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From the Departments of *Anesthesiology, and Cardiovascular Disease, Mayo Clinic, Jacksonville, Florida.
Address correspondence and reprint requests to Neil G. Feinglass, MD, Mayo Clinic, Jacksonville, FL. Address e-mail to ngf06{at}bellsouth.net.
Abstract
Two-dimensional ultrasound guidance has been used as an adjunct for neural blockade. With the development of newer ultrasound technology, three-dimensional ultrasound imaging is now available and may offer improved visualization of anatomic structures and relationships. We describe the successful blockade of the popliteal nerve with three-dimensional ultrasound guidance and image description.
Two-dimensional (2D) ultrasound is commonly used for guiding access to vascular structures, in transesophageal echocardiography, and most recently to guide peripheral nerve blocks (1–4). Several studies have shown the utility of 2D ultrasound to define the anatomy and to guide needle insertion (5). Peripheral nerves, being encased in fat, have ideal acoustic properties. Neighboring vascular structures often allow Doppler imaging (color, pulsed-wave, and continuous-wave) to provide additional structural detail and avoid vascular puncture and damage.
Nevertheless, 2D ultrasound has limited ability to visualize spatial relationships (3,5). This results from the nonlinear courses taken by vascular and neural structures as they traverse tissue planes (5). The 80-degree, cross-sectional, ultrasound beam can identify cross-sections of these structures only as they traverse the beam. However, visualizing the end of a structure, such as the needle tip, is often difficult.
Three-dimensional (3D) ultrasound can image the entire anatomical region, nerve thickness, and 3D relationships. Anesthetic distribution can be visualized in all 360-degree planes. This is generated from simultaneous reconstruction of two standard orthogonal 2D planes (X and Y axes), with the additional dimension of elevation (Z axis). The image may be digitally rotated 360 degrees for better visualization of the anatomic structures at the time of study, or at a later date for postblock analysis.
This report describes the first real-time application of 3D ultrasound reconstruction for guidance of the insertion of a popliteal nerve catheter for ankle surgery. This ultrasound technology is commercially available and is currently used in cardiac ultrasonography.
CASE REPORT
The criteria for publication and patient care were met by the Mayo Investigational Review Board. The patient was a 73-year-old woman scheduled for major reconstructive foot surgery. Informed consent was obtained from the patient for a continuous popliteal nerve catheter. The nerve block was performed in the preoperative patient holding area. After application of standard ASA monitors and administration of nasal oxygen, the patient was sedated with 1 mg midazolam and 50 µg of fentanyl IV. The block was performed with the patient in the prone position. A pillow was placed under the leg to allow for slight knee flexion. 3D ultrasound (3D Ultrasound System IE-33 with x 3-1 Matrix Array Probe, Philips Medical Systems; Andover, MA) was used during the procedure for needle guidance, confirmation of the catheter placement, and imaging of local anesthetic distribution.
The knee flexor crease was identified and marked. The borders of the biceps femoris and semitendinosus muscles were marked 8 cm above the knee crease. A line was drawn between the two muscles. The midline point of this line was the point of needle insertion. 3D ultrasound scanning confirmed the presence of the popliteal nerve at a depth of 3 cm from the skin at the surface mark. The 17-gauge, 50-mm Arrow® continuous peripheral block needle was directed cephalad toward the nerve at an 80 degree angle to the skin under continuous ultrasound guidance of the needle. As the needle approached the nerve, 2 Hz electrical stimulation was initiated at 1.5 mA. Ultrasound was used to guide the needle to the popliteal sciatic nerve. After obtaining toe flexion at 0.5 mA, a 19-gauge stimulating catheter (Stimucath®, Arrow International, Reading, PA) with an embedded wire to enhance echogenicity was inserted 5 cm past the tip of the needle with electrical stimulation guidance. The 3D ultrasound demonstrated the catheter to be in close proximity to the nerve (Fig. 1a).
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Under 3D ultrasound visualization, the initial injection of local anesthetic (3 mL followed by 7 mL of 0.5% ropivacaine) was observed to lie posterior to the nerve (Fig. 1b). Continuous injection of local anesthetic revealed complete encircle-ment of the nerve (Fig. 1c). Subsequent clinical examination revealed anesthesia in the sciatic distribution of the leg. A saphenous nerve block at the knee was added to complete the leg anesthesia. The patient was taken to the operating room and underwent uneventful surgery.
DISCUSSION
3D ultrasound images are a significant advance in digital ultrasound image processing. This technology has allowed the cardiac sonographers to better define valvular pathology as well as the size and function of cardiac chambers with improved definition of detail (6). 3D image reconstruction that required 20 min in the past can now be completed in real-time as demonstrated in this case report.
The 3D ultrasound transducer used for our patient was the first generation device that was designed for deep penetration of tissues and 3D cardiac reconstruction using frequencies of 1–3 MHz range. Second generation 3D transducers use frequencies of 2–7 MHz, which are better suited for common neural structures. Commercial vendors are customizing these systems for regional anesthesia blockade. The ease of use of these systems and improved image quality will follow rapidly. It should also be appreciated that while imaging in 3D, the clinician can at any time rapidly revert to standard 2D images. Although the application of 2D ultrasound to peripheral neural blockade is well established, we believe 3D application will further enhance the use of ultrasound in conjunction with regional anesthetic techniques.
Footnotes
This article has supplementary material on the Web site: www.anesthesia-analgesia.org.
REFERENCES
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