Caudal anesthesia and analgesia

INTRODUCTION — 

A caudal block is a type of epidural anesthesia, performed by injecting local anesthetic through the sacral hiatus at the caudal end of the spinal canal. A caudal approach can be used to insert epidural catheters that are then threaded to lumbar or thoracic locations. Caudal blocks are used primarily in neonates, infants, and young children and are most often used to provide postoperative analgesia.

This topic will discuss the relevant anatomy, indications for, technique, and complications of caudal blocks, with a focus on use in infants and children. Other types of neuraxial anesthesia techniques are discussed separately.

●(See "Epidural and combined spinal-epidural anesthesia: Techniques".)

●(See "Spinal anesthesia: Technique".)

●(See "Overview of neuraxial anesthesia".)

The use of regional anesthesia for postoperative pain control in children is also discussed separately. (See "Pharmacologic management and regional anesthesia for acute perioperative pain in infants and children", section on 'Regional anesthesia'.)

INDICATIONS AND USES

●Anesthesia versus analgesia – In the vast majority of infants and children, caudal block procedures are performed for analgesia as an adjunct to general anesthesia, with the caudal procedure performed after induction of anesthesia.

•Awake caudal anesthesia – Rarely, caudal block may be used for surgery in awake or very lightly sedated infants. This is usually done to avoid or reduce exposure to general anesthesia. In some cases, this is to minimize the risk of postoperative apnea, particularly in ex-premature infants. (See "Anesthesia for ex-premature infants and children", section on 'Regional versus general anesthesia'.)

Awake caudal block may be used to minimize the potential risk of neurotoxic effects of general anesthesia on the developing brain in young children. This issue is discussed in detail separately. (See "Neurotoxic effects of anesthetics on the developing brain".)

In an analysis of 18,650 caudal anesthetics reported to the Pediatric Regional Anesthesia Network (PRAN) registry, awake caudal anesthesia (without sedation or general anesthesia) was used in only 0.5 percent of cases, most of which were in ex-premature infants [1].

The use of awake caudal anesthesia is less reliable than spinal anesthesia, as the anesthetic is often not dense enough to provide complete motor and sensory block. Nonetheless, an awake caudal block may be used in low-resource settings where anesthetics may be scarce.

•Caudal analgesia – Like many regional nerve blocks, caudal blocks are used intraoperatively to provide effective antinociception and reduce volatile anesthesia consumption and the need for opioids. Caudal analgesia is also a reliable method for perioperative pain control and is particularly useful for any procedure requiring bilateral lumbar or sacral coverage. Bilateral thoracic analgesia can be achieved by placing a caudal catheter, threaded to the thoracic epidural space. (See 'Continuous block' below.)

Similar to epidural analgesia in adults, caudal analgesia has been shown to lower the stress response, decrease the requirement for postoperative respiratory support, allowing for earlier extubation and minimize total opioid consumption [2,3].

Large studies have found that caudal blocks are very commonly used in pediatric anesthesia. In the APRICOT study of pediatric anesthesia in 33 European countries in 2014 and 2015, of 4377 regional anesthetics, 43 percent were neuraxial blocks, of which 77 percent were caudal blocks [4]. Similarly, in an analysis of over 104,000 regional blocks from the PRAN registry in the United States through 2015, the most common procedure was single injection caudal (38,000, 44 percent), and almost all were placed in patients who were under general anesthesia [2,3,5]. In a subanalysis of data for 1371 infants who underwent inguinal surgery from the NECTARINE study, 76 percent of patients had regional anesthesia with or without general anesthesia; 65 percent of regional anesthetics were caudal blocks [6]. The NECTARINE study was a prospective observational database study of surgical procedures in infants who were <60 weeks postmenstrual age between March 2016 and January 2017.

●Use by age group

•Neonates – Neonates have anatomic differences that may increase some risks of neuraxial anesthesia techniques compared with older children [7]. In neonates, the dural sac and filum terminale both terminate relatively more caudally, which increases the risk of inadvertent dural puncture. In addition, in neonates sacral bones are incompletely ossified and very soft, such that placing the needle into bone may feel like placing the needle in the sacrococcygeal ligament. This could result in systemic administration of the block solution and local anesthetic systemic toxicity (LAST).

In addition, a relative paucity of epidural fat can make the epidural space narrower; when compounded by a thinner ligamentum flavum, these small margins often require more finesse for caudal needle placement. Increased joint laxity in neonates can make the vertebral column more mobile than in older infants and can increase the difficulty of alignment for needle placement and threading a catheter.

Continuous caudal block is not generally used for infants over 6 months of age. In young infants, a catheter can be fed to thoracic levels, as described below. Successfully reaching the desired thoracic level has been reported in 85 percent of premature infants and 95 percent of term infants [8-12]. Similar results have been reported in children up to 2 years of age, however, increasing age is associated with decreasing success [7,9,13]. This is likely due to the development of a lumbar lordosis and increasing density of epidural fat with lobulation and fibrous septae impeding successful passage of the catheter.

Young infants may be at increased risk of LAST due to immature metabolism of amide local anesthetics by the liver, as well as low levels of alpha-1-anti-globulin and albumin, which bind free local anesthetics. The metabolism of ester local anesthetics is comparable to older children. (See "Local anesthetic systemic toxicity", section on 'Patient risk factors'.)

•Older infants and toddlers – Caudal techniques are commonly used for children 12 months to four years of age. In the PRAN registry study described above, approximately 70 percent of single injection caudal blocks were placed in children six months to two years of age [5]. Some of these data may be explained by the fact that the procedures appropriate for caudal block (eg, urologic procedures, hernia repairs) are very common in this age group.

In this age group, caudal injection provides predictable segmental spread and effective analgesia.

•Older children and adults – As children grow past early childhood, their anatomy changes and becomes less ideal for caudal techniques. Epidural fat becomes more fibrous and loculated, resulting in less reliable LA spread, and the caudal hiatus begins to ossify, making needle entry more difficult and sometimes impossible [14-16]. One contributor to this topic commonly performs caudal anesthesia in children who weigh up to 25 kg, switching to a different block if the caudal is difficult.

In adolescents and adults, caudal techniques are more difficult to perform, often requiring fluoroscopy or ultrasound guidance. A caudal block may occasionally be preferred over lumbar epidural in specific circumstances (eg, if sacral anesthetic coverage is required for perineal or rectal surgery and other regional techniques are not possible).

●Type of surgery – A single injection caudal block is primarily used for intraoperative and postoperative analgesia for lower abdominal and perineal surgery (eg, inguinal hernia repair, orchidopexy, circumcision, other urologic procedures), and some lower extremity orthopedic operations [5].

A caudal approach can be used to thread a catheter cranially within the epidural space to provide higher lumbar or thoracic anesthesia. This technique can be used for a single injection block, but more commonly might be used to provide continuous postoperative analgesia for small children in whom thoracic or lumbar epidural needle placement may be difficult or associated with complications. Placement of lumbar or thoracic catheters via a caudal approach is much less common than single injection into the caudal space [5,17]. (See 'Continuous block' below.)

Limited evidence suggests that fascial plane blocks may provide equivalent or better analgesia than caudal block for some procedures (eg, inguinal hernia repair) and not others (eg, orchidopexy). In a 2024 network meta-analysis of randomized trials that compared 10 different regional anesthesia techniques for analgesia after pediatric inguinal procedures, caudal block was the only technique that prolonged the time to first rescue analgesic for patients who had orchidopexy (mean duration 4 hours, 95% CI 0.67-7.47 hours) [18]. For inguinal hernia repair, quadratus lumborum block, transversus abdominis plane block, and ilioinguinal-iliohypogastric block prolonged analgesia to a greater degree than caudal block. The quality of the evidence was judged to be low or very low for most comparisons.

CONTRAINDICATIONS — 

Absolute and relative contraindications to caudal blocks are similar to contraindications for other neuraxial procedures, including skin infection at the site, sepsis, coagulopathy, preexisting neurologic disorders, and parent or patient refusal.

In addition, caudal anesthesia is contraindicated in patients with spinal dysraphism (eg, spina bifida occulta, tethered cord). These congenital anomalies may distort landmarks and result in variable and possibly low-lying or tethered position of the dural sac, which increases the risk of inadvertent dural puncture and high spinal anesthesia. Spinal dysraphism may be asymptomatic and may not have been diagnosed in young children who present for surgery. Closed spinal dysraphism should be suspected in children with sacrococcygeal cutaneous findings associated with these disorders (eg, hypertrichosis, hypo- or hyperpigmentation, hemangioma over the spine, drainage, or tissue at the lumbar or sacral levels) (table 1). In children with these findings, caudal blocks should usually be avoided unless spinal dysraphism has been ruled out. Evaluation and diagnosis of closed spinal dysraphism are discussed separately. (See "Closed spinal dysraphism: Clinical manifestations, diagnosis, and management".)

AWAKE VERSUS ASLEEP BLOCK PLACEMENT — 

Unlike routine practice in adults, regional anesthesia procedures in young children are usually performed after induction of general anesthesia, since it may be safer to perform a block in a child who is not moving. Unexpected movement may contribute to injury during the procedure, and general anesthesia or heavy sedation may also make ultrasound guidance easier.

Support for performing caudal blocks in anesthetized children comes from an analysis of 18,650 caudal anesthetics reported to the Pediatric Regional Anesthesia Network [1]. Significant complications were very rare, and the rate of complications was similar in patients who had the block performed awake versus after induction of general anesthesia, after adjusting for age.

Awake versus asleep block placement in children is discussed separately. (See "Pharmacologic management and regional anesthesia for acute perioperative pain in infants and children", section on 'Awake versus asleep block or catheter placement'.)

ANATOMY — 

For a caudal block, a needle is inserted through the sacrococcygeal ligament and sacral hiatus into the caudal epidural space.

●The sacrum is a large triangular bone formed by the fusion of the 5 sacral vertebrae (picture 1) [19,20].

●The sacral hiatus is a bony defect caused by failure of the lamina of the fifth and often fourth vertebrae to fuse during development. This hiatus is bordered laterally by bony prominences (the sacral cornua), which are caudal projections of the inferior articular processes of S5. The position of the sacral hiatus is highly variable, but most commonly is at S5 (50 to 90 percent cases), S4 (10 to 30 percent cases), or is absent in 4 to 6 percent of cases [21]. The shape of the sacral hiatus is often described as an inverted “V” or “U” with the cornua defining the base, but it is occasionally dumbbell-shaped. The hiatus is covered by the sacrococcygeal ligament, subcutaneous fat, and skin. The sacral hiatus is often an easily palpated landmark in neonates, but an ultrasound may aid in visualization in toddlers or young children with more subcutaneous tissue.

●The sacral canal is a continuation of the lumbar spinal canal. It is bordered anteriorly by the sacral vertebral bodies, posterolaterally by the sacral laminae, and distally by the sacrococcygeal ligament. The canal contains the terminus of the dural sac, the filum terminale, the sacral and coccygeal nerve components of the cauda equina, epidural fat, and the valveless sacral epidural venous plexus. The pia matter of the sacral nerves extends caudally as the filum terminale (the terminal fibers of the spinal cord which do not contain nerves) and loose epidural fatty tissue.

●The anatomy of the sacral structures varies as the child ages. The posterior vertebral column of infants and small children is largely cartilaginous. In older children and adults, the sacrococcygeal ligament ossifies and may close, and the sacral cornua may be absent or may become less easily palpated [22]. In one magnetic resonance imaging (MRI) study in adults, no sacral hiatus was identified in 4 of 37 patients [23].

●The caudal space is the portion of the sacral canal distal to the termination of the dura.

•The distance between the termination of the dura and the sacrococcygeal ligament varies widely in young children. A pediatric MRI study found that the distance between the upper margin of the sacrococcygeal membrane and the dural sac varies from 13.6 to 57 mm [24].

•The median spinal level of the terminus of the dural sac in children is the upper third of S2, however this varies from the middle third of L5 to the middle third of S3 [25]. It ascends from the superior aspect of S2 at birth to the S1/S2 intervertebral disc level at 36 months, with little change in older children [25]. In an MRI study of 37 adults, the median position of the caudal limit of the dura was in the middle of the body of S2 [23].

•The termination of the dural sac moves cranially with flexion of the trunk [26].

•In a study of 20 MRIs performed on children zero to three years of age the median volume of the caudal space was 1.3 mL/kg (95% CI 1.08-1.51 mL/kg) [24].

TECHNIQUE

Patient positioning — Positioning is similar for landmark and ultrasound-guided caudal techniques.

●Infants and children – The lateral decubitus position is usually used for caudal blocks, with the hips and knees flexed to 90 degrees, which produces traction on the subcutaneous tissues of the lower back and provides optimal exposure of the sacrum. Right versus left lateral decubitus may be chosen to allow the clinician to hold the needle in their dominant hand (eg, left lateral decubitus for a right-handed clinician). For caudal block in anesthetized or sedated patients, the lateral decubitus position facilitates easier airway management. Alternatively, the prone position can be used, with a towel under the pelvis and the hips and knees flexed (ie, the “frog” position).

●Adults – Adults are usually positioned prone, with a towel under the pelvis and the heels rotated outward, to allow the buttocks to fall away from the needle insertion site and flatten the buttock cleft.

Ultrasound guidance versus landmark based block — Ultrasound guidance allows visualization of sacral structures and spread of local anesthetic. There is weak evidence to suggest that ultrasound guidance may improve efficacy and safety. In a 2022 meta-analysis of five randomized trials (904 patients) that compared landmark-based block versus ultrasound-guided block in children <12 years of age, success rates and time for block placement were similar [27]. However, first pass success was greater with ultrasound guidance (86 versus 65 percent, risk ratio 1.31, 95% CI 1.15-1.49). Subcutaneous injection was more frequent with landmark-based block (10 versus 0 percent), as was vascular puncture (15 versus 2 percent). There were no major complications in either group.

In a subsequently published randomized trial that compared the use of landmark-based, nerve stimulation-guided, or ultrasound-guided single injection caudal block in 300 children aged 1 to 5 years, success rates were similar in the three groups (97, 97, and 98 percent, respectively) [28]. The incidences of aspiration of blood after needle placement were similar as well (3, 2, and 2 percent, respectively).

Practice differs regarding the use of ultrasound guidance. Some use ultrasound for all patients. Others use it more selectively, for example, ultrasound guidance only for the following categories of patients:

●Neonates, in whom landmarks may not be palpable or reliable [29], and who may be at increased risk of dural puncture and injection into bone [30]. (See 'Indications and uses' above.)

●Children with or at risk for abnormal anatomy (eg, abnormal landmarks, with suspicion of spinal dysraphism or existence of syndromes associated with sacral anomalies [eg, anorectal malformations]) [31-33].

Ideally, these children will have had occult dysraphism ruled out via formal radiologic testing (ultrasound or MRI) prior to elective surgery. If the procedure is urgent or an emergency and caudal anesthesia is indicated, individual risks and benefits must be weighed with consideration of the provider’s expertise in pediatric neuraxial ultrasound acquisition and interpretation.

●For placement of caudal catheters. (See 'Continuous block' below.)

While ultrasound guidance may be optimal and provide the advantages described above, it requires unique training and expertise that may not be realistic for all practitioners or practice settings.

Needle type — Various types of needles can be used for caudal blocks, including standard cutting tip needles, short bevel block needles, and intravenous (IV) catheter sets. Historically, there was a concern that using a needle without a stylette could core soft tissue and seed epidermoid tumors into the neuraxis, but this theory has largely been discredited [34,35]. Some clinicians prefer blunt-tipped needles because they feel they have better tactile feedback (a “pop”) when passing the needle through the sacrococcygeal ligament. For single injection blocks, 21 to 23 gauge needles or intravenous catheter sets are often used.

For ultrasound-guided blocks, echogenic needles that are often used for peripheral nerve blocks may improve needle visualization.

For a continuous block, an epidural needle is often used to allow placement of a catheter through the needle (eg, 18 gauge needle with 20 gauge catheter). An IV catheter can also be placed, and a catheter threaded through it [36,37].

Use of a test dose — The value of an epinephrine test dose in anesthetized children has been questioned [36,37] and practice varies; one contributor to this topic does not routinely use a test dose because of negative predictive value.

The rationale for administering an epidural or caudal test dose is that it may determine whether the needle or catheter has been unintentionally placed in an epidural vein or the subarachnoid space. The unintentional subarachnoid injection of an epidural dose of local anesthetic (LA) could result in high or total spinal anesthesia, while an unintentional IV injection could cause LA systemic toxicity. In adults, the standard test dose includes local anesthetic as an indicator of subarachnoid injection, along with epinephrine as an indicator for intravascular injection. In children who are anesthetized and therefore cannot demonstrate motor block, a local anesthetic test dose for subarachnoid injection is likely not useful.

In anesthetized children, intravascular injection of epinephrine may be detected by increases in blood pressure, heart rate, or T wave amplitude on the electrocardiogram. The hemodynamic changes resulting from an intravascular epinephrine test dose in anesthetized children may vary depending on the type of general anesthetic and the age of the child. In children anesthetized with sevoflurane, electrocardiogram (ECG) changes may be the most sensitive indication, detecting more than 97 percent of intravascular injections. In contrast, during total intravenous anesthesia with propofol and remifentanil, intravascular injection may be best detected by an increase in blood pressure [38-42]. However, these changes can be subtle and challenging to identify in young patients with baseline elevated heart rates in the 100 to 180 beats per minute (bpm) range.

No test dose is one hundred percent sensitive, which reinforces the need to inject incrementally and to aspirate before every injection.

Single injection block

Ultrasound guided technique

●Select a high-frequency (12 MHz) linear transducer, with the starting depth at approximately 2 cm.

●Use a sterile transducer cover.

●Place the transducer in a transverse orientation over the sacral hiatus [43]. Slide the transducer in a cranial-caudal direction to identify the tip of the dural sac, location of the conus medullaris, sacral cornua, the sacrococcygeal ligament, and the sacral hiatus. Scan for unusual anatomy.

●With the transducer centered over the sacral cornua, a “frog-eye sign” (or “Mickey Mouse ears”) can be seen. The sacral cornua represent the frog’s eyes, with the slightly deeper hyperechoic sacrococcygeal ligament between the eyes, and the hypoechoic epidural space below the ligament.

The frog eye sign is useful when landmarks are unusual, or for identifying the cornua when palpating surface landmarks is challenging.

●Rotate the transducer 90 degrees to a sagittal orientation and center the image on the sacral spinous processes. The image should be triangular with the coccyx forming the apex of the triangle and the termination of the dura near the base. The hypotenuse will be the anterior sacral wall with dropouts for the sacral foramina.

●Insert the needle in plane to the transducer at a 20-degree angle, visualizing the needle tip throughout.

●Advance the needle tip through the sacrococcygeal ligament and one to two millimeters into the caudal space.

●After negative aspiration, inject a test dose of 2 mL of local anesthetic, if using (see 'Use of a test dose' above). Then, inject the desired volume of local anesthetic in fractionated doses, with gentle aspiration between injections, visualizing anterior displacement of the dura and cranial spread of local anesthetic. Local anesthetic volumes are discussed below. (See 'Total dose and volumes' below.)

●Scan in a transverse orientation at T12-L1 to verify circumferential spread of local anesthetic in the epidural space, adjusting needle position as necessary.

Landmark based technique — Here we describe performing the caudal block with the patient in the lateral decubitus position. The technique is similar for patients in the prone position.

●With the nondominant hand, palpate the sacral cornua bilaterally just lateral to the midline and just cephalad to the top (cephalad end) of the gluteal cleft. In older children, the sacral cornua are typically further cephalad from the top of the gluteal cleft.

The location of the sacral hiatus can be estimated by placing the tip of the index finger on the patient’s coccyx. The distal interphalangeal joint will be approximately at the level of the sacral hiatus (picture 2).

Note: With the patient in the lateral decubitus position, the gluteal cleft is not a reliable landmark for the midline, as gravity often pulls soft tissues towards the patient’s down side.

●Palpate the sacral hiatus between and just caudal to the sacral cornua. Mark the hiatus. In larger babies and toddlers, if the cornua are not easily palpable, ultrasound can be used to visualize the sacral hiatus.

Historically, the sacral hiatus was located by drawing an equilateral triangle, with the base formed by the posterior iliac spines, and the apex presumed to be the location of the sacral hiatus. However, multiple studies have found that the relationship between these landmarks is too variable to provide reliable landmarks for the block [29,44-46].

●Using the dominant hand, insert the needle in the midline through the sacral hiatus, aiming cephalad at a 30 to 45 degree angle.

●Slowly advance the needle to pierce the sacrococcygeal ligament. There will be an increase in resistance as the needle enters the ligament, and a loss of resistance when the needle tip is passed through it.

●When loss of resistance occurs, flatten the needle trajectory to 15 degrees and advance the tip one or two millimeters further into the sacral canal.

●After negative aspiration, inject the desired volume of the anesthetic solution slowly in fractionated doses, with gentle aspiration between injections. Local anesthetic volumes are discussed below. (See 'Drug choice, volumes and doses' below.)

Continuous block — Continuous caudal block with a catheter may be indicated for prolonged analgesia, beyond the duration of action of a single injection of local anesthetics. The needle placement technique for a continuous block is the same as for a single injection block, described above (picture 3).

●Equipment – A catheter through-the-needle technique is typically used, with a needle at least one size larger than the available catheter. For example, an 18-gauge Touhy needle or an 18-gauge intravenous cannula can be used with a 20-gauge epidural catheter.

●Estimating the required length of catheter – The first step in placing a lumbar or thoracic catheter via caudal insertion is to estimate the length of the catheter that will be required to reach the desired level for dermatomal coverage. Prior to block placement, we typically measure or approximate the distance from the sacrococcygeal ligament to the desired spinal level, using surface landmarks [10]. One author routinely uses ultrasound to confirm correct placement of the catheter, as described below.

●Use sterile technique – Similar to other neuraxial anesthesia techniques, strict aseptic technique must be used for caudal anesthesia and is especially important for catheter placement. The patient’s back should be widely cleaned with chlorhexidine with alcohol, allowing adequate time for the solution to dry. The injection site should be draped with a sterile drape, and the ultrasound transducer should be covered with a sterile sleeve. (See "Lumbar puncture: Technique, contraindications, and complications in adults", section on 'Aseptic technique'.)

●Placing the catheter – Insert the needle as described above for a single injection block (see 'Single injection block' above). Insert the catheter through the needle or catheter, advancing only if there is no resistance. If any resistance is felt, reassess the entry path and consider reapproaching. If the needle is beveled, keep the bevel oriented to the front or back of the patient to minimize the chance of coiling or passing the catheter laterally. Keep in mind that the catheter trajectory will be affected by the angle of the tip of the needle when utilizing a Tuohy needle; the angle of entry and orientation of the hub are important.

●Confirming the catheter position – It is important to confirm the location of the tip of the catheter, as 20 to 30 percent of caudally placed epidural catheters are incorrectly placed [47]. We confirm the location of the tip of the catheter with ultrasound, visualizing a pocket of local anesthetic and/or expansion of the epidural space with injection of a small volume of local anesthetic. The effectiveness of this technique for confirmation will depend on the equipment being used (eg, echogenicity of catheter, total volume injected) and practitioner experience.

Alternatives to ultrasound include confirmation with fluoroscopy and/or epidurography, nerve stimulation using a stimulating catheter [48,49].

●Securing the catheter – An important goal for securing the catheter and the dressing is to minimize the risk of infection, given the caudal insertion site near the gluteal cleft. This is particularly important in a diapered child. The authors use topical skin sealant (Dermabond) at the catheter insertion site and apply an occlusive dressing, with or without skin adhesive. One author applies a clear plastic sheet with an adhesive edge below the dressing to divert feces and urine away from the dressing in a diapered child. We tunnel catheters that are expected to be in place for more than three days, primarily to prevent soiling. We remove catheters if there is gross soiling.

A joint practice advisory on pediatric regional anesthesia from the American Society of Regional Anesthesia and Pain Medicine and the European Society of Regional Anesthesia suggests considering tunneling a caudal catheter that is expected to be in place for more than three days [50]. Tunneling may reduce the risk of caudal catheter colonization [51] though whether tunneling reduces the risk of epidural infection is unknown.

DRUG CHOICE, VOLUMES AND DOSES

Local anesthetics

Choice of drug — Since most caudal blocks are used for intra- and postoperative analgesia, longer acting local anesthetics are routinely used. The most commonly used local anesthetics for single injection caudal anesthesia are bupivacaine 0.25%, ropivacaine 0.2 or 0.25%, and levobupivacaine 0.25% (outside the United States and Australasia) [52]. Sensory block efficacy is likely similar among the three local anesthetics, whereas bupivacaine may result in greater motor block [53]. Thus, ropivacaine may be preferred for ambulatory surgery.

For continuous infusion, ropivacaine, bupivacaine, levobupivacaine, or chloroprocaine can be used. (See 'Infusion drug choice and dosing' below.)

Total dose and volumes — Doses and volumes of local anesthetics for caudal anesthesia are shown in a table (table 2).

●Total dose – A joint practice advisory on pediatric local anesthetic dosing from the American Society of Regional Anesthesia (ASRA) and Pain Medicine and the European Society of Regional Anesthesia (ESRA) recommended limiting the doses for single injection caudal to ≤2.5 mg/kg for bupivacaine, and ≤2 mg/kg for ropivacaine [50,54]. However, other experts have recommended a higher maximum dose for ropivacaine, at 3 mg/kg, based on the lower potency and lower toxicity of ropivacaine compared with bupivacaine [55]. (See "Local anesthetic systemic toxicity", section on 'Amide local anesthetics'.)

Doses of amide local anesthetics should be reduced for caudal anesthesia in infants <3 months of age due to immature hepatic function, reduced metabolism of amide local anesthetics, and lower levels of alpha-1-anti-globulin and albumin, compared with older children [56]. In addition, repeat block and caudal infusion of amide anesthetics should be avoided if possible in infants <3 months of age. However, in infants >3 months of age, repeat caudal blocks are safe if performed more than 4 hours after the initial block [56]. (See "Local anesthetic systemic toxicity", section on 'Patient risk factors'.)

●Volume – We typically use 1 mL/kg of dilute local anesthetic solution for a single injection caudal block for lower abdominal or perineal surgery. This volume generally provides reliable lower abdominal and pelvic coverage while minimizing the chance of dosing errors. Studies of weight based dosing of local anesthetic using ultrasound and fluoroscopy have found that 0.5 mL/kg injectate spreads to cover sacral levels, 1.0 mL/kg spreads to lumbar levels, and 1.25 mL/kg spreads to cover lower thoracic levels, though there is significant higher dermatomal spread [57,58].

At a fixed total dose, higher volumes and lower concentrations can be used to increase rostral spread and improve block quality and duration while minimizing the risk of toxicity [59]. As an example, one randomized trial compared the use of low concentration/high volume (LC/HV) versus high concentration/low volume (HC/LV) caudal block with a fixed total dose of ropivacaine in 75 children ages 1 to 5 years undergoing orchidopexy [59]. The HC/LV group received 1.0 mL/kg of 0.225% ropivacaine, while the LC/HV group received 1.5 mL/kg of 0.15% ropivacaine. The spread of local anesthetic in the LV/HC group reached a median level of T11 (range T8 to L2), compared with a median level of T6 (range T3 to T11) in the HV/LC group. Children in the HV/LC group were more likely to require rescue analgesia with acetaminophen after discharge and required rescue analgesia sooner, compared with the LV/HC group.

Spread of a given weight-based volume of local anesthetic may be greater in neonates. In one prospective study including 50 children who had a single injection caudal block with 1.5 mL/kg of ropivacaine 0.2% with local anesthetic spread visualized with ultrasound, the injection spread higher than T12 in 93 percent of neonates, 73 percent of infants age 1 month to one year, and 15 percent of children from 1 to 4 years of age [60].

Adjuvants — Adjuvant drugs may be added to local anesthetic solutions to prolong the duration of the block [54]. Only preservative-free preparations can be used as adjuvants for caudal and other blocks. The authors use only clonidine as an adjuvant for caudal anesthesia for single injections. One author uses a variety of opioids (morphine, hydromorphone, or fentanyl) and/or clonidine as an adjuvant for infusions, but this practice is highly variable due to institutional policies and resources (table 2).

Other caudal adjuvants have been used, but efficacy and lack of neurotoxicity have not been proven. As such, they are not recommended.

●Opioids

•Lipophilic opioids (fentanyl and sufentanil) – There is lack of evidence of benefit to the use of lipophilic opioids for single injection caudal anesthesia [61].

•Morphine – Morphine is an effective adjunct and may provide up to 24 hours of analgesia. It is associated with a significant risk of delayed respiratory depression and a dose-dependent incidence of nausea, vomiting, and pruritus [62-65].

Recommended dose – 10 to 30 mcg/kg caudally.

•Hydromorphone – Caudal hydromorphone provides analgesia approximately equivalent to morphine, with a similar side effect profile [65].

Recommended dose – 10 mcg/kg.

●Alpha-2 Agonists

•Clonidine – Caudal clonidine may prolong analgesia to an extent similar to morphine, with less nausea, vomiting, and pruritus [65-68]. Sedation can occur with caudal clonidine. We avoid using clonidine in ex-premature infants due to reported cases of postoperative apnea with its use [69,70].

Recommended dose – 1 to 2 mcg/kg caudally.

•Dexmedetomidine – Caudal dexmedetomidine has been shown to prolong analgesia compared with bupivacaine or ropivacaine alone [71,72]. As an example, in one randomized trial including infants who underwent hernia repair, the addition of dexmedetomidine 1 mcg/kg to bupivacaine 0.25% approximately doubled the time to first request for analgesia (mean 809 versus 396 minutes) [71].

Recommended dose – 1 mcg/kg caudally.

•Ketamine – We do not use ketamine as an adjunct for caudal anesthesia. Historically, adjunctive ketamine was shown to prolong the duration of analgesia after caudal block [73,74]. However, safety data are lacking, and animal studies have raised concerns of neuronal apoptosis [75]. In addition, the ASRA/ESRA consensus advises against its use in the neuraxis for this reason.

●Epinephrine – Epinephrine may be added to local anesthetic to decrease systemic absorption of local anesthetic, thereby speeding block onset and possibly prolonging analgesia, though neither author adds epinephrine routinely. A series of pharmacokinetic studies suggest that epinephrine reduces the initial absorption of caudal levobupivacaine, but there is a biphasic effect with increased absorption later [76].

Use of a test dose including epinephrine is discussed above. (See 'Use of a test dose' above.)

Infusion drug choice and dosing — For continuous epidural infusion via a caudal catheter, dilute solutions of local anesthetic are used, and can be combined with selected opioids or adjuncts, though this varies widely with institutional resources and practice patterns (table 2).

One author uses only solutions of local anesthetics without additives, while the other author varies the infusion solutions, which may include local anesthetics, with or without opioids and/or clonidine.

For infants less than three months of age where it is available chloroprocaine (an ester local anesthetic) may be used rather than the amide local anesthetics bupivacaine and ropivacaine because young infants have immature metabolism, clearance, and plasma binding of amide local anesthetics, whereas metabolism of ester local anesthetics is similar to older children. Neonatal levobupivacaine and ropivacaine epidural pharmacokinetics are well known and safe, and as such are appropriate for infusions, within recommended doses, as shown in a table (table 2).

Epidural bupivacaine infusion >0.2 mg/kg/hour can result in accumulation of local anesthetic and potential risk of local anesthetic systemic toxicity [77]. (See "Local anesthetic systemic toxicity", section on 'Patient risk factors'.)

Infusion doses of local anesthetics are shown in a table (table 2).

SIDE EFFECTS AND COMPLICATIONS — 

Caudal block is a very safe procedure, despite the fact that it is typically performed in anesthetized children. Side effects of caudals are typically related to the medication type, dose, and infusion rate and can include pruritus, nausea, hypotension, and urinary retention. Localized pain at the insertion site is also a possibility.

Serious complications — Serious complications of caudal blocks are very rare, with reported incidences of 0.12 to 0.33 percent, based on registry and database studies [1,3,5,17]. Rates vary between studies, reflecting different populations and definitions. Conclusions from these studies are limited by their observational nature, lack of information on block efficacy and patient comorbidities, and may not reflect the effect of increasing use of ultrasound guidance.

●Pediatric Regional Anesthesia Network (PRAN) database – PRAN is a United States multicenter network that collects prospective data on pediatric regional anesthesia [78].

A 2018 study of data on all types of regional anesthesia from the PRAN database included over 41,000 caudal anesthetics [5]. There were no permanent neurologic sequelae or epidural abscesses. There were three cases of serious local anesthetic systemic toxicity (LAST) in single-injection caudal blocks. Cutaneous catheter infection occurred in 18 of 3166 catheter blocks, a rate that was similar to lumbar or thoracic epidurals. Dural puncture occurred in 1:10,000 caudal anesthetics.

A 2016 study of data on neuraxial catheter blocks (170 placed caudally) in neonates from the PRAN database found no serious complications, long-term sequelae, or prolonged hospitalization [79]. The overall incidence of complications was 13.3 percent and was similar whether the catheter was threaded after caudal insertion or placed directly for lumbar or thoracic epidural anesthesia. The most common complications were catheter malfunction or contamination, and vascular puncture.

●The French-Language Society of Paediatric Anesthesiologists (ADARPEF) study – A one year prospective international (primarily French) multicenter study of pediatric anesthetics included approximately 8500 caudal blocks [17]. There were two cases of serious LAST, one related to a drug error. There were six cases of inadvertent dural puncture, all of which occurred in infants.

●Subset of the NECTARINE study – The NECTARINE study was a European multicenter prospective observational study of outcomes in infants <60 weeks postmenstrual age undergoing surgery [80]. A subanalysis of the NECTARINE database included 1371 infants who underwent inguinal surgery with general anesthesia (GA) with regional anesthesia (approximately 75 percent caudal) or awake regional anesthesia (approximately 80 percent spinal) [6]. Critical perioperative events were more common in patients who had GA (28.3 versus 9.3 percent; odds ratio [OR] 3.86, 95% CI 2.2-6.6). The incidence of hypoxemia was also higher in patients who had GA (14.2 versus 4.6 percent; OR 3.39, 95% CI 1.6-7.1). Conclusions are limited by a lack of data on other complications (eg, local anesthetic systemic toxicity), the indications for the choice of anesthetic technique, and wide variability in practice among the study sites.

Local anesthetic systemic toxicity (LAST) — LAST is more likely during caudal and epidural anesthesia than it is during many other types of regional anesthesia. (See "Local anesthetic systemic toxicity", section on 'Block site'.) However, the reported rate of LAST during regional anesthesia in children is very low, at approximately 8:100,000 regional anesthetics in two large database studies [5,81]. The presentation of LAST is highly variable in all patients, however, the central nervous system effects that often occur first in awake patients may not occur or may be missed in children who are anesthetized. In a review of 34 reported cases of LAST in children, the first manifestation was cardiac in 19 of 21 children who were under general anesthesia when LAST occurred [81]. Immediate administration of lipid emulsion in cases of suspected LAST is as important in children as it is in adults. The management of LAST in children is similar to adults and is discussed in detail separately. (See "Local anesthetic systemic toxicity", section on 'Management of LAST'.)

Lack of association with complications of hypospadias repair — Whether caudal blocks increase the risk of wound complications after hypospadias repair has been controversial [82]. However, the best available evidence suggests that caudals can safely be used for these procedures. In a meta-analysis of 17 studies (16 retrospective, one randomized, 3200 patients) that compared caudal versus penile block in infants undergoing hypospadias repair, the risk of fistulae or wound dehiscence was similar in the two groups [83]. Similarly, a multicenter database study of over 3300 infants who underwent hypospadias repair, 42 percent of whom had caudal blocks placed, found no association between the use of caudal block and the need for revision surgery [84].

SOCIETY GUIDELINE LINKS — 

Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Local and regional anesthesia" and "Society guideline links: Acute pain management".)

SUMMARY AND RECOMMENDATIONS

●Indications and uses

•Caudal blocks are used primarily in infants and young children and are most often used in children one to four years of age to provide postoperative analgesia.

•Single injection caudal block is primarily used for lower abdominal and perineal surgery (eg, inguinal hernia repair, orchidopexy, circumcision, other urologic procedures), and some lower extremity orthopedic surgeries.

•A caudal approach can be used to thread a catheter cranially within the epidural space to provide higher lumbar or thoracic anesthesia. (See 'Indications and uses' above.)

●Contraindications – Caudal blocks are contraindicated in children with spinal dysraphism (eg, spina bifida occulta, tethered cord), which can distort anatomy and may increase the risk of inadvertent dural puncture and high spinal anesthesia. (See 'Contraindications' above.)

●Awake versus asleep block placement – Caudal blocks are usually performed after induction of general anesthesia, since it may be safer to perform a block in a child who is not moving. Large database studies have found similar, rare complications with awake versus asleep block placement. (See 'Awake versus asleep block placement' above.)

●Ultrasound guidance versus landmark-based block – Caudal blocks can be performed by using surface landmarks or ultrasound guidance, and practice varies. Some use ultrasound for all caudal blocks. Others use it more selectively, for example, only for the following patients:

•Neonates, in whom landmarks may not be palpable or reliable, may be at increased risk of dural puncture and injection into bone

•Children with or at risk for abnormal anatomy (eg, abnormal landmarks, with suspicion of spinal dysraphism or with syndromes associated with sacral anomalies [eg, anorectal malformations])

•For placement of caudal catheters (see 'Ultrasound guidance versus landmark based block' above)

●Single injection block – Caudal block is performed by inserting a needle through the sacrococcygeal ligament into the caudal epidural space. It is performed as follows, with further explanation above (see 'Single injection block' above):

•Ultrasound-guided block – With the transducer in a transverse orientation, identify the tip of the dural sac, the location of the conus medullaris, the sacral cornua, the sacrococcygeal ligament, and the sacral hiatus. Scan for unusual anatomy. Rotate the transducer to a sagittal orientation and insert the needle at a 20-degree angle in plane, through the sacrococcygeal ligament. After negative aspiration, inject the local anesthetic solution incrementally, with gentle aspiration between injections. (See 'Ultrasound guided technique' above.)

•Landmark-based block – Palpate the sacral cornua, and the sacral hiatus between and just caudal to them. Insert the needle through the sacral hiatus in the midline, aiming cephalad at a 30 to 45 degree angle and through the sacrococcygeal ligament; feel for loss of resistance as the needle passes through the ligament. Flatten the needle to a 15-degree angle and advance the tip one or two millimeters further into the sacral canal. After negative aspiration, inject the local anesthetic solution in incremental doses, with gentle aspiration between injections. (See 'Landmark based technique' above.)

●Continuous block – Continuous block is performed as follows, with further explanation above (see 'Continuous block' above) :

•Estimate the length of the catheter that will be required to reach the desired dermatome.

•Using ultrasound guidance and sterile technique, insert the needle as for a single injection block.

•Thread the catheter to the estimated depth and confirm the location with ultrasound or an alternative technique.

•Secure the catheter.

●Drug choice and doses – Commonly used local anesthetics and adjuvants, including doses and volumes, appear in a table (table 2).

•Local anesthetics – Longer acting local anesthetics (eg, bupivacaine, ropivacaine, levobupivacaine) are typically used for single injection caudal anesthesia.

•Adjuvants – Adjuvants (eg, opioids, clonidine, epinephrine) may be added to local anesthetic solutions to improve the quality of analgesia and prolong the block; practice varies.

•Infusion drugs and doses – Dilute solutions of local anesthetics with or without adjuvants are used for continuous caudal anesthesia.

●Side effects and complications – Side effects of caudal blocks can include pruritus, nausea, hypotension, and urinary retention. Serious complications are very rare and include local anesthetic systemic toxicity and inadvertent dural puncture. (See 'Side effects and complications' above.)