As detailed within the supporting articles, our literature search terms identified up to 211 articles. After exclusion of those articles that did not fit inclusion criteria or were related to ultrasound uses other than regional anesthesia, most individual topic assessments were based on less than 25 applicable studies. In this executive summary article, pertinent results are summarized as a prelude to individual subtopics within the discussion.
Because study design and definitions of block characteristics vary widely among studies, we made no attempt to pool results for further statistical analysis. Useful information can be gleaned from case series and studies that compare various block approaches that use ultrasound guidance. However, the most valuable information for this project came from studies that compared specific block characteristics or complications as a function of UGRA versus another form of nerve localization. Studies that satisfied those criteria and their Jadad scores are listed in Table 3.
The literature of UGRA is a heterogeneous mix of generally small studies that compare ultrasound guidance with another form of nerve localization, usually peripheral nerve stimulation (PNS). Direct comparison of outcomes between studies is impossible because of variability in their chosen definitions for outcomes such as block performance time or success. Some studies compared the relative attributes of 2 or more approaches to a nerve or plexus block, all performed under ultrasound guidance. Other studies examined the ability to achieve neural blockade using differing volumes of local anesthetics. Although the latter 2 study methodologies contributed to our analysis, they were not used to infer any advantage or limitation of UGRA versus another form of nerve localization. What follows is a block-specific summary of results, discussion, and listing of recommendations when appropriate.
Nineteen studies met inclusion criteria for comparing UGRA to other methods of nerve localization for upper-extremity block; most of these comparisons were made with PNS. Although these studies represent level Ib evidence, their quality varied widely (Jadad score, 1-5; median, 3). We qualitatively defined a study as "positive" if any measure of UGRA block characteristic was statistically superior to the compared technique, "negative" if the compared technique was statistically superior to ultrasound, or "no net difference" if the techniques were statistically indistinguishable or split between comparison groups. This distinction is important in that we did not quantify the magnitude of time difference for a specific block characteristic. Thus, the clinician is left to decide, for example, whether a 4- to 12-min faster onset time is relevant to their practice, particularly if equipment setup time was not included or if overall block success was not different between techniques.19,20 Of the 19 studies, 15 were positive for ultrasound, 3 showed no net difference,21 and 1 demonstrated faster block performance time in the PNS group.22 Tables within the supporting articles detail the myriad comparisons that were made by individual studies, thereby giving readers a sense of the actual time advantage within the context of other measures of success. In addition to time-related block characteristics, 3 studies19,23,24 reported a reduced number of needle passes in the ultrasound group, yet this potential advantage did not consistently translate to improved patient satisfaction or block-related complication rates. Six upper-extremity UGRA studies compared 2 or more ultrasound-guided approaches. The results of these studies were mixed, with most but not all reporting higher success rates and lower complication rates (Horner syndrome and HDP) with infraclavicular or axillary block versus supraclavicular block. Lower success rates with the supraclavicular approach were consistently related to failure to anesthetize the lower trunk.11
Under the conditions of our analysis, there is level Ib, grade A evidence that ultrasound guidance results in faster sensory block onset and higher surrogate rates of block success, based on 6 of 7 conclusive studies for onset and 8 of 8 conclusive studies for success. Successful block, variously defined as sensory or motor anesthesia of 1 or more nerves, was reported positive for ultrasound as compared with the control technique: 75% to 86% versus 47% to 63%, respectively.10 Although higher success rates were shown for block onset and success when defined by nerves anesthetized, there was less distinction between groups when block success was defined by perhaps more clinically relevant measures such as readiness for surgery or the ability to complete surgery without block supplementation or provision of general anesthesia. When analyzed by these "block quality" indicators, about 20% of RCTs reported less need for rescue block, and ∼10% found less need for supplemental analgesia in the ultrasound study groups.10 Specific recommendations cannot be made for other block characteristics such as performance time or duration-most studies represent Ib evidence, but are either conflicting in their results or too few in numbers to justify definitive recommendations. Block performance time is noteworthy in that earlier studies often failed to include time for prescanning or equipment setup. However, 2 recent high-quality (Jadad score, 5) studies20,25 have shown shorter block performance times that include ultrasound prescanning and setup as compared with PNS.
The effect of ultrasound guidance on lower-extremity block characteristics has been evaluated in fewer studies as compared with the upper extremity; these studies support slightly more patients benefiting from the use of ultrasound guidance in terms of block success. Inclusion criteria were met by 4 RCTs (240 patients) that evaluated 3-in-1, femoral, and fascia iliaca blocks; 5 RCTs examined popliteal sciatic nerve block (214 patients); and 2 RCTs assessed combined ultrasound and PNS. Median Jadad score was 3 (range, 1-4). Perhaps reflecting the primarily analgesic use of these blocks in clinical practice, success of surgical anesthesia was rarely measured.15
The same criteria as described for upper-extremity block were used to judge lower-extremity UGRA as being positive, negative, or no difference compared with other localization techniques. Using these qualitative criteria to describe the superiority of ultrasound guidance to traditional techniques, 5 of 7 studies supported faster block onset, whereas 1 of 7 reported slower onset using ultrasound. Regarding block quality, there was no difference in the need for rescue anesthesia or supplemental analgesia, but 5 of 8 studies documented more complete block of all studied nerves in the ultrasound groups (97%-100% with ultrasound vs 71%-75% with other techniques). Three of 3 studies reported no difference in lower-extremity block duration.10 Two studies demonstrated the ability of UGRA to reduce the amount of local anesthetic necessary to achieve adequate block as compared with PNS guidance (absolute mean reductions of 9 mL for femoral block26 and 20 mL for sciatic block27). These data support level Ib, grade A recommendations in favor of ultrasound for increasing sensory block success and allowing a reduced volume of local anesthetic to achieve adequate block. Similar evidence (Ib, A) supports the use of ultrasound to decrease sensory block onset time by an average of 11 to 14 mins. Catheter placement block performance times were faster in the ultrasound groups for popliteal sciatic nerve block. Investigations of lower-extremity blocks lacked sufficient power to allow definitive recommendations regarding quality of sensory block, number of needle punctures and redirections, patient discomfort during the block, or block duration.15
Truncal blocks include paravertebral, intercostal, transversus abdominis plane (TAP), rectus sheath, and ilioinguinal/iliohypogastric (II/IH) blocks. The literature of ultrasonically guided truncal blocks largely consists of case series, audits, or anatomic studies that establish feasibility. Three RCTs compare rectus sheath28 or II/IH blocks29,30 to landmark-based techniques.
There currently are insufficient data to address the usefulness of ultrasound guidance for intercostal nerve block. Several case series and an anatomic study establish the feasibility of using ultrasound for paravertebral blocks (IIb, B), but there are no data available from which to compare the success or safety of paravertebral blocks using ultrasound versus traditional techniques (IV).9 Ultrasound guidance might be expected to reduce the incidence of visceral organ injuries and intraperitoneal needle placements linked to TAP blocks. However, the evidence for ultrasound-guided TAP blocks is limited to cadaver studies, retrospective audits, and noncomparative opioid-sparing studies. Although these studies establish feasibility and high success rates, there are no level I or II data that address the relative benefit of ultrasound-guided TAP to traditional approaches.9
Two small case series of pediatric patients established feasibility of ultrasound-guided rectus sheath block. A recent RCT compared the performance of trainees using ultrasound versus loss-of-resistance (LOR) technique. Given the inexperience of trainees with both approaches, it is notable that the needle was placed in the correct tissue plane twice as often using ultrasound. Intraperitoneal needle placement occurred in 21% of the LOR subjects28 (Ib, A). An RCT that compared ultrasound-guided to landmark-based II/IH block reported higher success for anesthesia and analgesia in those children randomized to ultrasound.30 Although there is insufficient evidence to demonstrate increased safety with ultrasound, this study establishes a limited (Ib, A) recommendation for ultrasound-guided II/IH block in children.
In summary for truncal blocks, limited RCT evidence supports the recommendation for ultrasound as the preferred localization technique for rectus sheath and II/IH blocks (Ib, A). There is insufficient evidence from which to judge the relative contributions of ultrasound to TAP, intercostal, and paravertebral blocks.9
The body of literature examining the role of ultrasound in neuraxial anesthetic techniques is smaller than that for PNBs. Seventeen studies met inclusion criteria and can be generally categorized as addressing (1) ultrasound-assisted techniques or (2) real-time ultrasound-guided techniques.
Ultrasound-assisted neuraxial techniques involve preprocedural scanning to determine midline, targeted interspace, or depth from skin to the epidural or subarachnoid spaces before performing the procedure using traditional methods. In adults, these basic measurements are often difficult to obtain because of intervening soft tissues or acoustic shadowing from bone and/or calcification. Nevertheless, ultrasound is superior to physical examination, but inferior to radiologic imaging, for correctly identifying spinal interspace levels (IIa). Ultrasound is highly accurate for predicting skin-to-epidural space depth in the cervical spine (adults) and the lumbar spine (adults and children) (Ib). The clinical relevance of these findings is uncertain. For instance, when ultrasound was compared with landmark-based examination before placement of labor epidurals, the anesthesiologist using ultrasound was able to complete epidural placement using fewer attempts at fewer interspaces, yet the success rate for labor analgesia was no different. Higher success was achieved if the operator was a trainee14 (Ib).
A single real-time ultrasound-guided neuraxial study of combined spinal epidural anesthesia in obstetric patients noted fewer attempts to successfully place the needle in the ultrasound group, but equal block success (Ib). There are no safety studies of ultrasound-facilitated versus traditional neuraxial techniques. Unfortunately, ultrasound guidance is likely to be most useful in patients who present challenging neuraxial anatomy secondary to obesity, spinal deformity, or previous spine surgery. However, there is often more difficulty obtaining images on these groups of patients, and data are still lacking at this early stage.14
The use of UGRA in pediatrics is of particular interest because children are often anesthetized before block placement and therefore unable to provide feedback related to needle-to-nerve contact or symptoms of local anesthetic intravascular injection. Existing studies are too small to address these patient safety issues. Twelve studies (6 RCTs and 6 case series) have assessed pediatric ultrasound-guided PNB, and 12 others (1 RCT, 1 comparative study, and 10 case series) have evaluated pediatric neuraxial block. The median Jadad score for these studies was 3 (range, 2-5).16
For PNB, a single study of infraclavicular block showed that the onset of sensory block was, on average, 6 mins faster with UGRA versus PNS,31 but the success of surgical anesthesia was not different (Ib, B). Conversely, ultrasound improved block success for pediatric anterior truncal blocks, which are typically performed using tactile or landmark-based techniques29,30 (Ib, A). Ultrasound guidance modestly prolonged neural blockade, as measured by duration time or decreased pain scores, in infraclavicular, sciatic, and/or femoral block models31,32 (Ib, A). Three studies demonstrated that ultrasound reduced the volume of local anesthetic required for various pediatric blocks, but limited duration of follow-up (4 hrs) and instances of early presentation of pain confound interpretation of these results with regard to whether reduced volumes can maintain or improve block quality and duration33-35 (Ib, A).
Real-time ultrasound-guided neuraxial blocks have proven valuable in pediatric patients whose smaller body mass allows the use of high-resolution linear transducers to image neuraxial structures. Feasibility studies demonstrate real-time observation of injectate spread through epidural needles, epidural catheter insertion, and final catheter position (III).14 Several investigations confirm the usefulness of UGRA for visualizing the ligamentum flavum and particularly the dura mater in neonates, infants, and children up to 12 years of age (Ib, A). Preprocedural scanning offers a moderate prediction of depth from skin to expected LOR.16 A comparison of ultrasound guidance to LOR for epidural placement found that ultrasound reduced the number of bone contacts and facilitated faster placement of the catheter, but did not affect analgesia or complications36 (Ib, B).
In summary, a modest body of literature addresses UGRA in the pediatric population. Similar to adults, studies show that sensory block onset is often faster, but ultrasound equipment setup time is typically not reported. Feasibility studies demonstrate the ability of ultrasound to identify dura mater and ligamentum flavum, particularly in neonates and young children, but to date there are little data linking this to actual clinical advantage in terms of improved block success or safety. The ability to use smaller volumes of local anesthetic is particularly appealing in children because of their small-size-related susceptibility to local anesthetic toxicity. Although smaller local anesthetic volumes are indeed possible in these patients, there is limited evidence regarding how this might affect block quality and no evidence regarding serious complications such as seizure. The common practice of placing blocks in anesthetized or heavily sedated children37,38 is another instance where neural visualization presents a theoretical advantage of ultrasound guidance, but nerve injury has not been studied in this group.
Chronic Pain Medicine: Interventional Procedures
Ultrasound guidance might offer similar benefits to pain physicians as it does for surgical and acute pain medicine practice,39 but acoustic shadowing and obesity make neuraxial imaging particularly difficult in adults. Compared with fluoroscopy or other radiographic imaging techniques, ultrasonography reduces radiation exposure to the patient and operator. The evidence base for interventional pain medicine is quite limited, with most reports classified as feasibility studies; that is, cadavers and/or noncomparative patient models are used to explore the potential for ultrasound guidance to facilitate block procedures. Preliminary feasibility studies support the use of ultrasound guidance for cervical selective nerve root block40 and stellate ganglion block.41 No data exist to compare the efficacy of ultrasound to fluoroscopic guidance for lumbar facet injection, lumbar nerve root injection, or cervical selective nerve root injection.
The single RCT within this topic area compared ultrasound with computed tomography guidance for lumbar facet joint intra-articular injection. Ultrasound was superior to computed tomography with regard to time for block placement and less radiation exposure, but there was no difference in pain relief between groups42 (Ib). A nonrandomized crossover trial of lumbar facet medial branch blocks noted that ultrasound-guided blocks (administered 1 month after a fluoroscopically guided block) were 95% successful for establishing proper needle placement. This study may not be applicable to Western populations because of the small physical stature (mean, 51 kg) of its subjects.43
As compared with other nerve localization methods, UGRA has the advantage of directly visualizing the target nerve, surrounding tissues, and injectate spread. It is reasonable to speculate that these advantages might reduce complications such as nerve injury, LAST, pneumothorax, or HDP. Unfortunately, the most serious of these complications (permanent nerve injury and severe LAST) are so rare as to defy statistical proof that ultrasound might affect their occurrence.13
Twenty-two RCTs and 4 large case series that together encompass ∼17,000 patients showed no difference in the frequency of PONSs as a function of localization technique. This finding is supported by a recent meta-analysis and systematic review.44,45 Two large audits found no statistical difference in the incidence of PONSs regardless of nerve localization by ultrasound or PNS.46,47 Importantly, the frequency of PONSs after UGRA (0.4/1000; 95% confidence interval [CI], 0.08-1.1/1000)46does not appear to be significantly different from historical frequencies reported using PNS techniques. However, cases of peripheral nerve injury have been reported after ultrasound-guided PNB.13,48
Seventeen RCTs and 2 large case series (∼15,000 patients) showed a reduction in the incidence of vascular puncture when ultrasound guidance was used. However, data are conflicting with regard to subsequent reduction in the occurrence of LAST-one audit showed no reduction as a function of localization technique,46 whereas another audit47 noted fewer seizures in the ultrasound group. Case reports49,50 describe seizures despite the use of ultrasound. The overall frequency of LAST after UGRA (95% CI, 0.42-1.9/1,000) is remarkably similar to that previously reported using PNS guidance.13,51
Three RCTs52-54 evaluated the potential for UGRA to reduce the incidence of HDP after above-the-clavicle block. Ultrasound-facilitated local anesthetic volume reduction caused less frequent and intense HDP, but HDP still occurred unpredictably (95% CI, 0.00%-0.14% for supraclavicular block53), which likely limits absolute reliance on small-volume, ultrasound-guided blocks in those patients for whom a potential 30% reduction in pulmonary function would be relatively contraindicated. Three RCTs24,53,55 and a case series56 report no pneumothoraces associated with UGRA (upper limit 95% CI, 0.5%), although pneumothorax associated with UGRA has been reported after single-injection and continuous techniques.57,58
In summary, there is no evidence that UGRA results in less frequent peripheral nerve injury than that historically reported using PNS guidance. Because of the extreme rarity of this complication, a statistically significant difference between nerve localization techniques, if indeed any difference exists, will likely never be realized (III). Ultrasound reduces the frequency of vascular puncture (Ia), but there is conflicting evidence whether this results in true reduction of LAST (III). Although the use of ultrasound and low local anesthetic volume reduces the frequency and intensity of HDP (Ia), it does so unpredictably, which may limit the usefulness of this technique in those patients most likely to benefit from it (IV). Finally, pneumothorax has been reported despite the use of ultrasound guidance (III).
The evidence base for UGRA as a nerve localization tool is expanding rapidly. Although existing studies are hampered by small numbers of subjects and varying definitions of block characteristics and success, their quality has improved substantially over the past 5 years. Current assessments of the advantages and limitations of ultrasound are hampered by (often unavoidable) methodological limitations. For instance, most studies were performed by ultrasound experts, which may limit the ability to generalize results to less experienced practitioners. Conversely, these same investigators are often highly skilled in the comparator technique, which should promote fairer comparison. More problematic are those studies that compare ultrasound to a less-than-ideal version of the comparator, such as not using the optimal number of PNS-guided injections or motor responses.59
Despite the literature's limitations, several general conclusions can be made. First, most studies found UGRA to be superior or equal to the comparator technique, and none showed that ultrasound guidance was clearly inferior or dangerous. Second, ultrasound offers statistically, but perhaps not clinically, proven advantages in block characteristics, particularly reduced onset time and improved intermediate measures of success. These advantages need to be qualified in that they are often block specific, and surrogate measures of block success are more likely to favor ultrasound guidance than do those measures that rely on supplement-free surgical anesthesia. Third, there is no evidence that ultrasound eliminates complications; indeed, the limited existing data suggest that complication rates are similar to historical norms reported using traditional nerve localization tools. There is reason to at least consider that poorly performed ultrasound guidance, such as failure to image the needle, misinterpretation of artifacts,7,8 or novice behavior,60,61 might actually increase the risk of injury. Furthermore, ultrasound is but another form of nerve localization, all having a potential role in the multifactorial process of nerve injury, which is also affected by local anesthetic neurotoxicity, underlying patient conditions, and surgical-related insults. The literature is silent with regard to patient- or situation-specific safety outcomes where ultrasound may prove to be particularly useful. For example, there is reason to suspect that UGRA may reduce the frequency of LAST more in children than in adults, or that preventing nerve injury may be more relevant in patients at increased risk for nerve injury (diabetes, chemotherapy-induced neuropathy, etc) as compared with the overall population.
In closing, the panel wishes to emphasize its belief that ultrasound guidance is a significant advance in the practice of regional anesthesia and pain medicine. At this early stage, the volume of evidence-based UGRA literature has already matched or arguably exceeded that for transesophageal echocardiography. Future studies will most certainly improve our understanding of its strengths and weaknesses. However, the use of ultrasound is but a single component of the practice of regional anesthesia. Ultrasound guidance does not remove traditional requirements for physician judgment, training, anatomic knowledge, and experience. Most importantly, ultrasound does not lessen the practitioner's responsibility for using time-proven strategies to improve block quality and patient safety-including proper anesthetic selection and dosing, aspiration for blood, appropriate test dosing, patient- and procedure-appropriate sedation, and vigilant intrablock and postblock monitoring.
The authors thank the following colleagues who made substantial contributions to this project through their coauthorship of the individual background articles from which this executive summary was drawn: Matthew Abrahams, MD; David B. Auyong, MD; Michael F. Aziz, MD; Raymond S. John, BA; Lisa Lin, MBBS; Alan J. R. Macfarlane, MBChB; Justin Ngeow, BA; L. Michele Noles, MD; Jennifer J. Pillay, BSc; and Uma Shastri, MD.
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2. Ootaki C, Hayashi H, Amano M. Ultrasound-guided infraclavicular brachial plexus block: an alternative technique to landmark-guided approaches. Reg Anesth Pain Med
3. Kapral S, Krafft P, Eibenberger K, et al. Ultrasound-guided supraclavicular approach for regional anesthesia of the brachial plexus. Anesth Analg
4. Ting PL, Sivagnanaratnam V. Ultrasonographic study of the spread of local anaesthetic during axillary brachial plexus block. Br J Anaesth
5. Sites BD, Chan VW, Neal JM, et al. The American Society of Regional Anesthesia and Pain Medicine (ASRA) and he European Society of Regional Anaesthesia and Pain Therapy (ESRA) Joint Committee recommendations for education and training in ultrasound guided regional anesthesia. Reg Anesth Pain Med
6. Brull R, Macfarlane AJR. Practical knobology for ultrasound-guided regional anesthesia. Reg Anesth Pain Med
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7. Sites BD, Brull R, Chan VWS, et al. Artifacts and pitfall errors associated with ultrasound-guided regional anesthesia. Part I: understanding the basic principles of ultrasound physics and machine operations. Reg Anesth Pain Med
8. Sites BD, Brull R, Chan VWS, et al. Artifacts and pitfall errors associated with ultrasound-guided regional anesthesia. Part II: a pictorial approach to understanding and avoidance. Reg Anesth Pain Med
9. Abrahams M, Horn J-L, Noles LM, Aziz MF. Evidence-based medicine: ultrasound guidance for truncal blocks. Reg Anesth Pain Med
. 2010;35(suppl 1):S36-S42.
10. Liu SS, Ngeow J, John RS. Evidence basis for ultrasound-guided block characteristics: onset, quality, and duration. Reg Anesth Pain Med
. 2010;35(suppl 1):S26-S35.
11. McCartney CJL, Lin L, Shastri U. Evidence-basis for the use of ultrasound for upper extremity block. Reg Anesth Pain Med
. 2010;35(suppl 1):S10-S15.
12. Narouze SN. Ultrasound-guided interventional procedures in pain medicine: evidence-based medicine. Reg Anesth Pain Med
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13. Neal JM. Ultrasound-guided regional anesthesia and patient safety: an evidence-based analysis. Reg Anesth Pain Med
. 2010;35(suppl 1):S59-S67.
14. Perlas A. Evidence for the use of ultrasound in neuraxial blocks. Reg Anesth Pain Med
. 2010;35(suppl 1):S43-S46.
15. Salinas FV. Ultrasound and review of evidence for lower extremity peripheral nerve blocks. Reg Anesth Pain Med
. 2010;35(suppl 1):S16-S25.
16. Tsui BC, Pillay JJ. Evidence-based medicine: assessment of ultrasound imaging for regional anesthesia in infants, children and adolescents. Reg Anesth Pain Med
. 2010;35(suppl 1):S47-S54.
17. US Department of Health and Human Services Agency for Health Care Policy and Research. Acute Pain Management: Operative or Medical Procedures and Trauma. Clinical Practice Guideline 1
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18. Jadad AR, Moore RA, Carroll D, et al. Assessing the quality of reports of randomized clinical trials: is blinding necessary? Control Clin Trials
19. Casati A, Danelli G, Baciarello M, et al. A prospective, randomized comparison between ultrasound and nerve stimulation guidance for multiple injection axillary brachial plexus block. Anesthesiology
20. Chan VW, Perlas A, McCartney J, et al. Ultrasound guidance improves success rate of axillary brachial plexus block. Can J Anaesth
21. Macaire P, Singelyn F, Narchi P, Paqueron X. Ultrasound- or nerve stimulation-guided wrist blocks for carpal tunnel release: a randomized prospective comparative study. Reg Anesth Pain Med
22. Gurkan Y, Acar S, Solak M, Toker K. Comparison of nerve stimulation vs. ultrasound-guided lateral sagittal infraclavicular block. Acta Anaesthesiol Scand
23. Liu SS, Zayas VM, Gordon MA, et al. A prospective, randomized, controlled trial comparing ultrasound versus nerve stimulator guidance for interscalene block for ambulatory shoulder surgery for postoperative neurological symptoms. Anesth Analg
24. Sauter AR, Dodgson MS, Stubhaug A, Halstensen AM, Klaastad O. Electrical nerve stimulation or ultrasound guidance for lateral sagittal infraclavicular blocks: a randomized, controlled, observer-blinded, comparative study. Anesth Analg
25. Brull R, Lupu M, Perlas A, Chan VW, McCartney CJ. Compared with dual nerve stimulation, ultrasound guidance shortens the time for infraclavicular block performance. Can J Anaesth
26. Casati A, Baciarello M, Di Cianni S, et al. Effects of ultrasound guidance on the minimum effective anaesthetic volume required to block the femoral nerve. Br J Anaesth
27. Van Geffen GJ, van den Broek E, 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
28. Dolan J, Lucie P, Geary T, Smith M, Kenny GN. The rectus sheath block: accuracy of local anesthetic placement by trainee anesthesiologists using loss of resistance or ultrasound guidance. Reg Anesth Pain Med
29. Weintraud M, Lundblad M, Kettner S, et al. Ultrasound versus landmark-based technique for ilioinguinal-iliohypogastric nerve blockade in children: the implications on plasma levels of ropivacaine. Anesth Analg
30. Willschke H, Marhofer P, Bosenberg A, et al. Ultrasonography for ilioinguinal/iliohypogastric nerve blocks in children. Br J Anaesth
31. Marhofer P, Sitzwohl C, Greher M, Kapral S. Ultrasound guidance for infraclavicular brachial plexus anaesthesia in children. Anaesthesia
32. Oberndorfer U, Marhofer P, Bosenberg A, et al. Ultrasonographic guidance for sciatic and femoral nerve blocks in children. Br J Anaesth
33. De Jose MB, Gotzens V, Mabrok M. Ultrasound-guided umbilical nerve block in children: a brief description of a new approach. Pediatr Anesth
34. Willschke H, Bosenberg A, Marhofer P, et al. Ultrasonography-guided rectus sheath block in paediatric anaesthesia-a new approach to an old technique. Br J Anaesth
35. Willschke H, Bosenberg A, Marhofer P, et al. Ultrasonographic-guided ilioinguinal/iliohypogastric nerve block in pediatric anesthesia: what is the optimal volume? Anest Analg
36. Willschke H, Marhofer P, Bosenberg A, et al. Epidural catheter placement in children: comparing a novel approach using ultrasound guidance and a standard loss-of-resistance technique. Br J Anaesth
37. Bernards CM, Hadzic A, Suresh S, Neal JM. Regional anesthesia in anesthetized or heavily sedated patients. Reg Anesth Pain Med
38. Neal JM, Bernards CM, Hadzic A, et al. ASRA practice advisory on neurologic complications in regional anesthesia and pain medicine. Reg Anesth Pain Med
39. Peng PWH, Narouze S. Ultrasound-guided interventional procedures in pain medicine: a review of anatomy, sonoanatomy and procedures. Part I: non-axial structures. Reg Anesth Pain Med
40. Narouze S, Vydyanathan A, Kapural L, Sessler D, Mekhail N. Ultrasound-guided cervical selective nerve root block: a fluoroscopy-controlled feasibility study. Reg Anesth Pain Med
41. Gofeld M, Bhatia A, Abbas S, Ganapathy S, Johnson M. Development and validation of a new technique for ultrasound-guided stellate ganglion block. Reg Anesth Pain Med
42. Galiano K, Obwegeser AA, Walch C, et al. Ultrasound-guided versus computed tomography-controlled facet joint injections in the lumbar spine: a prospective randomized clinical trial. Reg Anesth Pain Med
43. Shim JK, Moon JC, Yoon KB, Kim W, Yoon DM. Ultrasound-guided lumbar medial-branch block: a clinical study with fluoroscopy control. Reg Anesth Pain Med
44. Abrahams MS, Aziz MF, Fu RF, Horn J-L. Ultrasound guidance compared with electrical neurostimulation for peripheral nerve block: a systematic review and meta-analysis of randomized controlled trials. Br J Anaesth
45. Liu SS, Ngeow JE, YaDeau JT. Ultrasound-guided regional anesthesia and analgesia. A quantitative systematic review. Reg Anesth Pain Med
46. Barrington MJ, Watts SA, Gledhill SR, et al. Preliminary results of the Australasian Regional Anaesthesia Collaboration. A prospective audit of over 7000 peripheral nerve and plexus blocks for neurological and other complications. Reg Anesth Pain Med
47. Orebaugh SL, Williams BA, Vallejo M, Kentor ML. Adverse outcomes associated with stimulator-based peripheral nerve blocks with versus without ultrasound visualization. Reg Anesth Pain Med
48. Cohen JM, Gray AT. Functional deficits following intraneural injection during interscalene block. Reg Anesth Pain Med
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49. Gnaho A, Eyrieux S, Gentili ME. Cardiac arrest during an ultrasound-guided sciatic nerve block combined with nerve stimulation. Reg Anesth Pain Med
50. Zetlaoui RJ, Labbe J-P, Benhamou D. Ultrasound guidance for axillary plexus block does not prevent intravascular injection. Anesthesiology
51. Benhamou D, Auroy Y, Amalberti R. Safety during regional anesthesia: what do we know and how can we improve our practice? [editorial]. Reg Anesth Pain Med
52. Renes SH, Rettig HC, Gielen MJ, Wilder-Smith OH, van Geffen GJ. Ultrasound-guided low-dose interscalene brachial plexus block reduces the incidence of hemidiaphragmatic paresis. Reg Anesth Pain Med
53. Renes SH, Spoormans HH, Gielen MJ, Rettig HC, van Geffen GJ. Hemidiaphragmatic paresis can be avoided in ultrasound-guided supraclavicular brachial plexus block. Reg Anesth Pain Med
54. Riazi S, Carmichael N, Awad I, Holtby RM, McCartney CJL. Effect of local anaesthetic volume (20 vs 5 mL) on the efficacy and respiratory consequences of ultrasound-guided interscalene brachial plexus block. Br J Anaesth
55. Williams SR, Chouinard P, Arcand G, et al. Ultrasound guidance speeds execution and improves the quality of supraclavicular block. Anesth Analg
56. Perlas A, Lobo G, Lo N, et al. Ultrasound-guided supraclavicular block. Outcome of 510 consecutive cases. Reg Anesth Pain Med
57. Bryan NA, Swenson JD, Greis PE, Burks RT. Indwelling interscalene catheter use in an outpatient setting for shoulder surgery: technique, efficacy, and complications. J Shoulder Elbow Surg
58. Koscielniak-Nielsen Z, Rasmussen H, Hesselbjerg L. Pneumothorax after an ultrasound-guided lateral sagittal infraclavicular block. Acta Anaesthesiol Scand
59. Salinas FV, Neal JM. A tale of two needle passes [editorial]. Reg Anesth Pain Med
60. Sites BD, Gallagher JD, Cravero J, Lundberg J, Blike G. The learning curve associated with a simulated ultrasound-guided interventional task by inexperienced anesthesia residents. Reg Anesth Pain Med
61. Sites BD, Spence BC, Gallagher J, et al. Characterizing novice behavior associated with learning ultrasound-guided peripheral regional anesthesia. Reg Anesth Pain Med
62. Antonakakis JG, Scalzo D, Jorgenson AS, et al. Ultrasound does not improve the success rate of a deep peroneal nerve block at the ankle. Reg Anesth Pain Med
63. Danelli G, Fanelli A, Ghisi D, et al. Ultrasound vs nerve stimulation multiple injection technique for posterior popliteal sciatic nerve block. Anaesthesia
64. Dhir S, Ganapathy S. Use of ultrasound guidance and contrast enhancement: a study of continuous infraclavicular brachial plexus approach. Acta Anaesthesiol Scand
65. Dingemans E, Williams SR, Arcand G, et al. Neurostimulation in ultrasound-guided infraclavicular block: a prospective randomized trial. Anesth Analg
66. Dolan J, Williams A, Murney E, Smith M, Kenny GNC. Ultrasound-guided fascia iliaca block: a comparison with the loss of resistance technique. Reg Anesth Pain Med
67. Domingo-Triado V, Selfa S, Martinez F, et al. Ultrasound guidance for lateral midfemoral sciatic nerve block: a prospective, comparative, randomized study. Anesth Analg
68. Dufour E, Quennesson P, Van Robais AL, et al. Combined ultrasound and neurostimulation guidance for popliteal sciatic nerve block: A prospective, randomized, comparison with neurostimulation alone. Anesth Analg
69. Fredrickson MJ, Kilfoyle DH. Neurological complication analysis of 1000 ultrasound guided peripheral nerve blocks for elective orthopaedic surgery: a prospective study. Anaesthesia
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