Chapter 15. Caudal Anesthesia

Caudal anesthesia was first described at the turn of last century by two French physicians, Fernand Cathelin and Jean-Athanase Sicard. The technique predated the lumbar approach to epidural block by several years.1 Caudal anesthesia, however, did not gain in popularity immediately following its inception. One of the major reasons caudal anesthesia was not embraced arose from the wide variety of arrangements of sacral bones encountered in the general population and the consequent high failure rate associated with attempts to locate the sacral hiatus. The failure rate of 5% to 10% made caudal epidural anesthesia unpopular until a resurgence of interest occurred in the 1940s led by Hingson and colleagues, who used it primarily in obstetrical anesthesia. Caudal epidural anesthesia has many applications, including surgical anesthesia in children and adults, as well as the management of acute and chronic pain conditions. Success rate of 98% to 100% can be achieved in infants and young children before the age of puberty, as well as in lean adults.1 The technique of caudal epidural block in pain management has been greatly enhanced by the use of fluoroscopic guidance and epidurography, in which high success rates can be attained. Unfortunately, clinical indications, and especially therapeutic interventions for the relief of chronic pain in individuals with failed back surgery syndrome, are often most prevalent in patients with difficult caudal landmarks. It has been suggested that traditional lumbar peridural block should not be attempted employing an approach requiring needle placement through a spinal surgery scar, due to the likelihood of tearing the dura and the possibility of inducing hematoma formation over the cauda equina when blood from the procedure gets trapped between the layers of scar and connective tissues.2 Under these circumstances, it is recommended that fluoroscopically guided caudal epidural block be performed in lieu of the traditional approach. The second resurgence in popularity of caudal anesthesia has paralleled the increasing need to find safe alternatives to conventional lumbar epidural block in selected patient populations, such as individuals with failed back surgery syndrome.

The sacrum is a large triangularly shaped bone formed by the fusion of the five sacral vertebrae. It has a blunted, caudal apex that articulates with the coccyx. Its superior, wide base articulates with the fifth lumbar vertebra at the lumbosacral angle (Figure 15–1A–D). Its dorsal surface is convex and has a raised interrupted median crest with four (sometimes three) spinous tubercles representing fused sacral spines. Flanking the median crest, the posterior surface is formed by fused laminae. Lateral to the median crest, four pairs of dorsal foramina lead into the sacral canal through intervertebral foraminae, each of which transmits the dorsal ramus of a sacral spinal nerve (see Figure 15–1B). Below the fourth (or third) spinous tubercle an arched sacral hiatus is identified in the posterior wall of the sacral canal, due to the failure of the fifth pair of laminae to meet, exposing the dorsal surface of the fifth sacral vertebral body. The caudal opening of the canal is the sacral hiatus (see Figure 15–1A and B), roofed by the firm elastic membrane, the sacrococcygeal ligament, which is an extension of the ligamentum flavum. The fifth inferior articular processes project caudally and flank the sacral hiatus as sacral cornuae, connected to the coccygeal cornua by intercornual ligaments.

The sacral canal is formed by the sacral vertebral foramina and is triangular in shape. It is a continuation of the lumbar spinal canal. Each lateral wall presents four intervertebral foramina, through which the canal is contiguous with the pelvic and dorsal sacral foramina. The posterior sacral foramina are smaller than their anterior counterparts. The sacral canal contains the cauda equina (including the filum terminale) and the spinal meninges. Near its midlevel (typically the middle one third of S2, but varying from the midpoint of S1 to the midpoint of S3) the subarachnoid and subdural spaces cease to exist, and the lower sacral spinal roots and filum terminale pierce the arachnoid and dura maters.3,4 The lowest margin of the filum terminale emerges at the sacral hiatus and traverses the dorsal surface of the fifth sacral vertebra and the sacrococcygeal joint to reach the coccyx. The fifth spinal nerves also emerge through the hiatus medial to the sacral cornua. The sacral canal contains the epidural venous plexus, which generally terminates at S4, but which may continue more caudally. Most of these vessels are concentrated in the anteriolateral portion of the canal. The remainder of the sacral canal is filled with adipose tissue, which is subject to an age-related decrease in its density. This change may be responsible for the transition from the predictable spread of local anesthetics administered for caudal anesthesia in children to the limited and unpredictable segmental spread seen in adults.5

Considerable variability occurs in sacral hiatus anatomy among individuals of seemingly similar backgrounds, race, and stature.1 As individuals age, the overlying ligaments and the cornua thicken significantly. The hiatal margins often defy recognition by even skilled fingertips. The practical problems related to caudal anesthesia are mainly attributable to wide anatomic variations in size, shape, and orientation of the sacrum. Trotter3 summarized the major anatomic variations of the sacrum. The sacral hiatus may be almost closed, asymmetrically open, or widely open secondary to anomalies in the pattern of fusion of the laminae of the sacral arches. Sacral spina bifida was noted in about 2% of males, and in 0.3% of females. The anteroposterior depth of the sacral canal may vary from less than 2 mm to greater than 1 cm. Individuals with sacral canals having anteroposterior diameters less than about 3 mm may not be able to accommodate anything larger than a 21-gauge needle (5% of the population).1 Additionally, the lateral width of the sacral canal varies significantly. Since the depth and width of the canal may vary, the volume of the canal itself may also vary. Trotter found that sacral volumes varied between 12 and 65 mL, with a mean volume of 33 mL.3 A magnetic resonance imaging (MRI) study in 37 adult patients found the volume (excluding the foramina and dural sac) to be 14.4 mL, with a range of 9.5 to 26.6 mL.6 Patients with smaller capacities may not be able to accommodate the typical volumes of local anesthetics administered for epidural anesthesia via the caudal route. In a cadaver study of 53 specimens, the mean distance between the tip of the dural sac and the upper edge of the sacral hiatus as denoted by the sacrococcygeal membrane was 45 mm, with a range of 16 to 75 mm.3 In the MRI study mentioned earlier, the mean distance was found to be 60.5 mm, with a range of 34 to 80 mm.6 The sacrococcygeal membrane could not be identified in 10.8% of subjects using MRI.6 A recent anatomic evaluation of 92 isolated sacra found that 42% of cases had both a hiatus and cornu; 4% of the cases showed an absent hiatus. The apex of the sacral hiatus, in that study, was noted in 64% of cases to exist at the S4 level. The hiatus was closed in 3% of cases.7

The sacral foramina afford anatomic passages that permit the spread of injected solutions such as local anesthetics and adjuvants (see Figure 15–1C and D). The posterior sacral foramina are essentially sealed by the multifidus and sacrospinalis muscles, but the anterior foramina are unobstructed by muscles and ligaments, permitting ready egress of solutions through them.8 The sacral curvature also varies substantially.9 This variability tends to be more pronounced in males than in females. The clinical significance of this finding is that a noncurving epidural needle will more likely pass easily into the canal of females than males. The angle between the axis of the lumbar canal and the sacral canal varies between 7 and 70 degrees in subjects with marked lordosis. The clinical implication of this finding is that the cephalad flow of caudally injected solutions may be more limited in lordotic patients with exaggerated lumbosacral angles than in those with flatter lumbosacral angles, in whom the axes of the lumbar and sacral canals are more closely aligned.

The indications for caudal epidural block are essentially the same as those for lumbar epidural block, but its use may be preferred when sacral nerve spread of anesthetics and adjuvants is preferred over lumbar nerve spread. The unpredictability of ascertaining consistent cephalad spread of anesthetics administered through the caudal canal limits the usefulness of this technique when it is essential to provide lower thoracic and upper abdominal neuraxial blockade. Though this modality is described for perioperative use (diminishing role) and for managing chronic pain in adults (increasing role), it is essential to recognize that caudal block has an extremely wide range of applicability (Table 15–1).10–13

Other newer indications in adults bear special mention and will be described later, including the performance of percutaneous epidural neuroplasty;14,15 the use of caudal analgesia following lumbar spinal surgery;16 caudal analgesia after emergency orthopedic lower extremity surgery;17 administering local anesthetic adjuvants for postoperative analgesia;18 and caudal block for performing neurolysis for intractable cancer pain.19

The technique of caudal epidural block involves palpation, identification and puncture.1 Patients are evaluated for any epidural block, and the indications and relative and absolute contraindications to its performance are identical. A full complement of noninvasive monitors is applied, and baseline vital signs are assessed. One must decide whether a continuous or single-shot technique will be employed. For continuous techniques, a Tuohy-type needle with a lateral facing orifice is preferred.

Patient Positioning

Several positions can be used in adults, compared with the lateral decubitus position in neonates and children. The lateral position is efficacious in pediatrics because it permits easy access to the airway when general anesthesia or heavy sedation has been administered prior to performing the block. In pediatric patients, blocks may be performed with the patient fully anesthetized; the same is not recommended for older children and adults. In adults, the prone position is the most frequently utilized, but the lateral decubitus position or the knee–chest (also known as knee–elbow) position may be employed. In the prone position, the procedure table or operating room table should be flexed, or a pillow may be placed beneath the symphysis pubis and iliac crests to produce slight flexion of the hips. This maneuver makes palpation of the caudal canal easier. The legs are separated with the heels rotated outward to smooth out the upper part of the anal cleft while relaxing the gluteal muscles. For placement of caudal epidural block in the parturient, the woman is in the lateral (Sim position) or in the knee–elbow position.

Anatomic Landmarks

A dry gauze swab is placed in the anal cleft to protect the anal area and genitalia from povidone-iodine (Betadine) or other disinfectants (especially alcohol) used to sterilize the skin. The skin folds of the buttocks are useful guides in locating the underlying sacral hiatus. Alternatively, a triangle may be marked on the skin over the sacrum, using the posterior superior iliac spines (PSIS) as the base, with the apex pointing inferiorly (caudally). Normally, this apex sits over or immediately adjacent to the sacral hiatus. The hiatus is marked and the tip of the index finger is placed on the tip of the coccyx in the natal cleft while the thumb of the same hand palpates the two sacral cornua located 3–4 cm more rostrally at the upper end of the natal cleft. The sacral cornua may be identified by gently moving the palpating index finger from side to side (Figure 15–2). The palpating thumb should sink into the hollow between the two cornua, as if between two knuckles of a fist.1 A sterile skin preparation and draping of the entire region is performed in the usual fashion.

Technique

A small-gauge 1.5-in. needle is then utilized to infiltrate the skin over the sacral hiatus using 3–5 mL of 1–1.5% plain lidocaine HCl (Figures 15–3, 15–4, and 15–5). If fluoroscopy is utilized, a lateral view is obtained to demonstrate the anatomic boundaries of the sacral canal. We routinely leave the local anesthetic infiltration needle in situ for this view, since it demonstrates whether the approach is at the appropriate level for subsequent advancement of the epidural needle. With fluoroscopy, the caudal canal appears as a translucent layer posterior to the sacral segments (Figure 15–6). The median sacral crest is visualized as an opaque line posterior to the caudal canal. The sacral hiatus is usually visualized as a translucent opening at the base of the caudal canal. The coccyx may be seen articulating with the inferior surface of the sacrum.

Once the tissues overlying the hiatus have been anesthetized, a 17- or 18-gauge Tuohy-type needle is inserted either in the midline or, using a lateral approach, into the caudal canal (Figures 15–7 and 15–8). A feeling of a slight “snap” may be appreciated when the advancing needle pierces the sacrococcygeal ligament. Once the needle reaches the ventral wall of the sacral canal, it is slowly withdrawn and reoriented, directing it more cranially (by depressing the hub and advancing) for further insertion into the canal (Figure 15–9). We utilize the anteroposterior view once the epidural needle is safely situated within the confines of the canal, and the epidural catheter is advanced cephalad. In this projection, the intermediate sacral crests appear as opaque vertical lines on either side of the midline. The sacral foramina are visualized as translucent and nearly circular areas lateral to the intermediate sacral crests. The presence of intestinal gas may obfuscate the recognition of these structures. A syringe loaded with either air or saline containing a small air bubble is attached to the needle, and the loss-of-resistance technique is used to establish entry into the epidural space.

A “whoosh” test has been described for identifying correct needle placement in the caudal canal. This characteristic sound has been noted during auscultation of the thoracolumbar region during the injection of 2 to 3 mL of air into the caudal epidural space.20 The test has been modified in pediatrics, wherein local anesthetic, and not air injection, is auscultated during the performance of the block. Of the 108 patients with a successful block in one study, 98 had a positive test, with no false-positive results.21 Once the correct placement of the needle is confirmed, a catheter is inserted into the desired location (depth) (Figure 15–10), and its position confirmed fluoroscopically when desired (Figures 15–11 and 15–12).

Injected solutions may be absorbed very rapidly by bone marrow and toxic drug reactions result. In this situation, pain is typically noted over the caudal part of the sacrum during the injection. If this occurs, the needle should be withdrawn slightly and rotated on its axis until it can be reinserted in a slightly different direction.23–25

If injection is made anterior to the sacrum (between the sacrum and coccyx), it is possible to perforate the rectum, or, in parturients, the baby's head may be injured. This limits the use of caudal block in laboring women once the presenting part has descended into the perineum. Inadvertent venous puncture also may occur, and the incidence of this has been reported to be about 0.6%.26

Caudal block may be used with a single-shot or continuous catheter technique. For continuous block, the catheter may be advanced anterogradely (conventionally) or retrogradely. Continuous caudal block may be performed in retrograde fashion using needle insertion into the lumbar epidural space, but directed inferiorly instead of superiorly. In one study of 10 patients, epidural catheters were advanced through 18-gauge Tuohy-type epidural needles in retrograde fashion from the L4-L5 interspace. This technique was associated with a 20% failure rate with the catheter going into the paravertebral or retrorectal spaces, despite easy epidural space entry.27 Using the conventional approach, a Huber-tipped Tuohy needle is used as a conduit to pass the epidural catheter into the canal. This needle has a skilike tip that limits its being caught or snagged on the sacral periosteum. The needle is inserted with its shoulder facing anteriorly and its orifice dorsally. Alternatively, a standard 16- or 17-gauge catheter-over-needle assemblage (angiocatheter) may serve as the introducing needle for subsequent catheter placement. The catheter is advanced with fluoroscopic guidance, especially when it is performed for chronic pain management in failed back surgery syndrome. The catheters should be advanced gently, since there have been reports of dural puncture with rapid or aggressive advancement. The lateral and anteroposterior views should be obtained to demonstrate placement of the catheter in the epidural space (lateral view, see Figure 15–6) and to follow its path in a cephalad or cephalolateral direction (anteroposterior view, see Figure 15–11). When the desired level is attained, iodinated nonionic contrast media may be injected, followed by the injection of local anesthetics, corticosteroids or adjuncts (Figures 15–13 and 15–14). We usually do not advance the catheter higher than the level of the L4 vertebral body, although we have occasionally advanced it to the L1 or L2 level. Some authorities suggest avoiding advancement more than 8–12 cm cephaladly.

Characteristics of the Blockade

Caudal epidural block results in sensory and motor block of the sacral roots and limited autonomic block. The sacral contribution of the parasympathetic nervous system is blocked, causing loss of visceromotor function of the bladder and intestines distal to the colonic splenic flexure. Sympathetic block, though limited compared with lumbar or thoracic epidural block, does occur. However, the sympathetic outflow from the spinal cord ends at the L2 level, and, therefore, caudal block should not routinely result in peripheral vasodilatation of the lower extremities to the degree witnessed with lumbar epidural blockade. Caudal epidural local anesthetic block in adults may be chosen for surgeries of the lower abdomen, perineum, or lower extremities. The local anesthetic mixtures and doses are similar to those for lumbar epidural block (Table 15–2).

Spread of the Local Anesthetic Solutions

The large capacity of the sacral canal accommodates correspondingly large volumes of solution; significant volumes may be lost through the wide anterior sacral foramina. Therefore, the caudal dose requirements of local anesthetics are significantly larger to effect the same segmental spread than are the corresponding lumbar doses. Roughly twice the lumbar epidural local anesthetic dose is needed for caudal blockade to attain similar levels of analgesia and anesthesia, and solutions injected in the caudal space take longer to spread (see Table 15–2). Bromage noted that age is not correlated with caudal segmental spread in adults and the upper level of analgesia resulting from 20-mL doses of local anesthetic solution varies widely between S2 and T8.1 This unpredictability limits the usefulness of applying caudal anesthesia for surgical procedures that require cephalad analgesia levels above the pelvic level or the umbilicus. A recent study reconfirmed Bromage's findings. In 172 women undergoing minor gynecologic surgery using caudal anesthesia with 20 mL of 1.5% lidocaine, the highest sensory dermatome level reached was below T10.28

Indications in Adults

Caudal block is indicated whenever the area of surgery involves the sacral and lower lumbar nerve roots. The technique is suitable for anal surgery (hemorrhoidectomy and anal dilatation), gynecologic procedures, surgery on the penis or scrotum, and lower limb surgeries. Using a catheter technique, it is possible to use caudal epidural block for vaginal hysterectomy and inguinal herniorrhaphy.

Caudal epidural block is used less frequently than lumbar or even thoracic epidural block for providing perioperative analgesia in adults. The pelvis enlarges markedly in puberty while the epidural fat in the lumbosacral region undergoes compaction and increased fibrous content. This hinders cephalad spread of solutions particularly when compared with the spread in children.

As an alternative to caudal epidural block in adults, one might consider a median approach to transsacral epidural block. In the original description of that technique, 87% of blocks were successful for transurethral resection of bladder tumors versus 100% success for sacral procedures. Anesthesia level, side effects, and hemodynamics were similar between the two groups studied in that initial report.29

The sacral canal shares in the general engorgement of extradural veins that occurs in late pregnancy, or in any clinical condition in which the inferior vena cava (IVC) is partially obstructed. Since the effective volume of the caudal canal is markedly diminished during the latter part of pregnancy, the caudal dosage should be reduced proportionately in women at term. The segmental spread of local anesthetics may increase substantially in pregnant women at term, necessitating a 28% to 33% decrease of dose requirement in this patient population.1 The choice of a continuous catheter or a single-shot technique during active labor is limited by the relative lack of sterility at the sacral hiatus, which may be contaminated by feces and meconium.

Rare cases of Horner syndrome have been noted when large doses of local anesthetics are injected caudally during labor.1 This is most likely to occur if injection is made with the patient on her back (engorgement of epidural venous plexus and IVC compression are maximal). The so-called dual technique (lumbar and caudal) of epidural block for labor is no longer widely used. Since the pain of uterine contractions is mediated by sympathetic nervous system fibers originating from T10 to L2, a lumbar epidural catheter suffices for both stage I and stage II of parturition, with dosage adjustments being made depending on the exact circumstances and requirements. Labor analgesia is discussed in greater detail in Chapter 53 (Regional Anesthesia for the Obstetric Patient).

Characteristics of the Blockade

The sacral hiatus is usually very easy to palpate in infants and children, which makes this technique much easier and more predictable in children. Consequently, in many institutions with large numbers of pediatric patients, caudal epidural block is an integral part of the intra- and postoperative pain management for children undergoing a wide range of surgical procedures both below and above the diaphragm.

The technique is easily learned; one study demonstrated an 80% success rate in resident trainees after completing 32 procedures performed without fluoroscopic guidance.30 In infants and small children, a 21-gauge short-beveled 1-in. needle may be used for single-injection techniques. For continuous blocks, a standard epidural catheter may be advanced through an 18-gauge angiocatheter or a thin walled 18-gauge epidural needle. It has been noted that by 4 or 5 years of age the sacral canal is usually large enough to accept such a needle for passage of a catheter.1 The electrocardiogram has been used to verify appropriate thoracic catheter tip placement (epidural electrocardiography).31

Spread of the Local Anesthetic Solutions

Unlike in adults, the segmental spread of analgesia following caudal administration is more predictable in children up to about 12 years of age. Studies suggest that the cephalad spread of caudal solutions in children is not hampered by the same anatomic constraints that develop from puberty onward. Before puberty, anatomic impedance at the lumbosacral junction has not yet developed to a marked degree, and caudal solutions can flow freely upward into the higher recesses of the spinal canal. As a consequence, the rostral spread of caudal anesthesia is more extensive and more predictable in children than in adults.

Indications in Adults

In children, caudal block is usually combined with light general anesthesia with spontaneous ventilation. During lower abdominal and genitourinary surgery in children, caudal block with 0.25% bupivacaine (2 mg/kg) was shown to lower the metabolic and endocrine responses to stress, as measured by glucose concentrations, mean prolactin, insulin, and cortisol concentrations, as compared with general anesthesia alone.32 Thoracic placement of catheters is possible in neonates and small children. However, one radiographic study of 115 infants found 10 caudally placed catheters to be in the high thoracic or low cervical region, when their intended site was in the lower thoracic segments.33

Pharmacologic Considerations for Caudal Epidural Anesthesia in Children

Caudal block with bupivacaine (4 mg/kg) and morphine (150 mcg/kg) was found to lower fentanyl requirements during cardiac surgery and shorten extubation times in a group of 30 pediatric patients randomized to receive general anesthesia alone or a combination of general and caudal block.34

Anesthetic dose requirements are about 0.1 mL/segment/year of age for 1% lidocaine or 0.25% bupivacaine.1 The dose may also be calculated based on body weight. The relationship between age and dose requirements is strictly linear with a high degree of correlation up to 12 years old. Plasma bupivacaine concentrations in children receiving caudal block with 0.2% of the local anesthetic (2 mg/kg) were less than equivalent doses administered via ilioinguinal–iliohypogastric block for pain control following herniotomy or orchidopexy. Additionally, the times to peak plasma concentrations were faster in the peripheral nerve block group, indicating that caudal block is a safe alternative to local infiltration techniques in inguinal surgery.35 In a study of children 1 to 6 years of age who underwent orchidopexy, a caudal block using larger volumes of dilute bupivacaine (0.2%) was shown to be more effective than a smaller volume of the standard (0.25%) concentration in blocking the peritoneal response to spermatic cord traction, with no change in the quality of postoperative analgesia. In that study the total bupivacaine dose was identical in both groups (20 mg).36

Ropivacaine 0.5% was shown to provide a significantly longer duration of analgesia following inguinal herniorrhaphy in children 1.5 to 7 years of age compared with 0.25% ropivacaine or 0.25% bupivacaine.37 All children received 0.75 mL/kg of the local anesthetic. Unfortunately, however, the times to first voiding and to standing were significantly delayed in the group receiving 0.5% ropivacaine, and there was one case of motor block of the lower extremities. This demonstrates the tradeoff when one attempts to maximize analgesia by altering local anesthetic concentration or total dose.

Ropivacaine has also been used for caudal block for hypospadias repair in a double-blind, randomized study in 26 children. The minimal effective local anesthetic concentration of ropivacaine was found to be 0.11% under general anesthesia with a 0.5% monitored anesthesia care of enflurane.38 Plasma concentrations of ropivacaine after caudal block in 20 children 1 to 8 years of age, using 2 mg/mL, 1 mL/kg, demonstrated free fractions to be 5%, clearance of 7.4 mL/min/kg, and terminal half-life of 3.2 h, well below those associated with toxic symptoms in adults.39 Clonidine has been added to bupivacaine in 36 children undergoing elective surgery. A caudal catheter was placed using 1 mg/kg bupivacaine 0.125% with an equal volume of either clonidine (2 mcg/kg) or normal saline. No benefit of adding the clonidine was found, and, in addition, more children in the clonidine group vomited in the first 24 h postoperatively.40

The local anesthetics typically administered for single-shot caudal blocks in pediatric patients are listed in Table 15–3.

Other Considerations for Use of Caudal Epidural Anesthesia in Children

Although caudal block is a mainstay of perioperative pain management in pediatric surgery and represents probably 60% of all regional anesthetic techniques in this patient population, not all studies demonstrated a marked benefit of caudal block for postoperative analgesia compared with other modalities. Following unilateral inguinal herniorrhaphy, caudal block was shown to provide effective, but not superior, pain management compared with local wound infiltration in 54 children. The side effects and rescue analgesia requirements did not differ between the two groups.42

Caudal epidural block in children may induce significant changes in descending aortic blood flow while maintaining heart rate and mean arterial blood pressure. In a study of 10 children 2 months to 5 years of age, a transesophageal Doppler probe was used to calculate hemodynamic variables after the injection of 1 mL/kg of 0.25% bupivacaine with epinephrine 5 mcg/mL. The aortic ejection volume increased, and aortic vascular resistance decreased by about 40%.43 These data suggest that caudal block results in vasodilatation secondary to sympathetic nervous system blockade.

Radiculopathy Refractory to Conventional Therapy

In cases of radiculopathy that is refractory to conventional therapies, caudal epidural treatment can significantly reduce the pain. Percutaneous epidural neuroplasty uses a caudal catheter left in place for up to 3 days to inject hypertonic solutions into the epidural space to treat radiculopathy with low back pain and epidural scarring, typically from previous lumbar spinal surgery. In addition to local anesthetics and corticosteroids, hypertonic saline and hyaluronidase are added to the injectate. The technique relies on fluoroscopic guidance and caudal epidurography, because the fluoroscopic findings of a filling defect of injected iodinated nonionic contrast medium correlates with the patient's reported level of pain.15 Injection of solutions into the epidural space of a patient with adhesions may be quite painful because of distension of affected nerve roots.14 Triamcinolone acetate, dexamethasone, or betamethasone have been recommended instead of methylprednisolone since particulate steroids can occlude an epidural catheter or possibly cause infarction of spinal tissue via vascular injection. Hypertonic saline is also used to prolong pain relief due to its local anesthetic effect and its ability to reduce edema in previously scarred or inflamed nerve roots.14 The authors recommend a lateral needle placement into the caudal canal, directing the needle and catheter toward the affected side. Lateral placement tends to minimize the likelihood of penetrating the dural sac or subdural area. When 5–10 mL of contrast medium is injected into the caudal canal through an epidural catheter, a “Christmas-tree” appearance develops as dye spreads into the perineural structures inside the bony canal and along the nerves as they exit the vertebral column.14 Epidural adhesions prevent the spread of the dye so there is no outline of the involved nerve roots.

Once correct catheter placement in the epidural space is ensured, 1500 units of hyaluronidase in 10 mL of preservative-free saline is injected rapidly. This is followed by an injection of 10 mL of 0.2% ropivacaine and 40 mg of triamcinolone. Following these two injections, an additional injection of 9 mL of 10% hypertonic saline is infused over 20 to 30 min. On the second and third days, the local anesthetic (ropivacaine) injection is followed up by the hypertonic saline solution. Antibiotic coverage is provided to reduce the possibility of epidural abscess formation.

Postoperative Analgesia in Patients Undergoing Lumbar Spine Surgery

Another unique application of caudal block is to provide postoperative analgesia in patients undergoing lumbar spine surgeries. In one series, patients received 20 mL of 0.25% bupivacaine with 0.1 mg buprenorphine via the caudal epidural approach, performed prior to surgical incision. The patients underwent posterior interbody fusion and laminotomy for spinal stenosis, and postoperative pain control was compared in the caudal group with a group treated with conventional parenteral opioids. The caudal group required less rescue analgesic medication doses over the first 12 h following surgery.16 A reduction in blood pressure in the caudal group patients undergoing laminotomy, but not fusion, was noted in the patients with a prolonged duration (24 h) of postoperative analgesia.

Other Applications

Caudal epidural block has also been compared with intramuscular opioids in the treatment of pain after emergency lower extremity orthopedic surgery. The caudal group received 20 mL of 0.5% bupivacaine and had 8 h of superior analgesia with a concomitant significant reduction in the need for rescue opioid medications.17

Caudal injection of clonidine, 75 mcg with 7 mL bupivacaine 0.5% and 7 mL lidocaine 2% with epinephrine 5 mcg/mL has been used for postoperative analgesia after elective hemorrhoidectomy. Thirty-two adults received the clonidine–local combination while a control group received local anesthetic alone. Analgesia averaged 12 hours in the clonidine group, compared to <5 h in the group receiving only local anesthetic. Bradycardia occurred in about 22% of patients in the clonidine group.18 This contrasts with the results of an evaluation of clonidine used as an adjunct for pediatric caudal anesthesia as noted earlier.40

Caudal injections of alcohol or phenol have been used to treat intractable pain due to cancer. In a study of 67 blocks, it was found that the lower sacral roots were easily reached with the caudal injection, and that the S1 and S2 roots (contribution from the lumbosacral plexus) were spared.19

The complications of caudal block are similar to those occurring following lumbar epidural block and include complications related to the technique itself and complications related to the injectate (local anesthetic or other injected substance). Fortunately, serious complications occur infrequently. The list of possibilities includes epidural abscess, meningitis, epidural hematoma, dural puncture and postdural puncture, headache, subdural injection, pneumocephalus and air embolism, back pain, and broken or knotted epidural catheters.

Systemic Toxicity of Local Anesthetics

The incidence of local anesthetic-induced seizures occurs more frequently following caudal epidural block than it does following lumbar or thoracic approaches. In a retrospective study of 25,697 patients who received brachial plexus blocks, caudal or lumbar epidural blocks from 1985 to 1992, Brown noted 26 seizures.44 The frequency of seizures in adults was caudal > brachial plexus block > lumbar or thoracic epidural block. Nine overall seizures were attributed to local anesthetic injection in the caudal space, eight occurring with chloroprocaine and one occurring with lidocaine. There was a 70-fold increased incidence (0.69%) of local anesthetic toxic reactions with caudal epidural anesthesia than with lumbar or thoracic epidural anesthesia in adults.

In children, however, one retrospective review identified only two toxic reactions (ie, local anesthetic-induced seizures) in 15,000 caudal blocks.45 Dalens' group found that inadvertent intravascular injection occurs in up to 0.4% of pediatric caudal blocks,46 demonstrating the importance of performing epinephrine-containing test dosing in this age group. It has been suggested that an elevation of heart rate by >10 bpm or an increase in systolic blood pressure of >15 mm Hg should be taken as indicative of systemic injection. T wave changes on the ECG occur earliest following intravascular injection, followed by heart rate changes, and lastly, by blood pressure changes. These changes may be delayed for up to 90 sec following the injection.46

Development of Spinal Anesthesia

Total spinal anesthesia can occur when the injected solution of local anesthetic gains access to the subarachnoid space. In the case report of an 18-month-old child weighing 10 kg who received a caudal block postoperatively after undergoing emergency repair of a recurrent diaphragmatic hernia 4 mL of 0.5% bupivacaine and 2.5 mcg/kg of buprenorphine were injected in a total volume of 10 mL. Eye opening and hand movement were delayed for 3 h following this complication.47 In another infant undergoing revision of a fundoplication, a caudally placed catheter was inadvertently advanced to the cervical spinal region. Electrical stimulation of the catheter tip (Tsui test) resulted in phrenic nerve stimulation. On withdrawal and repositioning of the catheter further care was uncomplicated. This case report demonstrates the relative ease of passing the catheter to high vertebral levels in infants as opposed to adults.48

Infection

One case report documented the rare occurrence of distant discitis and vertebral osteomyelitis involving skip levels and without the development of epidural abscess formation in an elderly woman who received caudal epidural steroid and local anesthetic for degenerative spondylolisthesis. One month later she developed an L2-L3 and L4-L5 infective discitis, together with adjacent vertebral osteomyelitis. Cultures demonstrated Pseudomonas aeruginosa growth, which was treated with antibiotics.49

Caudal epidural block is a technique of providing analgesia and anesthesia of the lumbosacral nerve roots that predates conventional lumbar approaches. The block has undergone several periods of acceptability and although it is infrequently applied to routine surgical cases in adults, it is the most commonly performed regional anesthetic technique in infants and children. Caudal block has enjoyed a resurgence lately, largely due to its easy access to the lumbar epidural space beneath scarring from spinal surgeries and for performing epiduroscopy. Clinicians who routinely utilize fluoroscopy will find that it has many applications, both for routine and complicated cases.