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Brown: Atlas of Regional Anesthesia, 3rd ed., Copyright © 2006 Saunders, An Imprint of Elsevier
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Anatomy pertinent to caudal anesthesia centers on the sacral hiatus ( Fig. 50-1 ). This can be most effectively localized by finding the posterosuperior iliac spines bilaterally, drawing a line to join them, and then completing an equilateral triangle in a caudal direction. The tip of the equilateral triangle overlies the sacral hiatus ( Fig. 50-2 ). The caudal tip of the triangle rests 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 gender 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, whereas in women the sacrum is quite flat from S1 to S3, with a more pronounced curve in the S4–5 region ( Fig. 50-3 ).

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Figure 50-1  Caudal block: surface anatomy.

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Figure 50-2  Caudal block: surface anatomy for sacral hiatus localization.

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Figure 50-3  Caudal block: relation of sacral anatomy to gender.


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 underneath 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 50-4 , 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, making the lateral position clinically practical. To maximize 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 and allows easier identification of the sacral hiatus ( Fig. 50-5 ).

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Figure 50-4  Caudal block: pediatric position.

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Figure 50-5  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, at least a 22-gauge needle is recommended, as it is large enough to allow sufficiently rapid injection of solution to help detect misplaced local anesthetic injection. If a catheter is to be utilized, a needle large enough to allow passage of the catheter is required. As illustrated in Figure 50-6 , after the sacral hiatus is identified the index and middle fingers of the palpating hand are placed on the sacral cornu, and the caudal needle is inserted at an angle of approximately 45 degrees to the sacrum. As the needle is advanced, the anesthesiologist becomes aware of a decrease in resistance as it enters the caudal canal. The needle is then further 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 the angle of insertion relative to the skin surface is decreased. In male patients, this angle is almost parallel with the tabletop, whereas in female patients a slightly steeper angle is necessary.

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Figure 50-6  Caudal block: technique.

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

Potential Problems.

Caudal anesthesia is associated with 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. It is emphasized that in children the dural sac is more distally placed in the caudal canal, a fact that 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 the caudal technique and the needle passes anterior to the ventral plate of the sacrum, puncture of the rectum (or during obstetric anesthesia puncture of fetal parts) is possible. As illustrated in Figure 50-7 , the area surrounding the sacral hiatus can be imagined as a potential “circle of errors.” The practitioner may be faced with a slit-like hiatus that does not allow easy needle insertion; the hiatus may be 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.

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Figure 50-7  Caudal block: circle of errors.

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