Ultrasound imaging techniques

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1 Ultrasound imaging techniques for regional blocks in intensive care patients Albrecht Wiebalck, MD, PhD; Thomas Grau, MD, PhD Ultrasound imaging techniques have gained great popularity in anesthesia during the last decade. They have been shown to allow better quality of regional blocks, improving the outcome of patients and reducing the costs at the same time, for two major reasons. First, ultrasound imaging provides information of the individual anatomic structure and abnormalities before puncture. Second, the ultrasound-guided puncture is displayed in real time, and this enables the physician to correct the direction of the needle, both to improve the spread of local anesthetics and to avoid tissue damage. Ultrasound imaging allows control, even in difficult cases and in situations with variations of normal anatomy. Even positioning dependent variations of nerve roots can be managed most effectively. In addition, the time can be reduced considerably to perform regional blocks; the onset time is shorter, and the quality of blocks is better. So, ultrasound imaging techniques are routinely applied in the University Clinics Bergmannsheil, Bochum, Germany. (Crit Care Med 2007; 35[Suppl.]:S268 S274) KEY WORDS: ultrasound imaging; quality of regional anesthesia; regional block; time savings; cost savings; doughnut sign; fascicles; short onset time Ultrasound imaging techniques are used in anesthesia for diagnostic procedures, for peripheral blocks, and for neuroaxial anesthesia. Over the years, there have been several attempts to reduce failure in regional anesthesia procedures by varying the needle trajectory and evaluating the stimulation techniques to optimize the puncture procedure. More recently, several groups have developed techniques and methods for an ultrasound-guided demonstration of neural structures to enable ultrasoundguided puncture procedures in regional anesthesia. Techniques were developed to detect nerve roots and better define the surrounding tissue (1 3). The on-line application of catheters and needles for safe placement of blocks was also demonstrated (4 6). Today, many of these techniques are established; needle and catheter manipulations and the placement of medication can now be controlled effectively (7 11). From the Department of Anesthesiology, Intensive Care, Palliative, and Pain Medicine, University Clinics Bergmannsheil, Bochum, Germany. For information regarding this article, Copyright 2007 by the Society of Critical Care Medicine and Lippincott Williams & Wilkins DOI: /01.CCM New methods involving imaging techniques in the puncture procedures used for regional anesthesia are closely related to the modern possibilities for regional anesthesia. The high-frequency linear probes and depiction processing of the newer generations of ultrasound machines allow detailed definition of anatomic structures, especially using the small-parts ultrasound technique; these new techniques also allow examination of the nerve roots before performing puncturing procedures. Success rates of nearly 100%, with reduced processing time and delay until complete analgesia, have been demonstrated (12, 13). Thus, ultrasound-guided techniques have reduced misplacement and failure in clinical practice. The safer and more effective placement of the medication allows for reduction of the amount of administered drug solution, which might be of importance in the critically ill, in children, and in patients who need more than one block (i.e., nervi femoralis and ischiadicus block) (14, 15). Indications of Regional Anesthesia in Critically Ill Patients Regional anesthesia is indicated for many critically ill patients and a valuable option for several reasons. The first indication is pain therapy. It is helpful especially for those who are traumatized or who have undergone surgery. Regional analgesia provides the most effective pain treatment: pain can be avoided with minimal doses of medication. Hence, side effects of pain therapy are minimized. Systemic analgesia, in contrast, is of minor quality because pain reduction is less effective and side effects, like sedation, ventilatory depression, or reduction of bowel activity, may slow down the process of recuperation. Furthermore, regional analgesia allows for a better outcome of joint functionality because early training without pain results in better mobility, shorter hospital stay, and lower costs (16). The second indication for regional anesthesia techniques is sympathicolysis. Many studies show that stress is reduced, especially with neuroaxial techniques. They lower the rate of heart infarctions, shorten postoperative and posttraumatic ileus, and together with other means, improve the outcome and shorten the length of intensive care unit stay (17). The third indication for regional anesthesia is the prevention of chronic pain. Patients with amputations, thoracotomies, and other painful operations or severe trauma develop chronic pain in up to 70% of cases (18). They represent about 15 25% of all chronic pain patients, causing costs of 40 billion euros per year in Germany. Regional analgesia is the S268

2 most effective method to reduce the subsequent development of chronic pain. However, contraindications and difficulties in placing a regional analgesia catheter must not be overseen. Infections, bleedings, especially in the epidural space, and positioning of the patient during placement of the catheter require an individual decision for each patient. Schulz-Stubner et al. provide a good overview on these problems (19). Technique of Ultrasound-Guided Regional Anesthesia The mainstay of a successful ultrasound-guided regional block is the visibility and recognition of both the neural tissue and the needle. On one hand, the physician has to discern different types of tissues such as connective tissue, tendons, and nerves to know where to aim. On the other hand, the physician should be able to follow the tip of the needle. The following sections describe important factors for ultrasound imaging of nerves and needles. Nerve Imaging with Ultrasound. Nerve imaging with ultrasound is a special subject. Nerve roots are usually composed of connective tissue and nerve fibers. The connective tissue consists of highly compressed collagen fibers with hyperechoic material and is usually connected with vessels for nutritional purposes. The nerve fibers are highly insolated by Schwann cells. They are densely packed, and together, they form the nerve. The neural tissue is, on one hand, highly lipophil and, on the other, hypoechoic when using ultrasound for imaging. Dependent on several factors, the quality of the discrimination between the hypoechoic nerve roots and the hyperechoic fibers is extremely variable. The most important factors are the angle between the needle and beam, nature of the surrounding tissue, distance between the nerve and probe, and frequency of the transducer. Principally, nerves can be demonstrated in the short-axis view (transverse cross-sectional plane) they present as a round, oval, or triangular shape or in the long axis as longitudinal structures. It has not been completely understood why cross-sectional pictures of fascicles (interscalene block) represent hypoechoic and more peripherally located nerves impress more by a anisotropic honeycomb structure. Please compare Figures 1 7. Figure 1. Adult patient, interscalene area. Description of the sonoanatomy with the musculi scalenus anterior and medius and the nerve roots C5 C8. M, musculus; ant, anterior. Figure 2. Adult patient, interscalene region after administration of local anesthetic solution. Description of sonoanatomy. The picture shows an increased size and echogenicity of the nerve roots and a homogeneous distribution of the hypoechoic local anesthetic solution. M, musculus; ant, anterior. Figure 3. Adult patient, infraclavicular area. Description of the sonoanatomy with vena (V) subclavia, arteria (A) subclavia, and the infraclavicular plexus. M, musculus. Tendons might resemble peripheral nerves because they have an anisotropic structure, too. The easiest way to differentiate between nerves and tendons is to follow the questionable structure along its course. Tendons change their crosssection and end in muscle and bone tissue, whereas nerves do not. Needle Imaging with Ultrasound. Needle selection and guidance have great influence on the performance of a block. Larger-bored needles (e.g., 18 gauge) are more readily visualized and easier to direct under ultrasound control. They are preferred for deep blocks (e.g., an infraclavicular block). Smaller-bored needles (e.g., 22 or 24 gauge) are harder to see but adequately visualized during more superficial blocks (e.g., the axillary block). The authors prefer small needles, in the conviction that they cause less tissue damage. Visibility depends on more factors, including frequency of transducer, distance between needle and probe, angle between needle and beam, and nature of sur- S269

3 Figure 4. Adult patient, infraclavicular region after administration of anesthetic solution. Description of sonoanatomy and of the distribution of the medication and demonstration of the three major fascicles. M, musculus; V, vena; A, arteria. Figure 5. Adult patient, axillary region before administration of anesthetic solution. Description of sonoanatomy and of the localization of the peripheral nerves. M, musculus; N, nervus; A, arteria; N cutaneus antebrach med, nervus cutaneus antebrachii medialis. Figure 6. Adult patient, axillary region after administration of local anesthetic solution. Description of sonoanatomy and of the localization of the peripheral nerves. Note the increased diameters of the nerves in comparison with Figure 5. N cutaneus antebrach med, nervus cutaneus antebrachii medialis; M, musculus; A, arteria. rounding tissue. Note that the needle is better seen when the bevel faces the probe. Avoid air bubbles in syringes to maintain optimal visibility. Principally, needles can be demonstrated in the short-axis view (transverse cross-sectional plane), in which they present as round or oval shapes, or in the long axis, in which they present as straight lines. S270 General Remarks on Ultrasound- Guided Needle Advancements. Choose an optimal point of insertion. It should allow for reaching all necessary points by one injection (try for axillary block as well), without several perforations of the skin, and is best with only one perforation. Do not perforate superficial vessels, and do not insert the needle in lines or wrinkles to avoid the higher degree of moisture, which favors infections of the insertion point around catheters. This is crucial in intensive care patients. Needle control is extremely important. There should be no advancement of the needle without identification and localization of the tip. Possible means are direct visualization, shadow of the needle, movements, tissue displacement, and last but not least, injection of a small volume. The authors use much smaller volumes than recommended by Gray (20) (i.e., ml of solution). More solution is not necessary to identify the position of the needle tip if it is close to or in the plane of ultrasound. Recognize vital structures (e.g., vessels and pleura) adjacent to the target nerves and avoid unintentional puncture. Theoretically, the nerve and needle may be visualized in four different positions (20). Both structures are seen in the short-axis and the long-axis view, respectively, or both structures are seen in different axis views: the nerve in the longaxis and the needle in the short-axis view or vice versa. The authors prefer the short-axis view for both the nerve and the needle because the identification of nerves is easy due to the patchy pattern, nerve images are stable during probe manipulations, circumferential spread of local anesthetics is more easily assessed, and the needle trajectory is shorter. This proceeding offers the greatest safety and ease of performance. In critical moments, small manipulations with the probe allow for combining the short-axis view with oblique planes, resulting in a more three-dimensional imaging of the surrounding structures. When all of these points are taken into account, the advancement of the needle to the nerves is less limited in comparison with the traditional landmark techniques. Physicians may deviate from the landmark rules to optimize the trajectory in accordance to the individual conditions of the present patient. They may choose where to insert the needle into the skin, in which direction to forward the needle, and how much local anesthetic solution is required until the neural structure is completely surrounded by the injected fluid. Furthermore, needle control by ultrasound imaging techniques allows a more effective needle approach to the nerves, the so-called V technique. The V describes the movements of the needle: the advancement of the needle to one side of

4 Figure 7. Adult patient, distal sciatic region after administration of anesthetic solution. Axial scan. Description of the doughnut phenomenon: the nerves are completely surrounded by fluid. N, nervus. the nerve and injection of local anesthetic solution until that side of the nerve shows a sufficient fluid layer. Then, the needle is partially pulled back and redirected to the other side of the nerve. Again, the required amount of fluid is administered until sufficient fluid surrounds the total circumference of the nerve. By this technique, the doughnut sign is achieved more effectively, with less local anesthetic solution than with a single deposit. Ultrasound-Guided Blocks of Upper Limb Interscalene Block. This block is usually performed with an axial/transversal scan at the level of the cricoid. The most important structures can be identified easily: the carotid artery, the jugular vein, the lateral end of the musculus sternocleidomastoideus, and the musculi scalenus anterior and scalenus medius (Fig. 1). With short-axis scanning and under sterile conditions, the nerves can be identified in most patients as the roots of C5 C8, with C5 located closer to the surface and the other in a row, closer to the vertebral column. First, a small needle (24 gauge) is used for the initial injection. Local anesthetic solution, 1 ml, is administered for skin infiltration, 9 ml for direct blocking of the nerve roots C5 C8. Slow advance of the needle with contemporary injection of small amounts of local anesthetic solution allows for a painless proceeding and a good localization of the needle tip at the same time. When the needle tip is close to the nerve roots, the remaining local anesthetic solution is injected. Usually, homogeneous distribution of local anesthesia medication can be detected as a hypoechoic halo around the nerve roots. Within a short time, there is an enhancement effect due to the increased volume of the nerve roots C5 C8 (Fig. 2). Second, the 18-gauge Contiplex needle (B. Braun, Bethlehem, PA) is inserted into the anesthetized skin and advanced to the nerve roots. Depending on the innervation of the surgical field, the needle is directed more deeply to the segments C7/C8 or more to the upper segments C4/C5. Then, again 10 ml of local anesthetic solution is administered, the mandarin is removed and the catheter passed through the mandarin-free Contiplex needle. For the ease and speed of the whole procedure, the catheter should be advanced 10 cm. After removal of the introducer, the catheter should be pulled back into the optimal position. The optimal length of the insertion of the catheter is calculated as the depth of needle insertion plus 3 5 cm, usually 6 8 cm. Then, the catheter is fixed to the skin by a suture. For better fixation, a small piece of tape is wrapped around the catheter close to the skin, preventing the thread from gliding along the catheter. Finally, the correct position of the catheter is verified. The last 20 ml of local anesthetic solution for a sufficient block is given through the catheter. Ultrasound imaging must reveal an increase of the hypoechoic halo around the nerve routes. Otherwise, the tip of the catheter might be outside the effective area, requiring a new catheter placement. Infraclavicular Block. For blocking the plexus brachialis in the infraclavicular region, a linear scanning plane is chosen directly below the clavicle. The characterizing structures axillary artery, subclavian vein, and musculus pectoralis are easily identified. At depth, usually the first rib, the pleura and the surface of the lung can be recognized. Lateral to the artery, the plexus can be seen as a crescent or triangular shape (Fig. 3). The point of needle insertion defined by optimal visualization of the essential structures is different from that of the traditional vertical infraclavicular puncture technique. It is located 1 3 cm more lateral. The puncture is performed under sterile conditions. First, with a small needle (24 gauge), 10 ml of anesthetic solution is used: 1 ml for skin anesthesia and 9 ml in the area around the triangular shape. The enhancement effect is easily visible within 30 secs (Fig. 4). Then, the thicker 18-gauge Contiplex needle is used to administer another 10 ml of medication for easier insertion of the catheter in case a continuous block is needed. The technique of inserting the catheter, determining the optimal length, fixation, and evaluation of the function are described in detail in the previous section. Axillary Block. Use an axial scan to visualize the humerus, the axillary artery, the nerve roots surrounding the artery, and the musculus coracobrachialis, which is located lateral to the artery (Fig. 5). Veins in the axillary region are easily compressed by a light pressure when guiding the probe in the axilla. The nervus musculocutaneus can easily be identified within the musculus coracobrachialis. The nerve emerges the lateral fascicle close to the median nerve. Usually, it is nicely visible more anterior and a little lateral of the artery. It is helpful to know that the nervus musculocutaneus moves away from the artery the more distal the probe is held and vice versa; the nerve is located closer to the artery the more cranial the probe is gliding, almost like a silverfish swimming back and forth to the artery when the probe is gliding up and down the axilla. The other three nerves are located close around the artery, with the nervus radialis being the deepest behind the artery, the nervus medianus more anterior and lateral, and the nervus ulnaris more anterior and medial of the artery. After identification, each nerve can be blocked with 5 10 ml of local anesthetic solution. Start the axillary block with the nervus musculocutaneus. With a short needle, the injection point is about 1 2 cm anterolateral to the injection point for the other three nerves. Then, advance the needle to the radial nerve first because depositing the local anesthetic solution behind the artery will push it to the surface and, starting with S271

5 Ultrasound and Epidural Anesthesia Figure 8. Adult patient, distal sciatic region after administration of local anesthetic solution. Longitudinal scan. N, nervus. Figure 9. Adult patient, transversal scan in the lumbar area. Demonstration of the processus spinosi, processus (Proc) articulares, and processus tranversi and depiction of the corpus vertebrae. the other two nerves, would extend the trajectory to the radial nerve. Furthermore, placement of the catheter behind the artery is more successful than placement elsewhere. The enhancement effect can be demonstrated with a more hyperechoic signal and a 2- to 3-fold increase in the volume of the nerves (Fig. 6). The technique of inserting the catheter, determining the optimal length, fixation, and evaluation of the function are described in detail in the discussion of the interscalenus block. Ultrasound-Guided Blocks of Lower Limb Block of Distal Nervus Ischiadicus. The best posture of the patient is supine, with the leg slightly elevated (i.e., supported by a pillow or a box), providing free access for the probe from below. Demonstrate the artery, the peroneus, and the tibial nerve. Advance the probe in a more proximal direction where both nerves emerge the sciatic nerve. Apply a needle (18-gauge Contiplex) in line. Apply medication around the nerve. Hypoechoic signal and even hyperechoic depiction can be seen. Often, the doughnut sign can be demonstrated. For this block, it is essential to have the doughnut sign around the whole nerve (Figs. 7 and 8). The technique of inserting the catheter, determining the optimal length, fixation, and evaluation of the function are described in detail in the discussion of the interscalenus block. Block of Nervus Femoralis. The best posture of the patient is supine. Demonstrate the femoral nerve, artery, and vein in the groin, slightly below the ligamentum inguinale. The femoral nerve presents often as triangular, most often lateral to the artery. Sometimes, it is difficult to identify it before injection of local anesthetic solution. After injection, it appears brighter and is more easily seen (Fig. 8). Choose a 24-gauge needle, infiltrate the skin and the underlying tissue with 1 2 ml, advance the needle tip to the space between the femoral artery and nerve, and inject the remaining volume of local anesthetic solution. Take an 18-gauge Contiplex or an appropriate needle and inject another 10 ml in the space between the artery and nerve before insertion of the catheter. For further details, see the discussion of the interscalenus block. The loss-of-resistance technique is the standard approach to identify the epidural space. Although this technique has been used for a long time, only about 60% of punctures are successful at first attempt (21). Apart from the degree of personal experience, this high failure rate has been attributed to the quality of anatomic landmarks and of patient positioning. It may therefore be easier to identify the epidural space by ultrasonography whenever difficulties arise in connection with these variables. Ultrasound imaging techniques allow the demonstration of the lumbar epidural space. This might be of greater importance in special groups of patients like: Children, because the distance between skin and epidural space is unknown and much shorter (14, 22). Parturients, because puncture is complicated in this group by weight gain, edema, and less elastic collagen fibers (21). Patients with anatomic abnormalities (3). Patients with limited optimization of positioning, like those in the intensive care unit. Best used are a 5-MHz curved-array or a 7.5-MHz linear probe and a combination of transverse and longitudinal scans (Figs. 9 and 10). It is possible to identify all relevant landmarks in the thoracic epidural space by ultrasound. However, the potential of ultrasound-guided epidural puncture might seem somewhat limited by the interfering bone structure and the relatively deep position of the epidural space, which detracts from the quality of the images obtained. Despite the limited quality of the images, the results of these preliminary studies are encouraging (23 25). Off-line Technique. With the off-line technique, an ultrasound scan is performed in the transversal and the longitudinal planes. The examination is performed directly before the puncture. With these scans, the physician is provided with information about the configuration of the spine, such as kyphosis, lordosis, or scoliosis. Usually, lateral deviations of the processus spinosus and the processus articulares in relation to the corpus vertebrae can be seen very effectively (Fig. 10). S272

6 REFERENCES Figure 10. Adult patient, longitudinal median scan in the lumbar area. Demonstration of the processus spinosus, ligamentum flavum, dura mater, and intrathecal space. Shortest possible (large dotted line) and expected needle trajectory (dashed line) to the epidural space are indicated. In the longitudinal median scan, there is also a chance to measure the needle trajectory. The effective needle trajectory is defined by the cranial and caudal borders of the processus spinosus. The best point for needle insertion is where all structures can be identified: the skin, the intervertebral ligaments, the muscles, the ligamentum flavum, and the more deeply located dura mater. The distance between skin and epidural space can be measured for different approaches with the distance-measurement software of the ultrasound system. The ideal starting point of the puncture and the ideal puncture angle can be measured. With this concept and with the additional information of the measured depth of the epidural space, the off-line puncture with the loss-of-resistance technique is safe, effective, and easy. On-line Technique. With this technique, usually a paramedian ultrasound scan is used to visualize intraspinal structures. The puncture itself is performed in the median plane, and the monitoring of the needle processing is performed via the paramedian scan. Nearly all procedures of puncture processing can be performed under direct control. This concept eases the application of epidural and intraspinal procedures. A problem might be that a third hand is necessary for holding the probe and producing effective pictures while using both hands for needle guidance or catheter placement. In addition, all on-line applications have to be performed with sterile sleeves on the ultrasound probe to avoid any contamination. Usually, these proceedings are adequate for epidural punctures in children when neuroaxial blocks must be performed under general anesthesia. This concept can also be used for anesthetized patients in the intensive care unit. With the knowledge of the needle trajectory and the application of the puncture needles under epidural anesthesia, the puncture process is safe and perfect for unconscious patients. Conclusion Direct ultrasonographic visualization significantly improves the outcome of most techniques in peripheral regional anesthesia. With the help of high-resolution ultrasonography, the physician can directly visualize relevant nerve structures for upper and lower limb nerve blocks at all levels. Such direct visualization improves the quality of nerve blocks and avoids complications. The use of ultrasound seems to enhance not only the traditional brachial and lumbosacral plexus blocks, but also neuraxial techniques. Promising results have been obtained in different groups of patients: intensive care patients, parturients, and children, in whom most types of blocks are performed under sedation or general anesthesia. The benefits of directly visualizing targeted nerve structures and monitoring the distribution of local anesthetic are significant. In addition, ultrasound monitoring allows the physician to correct the needle position in the event of maldistribution. It is therefore justified to expect physicians to acquire the skills to use ultrasound guidance in clinical practice. The technique can be established in a cost-efficient way, as portable ultrasound systems with high-frequency probes are now available. It is hoped that these systems will promote the routine use of ultrasound guidance in regional anesthesia and in other fields. 1. Chan VW, Nova H, Abbas S, et al: Ultrasound examination and localization of the sciatic nerve: A volunteer study. 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