Caudal Block

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42 Caudal Block

Perspective

With advances in lumbar epidural anesthesia, caudal anesthesia has become an infrequently used and taught technique. Nevertheless, caudal anesthesia can be effectively used for anorectal and perineal procedures, as well as some lower extremity operations.

Patient Selection

Patient selection for caudal anesthesia should be determined by examining the anatomy of the sacral hiatus. In approximately 5% of adult patients, the sacral hiatus is nearly impossible to cannulate with needle or catheter; thus, in 1 of 20 patients the technique is clinically unusable. Likewise, there are patients in whom the tissue mass overlying the sacrum makes the technique difficult, and if another technique is applicable, caudal anesthesia should be avoided. Probably more so than for any other block, experience and confidence on the anesthesiologist’s part are necessary to carry out the technique effectively.

Pharmacologic Choice

When choosing local anesthetics for caudal anesthesia, the same considerations as those applied to epidural anesthesia are needed. Volumes of local anesthetic in the 25- to 35-mL range are necessary to predictably provide a sensory level of T12 to T10 with caudal injection for adults.

Placement

Anatomy pertinent to caudal anesthesia centers on the sacral hiatus (Fig. 42-1). This can be most effectively localized by finding the posterior superior iliac spines bilaterally, drawing a line to join them, and then completing an equilateral triangle caudad. The tip of the equilateral triangle will overlie the sacral hiatus (Fig. 42-2). The caudal tip of the triangle will rest near the sacral cornua, which are unfused remnants of the spinous processes of the fifth sacral vertebra. Overlying the sacral hiatus is a fibroelastic membrane, which is the functional counterpart of the ligamentum flavum. Perhaps more than with any other sex difference found in regional anesthesia, the sacrum is distinctly different in men and women. In men, the cavity of the sacrum has a smooth curve from S1 to S5. Conversely, in women the sacrum is quite flat from S1 to S3, with a more pronounced curve in the S4 to S5 region (Fig. 42-3).

Figure 42-1. Caudal block: surface anatomy.

Figure 42-2. Caudal block: surface anatomy showing sacral hiatus localization.

Figure 42-3. Caudal block: relationship of sacral anatomy to sex.

Position

Caudal block can be carried out in a lateral decubitus position or a prone position. In adults, I find the prone position with a pillow placed beneath the lower abdomen most effective. In this position, patients can be sufficiently sedated to make the block comfortable, and it makes the midline more easily identifiable than in the lateral position. As illustrated in Figure 42-4, pediatric caudal anesthesia is commonly carried out with the child in the lateral decubitus position. Because most pediatric caudal blocks are performed after induction with general anesthesia, the lateral position is almost mandatory. Identification of the midline and performance of the block are less complicated in the pediatric patient, thus making the lateral position clinically practical. To optimize identification of the sacral hiatus, the prone patient should have the legs abducted to a 20-degree angle with the toes rotated inward and the heels outward. This helps relax the gluteal muscles, making it easier to identify the sacral hiatus (Fig. 42-5).

Figure 42-4. Caudal block: pediatric position.

Figure 42-5. Caudal block: prone position.

Needle Puncture

As with lumbar epidural anesthesia, caudal anesthesia requires a decision about the use of a single-injection or a catheter technique. If a single-shot caudal block is to be performed, almost any needle of sufficient length to reach the caudal canal is acceptable. In adults, a needle of at least 22 gauge is recommended because it is large enough to allow sufficiently rapid injection of solution to help detect misplaced local anesthetic injections. If a catheter is to be used, a needle that is large enough to allow passage of the catheter is required. As illustrated in Figure 42-6, after the sacral hiatus is identified, the index and middle fingers of the palpating hand are each placed on the sacral cornua, and the caudal needle is inserted at an angle of approximately 45 degrees to the sacrum. As the anesthesiologist advances the needle, he or she will become aware of a decrease in resistance as the needle enters the caudal canal (needle position 1). The needle is then advanced until it contacts bone; this should be the dorsal aspect of the ventral plate of the sacrum. The needle is then withdrawn slightly and redirected so that the angle of insertion relative to the skin surface is decreased. In male patients, this angle will be almost parallel with the tabletop, whereas in female patients a slightly steeper angle will be necessary (needle position 2).

Figure 42-6. Caudal block: technique.

During the redirection of the needle and after noting loss of resistance, the needle should be advanced approximately 1 to 1.5 cm into the caudal canal. Further advance is not advised because dural puncture and unintentional intravascular cannulation become more likely. Before the injection of the therapeutic dose of local anesthetic, aspiration should be performed and a test dose administered because a vein or the subarachnoid space can be entered unintentionally, as is the case in lumbar epidural anesthesia.

Potential Problems

Caudal anesthesia entails most of the same complications that can accompany lumbar epidural anesthesia, although there are some differences. The frequency of local anesthetic toxicity after caudal anesthesia appears to be higher than it is with lumbar epidural block. Another distinct difference is that the incidence of subarachnoid puncture is exceedingly low with the caudal technique. The dural sac ends at approximately the level of S2; thus, unless a needle is inserted deeply within the caudal canal, subarachnoid puncture is unlikely. In children the dural sac is more distally placed in the caudal canal, and this should be considered when carrying out pediatric caudal anesthesia.

Perhaps the most frequent problem with caudal anesthesia is ineffective blockade, which results from the considerable variation in the anatomy of the sacral hiatus. If anesthesiologists are unfamiliar with caudal technique and the needle passes anterior to the ventral plate of the sacrum, puncture of the rectum or, in obstetric anesthesia, of fetal parts is possible. As illustrated in Figure 42-7, the area surrounding the sacral hiatus can be imagined as a potential “circle of errors.” The practitioner may be faced with a slitlike hiatus that does not allow easy needle insertion; the hiatus may be located more cephalad than anticipated or in fact may be closed. Likewise, loss of resistance may be encountered as the needle is inserted into one of the sacral foramina rather than the hiatus. In the lateral view, it is obvious that needles may be misdirected into subcutaneous or periosteal locations as well as into the marrow of sacral bones.

Figure 42-7. Caudal block: circle of errors.

Pearls

To produce effective caudal anesthesia, anesthesiologists should be selective about the patients in whom it is attempted. It makes no sense to use the technique in a patient whose anatomy is unfavorable. Because of the anatomic variations in the area around the sacral hiatus, this block seems to require more operator experience and a longer time to attain proficiency than many other regional blocks. As a result, anesthesiologists should develop their technique in patients whose anatomy is favorable.

One helpful hint that will confirm needle location when carrying out caudal anesthesia is illustrated in Figure 42-8. Once the needle has entered what is thought to be the caudal canal, the anesthesiologist should place a palpating hand across the sacral region dorsally. Then, 5 mL of saline solution should be rapidly injected through the caudal needle. By placing the hand as shown, the anesthesiologist should be immediately aware of the subcutaneous needle position overlying the sacrum. If the needle is mispositioned subcutaneously, a bulge during injection will develop in the midline. If the needle is correctly positioned in the caudal canal, no midline bulge should be palpable. In thin individuals, accurate needle placement in the caudal canal and rapid injection of solution may allow the anesthesiologist to feel small pressure waves more laterally overlying the sacral foramina. These smaller pressure waves should not be confused with those associated with a misplaced subcutaneous needle.