in many leading centers. The goal of this review was to evaluate the effect of US guidance compared with traditional nerve localization techniques for interventional management of acute pain and acute pain–related outcomes. Additionally, emerging trends and novel applications of US guidance for acute pain management are discussed.
The authors (SC and RB) systematically searched the electronic databases MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Clinical Trials (from January 1990 to January 2011) using the following medical subject heading (MeSH) words: “regional anesthesia” OR “regional analgesia” OR “peripheral nerve block” OR “nerve block.” These search results were combined with “ultrasound” AND “pain” using the Boolean search operator AND.
The study inclusion criteria were limited to randomized controlled trials (RCTs), English language, and humans. Each abstract was screened to identify studies that had randomized patients to compare US guidance with other nerve localization techniques such as mechanical elicitation of paresthesias, peripheral nerve stimulation (PNS), and surface anatomical landmarks. Studies were excluded if they did not specifically compare US guidance with another nerve localization technique and did not report at least one of the following acute pain outcomes: pain severity, opioid consumption, sensory block duration, and time to first analgesic request. The references of the retrieved articles were manually searched for any relevant articles not captured in the original search.
Data were extracted for comparison into an independently created template including author, year of publication, peripheral nerve block procedure performed, placement of perineural catheter, patient disposition, comparative nerve localization technique, number of subjects in each group, and primary outcome measured. The specific outcomes sought in each article were based on the American Society of Regional Anesthesia and Pain Medicine's acute postoperative pain (AcutePOP) database initiative.5 Acute pain outcomes sought were: (i) pain severity, (ii) sensory block duration, (iii) opioid consumption, and (iv) time to first analgesic request. Pain severity was further divided into early (<24 hours) versus late (>24 hours) and categorized into rest versus dynamic. If not otherwise stated, it was assumed that pain severity was assessed at rest. Additional related outcomes were broadly classified along patient-related outcomes, anesthesia-related outcomes, surgery-related outcomes, and hospital-related outcomes. The patient-related outcomes sought were: (i) opioid-related adverse events (nausea, emesis, pruritus, sedation, urinary retention, and respiratory depression), (ii) patient satisfaction with block procedure, and (iii) incidence of cognitive deficit. The anesthesia-related outcomes were: (i) incidence of undesirable motor block, (ii) perineural catheter failure (defined as dislodgement or ineffective analgesia requiring replacement), (iii) morbidity (nerve damage, vascular puncture, local anesthetic toxicity, pneumothorax, infection at block site, and hematoma), and (iv) development of chronic pain. The surgery-related outcomes were: (i) unplanned hospital readmission rate, and (ii) ability to ambulate (defined as ambulating sufficient distance as determined by the surgical team). The hospital-related outcomes were: (i) length of stay, and (ii) cost. The methodological quality of each trial was assessed using the Jadad score.6 We independently extracted data and reviewed and scored each RCT using this methodology. Differences in extracted data or scoring were resolved through discussion. Finally, several promising studies that were excluded from the initial analysis for lack of a comparator (i.e., traditional nerve localization technique) were identified for the present discussion in the context of emerging trends and future directions for investigation.
In total, 23 RCTs were identified that compared US guidance with another nerve localization technique for interventional pain management (Fig. 1). The 23 RCTs included a total of 1674 patients and all in the perioperative setting. Only 1 study7 qualified for a high-quality Jadad score of 5; 18 studies8–25 had an intermediate-quality score of 3; and 4 studies26–29 had a poor-quality score of 2. Table 1 presents the characteristics of the studies included herein whereas Table 2 summarizes the specific outcomes sought for the purposes of this review.
Acute Pain Outcomes
Sixteen studies evaluated differences in early postoperative pain (<24 hours) at rest.7–9,11–16,19–23,26,28 Of these, 8 reported improved analgesia associated with US guidance compared with PNS,7,8,12,23 or anatomical landmarks,11,15,16,28 whereas 8 reported no difference (Table 3).9,13,14,19–22,26 Among the 8 studies that reported improved analgesia at rest with US guidance, only a single study demonstrated a decrease in numeric rating pain scale of >1 interval.12 Of the 4 studies that evaluated dynamic pain,8,12–14 only one8 demonstrated improvement with US guidance whereas 3 did not.12–14
Eight studies reported sensory nerve block duration.9,10,17,18,24–27 Among these, 3 demonstrated prolonged sensory block duration with US guidance compared with PNS,17,18,24 whereas 4 did not demonstrate a significant difference compared with PNS,9,10,25,27 and 1 did not demonstrate a significant difference compared with anatomical landmarks.26
Seven studies reported differences in opioid consumption between US guidance and comparative nerve localization techniques.7,8,12–14,22,29 Among these, 3 demonstrated reduced opioid consumption with the use of US guidance compared with PNS,7,8,12 whereas 4 did not.13,14,22,29
There were 3 studies that reported time to first analgesic request.8,10,11 Of these, 1 study each reported a prolongation associated with US guidance compared with PNS8 and anatomical landmarks,11 respectively. Dufour et al.10 did not demonstrate a difference in time to first analgesic request when US guidance was combined with PNS compared with PNS alone.
Only 1 study reported opioid-related side effects (postoperative nausea and vomiting) and did not demonstrate any benefit for US guidance over PNS.8 Five studies assessed patient satisfaction during the block procedure,10,12,15,16,26 of which 2 favored US guidance compared with landmark techniques,15,16 2 found no difference between US guidance and PNS,10,12 and 1 found no difference between US guidance and landmark techniques.26 None of the studies assessed for differences in postoperative cognitive deficits.
No study reported the incidence and/or duration of undesired motor block. The 11 studies in which indwelling catheters were placed did not demonstrate a difference in the incidence of catheter failure between US guidance and traditional nerve localization techniques.8,12–16,19–22,29 Three studies demonstrated statistically significant differences in the incidence of complications in favor of US guidance by reducing vascular punctures19,21 and postepidural headaches.15 The remaining 20 studies did not show statistical significance or did not apply statistical analysis to the incidence of complications between US guidance and other nerve localization techniques. Finally and importantly, no study investigated the onset of previously undiagnosed chronic pain.
No study assessed for the ability to ambulate postoperatively or the incidence of unplanned hospital readmission.
Two studies compared the differences in length of stay in hospital between US guidance and PNS and did not find any difference.8,11 None of the studies reported any cost differential between nerve localization techniques.
Our review of the contemporary literature produced insufficient evidence to qualitatively or quantitatively define the effect of US guidance compared with traditional nerve localization techniques on acute pain and acute pain–related outcomes for interventional acute pain management. There are, however, no data to suggest that US guidance is inferior to traditional nerve localization techniques. Previously documented procedural and technical block-related advantages associated with US guidance, such as onset time, performance time, and “success,”1,2 do not seem to translate into superior acute pain outcomes. Although we found 8 studies that demonstrated a statistically significant difference in pain severity in favor of US guidance,7,8,11,12,15,16,23,28 the difference was of clinical significance30 in only one.12
The inability to demonstrate a clinically significant difference in acute pain outcomes between US guidance and traditional nerve localization techniques is likely attributable to several factors. First, the predominant comparator and “gold standard” nerve localization technique, PNS, is associated with a very high initial block success rate.31 Indeed, there is often no measurable difference in block success between US guidance and PNS when performed by skilled providers.31,32 It is therefore unlikely that clinically significant differences in acute pain outcomes would stem from such equally high block success rates. Moreover, many of the other important outcomes reported herein such as length of stay, cost, and hospital readmission are inherently multifactorial and beyond the control of even the most stringent study design. Last, because serious block-related complications and morbidity are so infrequent, prohibitively large numbers of patients would be required for study to reliably detect a difference between nerve localization techniques.33,34
There are several limitations inherent to this comprehensive literature review. Gross heterogeneity among studies relating to surgical procedure, block technique, anatomical location, and needle approach, as well as the type, concentration, volume, and frequency of local anesthetic administered prohibits statistical meta-analysis. Importantly, our results are presented in “vote counting” format primarily to facilitate descriptive presentation of the literature rather than offer any quantitative data analysis. Furthermore, pain severity, sensory block duration, opioid consumption, or time to first analgesic request was the designated primary outcome measure (with corresponding statistical power) in only 6 of the 23 studies reviewed herein.11,13,14,17,22,23 Furthermore, only 2 included studies that assessed pain severity before the intervention.15,16 Meaningful differences in pain severity are difficult to interpret without the context of the preinterventional state. In addition, the time to first analgesic request, arguably the most faithful measure of acute pain because it is most intimate to the patient and least dependent on assessment schedule or protocol, was only captured by 3 studies.8,10,11 Finally, modern multimodal analgesic regimens and accelerated clinical pathways designed to promote early mobilization and hospital discharge may have masked any material advantages of US guidance over traditional nerve localization techniques.
In the course of our systematic search, it was apparent that several novel and important descriptions of US guidance for the purpose of acute pain management have recently populated the literature. Although the available literature regarding these US-guided applications is primarily limited to feasibility and observational studies that did not meet our inclusion criteria for qualitative review, we fully expect that randomized data of acute pain outcomes will be forthcoming. Among the most promising of these emerging trends is US-guided transversus abdominis plane (TAP) blocks for analgesia in lower abdominal procedures including obstetric, gynecologic, and general surgery procedures. A number of studies have already demonstrated a significant reduction in acute pain in favor of TAP blocks compared with systemic or neuraxial opioids after cesarean delivery, open appendectomy, and laparoscopic cholecystectomy.35–37 However, no study has compared real-time US-guided infiltration of the transversus abdominis fascial plane to the traditional blind landmark approach.38
In the wake of cautiously optimistic retrospective data signaling that thoracic paravertebral blocks (PVBs) for postoperative analgesia may reduce the recurrence of adenocarcinoma of the breast after mastectomy,39 reports and demand for US-guided approaches to facilitate PVB placement abound.40–43 Whereas US-guided thoracic PVB has been shown to provide superior analgesia and reduce opioid consumption compared with systemic analgesia for both breast44,45 and thoracic surgery,46 US guidance has yet to be directly compared with traditional landmark techniques.47
Additional novel applications of US guidance for interventional acute pain management include that for the lumbar plexus,48–50 obturator nerve,51,52 superficial cervical plexus,53 intercostal nerve block,54–56 and proximal sciatic nerve.57–59 Beyond the TAP block, US guidance has enabled the identification and infiltration of other fascial planes rather than the target nerve itself, with promising results for acute pain,58 and potentially even nerve injury.60
In summary, there is insufficient evidence at this time to define the effects of US guidance compared with traditional nerve localization techniques on acute pain and related outcomes for interventional acute pain management. Further study is required to determine whether the procedural and technical efficiencies afforded by US guidance will ever translate into measurable improvements in acute pain outcomes. Although there is no single, definitive, and comprehensive measure of acute pain that is equally meaningful to the patient, the anesthesiologist, the surgeon, and the hospital manager, future studies must endeavor to capture all important outcomes so that all readers are equipped to make informed choices regarding nerve localization techniques.
Name: Stephen Choi, MD, FRCPC.
Contribution: This author helped analyze data and write the manuscript.
Attestation: Stephen Choi approved the final manuscript.
Name: Richard Brull, MD, FRCPC.
Contribution: This author helped analyze data and write the manuscript.
Attestation: Richard Brull approved the final manuscript.
1. Neal JM, Brull R, Chan VW, Grant SA, Horn JL, Liu SS, McCartney CJ, Narouze SN, Perlas A, Salinas FV, Sites BD, Tsui BC. The ASRA evidence-based medicine assessment of ultrasound-guided regional anesthesia and pain medicine: executive summary. Reg Anesth Pain Med 2010;35:S1–9
2. Gelfand HJ, Ouanes JP, Lesley MR, Ko PS, Murphy JD, Sumida SM, Isaac GR, Kumar K, Wu CL. Analgesic efficacy of ultrasound-guided regional anesthesia: a meta-analysis. J Clin Anesth 2011;23:90–6
3. Boezaart AP, Chelly JE, Buckenmaier CC, Beathe JP, Neal JM, Ligouri GA. Pro/con: fellowships in regional anesthesia should be renamed ‘Fellowship in Acute Pain Medicine.' ASRA News: a publication of the American Society of Regional Anesthesia and Pain Medicine, 2010:6–9
4. The Regional Anesthesiology and Acute Pain Medicine Fellowship Directors Group. Guidelines for fellowship training in regional anesthesiology and acute pain medicine: second edition, 2010. Reg Anesth Pain Med 2011;36:282–8
5. Liu SS, Warren DT, Wu CL, Ballantyne JC, Ginsberg B, Rathmell JP, Rosenquist RW, Viscusi ER. A lovely idea: forming an ASRA Acute Postoperative Pain (AcutePOP) database. Reg Anesth Pain Med 2006;31:291–3
6. Jadad AR, Moore RA, Carroll D, Jenkinson C, Reynolds DJ, Gavaghan DJ, McQuay HJ. Assessing the quality of reports of randomized clinical trials: is blinding necessary? Control Clin Trials 1996;17:1–12
7. Ponde VC, Diwan S. Does ultrasound guidance improve the success rate of infraclavicular brachial plexus block when compared with nerve stimulation in children with radial club hands? Anesth Analg 2009;108:1967–70
8. Aveline C, Le Roux A, Le Hetet H, Vautier P, Cognet F, Bonnet F. Postoperative efficacies of femoral nerve catheters sited using ultrasound combined with neurostimulation compared with neurostimulation alone for total knee arthroplasty. Eur J Anaesthesiol 2010;27:978–84
9. Domingo-Triado V, Selfa S, Martinez F, Sanchez-Contreras D, Reche M, Tecles J, Crespo MT, Palanca JM, Moro B. Ultrasound guidance for lateral midfemoral sciatic nerve block: a prospective, comparative, randomized study. Anesth Analg 2007;104: 1270–4
10. Dufour E, Quennesson P, Van Robais AL, Ledon F, Laloe PA, Liu N, Fischler M. Combined ultrasound and neurostimulation guidance for popliteal sciatic nerve block: a prospective, randomized comparison with neurostimulation alone. Anesth Analg 2008;106:1553–8
11. Faraoni D, Gilbeau A, Lingier P, Barvais L, Engelman E, Hennart D. Does ultrasound guidance improve the efficacy of dorsal penile nerve block in children? Paediatr Anaesth 2010;20:931–6
12. Fredrickson MJ, Ball CM, Dalgleish AJ. A prospective randomized comparison of ultrasound guidance versus neurostimulation for interscalene catheter placement. Reg Anesth Pain Med 2009;34:590–4
13. Fredrickson MJ, Ball CM, Dalgleish AJ, Stewart AW, Short TG. A prospective randomized comparison of ultrasound and neurostimulation as needle end points for interscalene catheter placement. Anesth Analg 2009;108:1695–700
14. Fredrickson MJ, Danesh-Clough TK. Ambulatory continuous femoral analgesia for major knee surgery: a randomised study of ultrasound-guided femoral catheter placement. Anaesth Intensive Care 2009;37:758–66
15. Grau T, Leipold RW, Conradi R, Martin E. Ultrasound control for presumed difficult epidural puncture. Acta Anaesthesiol Scand 2001;45:766–71
16. Grau T, Leipold RW, Conradi R, Martin E, Motsch J. Efficacy of ultrasound imaging in obstetric epidural anesthesia. J Clin Anesth 2002;14:169–75
17. Kapral S, Greher M, Huber G, Willschke H, Kettner S, Kdolsky R, Marhofer P. Ultrasonographic guidance improves the success rate of interscalene brachial plexus blockade. Reg Anesth Pain Med 2008;33:253–8
18. Marhofer P, Sitzwohl C, Greher M, Kapral S. Ultrasound guidance for infraclavicular brachial plexus anaesthesia in children. Anaesthesia 2004;59:642–6
19. Mariano ER, Cheng GS, Choy LP, Loland VJ, Bellars RH, Sandhu NS, Bishop ML, Lee DK, Maldonado RC, Ilfeld BM. Electrical stimulation versus ultrasound guidance for popliteal-sciatic perineural catheter insertion: a randomized controlled trial. Reg Anesth Pain Med 2009;34:480–5
20. Mariano ER, Loland VJ, Bellars RH, Sandhu NS, Bishop ML, Abrams RA, Meunier MJ, Maldonado RC, Ferguson EJ, Ilfeld BM. Ultrasound guidance versus electrical stimulation for infraclavicular brachial plexus perineural catheter insertion. J Ultrasound Med 2009;28:1211–8
21. Mariano ER, Loland VJ, Sandhu NS, Bellars RH, Bishop ML, Afra R, Ball ST, Meyer RS, Maldonado RC, Ilfeld BM. Ultrasound guidance versus electrical stimulation for femoral perineural catheter insertion. J Ultrasound Med 2009;28:1453–60
22. Mariano ER, Loland VJ, Sandhu NS, Bishop ML, Lee DK, Schwartz AK, Girard PJ, Ferguson EJ, Ilfeld BM. Comparative efficacy of ultrasound-guided and stimulating popliteal-sciatic perineural catheters for postoperative analgesia. Can J Anaesth 2010;57:919–26
23. McNaught A, Shastri U, Carmichael N, Awad IT, Columb M, Cheung J, Holtby RM, McCartney CJ. Ultrasound reduces the minimum effective local anaesthetic volume compared with peripheral nerve stimulation for interscalene block. Br J Anaesth 2011;106:124–30
24. Oberndorfer U, Marhofer P, Bosenberg A, Willschke H, Felfernig M, Weintraud M, Kapral S, Kettner SC. Ultrasonographic guidance for sciatic and femoral nerve blocks in children. Br J Anaesth 2007;98:797–801
25. Taboada M, Rodriguez J, Amor M, Sabate S, Alvarez J, Cortes J, Atanassoff PG. Is ultrasound guidance superior to conventional nerve stimulation for coracoid infraclavicular brachial plexus block? Reg Anesth Pain Med 2009;34:357–60
26. 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
27. van Geffen GJ, van den Broek E, Braak GJ, Giele JL, Gielen MJ, Scheffer GJ. A prospective randomised controlled trial of ultrasound guided versus nerve stimulation guided distal sciatic nerve block at the popliteal fossa. Anaesth Intensive Care 2009;37:32–7
28. Willschke H, Marhofer P, Bosenberg A, Johnston S, Wanzel O, Cox SG, Sitzwohl C, Kapral S. Ultrasonography for ilioinguinal/ iliohypogastric nerve blocks in children. Br J Anaesth 2005;95:226–30
29. Willschke H, Marhofer P, Bosenberg A, Johnston S, Wanzel O, Sitzwohl C, Kettner S, Kapral S. Epidural catheter placement in children: comparing a novel approach using ultrasound guidance and a standard loss-of-resistance technique. Br J Anaesth 2006;97:200–7
30. Liu SS, Wu CL. The effect of analgesic technique on postoperative patient-reported outcomes including analgesia: a systematic review. Anesth Analg 2007;105:789–808
31. 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
32. Borgeat A, Capdevila X. Neurostimulation/ultrasonography: the Trojan war will not take place. Anesthesiology 2007;106:896–8
33. Neal JM. Ultrasound-guided regional anesthesia and patient safety: an evidence-based analysis. Reg Anesth Pain Med 2010;35:S59–67
34. Hebl JR. Ultrasound-guided regional anesthesia and the prevention of neurologic injury: fact or fiction? Anesthesiology 2008;108:186–8
35. Belavy D, Cowlishaw PJ, Howes M, Phillips F. Ultrasound-guided transversus abdominis plane block for analgesia after Caesarean delivery. Br J Anaesth 2009;103:726–30
36. El-Dawlatly AA, Turkistani A, Kettner SC, Machata AM, Delvi MB, Thallaj A, Kapral S, Marhofer P. Ultrasound-guided transversus abdominis plane block: description of a new technique and comparison with conventional systemic analgesia during laparoscopic cholecystectomy. Br J Anaesth 2009;102:763–7
37. Niraj G, Searle A, Mathews M, Misra V, Baban M, Kiani S, Wong M. Analgesic efficacy of ultrasound-guided transversus abdominis plane block in patients undergoing open appendicectomy. Br J Anaesth 2009;103:601–5
38. McDonnell JG, O'Donnell BD, Farrell T, Gough N, Tuite D, Power C, Laffey JG. Transversus abdominis plane block: a cadaveric and radiological evaluation. Reg Anesth Pain Med 2007;32:399–404
39. Exadaktylos AK, Buggy DJ, Moriarty DC, Mascha E, Sessler DI. Can anesthetic technique for primary breast cancer surgery affect recurrence or metastasis? Anesthesiology 2006;105: 660–4
40. Cowie B, McGlade D, Ivanusic J, Barrington MJ. Ultrasound-guided thoracic paravertebral blockade: a cadaveric study. Anesth Analg 2010;110:1735–9
41. Marhofer P, Kettner SC, Hajbok L, Dubsky P, Fleischmann E. Lateral ultrasound-guided paravertebral blockade: an anatomical- based description of a new technique. Br J Anaesth 2010; 105:526–32
42. O'Riain S, O'Donnell B, Cuffe T, Harmon DC, Fraher JP, Shorten G. Thoracic paravertebral block using real-time ultrasound guidance. Anesth Analg 2010;110:248–51
43. Renes SH, Bruhn J, Gielen MJ, Scheffer GJ, van Geffen GJ. In-plane ultrasound-guided thoracic paravertebral block: a preliminary report of 36 cases with radiologic confirmation of catheter position. Reg Anesth Pain Med 2009;35:212–6
44. Boughey JC, Goravanchi F, Parris RN, Kee SS, Frenzel JC, Hunt KK, Ames FC, Kuerer HM, Lucci A. Improved postoperative pain control using thoracic paravertebral block for breast operations. Breast J 2009;15:483–8
45. Moller JF, Nikolajsen L, Rodt SA, Ronning H, Carlsson PS. Thoracic paravertebral block for breast cancer surgery: a randomized double-blind study. Anesth Analg 2007;105: 1848–51
46. Fibla JJ, Molins L, Mier JM, Sierra A, Carranza D, Vidal G. The efficacy of paravertebral block using a catheter technique for postoperative analgesia in thoracoscopic surgery: a randomized trial. Eur J Cardiothorac Surg 2011 [Epub ahead of print]
47. Eason MJ, Wyatt R. Paravertebral thoracic block: a reappraisal. Anaesthesia 1979;34:638–42
48. Ilfeld BM, Loland VJ, Mariano ER. Prepuncture ultrasound imaging to predict transverse process and lumbar plexus depth for psoas compartment block and perineural catheter insertion: a prospective, observational study. Anesth Analg 2010;110: 1725–8
49. Karmakar MK, Ho AM, Li X, Kwok WH, Tsang K, Ngan Kee WD. Ultrasound-guided lumbar plexus block through the acoustic window of the lumbar ultrasound trident. Br J Anaesth 2008;100:533–7
50. Morimoto M, Kim JT, Popovic J, Jain S, Bekker A. Ultrasound-guided lumbar plexus block for open reduction and internal fixation of hip fracture. Pain Pract 2006;6:124–6
51. Sakura S, Hara K, Ota J, Tadenuma S. Ultrasound-guided peripheral nerve blocks for anterior cruciate ligament reconstruction: effect of obturator nerve block during and after surgery. J Anesth 2010;24:411–7
52. Sinha SK, Abrams JH, Houle TT, Weller RS. Ultrasound-guided obturator nerve block: an interfascial injection approach without nerve stimulation. Reg Anesth Pain Med 2009;34:261–4
53. Tran de QH, Dugani S, Finlayson RJ. A randomized comparison between ultrasound-guided and landmark-based superficial cervical plexus block. Reg Anesth Pain Med 2010; 35:539–43
54. Stone MB, Carnell J, Fischer JW, Herring AA, Nagdev A. Ultrasound-guided intercostal nerve block for traumatic pneumothorax requiring tube thoracostomy. Am J Emerg Med 2011;29:697.e1–2
55. Guay J, Grabs D. A cadaver study to determine the minimum volume of methylene blue or black naphthol required to completely color the nerves relevant for anesthesia during breast surgery. Clin Anat 2011;24:202–8
56. Shankar H, Eastwood D. Retrospective comparison of ultrasound and fluoroscopic image guidance for intercostal steroid injections. Pain Pract 2010;10:312–7
57. Chan VW, Nova H, Abbas S, McCartney CJ, Perlas A, Xu DQ. Ultrasound examination and localization of the sciatic nerve: a volunteer study. Anesthesiology 2006;104:309–14
58. Karmakar MK, Kwok WH, Ho AM, Tsang K, Chui PT, Gin T. Ultrasound-guided sciatic nerve block: description of a new approach at the subgluteal space. Br J Anaesth 2007;98:390–5
59. van Geffen GJ, Pirotte T, Gielen MJ, Scheffer G, Bruhn J. Ultrasound-guided proximal and distal sciatic nerve blocks in children. J Clin Anesth 2010;22:241–5
60. Swenson JD, Davis JJ. Ultrasound-guided regional anesthesia: why can't we all just stay away from the nerve? Anesthesiology 2008;109:748–9