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Ultrasound and Regional Anesthesia Jim Sparrow, MD UAB Anesthesia Grand Rounds February 9, 2009
Topics We Will Cover <ul><li>Basic Science :  Ultrasound Technology and Terminology </li></ul><ul><li>Clinical Techniques ...
Why This is Important <ul><li>New technology requires thorough investigation to determine safety, efficacy, reliability an...
Introduction to the Basic Physics and Terminology of Ultrasound
Ultrasound Waves <ul><li>Form of Acoustic Energy </li></ul><ul><li>Generated by Piezoelectric Crystals in Specialized Tran...
Ultrasound Wave Propagation <ul><li>Longitudinally Propagated </li></ul><ul><li>Series of Brief </li></ul><ul><ul><li>Comp...
Acoustic Velocity <ul><li>Propagation Velocity of a Sound Wave </li></ul><ul><li>Is Constant in the Human Body </li></ul><...
How is an Image Created from Soundwaves?
Image Creation <ul><li>Requires Return of Soundwave to Probe ( Like a Boomerang ) </li></ul><ul><li>Probes rapidly cycle f...
Two Determinates of Ultrasound Image Quality <ul><li>Ultrasound Probes:  </li></ul><ul><ul><li>Transmits and Receives Ultr...
 
Signal Intensity <ul><li>Determined by degree of reflected waves returning to the transducer </li></ul><ul><li>Larger inte...
Ultrasound Wave Interaction with Tissues <ul><li>Reflection </li></ul><ul><ul><li>SPECULAR  (large smooth objects like a n...
Reflection of Ultrasound Waves <ul><li>Proportional to the difference in  acoustic impedance  between adjacent tissues </l...
Hyper vs. Hypoechoic Nerves
Refraction <ul><li>Occurs at tissue interfaces (unreflected) </li></ul><ul><li>Refraction can diminish image quality </li>...
Optimal Image Resolution is a Balance
Attenuation <ul><li>Progressive loss of energy with signal propagation </li></ul><ul><li>Results in progressive decrease i...
            5.0  Bone 1.3-3.3 Muscle 1.0  Kidney 0.5-0.94 Liver 0.63 Fat 0.18 Blood 0.002 Water Attenuation Coefficient  (...
Attenuation and Frequency <ul><li>Higher Frequency results in greater attenuation </li></ul>
Overcoming Loss of Signal from Attenuation <ul><li>Artificial Enhancement (Adjusting Gain) </li></ul><ul><li>Time Gain Com...
The Holy Grail:  Better Resolution <ul><li>Resolution refers to the ability to distinguish one object from another </li></...
Axial Resolution <ul><li>Separating two structures at Different Depths </li></ul><ul><li>Equal to ½ of pulse length </li><...
Lateral Resolution <ul><li>Separating two structures beside one another </li></ul><ul><li>Always worse than axial resoluti...
Temporal Resolution <ul><li>Directly related to U/S Frame Rate (FR) </li></ul><ul><ul><li>FR is the speed with which an im...
Review of Ultrasound Technology <ul><li>Image quality depends on probe technology and computer processor </li></ul><ul><li...
Basic Techniques of Ultrasound Guidance in Regional Anesthesia
All Ultrasound Guided Blocks Involve Three Steps 2 : <ul><li>Choosing One of Two Imaging Views </li></ul><ul><ul><li>Short...
Imaging Plane Options <ul><li>Long Axis View or Longitudinal View </li></ul><ul><ul><li>Rarely Used </li></ul></ul><ul><li...
The ART 3  of Scanning <ul><li>A lignment </li></ul><ul><ul><li>Sliding Movement of Trandsducer Along the Course of the Ne...
Where is The Needle Coming From? <ul><li>Out of Plane Technique </li></ul><ul><ul><li>Inserting the needle so that it cros...
Out of Plane Approach
In Plane Approach
Advantages <ul><li>Out of Plane Technique </li></ul><ul><ul><li>Shorter Needle Insertion Paths </li></ul></ul><ul><ul><li>...
Disadvantages <ul><li>Out of Plane Technique </li></ul><ul><ul><li>Unable to accurately track needle tip </li></ul></ul><u...
Reviewing the Basic Ultrasound Techniques
Literature Review:  Ultrasound Use in Regional Anesthesia
Just In Time!
Methods <ul><li>Inclusion Criteria </li></ul><ul><ul><li>RCT comparing ultrasound guided regional anesthesia with an alter...
Basis of the Liu’s Review Article <ul><li>14 Randomized Control Trials (RTCs) for Peripheral Nerve Blocks </li></ul><ul><l...
Ultrasound Guided Upper Extremity Anesthesia <ul><li>Seven RTCs compared US Guided regional block to alternative technique...
Ultrasound Guided Upper Extremity Anesthesia Continued: Any Advantages? <ul><li>Five Axillary Block Studies </li></ul><ul>...
Bucking the Trend:  Infraclavicular Blocks <ul><li>Dingeman et al 11 </li></ul><ul><ul><li>Compared Ultrasound vs. US with...
Ultrasound Guided Lower Extremity Anesthesia <ul><li>Four RCTs compared US guidance versus alternate technique </li></ul><...
Local Anesthetic Volume in Lower Extremity Nerve Blockade <ul><li>Casati et al 5  showed a significant reduction in the Me...
First Do No  Harm ! <ul><li>No RCT has shown that other techniques are safer than Ultrasound Guidance </li></ul><ul><li>No...
Is There Evidence of Benefit in the Use of Ultrasound Guidance? <ul><li>Faster Block Performance </li></ul><ul><li>Fewer N...
Is There a Safety Benefit in Using Ultrasound Guidance? <ul><li>Direct visualization of needle should reduce the rate of i...
The Question Remains :   Given that there is no definitive evidence of increased efficacy or safety benefit with the use o...
Sparrow’s Predictions <ul><li>I predict we will see large multi-center studies that show a safety and efficacy benefit </l...
Sparrow’s Beliefs <ul><li>I believe that Ultrasound guidance will be a necessary skill in the future and resident educatio...
Questions, Comments…..Standing Ovation……Call for an Encore?
Bibliography <ul><li>1Sites BD, Brull R, Chan VW, Spence BC, Gallagher J, Beach MI, Sites VR, Harman GS.  Artifacts and pi...
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Ultrasound And Regional Anesthesia Feb 2009

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UAB Department of Anesthesia Grand Rounds 2009

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Transcript of "Ultrasound And Regional Anesthesia Feb 2009"

  1. 1. Ultrasound and Regional Anesthesia Jim Sparrow, MD UAB Anesthesia Grand Rounds February 9, 2009
  2. 2. Topics We Will Cover <ul><li>Basic Science : Ultrasound Technology and Terminology </li></ul><ul><li>Clinical Techniques : Generalized Ultrasound Techniques used in Regional Anesthesia </li></ul><ul><li>Literature Review : Ultrasound Guidance Outcome Data </li></ul><ul><li>Discussion : Is Ultrasound the Future or Just a Fad </li></ul>
  3. 3. Why This is Important <ul><li>New technology requires thorough investigation to determine safety, efficacy, reliability and cost effectiveness. </li></ul><ul><li>Ultrasound is already here and certain “experts” are proclaiming that its use should be standard of care. </li></ul>
  4. 4. Introduction to the Basic Physics and Terminology of Ultrasound
  5. 5. Ultrasound Waves <ul><li>Form of Acoustic Energy </li></ul><ul><li>Generated by Piezoelectric Crystals in Specialized Transducer Probes </li></ul><ul><ul><li>Curved Array </li></ul></ul><ul><ul><li>Linear Array </li></ul></ul><ul><li>Specific Frequency Ranges </li></ul>
  6. 6. Ultrasound Wave Propagation <ul><li>Longitudinally Propagated </li></ul><ul><li>Series of Brief </li></ul><ul><ul><li>Compressions (High Pressure) </li></ul></ul><ul><ul><li>Rarefactions (Low Pressure) </li></ul></ul><ul><li>Velocity of Propagation Depends on the Medium </li></ul>
  7. 7. Acoustic Velocity <ul><li>Propagation Velocity of a Sound Wave </li></ul><ul><li>Is Constant in the Human Body </li></ul><ul><li>In Humans = 1540 meters/second </li></ul><ul><li>Represented by the Equation </li></ul><ul><ul><ul><li>C = ƒ* λ </li></ul></ul></ul><ul><ul><ul><li>c= 1540 m/s </li></ul></ul></ul><ul><ul><ul><li>ƒ= frequency </li></ul></ul></ul><ul><ul><ul><li>λ = wavelength </li></ul></ul></ul>
  8. 8. How is an Image Created from Soundwaves?
  9. 9. Image Creation <ul><li>Requires Return of Soundwave to Probe ( Like a Boomerang ) </li></ul><ul><li>Probes rapidly cycle from Transmission to Reception </li></ul><ul><li>Cycles can be 7000/second </li></ul><ul><li>Returning waves are converted to Electrical Impulses </li></ul><ul><li>Computer Processing creates a 2-Dimensional Image </li></ul>
  10. 10. Two Determinates of Ultrasound Image Quality <ul><li>Ultrasound Probes: </li></ul><ul><ul><li>Transmits and Receives Ultrasound Waves </li></ul></ul><ul><li>Computer Processing: </li></ul><ul><ul><li>Creates Computer Image from Electrical Signals Received from the Probe </li></ul></ul>
  11. 12. Signal Intensity <ul><li>Determined by degree of reflected waves returning to the transducer </li></ul><ul><li>Larger intensities = Strongly reflected = Hyperechoic image (Whiter) </li></ul><ul><li>Weaker intensities = Weakly Reflected = Hypoechoic (Darker) </li></ul>
  12. 13. Ultrasound Wave Interaction with Tissues <ul><li>Reflection </li></ul><ul><ul><li>SPECULAR (large smooth objects like a needle) (d) </li></ul></ul><ul><ul><li>SCATTERING (most neural images) (a) </li></ul></ul><ul><li>Refraction (c) </li></ul><ul><li>Transmission (b) </li></ul>
  13. 14. Reflection of Ultrasound Waves <ul><li>Proportional to the difference in acoustic impedance between adjacent tissues </li></ul><ul><li>Greater difference = better distinction = better resolution </li></ul><ul><li>Explains the varying appearances of nervous tissue on U/S imaging </li></ul><ul><ul><ul><li>Interscalene vs Popliteal </li></ul></ul></ul>
  14. 15. Hyper vs. Hypoechoic Nerves
  15. 16. Refraction <ul><li>Occurs at tissue interfaces (unreflected) </li></ul><ul><li>Refraction can diminish image quality </li></ul><ul><li>Increases with angle of incidence </li></ul><ul><ul><li>Optimal angle of incidence is 90° </li></ul></ul><ul><li>Perpendicular probe minimizes effect </li></ul>
  16. 17. Optimal Image Resolution is a Balance
  17. 18. Attenuation <ul><li>Progressive loss of energy with signal propagation </li></ul><ul><li>Results in progressive decrease in returning signal </li></ul><ul><li>Major source is conversion of acoustic energy to heat </li></ul><ul><li>Loss of signal is directly related to depth </li></ul><ul><li>Attenuation is medium dependent </li></ul><ul><li>Represented by the Attenuation Co-efficient </li></ul><ul><ul><li>Bone>>Air>>>Muscle>Brain>Fat>Blood>>>Water </li></ul></ul>
  18. 19.         5.0 Bone 1.3-3.3 Muscle 1.0 Kidney 0.5-0.94 Liver 0.63 Fat 0.18 Blood 0.002 Water Attenuation Coefficient (dB/cm at 1MHz) Body Tissue 7.8 Bone 1.71 Muscle 1.63 Kidney 1.65 Blood 1.65 Liver 1.34 Fat 0.18 Lung 0.0004 Air Acoustic Impedance (10 6 Rayls) Body Tissue
  19. 20. Attenuation and Frequency <ul><li>Higher Frequency results in greater attenuation </li></ul>
  20. 21. Overcoming Loss of Signal from Attenuation <ul><li>Artificial Enhancement (Adjusting Gain) </li></ul><ul><li>Time Gain Compensation </li></ul><ul><ul><ul><li>Adjusts gain independently at specified depth intervals </li></ul></ul></ul><ul><ul><ul><li>Most modern U/S machines do this automatically (autogain) </li></ul></ul></ul><ul><li>Choosing lower frequencies for deeper tissues (posterior sciatic) </li></ul>
  21. 22. The Holy Grail: Better Resolution <ul><li>Resolution refers to the ability to distinguish one object from another </li></ul><ul><li>Three important types </li></ul><ul><ul><ul><ul><ul><li>Axial </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Lateral </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Temporal </li></ul></ul></ul></ul></ul><ul><li>In General: Higher Frequency Ultrasound Yields Better Resolution </li></ul>
  22. 23. Axial Resolution <ul><li>Separating two structures at Different Depths </li></ul><ul><li>Equal to ½ of pulse length </li></ul><ul><ul><li>Distance between objects must be greater the ½ pulse length to be seen as separate </li></ul></ul>
  23. 24. Lateral Resolution <ul><li>Separating two structures beside one another </li></ul><ul><li>Always worse than axial resolution </li></ul><ul><li>Close U/S beams improve lateral resolution </li></ul>
  24. 25. Temporal Resolution <ul><li>Directly related to U/S Frame Rate (FR) </li></ul><ul><ul><li>FR is the speed with which an imaging device produces unique consecutive images </li></ul></ul><ul><li>FR is limited by sweep speed </li></ul><ul><li>Sweep speed is limited by image depth </li></ul><ul><li>Image depth should be just below target </li></ul>
  25. 26. Review of Ultrasound Technology <ul><li>Image quality depends on probe technology and computer processor </li></ul><ul><li>Signal intensity is dependent on the proportion of reflected waves returning to the transducer </li></ul><ul><li>Nerves appears hyper or hypoechoic depending on surrounding tissue </li></ul><ul><li>Resolution is improved with high frequency ultrasound but Attenuation is greater for higher frequency ultrasound: Must find the right balance for image optimization </li></ul>
  26. 27. Basic Techniques of Ultrasound Guidance in Regional Anesthesia
  27. 28. All Ultrasound Guided Blocks Involve Three Steps 2 : <ul><li>Choosing One of Two Imaging Views </li></ul><ul><ul><li>Short Axis View </li></ul></ul><ul><ul><li>Long Axis View </li></ul></ul><ul><li>Scanning the Nerve Track for Image Optimization </li></ul><ul><li>Choosing a Needle Approach Technique </li></ul><ul><ul><li>In Plane </li></ul></ul><ul><ul><li>Out of Plane </li></ul></ul>
  28. 29. Imaging Plane Options <ul><li>Long Axis View or Longitudinal View </li></ul><ul><ul><li>Rarely Used </li></ul></ul><ul><li>Short Axis View or Transverse View </li></ul><ul><ul><li>Most Commonly Used </li></ul></ul><ul><ul><li>Relatively Easy </li></ul></ul><ul><ul><li>Better Resolution of Fascial Barriers that Surrond Nerves </li></ul></ul><ul><ul><li>Dynamic Assessment of Circumferential Local Anesthetic Spread </li></ul></ul><ul><ul><li>Workable Image Even with Slight Movement of Transducer Probe </li></ul></ul>
  29. 30. The ART 3 of Scanning <ul><li>A lignment </li></ul><ul><ul><li>Sliding Movement of Trandsducer Along the Course of the Nerve Lengthwise (Used in Short Axis View) </li></ul></ul><ul><li>R otation </li></ul><ul><ul><li>Clockwise/Counterclockwise Transducer Movement (Particularly important when attempting a long axis view) </li></ul></ul><ul><li>T ilting </li></ul><ul><ul><li>Angling Movement of Transducer to Optimize the Angle of Incidence (90º) </li></ul></ul>
  30. 31. Where is The Needle Coming From? <ul><li>Out of Plane Technique </li></ul><ul><ul><li>Inserting the needle so that it crosses the plane of imaging near the target. </li></ul></ul><ul><li>In Plane Technique </li></ul><ul><ul><li>Inserted within the plane of imaging to visualize the entire shaft and tip. </li></ul></ul>
  31. 32. Out of Plane Approach
  32. 33. In Plane Approach
  33. 34. Advantages <ul><li>Out of Plane Technique </li></ul><ul><ul><li>Shorter Needle Insertion Paths </li></ul></ul><ul><ul><li>Less Patient Discomfort </li></ul></ul><ul><ul><li>Easier to Perform </li></ul></ul><ul><li>In Plane Technique </li></ul><ul><ul><li>Ability to Track the Needle Tip </li></ul></ul><ul><ul><li>Theoretically Safer </li></ul></ul>
  34. 35. Disadvantages <ul><li>Out of Plane Technique </li></ul><ul><ul><li>Unable to accurately track needle tip </li></ul></ul><ul><ul><li>Difficulty finding the echogenic “dot” as the needle crosses the US beam </li></ul></ul><ul><li>In Plane Technique </li></ul><ul><ul><li>More Time Consuming </li></ul></ul><ul><ul><li>More difficult to perform </li></ul></ul><ul><ul><li>False security when partial needle lineups give appearance of a needle tip </li></ul></ul><ul><ul><li>Can be more painful secondary to longer insertion paths </li></ul></ul>
  35. 36. Reviewing the Basic Ultrasound Techniques
  36. 37. Literature Review: Ultrasound Use in Regional Anesthesia
  37. 38. Just In Time!
  38. 39. Methods <ul><li>Inclusion Criteria </li></ul><ul><ul><li>RCT comparing ultrasound guided regional anesthesia with an alternative method </li></ul></ul><ul><ul><li>Large prospective case series to provide estimates of efficacy and safety (>100 cases) </li></ul></ul><ul><li>Definition of Efficacy </li></ul><ul><ul><li>Not requiring conversion to an alternative anesthetic technique </li></ul></ul>
  39. 40. Basis of the Liu’s Review Article <ul><li>14 Randomized Control Trials (RTCs) for Peripheral Nerve Blocks </li></ul><ul><li>2 Case Series for Peripheral Nerve Blocks </li></ul><ul><li>6 RTCs fot Neuro-axial Anesthesia </li></ul><ul><li>1 Case Series for Neuroaxial Anesthesia </li></ul>
  40. 41. Ultrasound Guided Upper Extremity Anesthesia <ul><li>Seven RTCs compared US Guided regional block to alternative technique </li></ul><ul><li>All trials used regional blockade for surgical anesthesia </li></ul><ul><li>No trial showed significant differences in efficacy between US guided and alternative technique (i.e. conversion to general anesthesia) </li></ul><ul><li>Six of the seven showed no difference in supplementation requirements </li></ul><ul><li>Two of the seven trials measured patient satisfaction and found no differences between techniques </li></ul>
  41. 42. Ultrasound Guided Upper Extremity Anesthesia Continued: Any Advantages? <ul><li>Five Axillary Block Studies </li></ul><ul><ul><li>Four of Five reported fewer needle passes or faster time for block performance </li></ul></ul><ul><ul><li>Four of Five reported faster or more complete early onset of sensory or motor block (none reported a significant difference in onset of surgical anesthesia) </li></ul></ul><ul><li>Soeding et al 9 showed earlier sensory or motor blockade for interscalene blocks but did not show a difference in duration of analgesia </li></ul><ul><li>Williams et al. 10 showed faster block performance with ultrasound but no difference in onset or success during supraclavicular block </li></ul>
  42. 43. Bucking the Trend: Infraclavicular Blocks <ul><li>Dingeman et al 11 </li></ul><ul><ul><li>Compared Ultrasound vs. US with Nerve Stimulation </li></ul></ul><ul><ul><li>Found US alone resulted in faster block performance, more complete early blockade and less need for supplementation </li></ul></ul><ul><li>Marhofer et al 12 </li></ul><ul><ul><li>Compared US with nerve stimulation in children </li></ul></ul><ul><ul><li>Found US resulted in less pain during block, faster block onset and longer duration of sensory blockade </li></ul></ul>
  43. 44. Ultrasound Guided Lower Extremity Anesthesia <ul><li>Four RCTs compared US guidance versus alternate technique </li></ul><ul><li>No RCT found differences in failed blocks </li></ul><ul><li>No RCT reported an persistent complications </li></ul><ul><li>Two RCTs showed shorter onset time with US guidance </li></ul><ul><li>One RCT reported better turniquet tolerance in midfemoral sciatic block for foot and ankle surgery with the use of ultrasound for the block </li></ul>
  44. 45. Local Anesthetic Volume in Lower Extremity Nerve Blockade <ul><li>Casati et al 5 showed a significant reduction in the Mean Effective Anesthetic Volume (MEAV 50 ) with the use of ultrasound guidance for femoral nerve blockade </li></ul><ul><li>Oberndorfer et al 14 reports both a significant reduction in required local anesthetic for both femoral and sciatic blocks as well as increased duration of analgesia for ultrasound guided blocks versus nerve stimulation alone </li></ul>
  45. 46. First Do No Harm ! <ul><li>No RCT has shown that other techniques are safer than Ultrasound Guidance </li></ul><ul><li>No RCT has shown that other techniques are superior in terms of efficacy </li></ul><ul><li>No RCT has shown that patient satisfaction is greater with an alternative technique </li></ul>
  46. 47. Is There Evidence of Benefit in the Use of Ultrasound Guidance? <ul><li>Faster Block Performance </li></ul><ul><li>Fewer Needle Passes </li></ul><ul><li>Faster Initial Onset of Blockade </li></ul><ul><li>Possible Reduced Local Anesthetic Requirements </li></ul>
  47. 48. Is There a Safety Benefit in Using Ultrasound Guidance? <ul><li>Direct visualization of needle should reduce the rate of intraneural and intravascular punctures </li></ul><ul><li>Reduced local anesthetic requirements suggests less local anesthetic systemic toxicity risk </li></ul><ul><li>Fewer needle passes suggests less damage to surrounding tissues </li></ul><ul><li>BOTTOMLINE : Current evidence is INSUFFICIENT to support these assumptions given the rarity of significant nerve injury and systemic toxicity of local anesthetics </li></ul>
  48. 49. The Question Remains : Given that there is no definitive evidence of increased efficacy or safety benefit with the use of Ultrasound Guidance, is this a passing fad or is US guidance here to stay?
  49. 50. Sparrow’s Predictions <ul><li>I predict we will see large multi-center studies that show a safety and efficacy benefit </li></ul><ul><li>I predict that the volume of local anesthetic used in the future will be significantly smaller than the accepted norms of today </li></ul><ul><li>I predict US technology will continue to improve and techniques will become easier as our collective experience grows </li></ul>
  50. 51. Sparrow’s Beliefs <ul><li>I believe that Ultrasound guidance will be a necessary skill in the future and resident education in the technique should be a top priority </li></ul><ul><li>I believe that the current body of evidence does not support the argument for Ultrasound Guidance as the new standard of care for regional anesthesia </li></ul><ul><li>I believe that certification for ultrasound use is a major mistake but there is already a growing number of certification proponents </li></ul><ul><li>And finally….I believe the children are our future </li></ul><ul><li>-Whitney Houston </li></ul>
  51. 52. Questions, Comments…..Standing Ovation……Call for an Encore?
  52. 53. Bibliography <ul><li>1Sites BD, Brull R, Chan VW, Spence BC, Gallagher J, Beach MI, Sites VR, Harman GS. Artifacts and pitfall errors associated with ultrasound-guided regional anesthesia. Part I: understanding the basic principles of ultrasound physics and machine operations. Reg Anesth and Pain Med . 2007;32:412-418. </li></ul><ul><li>2Gray AT. Ultrasound-guided regional anesthesia: current state of the art. Anesthesiology . 2006; 104:368-373, discussion 5A. </li></ul><ul><li>3Marhofer P, Chan VW. Ultrasound-guided regional anesthesia: current concepts and future trends. Anesth Analg . 2007;104:1265-1269. </li></ul><ul><li>4Liu et al. Ultrasound-Guided Regional Anesthesia and Analgesia: A qualitative systematic review. Reg Anesth and Pain Med . 2009;34:47-59. </li></ul><ul><li>5Casati 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;106:992-996. </li></ul><ul><li>6Chan VW, Perlas A, McCartney CJ, Brull R, Xu D, Abbas S. Ultrasound guidance improves success rate of axillary brachia plexus block. Can J Anaesth . 2007;54:176-182. </li></ul><ul><li>7Sites 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;50:678-684. </li></ul><ul><li>8Liu FC, Liou JT, Tsai YF, Li AH, Day YY, Hui YL, Lui PW. Efficacy of ultrasound-guided axillary brachial plexus block: a comparative study with nerve stimulator-guided method. Chang Gung Med J . 2005;33:396-402. </li></ul><ul><li>9Soeding PE, Sha S, Royse CE, Marks P, Hoy G, Royse AG. A Randomized trial of ultrasound-guided axillary brachial plexus anaethesia in upper limb surgery. Anaesth Intensive Care . 2005;33:719-725. </li></ul><ul><li>10Williams 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;97:1518-1523. </li></ul><ul><li>11Dingemans E, Williams SR, Arcand G, Chouinard P, Haris P, Ruel M, Girard F. Neurostimulation in ultrasound-guided infraclavicular block: a prospective randomized trial. Anesth Analg . 2007;104:1275-1280. </li></ul><ul><li>12Marhofer P, Sitzwohl C, Greher M, Kapral S. Ultrasound guidance for infraclavicular brachial plexus anaesthesia in children. Anaesthesia . 2004;59:642-646. </li></ul><ul><li>13Marhofer P, Schrogendorfer K, Wallner T, Koinig H, Mayer N, Kapral S. Ultrasonographic guidance reduces the amount of local anesthetic for 3-in-1 blocks. Reg Anesth Pain Med . 1998;23:584-588. </li></ul><ul><li>14Oberndofer U, Marhofer P, Bosenberg A, Willschke H, Felfernig M, Wientraud M, Kapral S, Kettner SC. Ultrsonographic guidance for sciatic and femoral nerve blocks children. Br J Anaesth. 2007;90:797-801 </li></ul>
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