Ultrasound-Guided Pediatric Regional Anesthesia for Orthopedic Surgery

Gaston Labat stated in the forward to his seminal “Regional Anesthesia” textbook, “I do not look forward to the day when regional anesthesia will wholly displace general anesthesia; but undoubtedly it will reach and hold a very high position in surgical practice” (Regional Anesthesia: Its Technic and Clinical Applications. 1922). The development of point-of-care ultrasonography (POCUS) as a technique for guiding regional anesthesia has further advanced the role of nerve blocks as part of a balanced anesthetic by decreasing the risks associated with landmark techniques. This is particularly true in children, in whom the margin of safety for needle placement is often just a few millimeters and the distance between critical structures is even less than in adults.

Particular interest has developed in the use of regional anesthesia in pediatrics as an adjunct to managing postoperative pain and reducing opioid consumption. In addition to constipation, altered mental status, and respiratory depression, the risks of postoperative opioid use are now understood to include the risk of prolonged opioid misuse (JAMA Surg 2017;152:e170504). Between 2019 and 2020, overdose deaths in adolescents (14-18 years) increased by 94% (JAMA 2022;327:1398-1400). During this same time period, another study estimated that approximately 90% of overdose deaths among adolescents involved opioids (MMWR Morb Mortal Wkly Rep 2022;71:1576-82). With this stark reality in mind, it is imperative to continue to develop alternative methods of postoperative pain control that can be used in children, and adolescents in particular.

Orthopedic surgery is often necessary for children and adolescents. In toddlers, orthopedic surgery may address congenital anomalies, bone malignancy, and acute traumas and fractures. In adolescents, sports-associated injuries are common. In all of these cases, there are distinct regional anesthetic techniques that can be used to decrease both intraoperative anesthetic requirements and postoperative opioid needs. One specific consideration for pediatric regional anesthesia is the need to perform these blocks under general anesthesia. While the vast majority of nerve blocks in adults are done awake, this method is less popular in children due to age, inability to remain still, anxiety, and lack of venous access in advance of inducing general anesthesia. In fact, an analysis of blocks from the Pediatric Regional Anesthesia Network showed that 93.7% of blocks performed in pediatric patients were done under general anesthesia. The same study demonstrated that the risk of neurologic complications or severe local anesthetic systemic toxicity (LAST) was 2.2 per 10,000 for blocks performed under general anesthesia and 15.2 per 10,000 for blocks performed while the patient was awake or sedated (Anesthesiology 2018;129:721-32). There is a significant volume of literature demonstrating the safety and efficacy of blocks performed under general anesthesia, which should reassure providers about this practice difference between adults and children (Anesthesiology 2018;129:721-32; Reg Anesth Pain Med 2015; 40:526-32).

Ultrasound is particularly important when performing a block under general anesthesia, as the patient is not able to give feedback on paresthesia or sensory changes. Previously, blocks were often performed using nerve stimulation along with landmark techniques to localize the needle tip for a regional block. Although we still utilize nerve stimulation for some blocks, it is worth noting that ultrasound has allowed for the placement of regional blocks in a unique pediatric patient population in whom nerve stimulation would otherwise be contraindicated – patients with osteogenesis imperfecta (OI). In patients with OI, who often need repeated orthopedic surgeries and experience significant bone pain, nerve stimulation is contraindicated due to the risk of fracture from muscle contraction. Landmark technique is also relatively contraindicated, due to the possibility of causing injury to the bone while “walking off” as a component of landmark technique for some blocks. The rapid rise in ultrasound guidance for nerve blocks is of great benefit to this patient population, who otherwise would have a significantly higher risk associated with placement of regional anesthesia.

Another important consideration for the pediatric population includes weight-based dosing of local anesthetic agents, which may vary widely depending on the age of the patient. In terms of selection of local anesthetic, ropivacaine and bupivacaine are commonly used agents in pediatrics. The generally accepted upper limit of ropivacaine is 2-3 mg/kg. When using a 0.2% solution and an upper limit of 2 mg/kg, a simple calculation results in the safe dose being the same quantity in mL as the patient’s weight in kilograms. This quick method lessens the risk of toxicity and provides a rapid way of calculating the dose for a wide variety of weights.

For upper-extremity procedures, such as open reductions and fixations of fractures, the major nerves that need to be blocked are those coming off the brachial plexus. These blocks are performed in much the same way as they are in adults. Commonly performed blocks include the interscalene nerve block for proximal humerus fractures, as well as the supraclavicular block, which provides good sensory coverage for humerus and elbow fractures. POCUS provides a safer alternative to performing these blocks than using a landmark technique in adults (Medicine 2020;99:e21684). In children, where the distance between the brachial plexus and the pleura may be just a few millimeters, compared to 0.5-1 cm in adults, ultrasound is particularly beneficial in avoiding complications with the supraclavicular block. For the interscalene block in young children, both major vascular structures and the spinal cord lie in close proximity to the nerve roots. As such, an in-plane view, where the full length of the needle is seen on the ultrasound image, moving from posterior to anterior provides a safer strategy for performing this block.

Unique considerations arise for lower-extremity procedures. Pelvic and femoral osteotomies are often done in children with neuromuscular hip dysplasia and congenital abnormalities of the hips. When this procedure is done bilaterally, an epidural provides excellent postoperative analgesia. However, many of these children may also have associated scoliosis or spinal abnormalities that may lead to an epidural being either contraindicated or particularly challenging to place. Furthermore, there are advantages to avoiding a neuraxial technique in patients who have developmental delay and may not be able to express signs of a complication, like an epidural hematoma. For these patients, one POCUS-guided regional technique that can be used is a lumbar plexus nerve catheter. This is considered an advanced regional technique, given the proximity to the epidural space, large vessels, and the risk of hematoma, as well as the technical challenges. The ability to utilize ultrasound with an in-plane view helps to prevent inadvertent injury to nearby structures, including kidneys, particularly in small patients in whom the distances between structures are very small. This nerve block targets the lumbar plexus, consisting of five nerves on each side. Within the psoas major muscle, the roots of L2, L3, and L4 come together before splitting off into branches, providing an excellent target on ultrasound for placement of a lumbar plexus block. This block is most often performed using a large linear probe. The patient is placed in a lateral position with the operative side up. The probe is placed vertically just cephalad to the ASIS, and the region is scanned to identify the “shamrock sign” of the lumbar vertebrae with the psoas, quadratus lumborum, and erector spinae muscles surrounding the transverse process. A needle is advanced from the posterior to anterior direction in-plane, and local is deposited around the lumbar plexus just anterior to the transverse process. The placement is often performed using a combined POCUS and nerve stimulation procedure, looking for quadriceps muscle stimulation at less than 1.0 mA, demonstrating good contact with the femoral nerve. Sensory and motor coverage of the lumbar plexus block includes the femoral, obturator, lateral femoral cutaneous, and genitofemoral nerves, making it an ideal block for hip and femur procedures. The addition of a quadratus lumborum block to a lumbar plexus catheter adds sensory coverage of the iliohypogastric and ilioinguinal nerves, improving sensory coverage for hip surgeries.

Another important group to consider is adolescent athletes undergoing knee surgery by orthopedic sports medicine experts. For these patients, an adductor canal block of the saphenous nerve can provide good analgesia to the medial knee and lower leg as well as the patellar region. This block is commonly performed with the large linear array transducer placed on the patient’s medial thigh, with the leg turned out in a frog-leg position. The needle is advanced in-plane from medial to lateral. The needle is directed through the sartorius muscle, and the saphenous nerve is identified adjacent to the femoral artery, with local injected around the nerve. One advantage of this block over the femoral nerve block is that it helps to avoid femoral-associated motor weakness that can pose a challenge to early mobilization and participation in physical therapy. The sciatic nerve block is commonly performed in pediatric orthopedic surgery patients, providing excellent coverage for tibial surgery and lower leg fractures, particularly if combined with an adductor canal block for saphenous coverage of the medial lower leg and foot. Good analgesic coverage of the full leg is particularly important in patients with pediatric osteosarcoma, who often undergo complex resections with subsequent repeat manipulations in an attempt to maintain mobility. For patients with osteosarcoma of the distal femur or proximal tibia, the combination of femoral and anterior sciatic catheters that can be placed above full-leg casts can be an excellent adjunct to multimodal analgesia.

POCUS continues to provide the ability to safely and efficaciously perform regional anesthesia techniques that will reduce postoperative pain and opioid consumption. Current literature supports the ability to safely perform these blocks under ultrasound guidance in a pediatric patient under general anesthesia. With a good understanding of neuroanatomy and sensory and motor innervation, there are multiple regional nerve blocks that can facilitate excellent anesthetic care. POCUS in the hands of an expert will optimize the provision of exceptional perioperative analgesia and enhance pediatric patient and parental satisfaction.