Caudal Anesthesia

Anatomy and Physiology

Clinicians perform caudal epidural techniques by accessing the epidural space via the sacral hiatus. In adults, the spinal cord terminates at L1-2 and the dural sac at S1-2. In children, the spinal cord terminates at L3-4 and the dural sac at S3-4, with cephalad progression over the first year of life. In young infants, it is possible to enter the dural sac during the performance of a caudal epidural block.[3]

The landmark-based technique is the most common technique for carrying out a caudal epidural block.

In adults, these are most common as single-shot techniques due to the difficulty of threading a catheter at this location. While single-shot techniques are more common in children, it is easier to place a catheter in this population than in the adult population. Studies have indicated that caudal catheters can safely be placed for short-term use of fewer than three days without the risk of systemic infection such as meningitis, epidural abscess, or systemic sepsis, or even local infection.[4][5][4] 

Indications

Caudal anesthesia can be useful in the pediatric population for sub-umbilical procedures, including inguinal hernia repair, urological interventions, anal atresia repair, and lower extremity procedures. Caudal anesthesia can stand alone or be a supplement to general anesthesia for these procedures.[6] 

Caudal epidural injections can also help in the management of chronic low back pain unresponsive to conservative medical management. While nonmalignant low back pain can have treatment with caudal epidural steroid injections, their indications are more proper for patients without facet joint pain or those with both discogenic and facet joint pain.[7] 

Historically, caudal epidural analgesia with catheter placement was also utilized in the obstetric population for labor analgesia during the second stage of labor. However, concerns regarding the efficacy of the block, the use of large amounts of local anesthetic causing limb paralysis, and significant maternal hypotension due to poor control of the sympathectomy lead to the adoption of lumbar epidurals as the mainstay of labor analgesia.[8]

Caudal blocks may be preferred over lumbar epidural blocks because they provide sensory and motor block of the sacral roots with limited sympathectomy (since the preganglionic sympathetic neurons extend from T1 to L2 level) and are associated with decreased risk of dural puncture. 

Contraindications

Absolute contraindications to caudal anesthesia include patient/guardian refusal, localized infection over the insertion site, severe coagulopathy, increased intracranial pressure, and allergy to medications used for the procedure. Increased intracranial pressure can potentially predispose to herniation by further increasing intracranial pressure after epidural injection.[9][10]

Relative contraindications are more diverse. Spinal stenosis confers an increased risk of neurologic complications after a neuraxial technique. Hypovolemic patients are at an increased risk of hypotensive responses due to the vasodilatory effects of the neuraxial technique. While severe coagulopathy is an absolute contraindication to neuraxial techniques, less severe coagulopathies merit further discussion. The most up-to-date guidelines for neuraxial techniques in the setting of thromboprophylaxis or anticoagulation can be referenced from the American Society of Regional Anesthesia.[11][12] Systemic infection can be considered a relative contraindication to any epidural technique, due to both the theoretical risk of seeding the epidural space and the risk of vasodilation contributing to hemodynamic instability. However, neuraxial techniques are safe to perform once a patient has demonstrated a response to antibiotic therapy.[13] In the pediatric population, other contraindications that require consideration include a pilonidal cyst, sacral anomalies (such as previous meningomyelocele), or spinal dysraphism (such as tethered cord syndrome).[6][14]

Equipment

 The following equipment is required to perform a caudal epidural block.

• Appropriately sized syringe
• Needle or IV access catheter
• Medication
• Skin cleaning solution, commonly alcohol, chlorhexidine, or an iodine solution
• Personal protective equipment (sterile gloves, mask, head covering)

Ultrasound can assist in caudal epidural placement in pediatric or adult patients. A study by Shin et al. demonstrated that identification of the sacral hiatus by ultrasound facilitated the completion of the caudal epidural placement.[15] 

The gold standard for a successful caudal epidural block is fluoroscopy-guided. However, this is rarely performed in an operating room environment due to impracticality and radiation exposure to both the patient and providers.

Personnel

A trained specialist should perform caudal anesthesia. These specialists can include an anesthesiologist, an anesthesiologist in training, or nurse anesthetists under the supervision of an anesthesiologist, or a chronic pain physician. The procedure may require an assistant to be present for patient positioning.

Preparation

To perform a caudal epidural block, the clinician should perform a review of the patient’s history and an exam, and obtain informed consent. Standard ASA monitoring should occur during the procedure. The patient positioning can be in the lateral decubitus or prone position. If lateral, the legs should be flexed at the hip and knee such that the patient is in a stable position. In the pediatric population, patients are commonly induced before caudal placement. Procedure time-out should take place, and the area prepped with betadine, alcohol, or chlorhexidine. Single-shot caudal blocks use a 22 to 25 gauge short-beveled Tuohy or Crawford needle that most commonly does not have a stylet.[7]

Caudal blocks are usually performed with 0.125 to 0.25% bupivacaine or 0.1 to 0.375% ropivacaine at doses of 0.5 ml/kg if sacral dermatome level is needed, 1.0 mL/kg for lumbar dermatome level, and 1.25 mL/kg lower thoracic dermatome level. To achieve less motor block, ropivacaine may be a better option than bupivacaine.[16] Caudal block additives have also been used.  Epinephrine and clonidine can help to prolong blockade, the former by vasoconstriction reducing uptake and the latter by direct stimulation of pre-and postsynaptic alpha-2 adrenoceptors.  Opioids such as morphine and fentanyl are options, but there can be side effects such as pruritus, nausea, and respiratory depression, often necessitating 24-hour observation.[17][18] In patients with chronic low back pain and radiculopathy, corticosteroids can be injected into the caudal epidural space. Corticosteroids such as dexamethasone, betamethasone, methylprednisolone, and triamcinolone are the agents of choice.[19]

Technique or Treatment

Technique 

Clinicians can perform caudal blocks via blind technique, ultrasound guidance, or fluoroscopic guidance, as described below.[3]

Blind Caudal Epidural Block

The sacral hiatus is identified by the landmarks of the sacral cornua found on each side superior to the gluteal cleft and at the apex of a triangle formed by the posterior superior iliac crests.  The beveled needle or angiocatheter is inserted at a 45-degree angle after skin preparation.  A "pop" or "give" may be felt, indicating progression through the sacrococcygeal ligament and entrance into the epidural space.  This loss of resistance technique correlates with a 26% miss rate.[20] Thus, many suggest performing the “whoosh test,” which has a much higher specificity; this uses auscultation of the thoracolumbar region while injecting air into the caudal epidural space.[21]

Ultrasound-Guided Caudal Epidural Block

With the patient in prone or lateral decubitus position, a 7 to 13 MHz linear transducer (2 to 5 MHz curved transducer if the patient is obese) can be placed transversely placed in the middle of the sacrum. The transverse view shows the following hyperechoic structures: the superficial sacrococcygeal ligament in between two sacral cornua, and the deeper sacral bone. The hypoechoic structure between the sacrococcygeal ligament and the sacral bone is the target. The probe is then turned 90 degrees for the longitudinal view so that the needle can be inserted “in-plane” into the sacral hiatus. To avoid a dural puncture, the needle should not be advanced beyond 5mm after the tip of the apex since the needle is not visible after the tip of the apex. Unidirectional flow on color doppler can help identify the success of a caudal block.

Fluoroscopy-Guided Caudal Epidural Block

With the patient in the prone position, the sacral hiatus is visualized as an abrupt drop-off at the end of the S4 lamina. The needle can advance into the sacral canal, and by injecting a contrast medium, needle tip placement can be confirmed, and intravascular or intrathecal injection can be ruled out.

For children that are already under general anesthesia, the efficacy of the caudal block can undergo an assessment by analyzing the laxity of the anal sphincter. A 223-patient study conducted by Dave et al. demonstrated the anal sphincter tone test was the best predictor for a successful caudal block as compared to the swoosh test or the heart rate response to the injection.[22]

Complications

The below are common complications associated with caudal anesthesia[6]: 

• Subdural, intravascular, or intraosseous injection
• Infection
• Hypotension
• Injury to the nerve roots
• Antesacral Injection with perforation of the rectum
• Hematoma formation
• Local anesthetic toxicity
• Delayed respiratory depression
• Urinary retention
• Sacral osteomyelitis.

A devastating complication of a caudal block is total spinal anesthesia that can occur from an inadvertent dural puncture with subsequent intrathecal injection of local anesthetic.[23] This issue is much more common in infants due to the caudad displacement of the dural sac that ends at the S3-4 level (as compared to S1-2 in adults). Also, caudal epidural blocks have a higher incidence of local anesthetic-related seizures than brachial plexus or lumbar or thoracic epidural blocks. Brown et al. reported a 0.69% rate of seizure development with caudal anesthesia as compared to 0.01% for patients with lumbar or thoracic epidurals.[24] Thus, administering a test dose with epinephrine is vital to detect an intravascular injection. 

Clinical Significance

Caudal anesthesia is one of the oldest neuraxial anesthetic techniques still employed in modern-day practice. While its early use in obstetric analgesia has dwindled, it has widespread use in the pediatric population for sub-umbilical procedures and the management of patients with chronic low back pain and radiculopathy. In pediatric surgeries, it can often be employed as the sole anesthetic technique, avoiding the risks associated with general anesthesia.  Overall, caudal blocks have a high success rate, are relatively safe, and are associated with a low risk of complications.

Enhancing Healthcare Team Outcomes

Coordination of care between the surgeon and anesthesiology team, coordinating as an interprofessional team, is essential to ensure the most appropriate anesthetic gets administered to the patient. This team paradigm allows the perioperative team to maximize patient safety, patient comfort, and team efficiency. Nursing will assist with patient preparation, help monitor vitals during the procedure, and engage in post-procedural care, informing the clinician of any concerns that may arise. As with other skills, the frequency of practice directly correlates to proficiency. Depending on case volume, various strategies may be necessary to improve outcomes in a given surgical center, but all of these are optimally managed by the interprofessional team to produce the best patient outcomes. [Level 5]