Caudal block

Key Points

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In approximately 5% of adult patients, the sacral hiatus is nearly impossible to cannulate with needle or catheter.
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The tissue mass overlying the sacrum in some patients makes the technique difficult.
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The sacral hiatus lies at the tip of equilateral triangle that joins the poster superior iliac spines bilaterally.
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Caudal block can be performed in a lateral decubitus or a prone position.
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Volumes of local anesthetic in the 25- to 35-mL range can be injected in adult patients to reach a sensory level of T12 to T10 with 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. Anatomy pertinent to caudal anesthesia centers on the sacral hiatus ( Fig. 42.1 ). 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 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 ).