Ultrasound-Guided PNBs in Children

• Introduction
• Technical and Practical Details
  • Nerve Block Techniques
    • Cross-sectional technique
    • In-line technique
    • Infection precautions
  • Special considerations
    • Adjustment of the ultrasound unit
      • Image depth
      • Gain
      • Focus
  • Nerve block preparation strategies
• Specific peripheral nerve block techniques
  • Nerve blocks of the upper limb
    • Interscalene approaches to brachial plexus block
    • Supraclavicular approaches to brachial plexus blockade
    • Infraclavicular approaches to brachial plexus blockade
    • Axillary approaches to brachial plexus blockade
  • Rescue blocks of the upper extremity
    • Radial nerve
    • Ulnar nerve
    • Median nerve
  • Lower-limb blocks
    • Psoas compartment block
    • The 3-in-1 block
    • Selective saphenous nerve block
    • Sciatic nerve block
    • Subgluteal approach
    • Midfemoral approach
    • Popliteal sciatic block
  • Abdominal wall blocks
    • Ilioinguinal/iliohypogastric nerve block
• References
  

Modern pediatric anesthesia would not be conceivable without the use of regional anesthetic techniques. For instance, regional anesthesia decreases the need for mechanical ventilation following major thoracic or abdominal surgery. Also decreased is the need for intraoperative and postoperative opioids. Perhaps most importantly, the entire perioperative experience is less stressful for children whose perioperative pain is adequately managed. Most of the advantages of perioperative regional anesthesia are demonstrated in central neuroaxial blocks, specifically for caudal continuous lumbar or thoracic epidural blocks.

In contrast to central blocks, peripheral nerve blocks have not been studied extensively in children. A modified Medline search in April 2005 yielded 42 reports with pediatric anesthesia & epidural and only 17 reports with pediatric anesthesia & peripheral nerve block as search criteria. This finding shows clearly that peripheral nerve blockade in children is infrequently used in clinical practice. This infrequency is compounded by the fact that many pediatric anesthesiologists are still reluctant to use the nerve stimulator, the accepted standard tool to locate nerves in adults. "Blind“methods, such as for blockade of the ilioinguinal/iliohypogastric nerves, continue to be the most prevalent approach in pediatric anesthesia. Even techniques that today are used exclusively in conjunction with nerve stimulators in adults, are performed more or less “blind” in children.; for instance, by using anatomic landmarks as sole reference or by using fascial click techniques. Giaufré and coworkers [1] reported in a much-quoted overview article on a study performed under the auspices of the French Language Society of Pediatric Anesthesiologists (ADARPEF). In that study, a total of 24,409 regional anesthetic procedures were performed in children over a 1-year period, 15,013 (>60%) of them being central blocks. By comparison, only 38% of these were peripheral blocks. In this large series, there were no complications reported, suggesting that peripheral nerve blocks in children can be used with remarkable safety. However, it is possible that some complications were minor or went clinically undetected. For example, complications during blockade of the ilioinguinal/iliohypogastric nerves were not observed in that study, although it is unlikely that complications were virtually nonexistent, since the conventional techniques described must, perforce, involve numerous cases of peritoneal puncture.

Ultrasound-guided nerve blocks are rapidly becoming popular in adults. The smaller body size of children, allows the use of high-frequency, high resolution probes, making ultrasound particularly suitable to facilitate the practice of peripheral nerve blocks in a pediatric patient.. The reader should be advised that at the time of the publication of this book, this area of regional anesthesia is in its infancy and at the present time there is limited scientific data available on the true efficacy and safety of ultrasound-guided nerve blocks in children. Consequently, some views expressed in this chapter necessarily reflect the authors’ subjective opinions. Finally, because of our group's specific interest in anesthesia for pediatric trauma, most discussions in the chapter focus on blocks in pediatric patients with traumatic injury of the upper and lower extremities.

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Most blocks can be performed with 5- to 10-MHz linear ultrasound transducers. In addition, small probes are required due to the narrow anatomic relationships in children. "Hockey-stick" probes, with a surface length of 25 mm, are particularly well suited for this purpose. Also, higher-frequency transducers are available for portable ultrasound units. Theoretically, superficial nerve structures can be better visualized using these higher frequencies. The discussion of techniques in the following sections, however, is based on ultrasound probes working at somewhat lower frequencies. Lower frequencies are preferable for deeper blocks, such as psoas compartment blocks in larger children, because the nerve structures to be visualized are located deeper in this situation. Therefore, we use 2- to 4-MHz sector transducers for this specific indication.

The term anisotropy indicates the degree to which peripheral nerves can be optimally visualized only if the sonographic signals are oriented perpendicular to the nerve. Different nerves are characterized by different degrees of anisotropy. In general, the nerves of the upper limbs, for example, are characterized by high anisotropy. However, even minute deviations from the optimal angulation of the probe can greatly reduce the quality of visualization. In this situation, the chances of effectively blocking the sciatic nerve under ultrasound guidance are limited. The phenomenon of different nerves having different anisotropic properties is still poorly understood. Presumably, however, the degree of anisotropy has to do with the inner architecture of the neuronal structures involved.

It is important to note that some of the images shown in the discussion that follows were obtained with high-end ultrasound units, which allow anatomic structures to be visualized in greater detail. However, this was solely done for publication purposes, with didactic considerations in mind. We specifically challenge the widespread view that ultrasound-guided regional anesthesia is a technique reserved for “rich” institutions, such as university hospitals. In fact, all techniques described in the chapter can be carried out perfectly well with portable systems, which can be acquired for a fraction of the price typically expended for anesthesia machines.

In accordance with the immobile needle concept, as described by Winnie, we use short-beveled needles with flexible injection tubing for most peripheral nerve block techniques. These authors feel that short-beveled needle design optimizes the precision of needle guidance inside the tissue. The surgical instrument industry is making major efforts to develop more suitable needles and catheters for better ultrasound visualization. The future will show whether it will be possible to strike a meaningful balance between sonographic visualization of the canula and the appearance of artifacts.

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Techniques of nerve blockade fall into two major groups depending on the position of the needle relative to the ultrasound transducer: the cross-sectional and the in-line technique.

Cross-sectional technique

With the cross-sectional technique (Figures 52-1 and 52-2), the needle is positioned transversal to the ultrasound probe, such that visualization in the ultrasound image is confined to the needle tip. The angle of needle insertion must be selected in such a way that the needle tip can be advanced precisely to the depth of the target structure. In addition to direct visualization, the needle is identified in the ultrasound image both by tissue displacement and by an acoustic shadow emerging dorsally at its tip. Attention must be paid when injecting the local anesthetic to visualize the spread of the anesthetic. Failure to visualize the local anesthetic in the ultrasound image during injection indicates that the needle tip is located outside of the ultrasound window. The described technique is used for most nerve blocks described in this chapter.

Clinical pearls

• The most reliable way to obtain ultrasound-assisted nerve blockade is by using a transversal pathway
• The needle to nerve distance is shorter with the cross-sectional than with the in-line technique; in addition, the shorter distance is associated with less needle trauma in tissue and less pain
• Precise location of the needle tip in the ultrasound image, although an important requirement, is not a decisive factor for successful blockade; always remember:
  1. Nerves are blocked not by the puncture needle but by the local anesthetic!
  2. Discernment of the location of the needle on ultrasound is helped by identifying both tissue displacement and an acoustic shadow, which emerges posterior to its tip

In-line technique

With the in-line technique (Figures 52-3 and 52-4), the needle is advanced longitudinally to the ultrasound probe. The advantage of this technique is that visualization is not confined to the tip but also extends to the shaft of the needle. This result can only be achieved, however, if the needle is located strictly within the range of the emitted ultrasound signals. Therefore, the requirements of positioning the probe relative to the needle are even more exacting. In case of transversal deviations as small as 1–2 mm, the needle will disappear from the image. In practice, this technique remains confined to a few specific applications.

Infection precautions

The approach to pediatric regional anesthesia with regard to infection control is essentially the same as in adults. For single punctures, a surface disinfectant is used on the transducer, making sure that the disinfectant selected is compatible with the manufacturer’s recommendations regarding probe cleaning. Subsequently, the area for needle insertion is disinfected, and a sterile ultrasound gel is applied. A no-touch strategy is then followed, avoiding contact of the needle with the transducer or any other objects.

For perineural catheter insertion, sterile draping is used and the ultrasound probe is enclosed in sterile wrapping. For this purpose, an ultrasound gel is filled into a sterile plastic pouch or glove, and the sterile gel is again applied to the pouch or glove.

Special considerations

The success of PNBs in children can be difficult to evaluate because pain or postoperative anxiety in children depend on numerous criteria and need to be evaluated on an individual basis. There is no consensus on using smiley scales or other modes of evaluating perioperative pain in a uniform manner. However, information on pain and well being of children is fundamental, since they enable us to evaluate the efficacy of our therapeutic interventions.

Assessment of postoperative pain versus anxiety in children is age dependent and makes it difficult to accurately assess the efficacy of pain blocks.[3] Currently there are only limited data on the efficacy of the landmark-oriented techniques, nerve stimulator-guided blocks, and surface nerve mapping techniques.[2] For these reasons alone, children in particular may benefit from the more exacting, ultrasound-guided techniques. In addition, more precise ultrasound-guided techniques may allow for reduction of the dose of the local anesthetic.[4] [5] Although systemic toxicity of local anesthetic in pediatric regional anesthesia is rare, it is very likely that such events are underreported. Local anesthetics are mainly bound by acidic a1-glycoprotein and albumin, which are not sufficiently produced in younger children, making the pediatric population at particular risk for systemic toxicity from local anesthetics.[6]

Additional advantages of ultrasound-based nerve block techniques are that anatomic structures can be visualized, the spread of the local anesthetic monitored, and intravascular or intraneuronal punctures are less likely to occur. However, adequacy of the clinician’s training in ultrasound-guided nerve blocks deserves special consideration. Such training is currently offered only through specialized workshops and self-study methods. However, more extended period of training, best under a supervision by a regional anesthesiologist with experience in ultrasound-guided blocks until adequate expertise is achieved is indispensable.

Finally, adequate technical specifications, proper selection of ultrasound probes, and proper adjustment of the ultrasound unit are important for the success and safety of peripheral nerve blocks. This knowledge can be acquired in specialized workshops. The technical potential of these systems to optimize imaging must be fully utilized precisely because anatomic structures are highly condensed in children.

Clinical pearls: The pediatric nerve block techniques described in this chapter can be greatly simplified if the ultrasound unit is correctly configured along <AU: WHAT LINES?>these lines; In fact, expertise in optimizing images is what sets “ultrasound professionals” apart

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Adjustment of the ultrasound unit

Ultrasound machine must be properly configure and adjusted in order to make it suitable for use an ulstrasound-guided nerve blocks in children. Below is a short introduction on the important parameters that must be paid attention to.

Image depth. It is necessary to strike a balance between overview and detail, considering that the quality of the ultrasound image gets significantly reduced at large magnifications as the individual pixels become visible.

Gain. Care must be taken to select an optimal gain relative to the image depth. Some ultrasound machines feature selection of independent gain in different sections of the image (TGF – time gain compensation). Other systems offer only a coarse type of depth gain adjustment (surface/depth gain).

Focus. Given the dense vertical structures in children, the focus of the ultrasound image has to be adjusted in such a way that the level of the target structures is optimally visible. With high-end systems, different focal zones can be defined. Here, the zone of optimal resolution becomes smaller as the focal zones decrease. As a rule, two or three focal zones are selected.

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The success of peripheral nerve blocks in children is not only a function of the blocking procedure itself but also requires an appropriate general strategy. Particularly when “novel” techniques are used, the environment and concomitant measures must be selected with great care, since first impressions by the surgeons, colleagues anesthesiologists, parents and other involved care-givers may go a long way. Once a poor general impression is created, it often takes heroic efforts to improve it.

Whether a child is best kept sedated or alert during the block procedure depends on the individual clinical circumstances. While it is possible in an occasional child to conduct the block procedure without premedication, as a general rule, however, sedation is performed and preferred in most instances. The selection of the medications is left to the anesthesiologist’s discretion and experience. One sedation regimen commonly used in our institution consists of midazolam 0.1 mg/kg and ketamine 0.5–1.5 mg/kg, with or without a bolus of a hypnotic, such as propofol (0.5–1 mg/kg). It must always be kept in mind, however, that acutely injured children are rarely hospitalized with an empty stomach.[7] Appropriate intubation equipment and medications must be present and ready for use. When deeper levels of sedation are necessary to perform a nerve block procedure or comfort the child intraoperatively, consideration of the use of general anesthesia with protection of the airway may often be a safer alternative to mask-ventilation.

Presence of the parents prior to administration of sedatives and often during the block placement is invaluable. Experience in regional anesthesia and ultrasound-guided nerve block procedures is essential. In our institution, anesthesiologists on duty without proper training are not allowed to perform ultrasound-guided nerve blocks.

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The following sections are dedicated to the various types of peripheral nerve blockade. Special emphasis in the chapter is placed on the implications of ultrasound guidance and not on extensive review of the anatomy; anatomic structures are only discussed if they are clearly relevant to the execution of specific block types. For in-depth treatment of anatomic details, the reader is referred to the numerous textbooks available on the subject.

Clinical pearls: The block needle-syringe system must be completely purged of air because even minute air inclusion can cause enormous artifacts in the ultrasound image.

Prior to conducting the block procedure, the equipment must be properly prepared and checked—including an ultrasound unit, an appropriate ultrasound probe, sterile ultrasound gel, a needle and, of course, an appropriate local anesthetic. Other accessories that are required for all types of block procedures include disinfectant swabs, a 2-mL syringe, and a small-gauge hypodermic needle to anesthetize the skin prior to the needle insertion. The block needle-syringe system must be completely purged of air because even minute air inclusion can cause enormous artifacts in the ultrasound image.

In our pediatric regional anesthesia practice, we primarily use newer amide local anesthetics such as levobupivacaine or ropivacaine for their decreased cardiotoxicity potential. By selecting the appropriate concentration (levobupivacaine: 0.125, 0.25, or 0.5%; ropivacaine: 0.2%, 0.475%, or 0.75%), differential (sympathetic, sensory, motor) nerve blockade of desired density and duration can achieve nerve blockade.

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Although nearly all surgical interventions on upper limbs can be conducted under regional anesthesia, there are only limited reports on the use of upper-limb blocks in children. Lack of training in regional anesthesia, and pediatric regional anesthesia in particular, is likely the main reason. However, at the Department of Anesthesia and Intensive Care at the Medical University of Vienna, anesthetic management of children with upper-limb injuries is routinely performed using brachial plexus blockade and conscious sedation.

Clinical pearls

• In adults and children alike, any approach to the brachial plexus is possible
• The most useful brachial plexus blocks in children are supraclavicular, infraclavicular, and axillary blocks
• Axillary blocks can be conducted for all procedures below the elbow; infraclavicular or supraclavicular blocks are better suited for procedures above the elbow

Interscalene approaches to brachial plexus block

Interscalene block is the most proximal approach to the brachial plexus.[8] Shoulder surgery is the main indication for scalene blocks in adults. However, these procedures are relatively infrequently performed in children. One specific issue with interscalene blocks with interscalene blocks in children is the difficulty in achieving block of the roots of C8 and T1. Using a perpendicular needle orientation, these roots are not blocked at all or require very large amounts of local anesthetic. Use of a tangential route under guidance of a nerve stimulator carries a high risk of pleural injury. Ultrasound guidance is greatly advantageous in this situation, as it allows direct visualization and blockade of both roots C8 and T1.

Tobias reported on the technique of interscalene brachial plexus blockade using a perpendicular (90 degrees) needle insertion plane relative to the skin.[9] This approach, however, is not well suited for application in children. The narrow anatomic relationships in the neck areas of children pose a special risk of an inadvertent puncture of the vertebral artery or the epidural/subarachnoidal space. Instead, Büttner and Meier used a tangential insertion in adults [10] which also may be a safer alternative in pediatrics. Dalens and colleagues reported on a technique of parascalene brachial plexus blockade for pediatric shoulder surgery that uses an exaggerated, retroflected head position and a needle insertion site between the lower and middle thirds of the line extending from the clavicle center to the C6 transverse process (Chassaignac).[11] The rationale for this technique was to decrease the risk of puncturing the vertebral artery and pleura. Unfortunately, the success of the blockade depends on the use of large volumes of local anesthetic (1 mL/kg).

Clinical pearls

• To visualize the anatomic structures of a child’s neck, linear ultrasound probes working at frequencies as high as possible should be used
• The exposure is facilitated by slightly turning the child’s head to the contralateral side
• The ultrasound probe should be oriented from the medial to the lateral aspect

To visualize the anatomic structures of a child’s neck, linear ultrasound probes working at frequencies as high as possible should be used. The exposure is facilitated by slightly turning the child’s head to the contralateral side. The probe should be oriented from the medial to the lateral aspect. Medially, the thyroid gland and the major vessels in the neck area (carotid artery and internal jugular vein) are easily identified (Figure 52-5). Then, the probe is moved along the sternocleidomastoid muscle until its lateral border is reached. At the same time, the transducer is descended in a caudal direction such that the posterior scalene gap and the upper anterior roots (C5–7) of the brachial plexus become visible between the anterior and medial scalene muscles. In very small children, all roots of the brachial plexus (C5–TH1) can be visualized simultaneously (Figure 52-6). Special care must be exercised to place the needle accurately, due to the narrow spatial relationship between the plexus and the neck vessels. It should be noted that in children, the interscalene groove is not always located exactly at the lateral border of the sternocleidomastoid muscle; it is often situated away either medially or laterally.

The needle is inserted in a tangential direction relative to the neck above the transducer (Figure 52-7). The C5 root will be encountered only a few millimeters deep. As a rule, the needle should be lateral to the C7 root, which will ensure that the neck vessels remain at an adequate distance. Once the local anesthetic is injected, it will invariably spread toward the C5 root, which can be observed in the ultrasound image (Figure 53-8). Depending on the blockade required, the needle can be advanced to a deeper level for injection after the deep roots (C8 and T1) are visualized. In the majority of cases, the local anesthetic will spread medially, even when the needle is in a lateral position. However, if the local anesthetic fails to spread adequately in a medial direction, the needle is withdrawn to the subcutaneous level and repositioned on the medial side to the posterior scalene gap in the area of the C7 root. The injected volume of local anesthetic should be adequate to cover the root surfaces, rather than use of a specific, arbitrary volume. In general, complete blockade of the brachial plexus in the interscalene groove can be accomplished with approximately 0.15–0.25 mL/kg of local anesthetic.

In contrast to many of the techniques presented in the chapter, interscalene blocks are almost always best performed under general anesthesia because the patient needs to be absolutely immobile to avoid puncture-related complications due to the narrow anatomic relationships in the neck region. The posterior scalene gap is especially well suited for catheter techniques, since a catheter can be conveniently positioned and easily secured in place. Based on current knowledge, however, catheters or single punctures through a scalene approach are rarely indicated in children.

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Supraclavicular approaches to brachial plexus blockade

Pediatric applications for supraclavicular brachial plexus blockade are described in published reports. [12] Because of the anatomic proximity of the cervical pleura and the consequent risk of pneumothorax, we use this approach only with ultrasound guidance and in those exceptional cases where infraclavicular visualization in the ultrasound image is inadequate. The brachial plexus is located close to the surface in this area, and it can be visualized readily. However, adequate experience is mandatory for this access route because the risk of puncturing the cervical pleura can be unacceptably high in inexperienced hands.

Clinical pearls

• The proximity of the cervical pleura poses a specific risk of pneumothorax with supraclavicular block
• We use this approach only as ultrasound guided-technique and when infraclavicular visualization is inadequate
• Adequate experience is mandatory to decrease the risk of injuring the cervical pleura

Anatomically, in the supraclavicular region, the brachial plexus is approached at the region where the trunks become divisions or cords. It is, therefore, nearly impossible to identify the neuronal structures visible in the ultrasound image with any certainty. However, the brachial plexus, including the musculocutaneous and axillary nerves, remains located in a medial position to the artery (Figure 52-9). The suprascapular nerve, however, occasionally may leave the upper trunk at a more cranial level.

Using a high-frequency, linear ultrasound probe with a small array surface (preferably a "hockey-stick" probe), the brachial plexus is approached lateral to the subclavian artery and above the level of the lateral clavicle. The needle is inserted according to the in-line technique, that is, parallel to the long axis of the ultrasound probe (Figure 52-10). In this way, the shaft of the needle can be visualized as well, such that the needle can be positioned very accurately between the artery and plexus. This approach offers complete nerve blockade at doses of local anesthetic as low as 0.15–0.2 mL/kg.

At our institution, the supraclavicular approach is the preferred method for catheter techniques. Although catheters are more challenging to place using the infraclavicular route and difficult to maintain in a stable position using the axillary approach, supraclavicular catheters can be placed and stabilized readily, when a supraclavicular access is used. The technique, as such, is similar to the single-puncture technique, although the needle insertion site is selected so that it offers maximum immobility. The catheter is advanced once an appropriate volume of local anesthetic (see previous discussion) is injected. Today, suitable catheter kits, which feature a hemostatic valve, are available, thus enabling the anesthesiologist to administer the local anesthetic and subsequently place the catheter without having to manipulate the canula. Even though the catheter can be visualized directly if the ultrasound technique is handled correctly, the best way to verify its position is by visualizing the distribution of the local anesthetic.

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Infraclavicular approaches to brachial plexus blockade

Although infraclavicular blockade with the help of a nerve stimulator is reported to be safe and effective, [13,14] in children, the vertical approach to infraclavicular plexus blockade is not recommended because any puncture halfway between the jugular incisure and the acromion carries a risk of injuring the cervical pleura. [15] Fleischmann and coworkers used a lateral approach below the level of the coracoid process under nerve stimulation and thereby achieved a more effective sensory blockade of the musculocutaneous, axillary, and medial brachial cutaneous nerves, as well as better motor blockade of the musculocutaneous and axillary nerves, than through the axillary route. [13] Based on Vester-Andersen’s criteria, 100 percent of these infraclavicular blocks, as compared to 80 percent of axillary blocks, were successful. This technique of lateral infraclavicular blockade is relatively simple. A 40-mm needle attached to a nerve stimulator is inserted 0.5–1 cm below the coracoid process in the saggital plane. The local anesthetic is injected after peripheral muscle stimulation is accomplished. It is often necessary to slightly reposition the needle in a cranial or caudal direction.

Ultrasound guided block may result in shorter sensory/motor onset times than a nerve stimulator-guided technique (mean difference: 9 vs 15 min) as well as significantly longer block durations (mean difference: 1 h). [16] Additionally, the block placement in awake, sedated children resulted in less discomfort using ultrasound-guided nerve blocks as compared to nerve stimulation.

Clinical pearls

• A 5- to 10-MHz linear ultrasound probe is positioned close to the subclavian artery in the infraclavicular area
• Visualization of the artery as a round structure is essential in this technique because the brachial plexus is located lateral to the artery
• Individual cords are difficult to identify in the infraclavicular technique

The ultrasound-guided technique consists of advancing a 5- to 10-MHz linear ultrasound probe into the subclavian artery in the infraclavicular area. It is essential to visualize the artery as a round structure because the brachial plexus is located lateral to the artery. Individual cords are difficult to identify. The lateral cord, being the most ventral and medial cord relative to the posterior cord in this area, is usually identified first. As the structures are tracked further in a lateral direction to the medial border of the coracoid process, the brachial plexus will descend, and the distance to the pleura will increase. At the same time, however, the quality of neural structure imaging will deteriorate as overlapping muscle structures (major and minor pectoral muscles) will impose limitation on the high-frequency ultrasound spectrum. The area where the ultrasound image offers the best view of all anatomic structures is selected as a needle insertion site (Figure 52-11). The needle is inserted along the short axis either below (Figure 52-12) or above the transducer and advanced to a point around the lateral or medial cords where the needle tip is located lateral to the subclavian artery. Since the clavicle is located above the transducer, it is easier to insert the needle below the transducer. In this case, the needle is advanced toward the pleura, which requires great care and tactile sensitivity to obtain correct positioning. Therefore, it should be noted that the technique is not “vertical” in a strict sense. In very small children, the brachial plexus may be close to the pleura even when the lateral infraclavicular approach is selected.

Clinical pearls

• With the infraclavicular block, the needle has to pass through several muscle and fascia layers to reach the plexus, therefore, the local anesthetic may not spread correctly at the first injection attempt
• Injection into the wrong tissue layer is easily recognized on ultrasound at the beginning of the injection
• This mistake is easily corrected by advancing the needle to a deeper layer

Because the local anesthetic will normally spread such that it encircles the artery, there is no need to reposition the needle. In contrast to the axillary approach, this method is essentially a single-shot technique. However, since the needle has to pass through several muscle and fascia layers to reach the plexus, there is always a chance that the local anesthetic may not spread correctly at the first injection attempt. Such maldistribution usually occurs cranial to the plexus as the needle tip is located within a wrong layer. However, this mistake is recognized on the initiation of the injection and easily corrected by advancing the needle to a deeper layer. Since the fascial layers are very elastic in children, accurate needle positioning occasionally may be difficult to achieve; in many cases, practical experience is required to implement the nerve blockade quickly and safely.

Although the published report on this ultrasound-guided block technique was based on a volume of local anesthetic of 0.5 mL/kg [16], we currently use as little as 0.3 to 0.4 mL/kg. In contrast to other techniques where an optimal volume is administered depending on how much of the substance is needed to fully cover the surface of the targeted nerve structures, the infraclavicular block technique requires the use of a defined volume of local anesthetic. This requirement arises from the fact that all cords in the infraclavicular area cannot be visualized in a single ultrasound section, so that the distribution of the local anesthetic cannot be readily visualized in its entirety. Rather, the local anesthetic has to be discreetly repositioned during injection to visualize the exact distribution pattern, including the posterior and medial fascicles.

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Axillary approaches to brachial plexus blockade

The axillary route is the most common approach to the brachial plexus. It is indicated for surgical procedures below the level of the cubital fossa. The reasons are that most anesthesiologists are familiar with this technique and the potential for serious complications is significantly lower. These advantages are, however, offset by significant disadvantages, such as incomplete blockade or the need for arm positioning required for the block, which may be painful in cases of arm fracture.

Fisher and coworkers used a tangential route to advance the needle to the neurovascular sheath very close to the chest area, using a fascial click to verify that the needle is in its correct position. [17] The mean volume of local anesthetic in this report was relatively large (0.55 mL/kg), and additional perioperative analgesics had to be administered in 46 percent of the children. "Blind" perivascular injection of 0.75 mL/kg local anesthetic also was recommended in the text by Jöhr, which is popular in German-speaking countries. [18] This recommendation referred to children less than 8 years old; in larger children, the author favored the use of a nerve stimulator. He also indicated additional signs of appropriate canula positioning when the “blind” technique was used, such as pulsation of the needle and a spindle/sausage-like distribution pattern of local anesthetic.

Carre and colleagues compared the success rate between single and multiple injections for axial plexus anesthesia by advancing the needle with the help of a nerve stimulator and injecting upon stimulation of one or two nerves (0.5 mL/kg of local anesthetic). [19] Although a better success rate was reported with the multiple injection technique, the nerve sensory/motor blockade was still incomplete in 54% of multiple injection blocks.

Clinical pearls

• The ultrasound probe must be perpendicular to the axis of the body when the axillary technique is used
• Nerve structures must be followed in a distal direction to be identified properly
• The median nerve always remains close to the artery
• The ulnar nerve is located near the surface on its path to the ulnar nerve sulcus
• The radial nerve becomes deeper on its descent toward the radial sulcus

When the ultrasound is used, the various neuronal structures involved (radial, median, ulnar, and musculocutaneous nerves) should be identified in the ultrasound image prior to injection, which rarely succeeds at the first attempt. Usually, the nerve structures must be followed in a distal direction to be properly identified. The median nerve always remains close to the artery, while the ulnar nerve is located near the surface on its path to the ulnar nerve sulcus, and the radial nerve quickly becomes deeper on its path to the radial sulcus. The ultrasound probe must be perpendicular to the axis of the body when the axillary technique is used. Therefore, if the upper arm is in 90-degree abduction, which is the optimal arm position for this type of blockade. Figure 52-13 and Figure 52-14 illustrate the direction of needle insertion and the needle position relative to the ultrasound probe. The needle insertion should be in the lower third, near the distal border of the ultrasound probe. In this way, all targeted nerves are accessible while the vessels remain protected. The pressure exerted by the probe itself should be very light to avoid compression of the venous vessels on the ultrasound image. Excessive pressure by the probe may change the relative position of the nerves, as well as the relationship of the nerves to the vessels.

The radial nerve, which can be easily located dorsal to the axillary artery, is routinely blocked first. Depending on the distribution of the local anesthetic, the needle is repositioned such that the ulnar and median nerves are blocked, which are invariably located superficially to the axillary artery (Figure 52-15). The musculocutaneous nerve, which branches off the lateral fascicle and is most commonly located between the short head of the biceps muscle and the coracobrachial muscle, has to be blocked separately (Figure 52-16). In very small (and some larger) children, the musculocutaneous nerve may be located close to the median nerve. In these cases, the amount of local anesthetic injected to block the median nerve may be sufficient to block the musculocutaneous nerve as well. In addition, separate blockade of the brachial cutaneous and medial antebrachial nerves (branching off the medial fascicle) is recommended. These nerves are located within a fascial layer above the other segments of the brachial plexus and often cannot be well imaged. Occasionally however, the nerves in this area may be seen after insertion of the needle underneath the fascia and injection as little as 0.5 mL of local anesthetic. In very small children, however, the local anesthetic will diffuse into this fascial space. Furthermore, the axillary nerve can be visualized close to the humeral circumflex artery on the medial side of the humerus. However, patients in whom blockade of the axillary nerve is required should normally receive regional anesthesia through a supraclavicular or infraclavicular approach. Therefore, this nerve is virtually never blocked with the axillary brachial plexus techniques.

As in other ultrasound-guided peripheral nerve blocks, we use the minimum amount of local anesthetic required for effective brachial plexus blockade. As a general rule, 0.2 to 0.3 mL/kg is sufficient.

The axillary route is also suitable for catheter insertion. The bigger problem however, is maintaining the catheter in a stable position; the catheters often dislodge, especially in very small children. For this reason, we prefer to use the supraclavicular route for catheters in children (see previous discussion).

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Specific blocks of the upper-limb nerves have been used in children to compensate for incomplete brachial plexus blockade through the axillary route. The higher success rate of axillary blockade using nerve stimulation, multiple stimulation, and ultrasound techniques made specific distal nerve blockade largely obsolete. Consequently, indications for these procedures are narrowed down to localized surgical procedures in the sensory regions supplied by the individual nerves.

Although the nerves discussed as follows essentially can be blocked at any location visible in the ultrasound image, the cubital area is generally preferable. Distal blocks in the wrist area are challenging because the targeted nerves are located very close to the surface—which requires the use of extremely high ultrasound frequencies—and are firmly embedded in surrounding structures including tendons, muscles, and connective tissue. Consequently, there is a theoretic risk of nerve damage due to the pressure increase caused by injection of the local anesthetic. In general, it is advisable to avoid nerve block injections in anatomic locations with limited space for the nerves to escape the increase in the compartmental pressure. Alternatively, injections may be made but the injection and post-injection compartmental pressure should be monitored. For the same reasons, punctures should not be placed in the vicinity of bone structures or the ulnar nerve sulcus.

All three nerve blocks discussed require a high-frequency probe (at least 10-MHz). They also require insertion of the needle along the short axis with a 40-mm facet needle. The amount of local anesthetic should be minimized such that the nerve is only covered by thin film of the injected substance.

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Radial nerve

The radial nerve starts at the posterior fascicle and is located along the cubital fossa between the biceps tendon and the brachioradial muscle. In most cases, the superficial and deep segments are already distinguishable in this area, although both rami are still embedded in the same fascial sheath. Therefore, both nerves can be blocked from the same needle position at the same time (Figure 52-17). Figure 52-18 illustrates the position of the ultrasound probe relative to the puncture needle. In the majority of cases, the needle can be placed successfully between the two rami of the radial nerve, such that both are reached by the local anesthetic.

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Ulnar nerve

The ulnar nerve can be blocked either above or below ulnar nerve sulcus. The level selected will depend mainly on the quality of visualization in the ultrasound image. The ulnar nerve is formed from the medial fascicle and remains at a very superficial level as it proceeds from the axillary region in a distal direction. In the area of the ulnar nerve sulcus, its visualization is impeded by bone artifacts. Farther distally, it comes close to the ulnar artery. Figure 52-19 illustrates the ulnar nerve distal to the ulnar nerve sulcus. Sometimes, it is helpful to use the ulnar artery as reference, which is located more distally. Subsequently, the nerve can be tracked back in a proximal direction to the selected puncture site. Figure 52-20 shows the position of the ultrasound probe relative to the needle; the puncture site is located distal to the ulnar nerve sulcus.

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Median nerve

The median nerve is formed from both the lateral and medial fascicles and is located between the axillary and cubital areas. There is, invariably, a close anatomic relationship to the axillary/brachial artery. As a general rule, it is located ventral to the artery in the axillary area and medial (hence, ulnar) to the artery in the cubital area. Its level in the cubital area is very superficial, and sometimes it is larger than the artery in diameter (Figure 52-21). The position of the probe relative to the needle is shown in Figure 52-22. For nerve blockade, the needle is first advanced to a point ulnar to the nerve. If the local anesthetic fails to spread in an adequate manner, the needle is repositioned between the artery and the nerve, making sure that these structures are not damaged in the process. With superficial blocks, a skin-nick can facilitate insertion of the short-bevel needle.

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Traditionally, lower-limb peripheral nerve blocks have not been popular in children; caudal blocks are more frequently used. [1]. Nevertheless, selective blockade of children’s lower limbs can be very useful in a number of clinical scenarios. Because most of the data available on lower-limb blocks were collected in adults, the volumes of local anesthetic used in children frequently were derived from adult studies. The insertion techniques used in children were derived almost exclusively from adults as well. All available techniques that rely on ultrasound guidance for lower-limb nerve blockade in children are described in the section that follows.

Psoas compartment block

Some 30 years ago, Chayen and coworkers [20] and Winnie and colleagues [21] described a posterior approach to the lumbar plexus in adults. The clinical term psoas compartment block was coined by the Chayen group at that time. [20] Although it is normally inappropriate by both physiologic and anatomic criteria to think of children as “small adults,” the lumbar plexus is usually characterized by almost identical anatomic and topographic conditions, except that it is naturally less deep in children. Dalens and coworkers investigated two posterior approaches to the lumbar plexus in children undergoing surgical procedures of the hip and femur, using either the technique described by Winnie or a technique modified from Chayen [22] and found a considerable age-dependent variability. More recently, Dalens provided data on the depth of the lumbar plexus based on body weight. [23]

Dadure and investigators used CT scanning in an attempt to measure the depth of the lumbar plexus, but their attempts to visualize neural structures failed in most children. [24] Therefore, they had no choice but to take an educated guess as to the depth of the plexus inside the posterior segment of the psoas major muscle. With the help of ultrasonography, we were able to visualize the lumbar plexus and its surrounding structures, and to measure its distance, in an accurate manner. [25] The fact that the neural structures can be visualized in children while they cannot be visualized in adults is due to the ability to use higher resolution probes because of the shallower depth of the plexus. Note that the lumbar plexus is located in the transition zone between the posterior and medal thirds of the psoas major muscle both in adults and in children.

Clinical pearls

• Peripheral nerves are usually visualized with linear transducers
• Linear transducers with a small array surface are preferable in newborns and infants
• Convex transducers are preferable in the lumbar paravertebral region because the convex geometry of the ultrasound field allows for better imaging of the paravertebral structures

Although peripheral nerves are usually visualized with linear transducers, better results were obtained with convex transducers in the lumbar paravertebral region, since the convex geometry of the ultrasound field allows for better imaging of the paravertebral structures. In newborns and infants, however, linear transducers with a small array surface are preferable.

The first step toward visualizing the lumbar plexus by ultrasonography is to locate the access level (usually L4 or L5). In a paravertebral longitudinal section, the costal processes of the lumbar vertebrae are visualized and counted one by one in a caudocranial direction, beginning at the dorsal ultrasound reflection of the sacrum. The transducer is then gradually shifted parallel to the spinous processes in a cranial direction. Once the L4-5 intervertebral space is reached, the transducer is turned by 90 degrees to a transversal plane (Figure 52-23). Based on this configuration, the lumbar plexus can be targeted inside the posterior segment of the psoas major muscle. In infants and small children, a perpendicular needle orientation transversal to the transducer should be selected because of the limited space and short distance to the plexus (only 2–3 cm; Figure 52-24). By contrast, the in-line technique, as used in adults, is also the method of choice in larger children and adolescents. [26]

Potential indications for posterior blockade of the lumbar plexus in children include surgical treatment of the hip, femur, and knee joint. The use of ultrasonography in psoas compartment blocks is justified by the risk of epidural/intrathecal injection. Damage to the kidney is another potential risk (the kidneys extend down to the L4-5 level in small children). [27]

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The 3-in-1 block

The technique of inguinal perivascular blockade of the femoral, obturator, and lateral cutaneous femoral nerves was first described by Winnie and colleagues in 1973. [28] Much debate ensued on whether this technique was really capable of blocking all three nerves and on the spread direction of the local anesthetic. Originally, it was assumed that the local anesthetic spread proximally from the inguinal puncture site to the lumbar plexus along a muscle-fascia sheath. This assumption was clearly refuted by our study group in an MRI investigation that demonstrated that the local anesthetic exclusively spread in a lateral and medial direction with this technique. [29] The quality of sensory blockade depends more on the needle insertion technique rather than on the volume of local anesthetic. [4], [30] This finding in particular has important implication in children, where the use of large doses of local anesthetic may be prohibitive in this technique.

Unlike other lower-limb peripheral blocks, however, the 3-in-1 technique is relatively well documented with conventional methods of nerve identification in children. Most commonly, this technique is used for muscle biopsy in children (e.g., in making the diagnosis of malignant hyperthermia or neuromuscular diseases). [31-33] Various investigators used the technique for both singe-shot and continuous applications of perioperative pain therapy in femoral fractures. [34-38] They obtained respectable success rates (up to 96 percent) with this approach. [37] However, ultrasound guided 3-in-1 block offers a number of advantages over other techniques:

The volumes of local anesthetic can be further reduced, and combined nerve blocks can be performed more safely. For example, sensory supply to the femoral shaft is affected by both the femoral and sciatic nerves; hence the sciatic nerve should be additionally blocked for effective pain therapy in femoral shaft fractures.

Because the femoral nerve is located very close to the femoral artery, there is also a risk of arterial puncture.

Using ultrasound guidance, it should be possible to direct the spread of the local anesthetic in a lateral and (to a smaller extent) medial direction, such that a true 3-in-1 block is achieved. Also, it should be possible to selectively block the femoral nerve only by reducing the amount of local anesthetic (volume-dependent differential blockade).

A high-frequency ultrasound probe is advanced to a point in the immediate distal vicinity of the inguinal ligament to visualize the femoral artery and, more laterally, the femoral nerve. The weight of the transducer is usually sufficient to compress the femoral vein, which is located medial to the artery. The space between the artery and the nerve harbors the iliopectineal fascia, representing the deep folium of the inguinal ligament. The femoral nerve is usually very close to the skin and only can be visualized from a position immediately distal to the inguinal ligament (Figure 52-25) because it soon gives its distal branches.

Clinical pearls: With 3-in-1 block, the blockade of the obturator nerve is limited to only the anterior (cutanous) ramus; consequently, a better name for the obturator block should be 2.5-in-1 block

As in most peripheral blocks, the needle is inserted in a cross-direction relative to the transducer (Figure 52-26). The needle can be placed either lateral or medial to the femoral nerve. Note that often, the nerve is located very close to the artery, so the needle must be advanced with care if a medial position (toward the artery) is selected. It is, therefore, better to always select a lateral position. The amount of local anesthetic to be injected depends on how many nerves are targeted. For selective blockade of the femoral nerve, it is sufficient if injectate covers just the surface of the nerve. However, if a 3-in-1 block is required, a larger volume has to be injected, such that the local anesthetic visibly spreads in a lateral and medial direction. Note that blockade of the obturator nerve is usually confined to its anterior ramus. Therefore, the 3-in-1 block is really a “2.5-in-1” block. Direct visualization of the lateral cutaneous femoral nerve requires the use of a high-resolution transducer and is only possible in larger children. A limitation to this technique is that the ultrasound-assisted technique for 3-in-1 blocks still relies on the lateral and medial distribution pattern of the local anesthetic to reach the obturator nerve because this nerve normally cannot be visualized by ultrasonography due to its position between the adductor muscles and the small diameter of its two branches.

The 3-in-1 technique is particularly well suited for continuous nerve blockade. This approach was described for conventional methods of needle guidance as well. [34,35] The same puncture technique is used as with the single-shot approach. Following injection of the local anesthetic, the catheter is placed underneath the iliopectineal fascia under ultrasound guidance. It is also possible to selectively block the femoral nerve in this way. The catheter is not directly visible in the majority of cases; however, a small amount of local anesthetic injected on a preliminary basis will be enough to foresee the spread direction and whether successful blockade can be expected, once the full volume is used. It is essential to decide beforehand whether a selective femoral nerve block or a complete 3-in-1 block is required. For selective femoral nerve blockade, the local anesthetic can be applied continuously through the catheter (e.g., 0.1–0.2 mL/kg of local anesthetic in a low concentration). For 3-in-1 blockade, an initial bolus dose is recommended, although low concentrations of a long-acting substance, such as levobupivacaine 0.125% or ropivacaine 0.2% twice daily, usually is sufficient. Ultrasound monitoring can be performed while the bolus is being applied through the catheter to identify its position.

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Selective saphenous nerve block

The saphenous nerve is best located with a high-resolution ultrasound probe at the distal-medial thigh level in the transition zone between the sartorius/gracilis muscles and their attachment of their respective tendons (Figure 52-27). The puncture should be conducted transversally from the proximal aspect toward the transducer (Figure 52-28) or using the in-line technique. Only small amounts of local anesthetic are required for blockade. In addition, smaller volumes are advisable because larger volume of local anesthetic may cause excessive pressure in this tissue compartment and, consequently, increase the risk of nerve injury.

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Sciatic Nerve Block

Sciatic nerve blocks should form an integral part of every well-trained anesthesiologist’s repertoire. It is desirable that several approaches to the sciatic nerve are mastered because the need for various approaches is dictated by the nature of the surgical procedure, as well as positioning of the child and the affected limb. In clinical practice, good results were obtained with the subgluteal, the midfemoral, and the popliteal access route. A clear-cut distinction between these three approaches cannot always be made. Perhaps the greatest advantage of ultrasound guidance for sciatic blockade is that it enables the anesthesiologist to block nerves at any location without the need to use landmarks as reference. Therefore, selecting a site of optimal sonographic visibility is the only consideration in addition to selecting the level of blockade depending on the type of surgery and patient positioning. The sciatic nerve is not uniformly accessible to ultrasound imaging over its entire course.

The success rates achieved with conventional guidance techniques (mainly identification of the nerve with a nerve stimulator) for sciatic nerve blockade in children are excellent. For instance, Konrad and investigators and Tobias and colleagues reported successful blocks in over 90 percent of cases. [39,40] However, the large volumes of local anesthetic (0.75–1.0 mL/kg) used in these studies may not allow the use the additional combined blocks (e.g., femoral or 3-in1 blocks). Furthermore, nerve stimulation or other indirect techniques of nerve identification carry a certain risk of damaging the targeted nerve during puncture due to the shear size of the sciatic nerve. Ultrasound guidance may be superior in this regard because theoretically, it should allow the needle to be safely inserted, avoiding direct nerve contact.

When it comes to ultrasound-guided sciatic nerve block, the choice of approach varies in comparison to the nerve-stimulator guided techniques. For instance, the approach described by Labat, which enjoys widespread popularity in adults, should not be used because ultrasound visualization may be limited in this area. This is because the nerve is located underneath several muscle layers, such that the high-frequency ultrasound probes cannot be used. A similar problem is encountered with the anterior approach, where the sciatic nerve is overlapped by the trochanter minor. In addition, the anterior approach is very uncomfortable due to the deep location of the nerve. For these reasons, we do not use the anterior approach, even though Aizenberg and investigators reported on its use in children. [41] Dalens and coworkers demonstrated, in a comparative study, that the posterior and lateral access routes were both more reliable and more practical than the anterior approach. [42] Their findings are generally in agreement with the following discussion of meaningful approaches to ultrasound-guided sciatic nerve blocks.

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Subgluteal approach

The subgluteal approach is the most proximal approach that we use for sciatic nerve blockade under ultrasound guidance. Bösenberg and colleagues employed a nerve stimulator for this access route, [38] thereby, achieving good success rates despite injecting relatively small amounts of local anesthetic (0.5 mg/kg for unilateral and 0.3 mg/kg for bilateral blocks). Gray and coworkers mention ultrasonography as an alternative option to guide sciatic blocks through the subgluteal approach. [43]

The child may remain in a supine position for this technique, but a prone or side position is also possible. We always try to meet individual requirements, thus selecting the most comfortable position for the child.

The sciatic nerve is located close to the surface in the immediate subgluteal area, requiring the use of a high-frequency linear ultrasound probe. Figure 52-29 illustrates the position of the sciatic nerve between the glutaeus maximus and quadratus femoralis muscles (lateral) on the one hand and the biceps femoris muscles (medial) on the other. The posterior cutaneous femoral nerve usually can be visualized medial and slightly more superficial to the sciatic nerve. In association with a thigh tourniquet, this nerve should also be blocked. Therefore, indications for this approach include not only situations in which good ultrasound visibility is required but also the use of a tourniquet.

Figure 52-30 illustrates the needle position relative to the ultrasound transducer, the child being in a supine position with the hip and knee flexed. After the needle has been placed medial to the sciatic nerve, the local anesthetic usually spreads to the posterior cutaneous femoral nerve. If the initial injection fails to reach the nerve, the needle is repositioned more medial to the posterior cutaneous femoral nerve to optimize the distribution of local anesthetic. As a rule, however, a single shot will suffice.

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Midfemoral approach

The midfemoral approach to the sciatic nerve is usually selected only if a subgluteal or popliteal approach is not possible, usually because some segments of the sciatic nerve are not accessible to ultrasonography. A clear-cut distinction between the midfemoral and popliteal approach cannot always be made.

The same needle position is selected as with the subgluteal approach (Figure 52-31). The in-line technique is a viable option for this type of puncture. With increasing displacement of the transducer in a distal (popliteal) direction, practical considerations will dictate that the needle insertion be parallel to the long axis of the transducer.

It is essential to track the route of the sciatic nerve in a distal direction, thereby visualizing its separation into the tibial and peronaeus nerves. Schwemmer and coworker reported that the level at which this separation takes place varies widely, [44] which is in accordance with our own observations. This variability is not known to correlate with body weight or body height. Therefore, if complete blockade of the sciatic nerve is required, the needle insertion site should be proximal to this point of separation. Again, this requirement can only be accurately met through direct sonographic visualization.

Figure 52-32 illustrates anatomic conditions in the midfemoral access area proximal to the furcation site of the sciatic nerve as visualized by ultrasound. The puncture itself is carried out in the same way as the subgluteal puncture. It should be placed between the biceps femoris and semimembranosus muscles. Puncturing the muscles should be avoided to reduce the risk of hematoma during blockade. Depending on how deep the nerve is located, the use of a longer needle (70 mm) may be indicated. In the overwhelming majority of cases, the needle has to be repositioned several times to optimize the distribution of the local anesthetic.

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Popliteal sciatic block

The popliteal approach to the sciatic nerve, also referred to as fossa poplitea block, is very useful in pediatric anesthesia. One of its advantages is that blockade from a dorsal route it is relatively painless in this rhombus-style knee area (whose upper sides are formed laterally by the femoral biceps muscle and medially by the semimembranosus and semitendinosus muscles), as no muscle bellies are perforated during puncture. One shortcoming of conventional guidance by nerve stimulation is, however, that no information is obtained about which level the sciatic nerve furcates into the tibial and peronaeus nerves. The only practical way to identify this level, which varies widely between children, is by ultrasonography. [44]

The conventional technique is described as proximal to the fold of the popliteal fossa, with the puncture in a somewhat lateral position to the midline at a 45-degree angulation relative to the skin, using 0.75 to 1.0 mL/kg of local anesthetic. [45] According to Konrad and investigators., body weight shows the best correlation with tibial nerve depth in children. [39]

A high-frequency probe should be used for popliteal access to the sciatic nerve in order to accurately identify the point at which the nerve furcates into its two branches, Figure 52-33 illustrates the sciatic nerve proximal to this furcation site. More distally, the peroneal nerve divides at a very superficial level, while the tibial nerve courses distally and deeper. The lateral approach to popliteal block is particularly suitable (Figure 52-34) because the child may remain in a supine position during the blockade, similarly to the technique in adult patients.[46,47] The exact puncture site is selected based on the depth of the nerve visualized in the ultrasound image. The needle tip is first positioned above and then below the sciatic nerve, which will ensure an optimal distribution pattern of the local anesthetic. Naturally, the advantage of not transversing the muscles is lost with this technique. Therefore, a distinction must be made between the lateral (in-line) and dorsal (cross-sectional) techniques.

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Blockade of the ilioinguinal/iliohypogastric nerves is the only documented application for ultrasound-guided techniques performed through the abdominal wall. Since this technique is used very frequently in clinical practice, a detailed discussion of its anatomic implications is provided, with the focus on ultrasound-guided puncture techniques.

Ilioinguinal/iliohypogastric nerve block

Blockade of the ilioinguinal/iliohypogastric nerves is a frequently used regional anesthetic technique for surgical procedures carried out in the sensory regions supplied by both nerves. For procedures in the inguinal region (inguinal hernia, orchiopexy), the effectiveness of this technique is similar to that of caudal blocks. [48] The needle insertion site for ilioinguinal/iliohypogastric blockade is usually located 1 cm medial to the anterior superior iliac spine, and the exact needle position is identified by a fascial click. [49] Considering the inaccuracy of this approach, it is not surprising that ilioinguinal/iliohypogastric nerve blocks yielded failure rates of 20 percent to 30 percent. [50] Furthermore, severe complications, such as intestinal puncture or pelvic hematoma, were reported [51–53].

These introductory remarks illustrate that the safety and effectiveness of ilioinguinal/iliohypogastric nerve blockade can be greatly improved by direct visualization. [5]

The following paragraphs illustrate the anatomic and sonographic principles of this technique. The anatomy of the lateral abdominal wall is more complicated than one might assume. Back in 1952, Jamieson and coworkers indicated that the position of these nerves relative to the muscles is subject to great anatomic variability. [54] Therefore, it is not surprising that “blind” needle insertion yields a relatively low success rate. Schoor and colleagues demonstrated this point in an anatomic study performed with children, [55] where most of the failed injections in that study were too medial.

The anatomic relationships can be summarized as follows. Both the ilioinguinal and the iliohypogastric nerves pass through the fascia lumborum at the lateral border of the quadratus lumborum muscle and then extend to the area between the obliquus internus abdominis and transversus abdominis muscles. The iliohypogastric nerve is located superior and medial to the ilioinguinal nerve and, in the area of the anterior superior iliac spine, furcates into the lateral and medial cutaneous rami as its two terminal branches. The lateral cutaneous ramus passes through obliquus internus abdominis and externus abdominis muscles and provides sensory supply to the skin in the anterior buttocks region. The medial cutaneous ramus passes both through the obliquus internus abdominis muscle and the aponeurosis of the obliquus externus abdominis muscles and supplies the skin in the abdominal wall region above the symphysis. The ilioinguinal nerve supplies the skin region underneath the area supplied by the iliohypogastric nerve as well as the anterior region of the scrotum.

The ultrasound examination should be performed with a high-frequency linear probe. The ilioinguinal nerve is best visualized immediately medial to the anterior superior iliac spine. (Figure 52-35) From our studies, we found that the anterior superior iliac spine is located at a mean distance of 7 mm to the nerve. The iliohypogastric nerve is located very close to the ilioinguinal nerve (3 mm on average). It is important to note that in 50 percent of cases, only two muscle layers are present in the puncture area, representing the obliquus internus abdominis and transversus abdominis muscles. Very often, the obliquus externus abdominis muscle is only present as an aponeurosis in the puncture area. Note that the nerves are located close to the peritoneum. In our investigations, we observed a mean distance of 3 mm (the shortest distance measured was 1 mm).

As illustrated in Figure 52-36, the needle is inserted transversal to the ultrasound probe and it is placed between the obliquus internus abdominis und transversus abdominis muscles. The volume of local anesthetic required to anesthetize both nerves is 0.2 mL/kg. These doses are considerably smaller than those recommended in other reports, which, especially in infants, adds greatly to the safety of the procedure, considering that very high serum levels were reported for this technique. [56] There is rarely a need to reposition the needle for blockade of the iliohypogastric nerve.

Ultrasound-guided blockade of the ilioinguinal/iliohypogastric nerves—using surgical analgesia with a combined approach consisting of inhalation anesthesia with 1 MAC of anesthetic gas and nerve blockade—yields a 96 percent success rate, even at low doses of local anesthetic (0.2 mL/kg). In addition, potential complications, such as intestinal puncture, are avoided safely with this approach. Furthermore, the risk of accidental femoral paresis is eliminated at lower doses of local anesthetic. [57] In addition, the work of Willschke and colleagues clearly demonstrated that body weight, body height, or similar parameters correlate neither with the distance between the anterior superior iliac spine and the ilioinguinal nerve nor with the depth of the ilioinguinal/iliohypogastric nerves nor with the distance between the nerves and the peritoneum. [5]

In summary, ultrasound guidance for ilioinguinal/iliohypogastric nerve blocks offers several advantages over traditional, "blind" techniques because it decreases the risk of complications and increases the success rate.

In summary, almost all regional anesthetic techniques used in adult patients can be used in children. Numerous published study results are available on the subject, however, many of the various puncture techniques used with conventional guidance techniques are not described very precisely. The widely held view, that local anesthetic spreads extensively and in all directions in very small children, making optimally exact puncture techniques unnecessary, is inaccurate. Ultrasound guidance is an excellent tool to optimize these nerve blocks. Ultrasound-guided nerve blocks require an adequate level of extra training. Workshops to convey the elementary hands-on skills are indispensable, but competent supervision must also be available in the early phase of practical application.

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