Regional anesthesia can provide a useful adjunct for a variety of procedures in pediatric patients, either as a single injection or with postoperative infusion of local anesthetic or other adjuncts. Advantages of regional anesthesia, such as postoperative analgesia, avoidance of narcotic therapy with decreased nausea and vomiting, and early discharge from the recovery area, apply to pediatric patients. This chapter presents particular applications in pediatric anesthesia; further details on standard regional techniques are found in Chapters 46 to 49.
Performing a regional anesthetic in children who are too young to cooperate may require that the block be done during general anesthesia. Using a nerve stimulator to perform "surface mapping" before placing the needle may improve accuracy and decrease the number of attempts required.32 Ultrasound imaging is becoming more common for both neuraxial and peripheral blocks in children. Potential complications of regional techniques in anesthetized patients include intraneural injection, direct needle damage, and local anesthetic toxicity, although these complications are rare. Venous air embolism with hemodynamic consequences has been described during caudal or epidural placement in small children as has neurologic injury been believed to be caused by cerebrovascular air embolism or ischemic injury33; loss of resistance to air is not recommended in pediatric patients. The pediatric anesthesia community has endorsed epidural placement under anesthesia as appropriate practice when it is perceived that the patient will benefit from having the regional anesthetic and there is a risk that the patient might otherwise move during the block.34 The risks and benefits must be weighed in each individual pediatric patient, especially if the procedure is technically difficult.
Local anesthetic toxicity may result from intravascular injection, rapid absorption of an inappropriately large dose, or intravascular accumulation of drug over time. If combinations of local anesthetic agents are used, the toxicity of the agents should be considered to be additive. Local anesthetic blood levels after caudal and peripheral blocks in pediatric patients are generally within acceptable limits. Several cases of toxicity caused by accumulation of high levels in blood occurred in the early 1990s in the setting of postoperative infusion of local anesthetics; these resulted in revision of the recommendations of doses for pediatric infusion, with a maximum dose of 0.4 to 0.5 mg/kg/h for bupivacaine.35 Infants may be at higher risk for toxicity because of lower levels of plasma-binding proteins, diminished clearance, or both, particularly with redosing or catheter infusion techniques. The maximum recommended infusion rates of bupivacaine for patients 6 months and younger is 0.25 to 0.3 mg/kg/h.
Local anesthetic toxicity may not be obvious in the anesthetized patient; aspiration of blood may not reliably occur, and central nervous system signs are difficult to detect. The use of a test dose is recommended to detect inadvertent intravascular injection. Heart rate changes may be less sensitive in the pediatric population, particularly with volatile anesthetics; changes in T-wave morphology on the ECG are a useful indicator. Criteria for a positive test dose in an anesthetized child are heart rate increase greater than 10 beats/min, systolic blood pressure increase greater than 15 mm Hg, and change in T-wave amplitude greater than 25% in lead II. The recommended test dose in children is 0.5 mcg/kg epinephrine (0.1 mL/kg of local anesthetic containing 1:200,000 epinephrine),36 up to the 15-mcg adult test dose. Use of a short-beveled needle or Angiocath may minimize the risk of intravascular injection. In addition, slow incremental injection of local anesthetic is recommended (after test dose, administer a total dose over 1-2 min). Because small veins may easily collapse, observing for passive blood return may be useful in addition to aspiration.
Specific Techniques for Pediatric Regional Anesthesia
Caudal Blocks and Alternatives
The caudal approach to the epidural space is simple in young children, easy to learn, and has a good safety record (Fig. 64-4). Potential complications in anesthetized patients include intravascular injection of local anesthetic, which occurs in approximately 4 in 10,000 patients, and intrathecal injection with total spinal, with a reported incidence of 2.6 in 10,000 cases.37 Children may not develop hypotension or bradycardia even in the presence of a total spinal, but apnea may still occur because of medullary blockade.
Surface landmarks for caudal block. Both sacral cornua and the lateral borders of the sacrococcygeal hiatus can be palpated and outlined. The needle is inserted at the midpoint of the triangle at an approximately 45-degree angle to start.
Caudal blocks provide excellent analgesia for lower extremity, lower abdominal, and penoscrotal surgery. A short-beveled needle is placed through the sacral hiatus until a typical "pop" is felt, and the needle is anchored in the sacrococcygeal ligament (Fig. 64-5). Aspiration and free drainage should be negative for blood and cerebrospinal fluid (CSF). With correct placement, injection will be easy and will not result in swelling of the subcutaneous tissue. After an epinephrine-containing test dose, the full dose is injected incrementally. Clinical signs of correct placement are generally adequate, but use of a nerve stimulator to confirm caudal needle placement has been described. Laxity of the anal sphincter after placement of a caudal block has been shown to predict success of the block.38 If there is doubt as to efficacy, this sign may assist with the decision to provide additional analgesia. Although the time to first urination may be longer than that without a caudal block, urinary retention is generally not a significant clinical problem. Hemodynamic changes after a caudal block usually are minimal in normovolemic patients.
Caudal block. [Reprinted from Hahn MB, McQuillan PM, Sheplock GJ, eds. Regional Anesthesia: An Atlas of Anatomy and Techniques. St. Louis, MO: Mosby; 1996, with permission.]
Bupivacaine in concentrations of 0.125% to 0.25% traditionally has been used for caudal blocks in children in a dose of 1 mL/kg. Freshly added epinephrine to a concentration of 1:200,000 (5 mcg/mL) may improve the duration of analgesia. Because the block will begin to regress after several hours, the more concentrated solution or redosing the block at the end of the case is appropriate for longer procedures. Duration of analgesia from a single-shot caudal injection ranges from 4 to 12 hours. Use of a larger volume of local anesthetic to achieve a higher level may block stimulation from traction during procedures such as orchidopexy.39 The newer local anesthetics ropivacaine and levobupivacaine offer the advantages of decreased cardiac toxicity40 and reduced motor block. Ropivacaine and levobupivacaine have equivalent efficacy at either 0.2% or 0.25% compared with bupivacaine 0.25% (all given at 1 mL/kg); ropivacaine produced the least motor blockade.41
Caudally administered clonidine has shown good efficacy for augmenting and prolonging the analgesia produced by local anesthetics in a variety of procedures.42 A few studies question the benefit.43,44 Single doses of 1 to 2 mcg/kg provide analgesia with a lower incidence of nausea and vomiting than produced by opioids. Some sedation is seen at the higher dose of 5 mcg/kg. Most studies have not shown respiratory depression with epidural or caudal clonidine, although 2 case reports suggest apnea risk in premature infants. Use of epidural or caudal clonidine is fairly common in children in the United States, although a Food and Drug Administration (FDA) "black box" label warns of hypotension in adult patients after epidural clonidine administration. Ketamine has been shown to have good efficacy by the caudal route, but appropriate preparations of preservative-free S-ketamine are not available in the United States.45
Ilioinguinal or iliohypogastric nerve blocks can be performed preoperatively by the anesthesiologist or intraoperatively by the surgeon for procedures such as hernia repair and orchidopexy in children. Some surgeons believe that the injected local anesthetic distorts the surgical dissection planes and prefer to perform the block at the end of surgery. In this situation, a caudal block might be preferable to allow a contribution of the block during surgery. Ilioinguinal blocks generally have equivalent efficacy to caudal blocks, but this may be operator dependent. Cadaver dissection has shown that the optimal insertion site is more lateral than is generally taught and is located approximately 2.5 mm medial to the anterior superior iliac spine on both sides of a line drawn between the anterior superior iliac spine and the umbilicus.46 Ultrasound guidance may improve success and allow use of a lower volume of local anesthetic.47 Although quite safe, complications such as puncture of the bowel wall with hematoma formation have been reported after ilioinguinal block. Other techniques, such as paravertebral or lumbar plexus blockade, have been used in pediatric patients in select settings. Further experience with these techniques is needed before their use can be recommended outside of centers performing them frequently.
Penile block is commonly performed for circumcision and sometimes for simple hypospadias repair. Epinephrine should never be injected in a penile block because of the risk of vascular compromise. As with ilioinguinal blocks, many studies have compared caudal and penile blocks with variable results; most suggest that they are approximately equal. In the traditional dorsal penile block, the needle is passed from the base of the penis until the symphysis pubis is contacted and then withdrawn slightly and redirected to each side of the midline before local anesthetic is deposited. Because of the small risk of hematoma or damage to the dorsal penile vessels, some advocate a "ring block" or subcutaneous injection around the base of the penis. A combination of dorsal and ring blocks may provide the best analgesia. Simple application of topical anesthetic cream (eutectic mixture of local anesthetics [EMLA]) provided equivalent analgesia to dorsal penile block, but the duration of blockade was significantly longer with the injected nerve block.48
The primary use of spinal anesthesia in the pediatric population is for hernia repair or other relatively minor surgery in infants considered to be at risk for postoperative apnea. The dose requirement on a weight basis is significantly higher than in adults, and the duration is relatively shorter: 1 mg/kg hyperbaric bupivacaine has a duration of 1 to 2 hours. Levobupivacaine and ropivacaine also have been used. The decision to administer spinal anesthesia should depend on the patient's medical condition and the extent of the procedure. The perceived benefit of a reduced apnea frequency compared with general anesthesia in premature or former premature infants is valid only if no sedation is given. Spinal anesthesia may not be a good choice for a large or incarcerated hernia because of the limited duration and the fact that unsedated babies may fuss and strain.
Either thoracic or lumbar epidural catheters can be placed in children. Postoperative epidural analgesia may be of benefit to pediatric patients after major thoracic, abdominal, urologic, and lower extremity surgery. For patients weighing between 10 and 25 kg, the approximate depth of the epidural space in millimeters will be predicted by the weight in kilograms. Postoperative infusions should be prescribed to optimize analgesia and minimize side effects. Patient-controlled epidural analgesia can be given to children as young as 5 years of age and may decrease total drug administration.49 The pediatric orthopedic community has expressed concern that epidural analgesia may "mask" development of a compartment syndrome, but in the reported cases, pain was out of proportion to what was expected and was unrelieved by the epidural analgesia.50 Nevertheless, complications other than inadequate epidural analgesia must always be considered and evaluated promptly.
An epidural catheter can be threaded via the caudal route either to allow redosing for longer infraumbilical surgery or for the purpose of threading the tip of the catheter to a higher thoracic or lumbar level.51 In general, the ability to thread the catheter cephalad is best in infants because the epidural fat is not as dense as in older patients. The type of catheter may affect the success rate, and some recommend using a styletted catheter. Radiographic confirmation of tip placement52 or stimulation of the trunk musculature53 may be helpful in positioning the catheter.
Regional anesthesia of the upper extremity can be used in children for procedures performed on the arm and hand. Performing the entire surgical procedure under a regional technique is less common in children than in adults. In conjunction with general anesthesia, even distal blocks can provide excellent analgesia for hand procedures. Axillary blockade is the most common brachial plexus approach in children, although various infraclavicular approaches have been reported. Because of case reports of syrinx formation in adults after interscalene blocks placed under general anesthesia or deep sedation,54 this approach has not been recommended unless the patient can cooperate with block placement with minimal sedation. Some consider that ultrasonography may improve the safety adequately to permit this block under anesthesia.
A number of regional techniques can be performed in children for lower extremity surgery. A psoas compartment approach to the lumbar plexus has been described in children using a nerve stimulator and can be used for unilateral surgery on the hip, thigh, or knee.55 This block may require significant experience for the anesthesiologist to develop mastery,56 and there is some potential for vascular puncture. Femoral nerve blocks are useful in managing pain from a femur fracture even preoperatively. The "fascia iliaca" block has a high rate of success in children when anesthesia of the obturator and lateral femoral cutaneous nerves is needed in addition to the femoral nerve. The sciatic nerve can be blocked by the traditional posterior approach, at the midthigh, or in the popliteal fossa.