Spinal Anesthesia

Spinal anesthesia can be performed in children as an alternative to general anesthesia for lower abdominal, urologic, and lower extremity procedures. The most common use of spinal anesthesia in the pediatric population is for inguinal surgery in the preterm infant at risk for postoperative apnea after general anesthesia, especially in light of recent evidence of the possibility of neurotoxic effects of general anesthesia on the developing brain. Spinal anesthesia is an option when the duration of the surgical procedure is less than 90 minutes. If the procedure is expected to be longer, a combined spinal-epidural or a continuous caudal-epidural anesthesia technique can be considered ( Table 20.1 ). Contraindications to spinal anesthesia include infection at the site, increased intracranial pressure, and clinically significant hypovolemia.

Preoperative considerations before spinal anesthesia include normal fasting guidelines and a stable hemoglobin level. Preoperative application of a topical anesthetic cream over the lumbar spine may decrease pain from the spinal injection. Some pediatric anesthesiologists prefer to obtain IV access before performance of the spinal anesthetic.

Although cardiorespiratory effects are uncommon after spinal block in infants, complications from spinal anesthesia have been reported. Intra- and postoperative apnea, bradycardia, and hypoxemia may occur, necessitating immediate ventilatory assistance and possible atropine administration. A “high spinal” will cause respiratory and neurologic depression with rapid onset of hypoxemia. Therefore vigilance is required during and after the administration of the spinal anesthetic. Hypotension from a spinal anesthetic-induced sympathetic block rarely occurs in children under the age of 5 years. This may be because of the relatively immature sympathetic nervous system in children compared with adults, or because of the relatively smaller intravascular volume in the lower extremities of children such that lower extremity vasodilation does not reduce preload to an appreciable extent. Postdural puncture headache may occur in children. The headache will usually resolve within 3 to 5 days, but in some children, it may last longer.

The choice of intrathecal local anesthetic agent will depend on the expected duration of surgery. A larger dose is required than for adults because of the relatively larger ratio of cerebrospinal fluid (CSF) volume to bodyweight in neonates (6–10 mL/kg) compared with adults (2 mL/kg) and the resulting dilutional effect. Most reports in the literature use 1% tetracaine or 0.5% to 0.75% bupivacaine at doses varying from 0.3 to 1 mg/kg to provide 45 to 90 minutes of effective surgical anesthesia up to the T5–T6 level. To prolong the duration of the spinal block, epinephrine can be added using an “epi wash” which involves drawing up epinephrine (1:1000) into a tuberculin syringe and then ejecting it all out thereby leaving a small amount lining the syringe and the hub of the needle before drawing up the local anesthetic solution.

Spinal anesthesia can be performed in either the sitting or lateral position, depending on the personal preference of the anesthesiologist. Lumbar puncture is performed at the L4 to L5 interspace because the spinal cord in the small infant ends at a more caudad level (L3) than in older children (L1). This landmark can be found parallel to the top of the iliac crest. Using a sterile aseptic technique, a 1.5-inch, 22-gauge spinal needle is most often used and inserted approximately 1 to 2 cm until a light “pop” is felt as the needle penetrates the dura and subarachnoid membrane. When the stylet is removed, free flow of CSF is observed, and the syringe is firmly attached to the hub of the inserted spinal needle (a common cause of a failed spinal block is leakage of the local anesthetic solution during injection). The local anesthetic solution is injected over 5 to 10 seconds. Once the block has been performed, the infant is rapidly placed supine on the operating room table. Precautions should be taken to prevent the infant’s legs from being lifted up by operating room (OR) staff, which may result in a high spinal block. When the electrocautery pad is placed on the infant’s back, the entire infant should be lifted parallel to the table. The blood pressure cuff should be placed on a numb lower extremity to minimize stimulation of the conscious infant. A few minutes after the spinal block is completed, the anesthesiologist can assess if the infant’s legs become limp to assess the success of the spinal block ( Fig. 20.1 ). If the block is not successful, induction of general anesthesia is indicated.

Immediately after spinal insertion, the lower extremities should become numb. Andrew is very proud of his working spinal. Photo credit Ronald S. Litman.

With a successful spinal block, the anesthesiologist is left with a conscious infant who must be kept calm during the surgical procedure because crying or fussing increases intraabdominal pressure, which increases the technical difficulty of inguinal surgery. Most infants will sleep during the procedure or rest quietly if offered a pacifier dipped in glucose water ( Fig. 20.2 ).

The conscious infant must be kept calm when using spinal anesthesia, so Andrew drips glucose water in the infant’s mouth while the hernia repair proceeds. Photo credit Ronald S. Litman.

What is the course of action when the infant is inconsolable during the surgical procedure? First, the anesthesiologist and surgeon should determine whether the surgical area is properly anesthetized. In some cases of a patchy block, the surgeon can administer local anesthesia into the wound with satisfactory results. However, if doubt remains, induction of general anesthesia is the most prudent action.

Epidural Anesthesia

Epidural anesthesia can be administered in a variety of ways to infants and children. The decision will depend on the nature and duration of the surgical procedure. For ambulatory patients, a single dose of epidural anesthesia is administered, usually via the caudal space. For hospitalized patients, whose pain is expected to be severe for more than a day, insertion of an epidural catheter will provide continuous postoperative analgesia. Ideally, the epidural injection or catheter tip should be located at the level of the surgical incision. In infants, a thoracic level epidural catheter can be threaded cephalad via the caudal space. The use of ultrasound or fluoroscopy can be used to visualize the catheter as it travels from the caudal to the thoracic space to detect coiling of the catheter as it advances cephalad.

The choice of epidural analgesic medications includes a local anesthetic, an opioid, clonidine, or any combination of these. Opioids will usually be used in hospitalized children over 1 year of age who are expected to have severe pain. More specific dosing regimens are discussed in subsequent sections of this chapter and in Chapter 34 .

Side effects and complications from epidural analgesia are the same for children as for adults. Common side effects include motor blockade of the lower extremities and urinary retention. Local anesthesia toxicity from accidental intravascular injection is rare and manifests as seizures in an unanesthetized child or cardiac collapse in an anesthetized child. Treatment involves standard resuscitation methods plus the administration of 20% Intralipid emulsion, 1.5 mL/kg. This dose can be repeated as necessary to control cardiac arrhythmias and ideally should be followed by an infusion of 0.25 mL/kg/min titrated to hemodynamic stability. Additional rare complications include epidural hematoma, epidural abscess formation, intraneural trauma causing a residual neurologic deficit, and unintentional dural puncture with spinal blockade. Postdural puncture headache is rarely seen in children less than 8 years of age secondary to the increased volume of CSF and greater CSF turnover. Devastating neurologic complications after seemingly error-free epidural catheter placements have been reported in children.

Caudal-Epidural Anesthesia

The most common neuraxial regional technique in neonates and infants is the caudal epidural block, which is relatively easy to perform once the proper landmarks have been identified. It can be performed before surgery to be used in combination with general anesthesia, performed after surgery to be used for postoperative analgesia, or used instead of general anesthesia for lower abdominal and lower extremity procedures. A caudal epidural block can be performed with the patient in the prone position with the legs tucked under, the lateral position with the hips flexed ( Fig. 20.3 ), or even the supine position with the legs lifted up over the head. The important landmarks are the coccyx and the sacral hiatus located between the two sacral cornua. A 22-gauge short-beveled needle is inserted 1 to 2 mm caudad from a point midway between the two cornua. The needle is inserted at a 30- to 45-degree angle to the skin and advanced through the sacrococcygeal ligament. As the needle is advanced through the ligament and into the epidural space, a characteristic loss of resistance is felt. Once the epidural space is entered, care is taken to avoid advancing the needle too far, as the dural sac may extend down as far as S3 or S4 level in small infants (as opposed to S1–S2 in adults), and an unintentional dural puncture may occur. Because ossification of the sacrum is not complete until adulthood, the epidural needle can be accidentally inserted into the sacrum without much resistance. Some anesthesiologists prefer to make a small nick at the skin with an 18-gauge needle to serve as an entranceway for the block needle and to prevent tissue coring.

(A) Infant prepped and positioned for caudal block. (B) The anesthesia provider’s right hand identifies the landmarks while the left hand is used for injection through the sacrococcygeal ligament.

Before the administration of the local anesthetic solution into the epidural space, the anesthesiologist should attempt to rule out unintentional placement of the catheter or needle into the intravascular or intrathecal space. Initially, the caudal needle is gently aspirated to detect blood or CSF. However, this test is not completely reliable owing to the high compliance of the epidural veins and intrathecal space in children, which collapses easily with even slight negative pressure. A test dose is recommended to help detect intravascular placement of the epidural block. In children, the dose of epinephrine that consistently results in hemodynamic or electrocardiogram (ECG) changes is 0.5 μg/kg. This translates into a test dose of 0.1 mL/kg of a local anesthetic solution that contains epinephrine in a concentration of 1:200,000 (5 μg/mL). Sixty seconds is allowed to elapse to assess for accidental IV or intraosseous injection. Although the efficacy of the test dose has been questioned, especially if administered during the use of inhalational anesthetic agents, its reliability can be increased by observing the change in T-wave amplitude, the heart rate, and the blood pressure response. An increase in T-wave amplitude of greater than 25% over baseline or an increase in heart rate greater than 10 beats/min are indicative of an IV injection of epinephrine. Systolic blood pressure has been described to rise by 15 mm Hg but is less reliable than heart rate or T-wave changes. Changes in any of these parameters indicate an unintentional IV injection and the need to reposition the needle. One caveat to test-dosing in children is that the expected increase in T-wave amplitude in response to IV epinephrine may not occur during a propofol-remifentanil general anesthetic; thus practitioners should rely on the blood pressure response. If no response to the test dose is noted, the remainder of the calculated dose is administered slowly over 1 to 2 minutes while the vital signs are continually monitored for evidence of intravascular injection. The choice of ECG lead does not appear to influence the accuracy of the test dose response.

A caudal epidural block can be achieved using any local anesthetic agent. The concentration and volume of the solution are usually determined by the height and density of the blockade required. The volume of local anesthetic determines the height of the block, which depends on the level of the surgical incision. Volumes of 1.2 to 1.5 mL/kg provide analgesia to the T4 to T6 level. A dose of 1 mL/kg will provide postoperative analgesia for inguinal procedures, while 0.5 to 0.75 mL/kg is sufficient for lower extremity or urogenital procedures. Regardless of the volume used, the concentration is adjusted to ensure that no more than 2.5 mg/kg of bupivacaine or 3 mg/kg of ropivacaine is administered. With bupivacaine, the majority of experience is with the 0.25% solutions. However, effective postoperative analgesia can be achieved using a 0.125% solution, thereby limiting the total dose and decreasing the intensity of the motor block.

Caudal ropivacaine provides a faster onset of analgesia and less motor blockade than bupivacaine. A 0.2% ropivacaine solution provides the best efficacy with the least amount of motor blockade. Although peak plasma concentrations of both bupivacaine and ropivacaine will be achieved 20 to 40 minutes after epidural administration, ropivacaine is absorbed into the systemic circulation more slowly than equivalent doses of bupivacaine. Ropivacaine is less cardiotoxic than bupivacaine at equipotent plasma concentrations and is being increasingly used by pediatric anesthesiologists for regional blockade. Intraoperative bolus doses can be readministered every 1 to 2 hours, or administered as a continuous infusion throughout the procedure (see Table. 35.3, Table. 35 ).

Epinephrine can be added to the local anesthetic solution to slightly prolong the duration of action of the sensory block and limit potentially rapid systemic absorption via epidural blood vessels. The addition of clonidine or dexmedetomidine, 1 µg/kg, will enhance the quality and duration of postoperative analgesia when combined with epidural local anesthetics and is now routinely included in the epidural anesthetic solution in many pediatric centers. Concomitant administration of IV dexamethasone has also been shown to prolong the duration of epidural analgesia. The addition of opioids has been found to be beneficial, but must be used with caution and with appropriate postoperative monitoring of the patient’s respiratory status.

Thoracic Epidural Analgesia via the Caudal Approach

Segmental anesthesia may be achieved with relatively smaller doses of local anesthetic when the epidural catheter tip is placed in the close vicinity of the spinal segment of the surgical incision. In anesthetized infants, direct thoracic epidural placement may entail the risk for spinal cord trauma and should only be undertaken by those with considerable clinical experience in the technique. Alternatively, in neonates and infants, when thoracic level anesthesia is desired, a catheter can be advanced through the epidural space via the caudal space to the desired level, based on an approximate measurement, or using radiographic or ultrasound guidance. Minor resistance may be encountered, but the catheter should advance relatively easily. If it does not, it is not positioned correctly. Even when it advances easily, there is a high incidence of malpositioning because of coiling of the catheter within the epidural space. Use of a styletted catheter may decrease the incidence of coiling, but may increase the risk for unintentional intravascular and subarachnoid penetration. Once the catheter has been advanced to its expected position, a small amount of nonionic radiographic contrast (Iohexol-Omnipaque 180) is injected while simultaneously obtaining a radiograph or fluoroscopy of the chest and abdomen to identify the level of the epidural catheter and tip and to confirm appropriate placement in the epidural space. Ultrasound can be used in infants younger than 4 to 6 months, and nerve stimulation guidance (Tsui test ) is a third way to identify the level of the tip of the catheter.

Direct Lumbar or Thoracic Epidural Analgesia

Direct lumbar or thoracic epidural catheter placement in children differs from that in adults. The first major difference is that the distance from the skin to the epidural space is less in children. In children between 6 months and 10 years of age, the epidural space at the lumbar level will be encountered at a depth of 1 mm per kilogram of weight. The second major difference is that children have a much softer ligamentum flavum than adults. Thus it is more difficult to identify the ligament with certainty during epidural needle placement. An important consequence of these two differences is that unintentional dural puncture is more likely in a child than in an adult. Therefore the epidural space is approached with caution with the loss-of-resistance technique being started just beneath the skin, while advancing the needle slowly until the epidural space is identified. A small skin nick is made at the site before placing the epidural needle so that the pressure required to advance the epidural needle through the skin does not cause the needle to advance too far and puncture the dura. Once the space is identified, an epidural catheter is threaded so that 2 to 4 cm remains in the epidural space. Gentle aspiration for blood or CSF is then performed before the local anesthetic solution is administered. A test dose is given through the catheter using the same diagnostic criteria as described above in the section on caudal block. The initial bolus dose of local anesthesia depends on the level of catheter placement. When the catheter is placed as an adjunct to general anesthesia, 0.25% bupivacaine or 0.2% ropivacaine is used. Suggested starting guidelines for dosing include an initial bolus dose of 0.3 mL/kg (maximum 10 mL) followed by initiation of an epidural infusion of local anesthetic.

Complications of epidural catheter placement and analgesia include dural puncture, nerve root irritation, infection, epidural hematoma, and abscess formation. This technique is contraindicated in children with a coagulopathy (platelet count ≤100,000/mm, an elevated PT (PT = prothrombin time) or elevated PTT (PTT = partial thromboplastin time), or qualitative bleeding dysfunction (e.g., hemophilia or von Willebrands disease). New neurologic deficits and back pain are signs of an epidural hematoma. Placing the epidural below the intercristal line (line connecting the tops of the iliac crests) will avoid direct trauma to the spinal cord.

Upper Extremity Regional Anesthesia

There are multiple approaches to regional anesthesia of the upper extremity, depending on the specific nerves to be blocked and on the expertise of the practitioner. The axillary block is appropriate for elbow or more distal upper extremity surgery. For this block, the ultrasound probe is placed in the axilla perpendicular to the course of the axillary artery and at the level of the crease formed by the pectoralis major and biceps muscles, to visualize the axillary artery and vein in the short-axis view. The median, ulnar, and radial nerves most likely will surround the artery in a triangular pattern. Using an in-plane approach the needle is advanced and 0.2 to 0.5 mL/kg up to 10 to 20 mL of local anesthetic is injected in a circumferential pattern around the axillary artery producing the characteristic “donut sign.” The axillary approach will invariably miss the musculocutaneous nerve; therefore, a separate block can be performed using the same needle insertion site as the axillary block, and injecting part of the local anesthetic solution into the body of the coracobrachialis muscle.

The supraclavicular block is applicable for almost all upper extremity procedures. It is performed with the ultrasound probe placed parallel to the clavicle. A needle is placed in-plane with the local anesthetic deposited around the trunks of the brachial plexus, often referred to as a “cluster of grapes” lateral to the subclavian artery. The infraclavicular block of the brachial plexus is appropriate for humeral shaft, elbow, and distal upper extremity procedures. The ultrasound probe is placed perpendicular under the clavicle and the axillary artery is identified. An appropriately sized needle is placed using an in-plane technique and the local anesthesia is deposited posterior to the axillary artery and spread is observed to the posterior, lateral, and medial cords of the brachial plexus.

Lower Extremity Regional Anesthesia

Femoral Nerve Block

The femoral nerve block provides analgesia for procedures of the anterior portion of the thigh, femoral shaft, and knee. After passing under the inguinal ligament, the femoral nerve divides into an anterior and a posterior branch to supply sensation to the anterior and lower medial portion of the thigh, femur, and knee, as well as sensation to the medial aspect of the leg below the knee down to the foot through the saphenous nerve (terminal branch of the posterior division of the femoral nerve).

To perform this block, a needle is inserted 1 to 2 cm lateral to the femoral artery and 1 to 2 cm below the inguinal ligament. The needle is then advanced at a 45-degree angle in a cephalad direction until a double loss of resistance is felt as the needle passes through the fascia lata and fascia iliaca.

Ultrasound guidance of the femoral block improves the quality and prolongs the duration of analgesia with a lower risk for accidental arterial puncture ( Fig. 20.4 ). Using a linear probe placed along the inguinal crease and below the inguinal ligament, the femoral artery is first identified and confirmed with Doppler. The femoral nerve lies lateral to the artery and appears as a triangular, hyperechoic structure below the fascia iliaca and superficial to the iliopsoas muscle. An in-plane or out-of-plane technique can be used in this block. With the in-plane technique, the needle is inserted from lateral to medial until it penetrates the fascia iliaca. After negative aspiration, 0.2 to 0.3 mL/kg of the local anesthetic is injected until a donut-shaped spread around the femoral nerve is seen.

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