Introduction. Caudal epidural block is one of the most used regional techniques both for intraoperative anesthesia and for prolonged postoperative analgesia in pediatric patients (80 % of all neuraxial blocks). Its advantages include technical simplicity, efficacy and safety due to the low risk of inadvertent dural puncture and epidural hematoma. However, it is less popular with adult patients because of (1) technical difficulties and rather high failure rate owing to problems with the sacral hiatus identification; (2) the limited cranial spread of local anesthetic solution; (3) other techniques (spinal and lumbar epidural blocks) typical of our anesthesiologists. On the other hand, such benefits as the absence of respiratory complications and infrequent bradycardia or arterial hypotension would be especially valuable for adult patients during and after pelvic or lower limb surgery.
The purpose of our study was to assess the radiological contrast spread (distribution) after caudal epidural block in adult cadavers.
Materials and methods. In 12 fresh unembalmed cadavers (height 159 ± 14 cm, weight 69 ± 26 kg), positioned prone, the sacrococcygeal membrane was punctured with a styletted needle in ventro-cranial direction, at 70-80° angle to the skin. After the "pop" feeling, the needle was pressed to the intergluteal fold and advanced 1-2 cm more. The suspension of red lead in glycerol, 20 ml, was injected through the sacral hiatus into the sacral canal with a blind technique. Ten minutes after, X-ray radiography in antero-dorsal and lateral projections was performed.
Results. In one cadaver (8 %) the contrast missed the sacral canal and proved to be in the presacral space; this finding demonstrates the need for more complex identification of epidural space with the caudal approach, perhaps with the help of ultrasound or fluoroscopic navigation. In other 11 cadavers the contrast always surrounded all sacral and most of lumbar radices. S1 and L5 segment levels were reached in 100%, L4 level in 10 (91 %), L3 in 7 (64 %), L2 in 4 (36 %), L1 in one cadaver (9 %). Besides, the contrast reliably surrounded the lumbosacral trunk, formed by the anterior branch of the fifth lumbar nerve and a part of the anterior branch of the fourth lumbar nerve, with the anterior branches of all sacral nerves. The thickest S1 root was consistently and reliably surrounded by the contrast, as distinct from the lumbar epidural approach, with its failure rate of 6.7 % to 21 % for S1 segment anesthesia. In almost all cases we have seen more or less distant drain of the contrast outside the caudal canal and epidural space, especially between L5 and S1, with its distribution into the presacral space around the nerve roots. Our results are in agreement with the data of other researchers. In spite of almost 100 % success rate in pediatric patients, different authors showed rather low (62 % to 80 %) rate of success for the caudal epidural block in adults. This is predetermined by a more varied sacral anatomy in adults: the antero-dorsal diameter, ranging from 4.6 ± 2.0 to 6.1 ± 2.0, decreases with age. In dry sacral bone studies, the diameter was less than 3 mm in 8.77 % and less than 2 mm in 1-6.25 %. The subjective "pop" or loss of resistance feeling means the sacrococcygeal membrane puncture, but it is unreliable and may lead to the failure rate up to 26 % even in experienced hands. The caudal epidural block usually needs two doses of local anesthetic used for lumbar epidural block, because of wider sacral canal and the drain of local anesthetic solution through the anterior sacral foramina. We used only 20 ml and our study showed that this volume is enough for blocking the whole sacral plexus in most adult patients.
Conclusions. The solution injected through the sacral hiatus consistently and reliably surrounded coccygeal, all sacral and lower lumbar radices. Ultrasound-guided technique may give less failure rate than the blind one.
Article recieved: 27.07.2018
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