Figure 52–1. Needle position relative to the ultrasound probe (cross-sectional technique).

Clinical Pearls

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.

Figure 52–2. Sonographic visualization of the needle using the cross-sectional technique (in gel cushion). There is only one hyperechoic area (center), representing the needle tip.

Figure 52–3. Needle position relative to the ultrasound probe (in-line technique).

Figure 52–4. Sonographic visualization of the needle using the in-line technique (in gel cushion). Due to reverberation artifacts, the needle shaft emerging from the left margin of the image appears thicker than it really is.

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 technique is then followed; contact between the needle and the transducer or any other objects is avoided.

        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 face scales” or other modes of evaluating perioperative pain in a uniform manner. Flowever, information on pain and well-being of children is fundamental, since these patients 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.² Currently only limited data are available on the efficacy of the landmark-oriented techniques, nerve stimulator-guided blocks, and surface nerve- mapping techniques.³ 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 α₁-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 selfstudy methods. A more extended period of training, best done under the supervision of 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 all important for the success and safety of PNBs. 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

Adjustment of the Ultrasound Unit

The ultrasound machine must be properly configured and adjusted to make it suitable for use in ultrasound-guided nerve blocks in children. The following list of steps delineates the important parameters of that adjustment:

1.  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.

2.  Gain. Care must be taken to select an optimal gain relative to the image depth. Most modern 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).

3.  Focus. Given the dense vertical structures in children, the focus of the ultrasound image has to be adjusted so 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.

Nerve Block Preparation Strategies

The success of PNBs 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, colleague anesthesiologists, parents, and other involved caregivers are very important to the success of the new techniques. 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. Although it is possible in an occasional child to conduct the block procedure without premedication, as a general rule, however, sedation or general anesthesia is beneficial 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 (0.51 mg/kg). Always bear 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, 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 must have adequate training to be allowed to perform ultrasound-guided nerve blocks.

        SPECIFIC PERIPHERAL NERVE BLOCK TECHNIQUES

The following sections are dedicated to the various types of peripheral nerve blockade. We place special emphasis 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

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 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 a minute quantity of air can result in artifacts in the ultrasound image.

        In our pediatric regional anesthesia practice, we primarily use newer amide local anesthetics such as levobupivacaine or ropivacaine because of 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 be achieved.

        NERVE BLOCKS OF THE UPPER LIMB

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

Clinical Pearls

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 concern with interscalene blocks in children is the difficulty in achieving blockade of the roots of C8 and Tl. 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 advantageous in this situation, as it allows direct visualization and blockade of both roots C8 and Tl.

        Tobias reported on the technique of interscalene brachial plexus blockade using a perpendicular (90-degree) 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 pediatric patients. Dalens and colleagues reported on a technique of parascalene brachial plexus blockade for pediatric shoulder surgery that uses an exaggerated, retroflexed 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–s tubercle).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 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 to C7) of the brachial plexus become visible between the anterior and medial scalene muscles. In very small children, all roots of the brachial plexus (C5 to Tl) 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.

Figure 52–5. Sonographic visualization of anatomical structures in the medial neck area (left side = medial; Toshiba Aplio ultrasound unit with a 14-MHz linear probe).

Figure 52–6. Sonographic visualization of the brachial plexus inside the posterior scalene gap (arrows indicate the roots of the brachial plexus; left side = lateral; SonoSite TITAN ultrasound unit with a 10 MHz linear probe).

        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 52-8). Depending on the blockade required, the needle can be advanced to a deeper level for injection after the deep roots (C8 and Tl) 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. Rather than using a specific, arbitrary volume, the injected volume of local anesthetic should be adequate to cover the root surfaces. 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.

Figure 52–7. Needle position relative to the ultrasound probe during interscalene brachial plexus blockade.

Figure 52–8. C5 to C7 roots covered by 4 mL of local anesthetic. The tip of the needle is placed on the medial side of the nerve roots (left side = lateral; Toshiba Aplio ultrasound unit with a 14?MHz linear probe).

        Interscalene blocks are almost always best performed under general anesthesia because the patient needs to be 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 the current knowledge, however, catheters or single punctures through a scalene approach are rarely indicated in children.

Figure 52–9. Ultrasound visualization of the brachial plexus (between the colored arrows) at the supraclavicular level, which is seated directly on top of the cervical pleura (SonoSite MicroMaxx ultrasound unit with a 6-13-MHz linear probe).

Supraclavicular Approaches to Brachial Plexus Blockade

Pediatric applications for supraclavicular brachial plexus blockade have been previously described.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 the few 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

Anatomically, in the supraclavicular region, the brachial plexus is approached at the region where the trunks become divisions or cords. It is, therefore, difficult 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 cannula. 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.

Figure 52–10. In-line puncture technique for supraclavicular plexus blockade using a hockey-stick probe (array surface: 25 mm).

Infraclavicular Approaches to Brachial Plexus Blockade

Although infraclavicular blockade with the help of a nerve stimulator is reported to be safe and effective in children,^13–14 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 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-Andersens criteria, 100% of these infraclavicular blocks, as compared with 80% 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 sagittal 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 than with nerve stimulation.

Clinical Pearls

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) 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, a maneuver that 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.

Figure 52–11. Sonographic visualization of the puncture area during lateral infraclavicular blockade of the brachial plexus (left side = medial; Toshiba Aplio ultrasound unit with a 12-MHz linear probe).

Figure 52–12. Puncture technique below the ultrasound probe during lateral infraclavicular blockade of the brachial plexus.

Clinical Pearls

Because the local anesthetic will normally spread so 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 0.3–0.4 mL/kg. In contrast to other techniques in which an optimal volume is administered depending on how much volume 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 not all cords in the infraclavicular area can 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.

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 frequently 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% of the children. Blind perivascular injection of 0.75 mL/kg of local anesthetic also was recommended in the text by Jöhr, which is popular in parts of Europe.¹⁸ This recommendation referred to children younger than 8 years old; in larger children, the author favored the use of a nerve stimulator. He also indicated additional signs of appropriate cannula 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 on 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

Related posts:

Regional Anesthesia in the Patient with Preexisting Neurologic Disease. The History of Local Anesthesia. Stimulating Catheters. Ultrasound-Assisted Nerve Blocks in Adults. Cutaneous Blocks for the Upper Extremity. Cervical Plexus Block.