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Canadian Journal of Anesthesia 54:392-396 (2007)
© Canadian Anesthesiologists' Society, 2007
Images in Anesthesia

Cadaveric ultrasound imaging for training in ultrasound-guided peripheral nerve blocks: upper extremity

Ban C.H. Tsui, MSc MD FRCPC, Derek Dillane, MB MMedSci FFARCSI and Anil H. Walji, MD PhD

University of Alberta Hospitals, Edmonton, Canada E-mail: btsui{at}ualberta.ca


   Introduction
TOP
 Introduction
Blocks above the clavicle...
 Brachial plexus below the...
 Terminal nerves in the...
 References
 
ULTRASOUND-GUIDED peripheral nerve blocks (PNBs) can offer many benefits, but their performance requires excellent knowledge of the related clinical anatomy and confidence with obtaining reproducible ultrasound images while simultaneously handling the probe and needle.1 Unfortunately, there has not yet been a set of standard training modalities developed to improve clinical performance with ultrasoundguided PNBs.2 Although underutilized, cadavers are useful tools for practical training in regional anesthesia. 3 Utilizing cadavers could increase block-related anatomical knowledge and confidence in performing these blocks, both of which may ultimately enhance the learning of ultrasound-guided PNBs.4 Specific elements that could benefit from teaching with a cadaver model include probe handling on irregular surfaces (e.g., supraclavicular region), accurate probeneedle alignment to enable clear visibility of the entire needle, and needle tracking to the target nerve structure. 5–8 While not every medical school will have the accessibility or desire to use cadavers for training with nerve block techniques, this medium may be very suitable for large group teaching sessions.

In this Images in Anesthesia feature, ultrasound images (MicroMaxx, SonoSite Inc, Bothel, WA, USA; HFL38 or SLA, 13-6MHz linear probe) obtained from a male adult cadaver [body mass index (BMI) 28 and embalmed six months previously in the usual manner (using a solution containing a combination of 4% formaldehyde, 95% ethanol, glycerol, phenol and water that was perfused under pressure through the femoral artery) at the authors’ institution] are compared to the images from an adult male (BMI 22). The cadaver was in legal custody of the Division of Anatomy of the authors’ institution. The embalming and imaging procedures were performed with permission from the Division of Anatomy in compliance with the institutional ethical standards for the use of human material in medical education. Ethics approval was obtained from the local Institutional Research Ethics Board for ultrasound scanning on the volunteer (one of the authors).

In addition to demonstrating the similarity between cadaveric and live imaging, some of the site-specific benefits and obstacles related to scanning the cadaveric specimen are highlighted. These images also consider several non-traditional block locations (i.e., radial nerve at the elbow and ulnar nerve at mid-forearm). Although these sites can be used for either hand surgery/procedures or rescue analgesia,9,10 their safety and efficacy have not been evaluated in any large study.

The following notes are related to all of the figures: 1) the number (depth in centimetres) in the far right lower corner of each image indicates that the images were taken at similar depths and show equal magnification for both cadaveric and live subjects; 2) the needle is shown in the clinical pictures to illustrate technique, particularly probe placement, but the needle was not used during the scans and will not be found in the image; and finally, 3) the cadaveric images have minimal labelling to minimize obstruction of view.


   Blocks above the clavicle (Figure 1Go)
TOP
 Introduction
 Blocks above the clavicle...
Brachial plexus below the...
 Terminal nerves in the...
 References
 
The image of the live subject in (a) shows the hyperechoic (bright) surface of the clavicle (with deep dorsal shadowing) inferiorly and the brachial plexus trunks/divisions as a tightly enclosed cluster (‘honeycomb’) of hypoechoic (dark) nodules superolateral to the pulsating subclavian artery. The cadaveric image had a similar resolution except the artery was non-pulsatile. At the interscalene groove (b), the plexus roots/trunks were captured in the live subject as three distinct hypoechoic nodules between anterior and middle scalene muscles. Although the roots/trunks appeared quite distinct in the cadaver, identifying them between the poorly delineated scalene muscles was challenging. Optimizing the interscalene image captured from the cadaver, typically done by rotating the neck contralaterally, was difficult due to rigidity which depends on both the timing of the embalming and the position of the cadaver.


Figure 1
Figure 1
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  		FIGURE 1 Ultrasound images captured at the supraclavicular (a) and interscalene (b) locations. Arrows: ner ve structures; ASM and MSM = anterior and middle scalene; SCM = sternocleidomastoid muscles; SA = subclavian artery.

 

   Brachial plexus below the clavicle (Figure 2Go)
TOP
 Introduction
 Blocks above the clavicle...
 Brachial plexus below the...
Terminal nerves in the...
 References
 
Scanning in the axillary region of the cadaver (a) was limited by the tissue rigidity and poor range of motion, making it difficult to capture an ideal image at a transverse axis to the nerves. The poor quality of the axillary vs infraclavicular (b) imaging in this cadaver is evident from the collapsed axillary vessels and reduced resolution and demarcation of the surrounding tissues. The useful landmark-based identification of the various nerves according to their relationship with the axillary artery (although much variability exists) was difficult due to the cluster of flattened neurovascular structures and inability to use colour Doppler to identify vascular structures. In contrast, the infraclavicular cadaveric image illustrates that ultrasound imaging can be useful to clearly mark vital structures (vessels, pleura) and could be used to practice an anatomical landmark-based technique. In the infraclavicular region, the dense and hypoechoic axillary vessels are well demarcated and distinct, adjacent to the plexus cords (typically appearing as round to slightly elliptical hypoechoic structures, with a gross punctate internal pattern seen within a homogeneous hyperechoic connective tissue background). The contrast between the cadaveric and live infraclavicular images is related to the difference in BMI, as there was less sc depth in the live subject. Interestingly, the plexus structures at the infraclavicular level were quite distinguishable in the cadaver, unlike the often limited identification in many subjects.11


Figure 2
Figure 2
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  		FIGURE 2 Ultrasound images from scanning at the axillary (a) and infraclavicular (b) regions. Arrows = ner ve structures; R = radial; M = median; MC = musculocutaneous; and U = ulnar ner ves. L = lateral; M = middle; and P = posterior cords. BB = biceps brachii; CB = coracobrachialis; TB = triceps brachii; PM and Pm = pectoralis major and minor; AA and AV = axillary artery and vein.

 

   Terminal nerves in the periphery (Figure 3Go)
TOP
 Introduction
 Blocks above the clavicle...
 Brachial plexus below the...
 Terminal nerves in the...
References
 
Ultrasound images were captured at potential block locations for the radial, ulnar and median nerves. In contrast to the proximal blocks, the nerves in the periphery are often largely hyperechoic. At the elbow, the triangular radial nerve appears superficial to the hyperechoic-outlined lateral epicondyle (a). At this block location the posterior forearm will not be anesthetized due to the more proximal branching of the posterior antebrachial cutaneous nerve. Hence, this block is used mainly for rescue analgesia.


Figure 3
Figure 3
Figure 3
Figure 3
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  		FIGURE 3 Ultrasound images from scanning the upper extremity and capturing the radial (a & b), ulnar (c) and median (d) ner ves. Arrows = ner ves (neurovascular bundle at radial groove); DBA, UA and BA = deep brachial, ulnar and brachial arteries; TB, BM and BR = triceps brachii (lateral head), brachialis and brachioradialis muscles.

 
To confirm the radial nerve’s identity, we used a traceback methodology to follow along its course proximally and posterior to the radial/spiral groove, where the nerve abuts the oval-shaped humerus and lies adjacent to the deep brachial artery (b);12 although the needle is shown in the clinical picture, this location has yet to be described as useful. The images of the ulnar [at mid-forearm (c)] and median [at antecubital fossa (d)] nerves in the cadaver illustrate that nerve localization techniques using vascular landmarks (ulnar and brachial artery, respectively) can be easily practiced. Arterial pulsation is of great benefit in identifying the ulnar nerve at the forearm/wrist (ulnar artery) but of diminished value for identification of the radial nerve at the elbow (radial collateral or recurrent artery). Despite this, scanning and needling of the terminal nerves is easily accomplished in cadavers as the rigidity of the embalmed tissues is less of an obstacle at these locations.

While imaging in cadavers may not be ideal in all cases,13 most images can be interpreted to a reasonable extent and can be useful for training purposes. Although using special solutions or fresh (unembalmed) cadavers may provide better imaging and improved manipulation for easier access to some areas (e.g., neck), these would likely increase the cost significantly and limit widespread availability. The clarity of the images in this article illustrates that the cadavers available through most medical schools and embalmed in the usual manner can be useful for teaching these specialized techniques. In fact, this learning model may also provide excellent opportunities for introducing and teaching medical students ultrasonographic anatomy as well as its clinical application in regional anesthesia. Limitations include the inability to use nerve stimulation for confirming specific nerve localization, and the lack of pulsatile arteries for Doppler confirmation. Artificial pulses have been generated via pneumatic devices and may be beneficial for regional anesthesia training in cadavers; this simulation requires tissue incision and a catheter for balloon insufflation,14 both of which may interfere with ultrasound imaging.

Many of the images shown here contain easily identifiable vessels regardless of their static nature. Many regional anesthesia training programs need improvement15 and using cadavers more frequently as training models could be useful for teaching the relevant anatomy and methodology of traditional blocks (through dissections and needling practice) as well as ultrasound-guided techniques (through static and real-time imaging and needling practice). The opportunity to use a stress-free preclinical setting to practice the intricacies of both needle-probe alignment and dynamic needle tracking within the target tissue could be of great value.


   Footnotes
 
Supported in Part by Education and Research Fund, Department of Anesthesiology and Pain Medicine, University of Alberta Hospitals, Edmonton, Canada, and Clinical Investigatorship Award, Alberta Heritage Foundation for Medical Research, Alberta, Canada.

Accepted for publication February 13, 2007.


   References
TOP
 Introduction
 Blocks above the clavicle...
 Brachial plexus below the...
 Terminal nerves in the...
 References
 
1 Kirchmair L, Entner T, Kapral S, Mitterschiffthaler G. Ultrasound guidance for the psoas compartment block: an imaging study. Anesth Analg 2002; 94: 706–10.[Abstract/Free Full Text]

2 Kessler J, Bolger AF, Gray AT. An essential skill. Reg Anesth Pain Med 2006; 31: 498–500.[Medline]

3 Lirk P, Colvin JM, Biebl M, et al. Evaluation of a cadaver workshop for education in regional anesthesia (German). Anaesthesist 2005; 54: 327–32.[Medline]

4 Broking K, Waurick R. How to teach regional anesthesia. Curr Opin Anaesthesiol 2006; 19: 526–30.[Medline]

5 Gray AT. Ultrasound-guided regional anesthesia: current state of the art. Anesthesiology 2006; 104: 368–73, discussion 5A.[Medline]

6 Tsui BC, Dillane D. Needle puncture site and a "walkdown" approach for short-axis alignment during ultrasound- guided blocks. Reg Anesth Pain Med 2006; 31: 586–7.[Medline]

7 Tsui BC, Twomey C, Finucane BT. Visualization of the brachial plexus in the supraclavicular region using a curved ultrasound probe with a sterile transparent dressing. Reg Anesth Pain Med 2006; 31: 182–4.[Medline]

8 Tsui BC. Facilitating needle alignment in-plane to an ultrasound beam using a portable laser unit. Reg Anesth Pain Med 2007; 32: 84–8.[Medline]

9 Gray AT, Schafhalter-Zoppoth I. Ultrasound guidance for ulnar nerve block in the forearm. Reg Anesth Pain Med 2003; 28: 335–9.[Medline]

10 Liebmann O, Price D, Mills C, et al. Feasibility of forearm ultrasonography-guided nerve blocks of the radial, ulnar, and median nerves for hand procedures in the emergency department. Ann Emerg Med 2006; 48: 558–62.[Medline]

11 Perlas A, Chan VW, Simons M. Brachial plexus examination and localization using ultrasound and electrical stimulation: a volunteer study. Anesthesiology 2003; 99: 429–35.[Medline]

12 Tsui BC, Finucane BT. The importance of ultrasound landmarks: a "traceback" approach using the popliteal blood vessels for identification of the sciatic nerve. Reg Anesth Pain Med 2006; 31: 481–2.[Medline]

13 Eichenberger U, Greher M, Kirchmair L, Curatolo M, Moriggl B. Ultrasound-guided blocks of the ilioinguinal and iliohypogastric nerve: accuracy of a selective new technique confirmed by anatomical dissection. Br J Anaesth 2006; 97: 238–43.[Abstract/Free Full Text]

14 Schwarz G, Kleinert R, Dorn C, Litscheer G, Feigl G, Bock N. Pneumatic pulse simulation in cadavers for teaching peripheral plexus blocks. Internet Journal of Anesthesiology 2007; 4.

15 Broking K, Waurick R. How to teach regional anesthesia. Curr Opin Anaesthesiol 2006; 19: 526–30.[Medline]




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