The caudal approach to the epidural space is used to treat pain in the lower back and pelvis.
After informed consent is obtained, the patient may be placed in a variety of positions, with patient comfort probably as the prime concern. The preferred position is the lateral Sims’ position with the left side down for right-handed clinicians. With the upper leg flexed, the buttocks are separated, allowing easy access to the sacral-coccygeal junction. The patient is prepared in a standard aseptic fashion over an area large enough to allow palpation of landmarks, and sterile technique is used throughout the procedure. The midline is identified by palpating the tip of the coccyx with a finger and moving cephalad about 4 to 5 cm in an adult, until the fingertip lies over the sacral hiatus with the sacral cornua palpable on each side. The palpating hand is kept in position, and a 2-in. (5-cm), 18-gauge short, beveled needle is inserted. The initial angle of insertion is about 120 degrees to the coccyx. A “pop” is felt as the sacrococcygeal ligament is penetrated. The needle is then depressed to align with the long axis of the canal and inserted 1 cm. Once the caudal space has been entered, epidural positioning is confirmed by negative aspiration blood or CSF, then 40 to 80 mg of methylprednisolone acetate or 6 mg mixture of betamethasone sodium phosphate and acetate is injected. The steroids can be injected as is or diluted in 5 to 10 mL of preservative-free normal saline (Fig. 67-11).
FIGURE 67-11. Caudal injection. A: Landmarks and approach for needle insertion. B: Needle insertion through sacral- coccygeal membrane for injection.
Epiduroscopy, a technique used to visualize the lumbar epidural space, depends on this approach because the fiberoptic catheter cannot tolerate bending. Advantages of this approach include minimal risk for inadvertent dural puncture. Continuous catheter techniques can be used, but maintenance of site cleanliness is more difficult when compared with the lumbar approach to the epidural space. A Tuohy needle is not used for catheter placement because it will direct the catheter against the wall of the caudal canal and make catheter advancement difficult. Caudal epidurals and epidural lysis of adhesions can be performed via radiopaque catheter through a nonshearing needle under fluoroscopic guidance. Betamethasone sodium phosphate and acetate mixture is best used for localized nerve root irritation. Triamcinolone diacetate is water soluble and results in optimal outcome in generalized nerve root irritation such as arachnoiditis.
Improper needle placement can result in inadequate or absent block. This is due to variability in anatomy and inexperience. Rapid injection of large volumes of fluid is not recommended because this may result in large increases in CSF pressures, with the risk for cerebral hemorrhage, visual disturbances, headache, or compromised spinal cord blood flow. Pain at the injection site is a common complaint. Urinary retention can result from local anesthetic injection and should last only as long as the block.