The effect of flexion on the level of termination of the dural sac in paediatric patients

Abstract

SummaryAlthough the anatomy of the spinal cord and its associated structures have been well defined, the effects of body position relevant to neuraxial blockade have not been elucidated. This study was designed to determine the effect of body position on the end of the dural sac in children. After induction of anaesthesia, ultrasound examination was performed to evaluate the location of the dural sac end in the lateral position with a straight back and knee, and in the lateral position with the knees, legs, and neck flexed. The level of the end of the dural sac was determined in relation to the vertebrae. Our data demonstrate that the dural sac shifts significantly cephalad in the lateral flexed position used for neuraxial blockade (p < 0.001). These results suggest that the safety margin to avoid dural puncture during hiatal or S2-3 approach for caudal block can be increased in younger children. Dural puncture is a serious technical complication during single-shot caudal block, which is the most common regional technique for postoperative analgesia for paediatric subumbilical surgery. The prevalence of dural puncture associated with caudal analgesia is relatively low. It has only been shown in several case reports [1,2] or at a rate of 1.2% in previous large-scale studies [3,4]. In the study of 760 children, Busoni did not find any case of dural puncture and Dalens [5] reported only one dural puncture in his series of 750 paediatric caudals. Sometimes it is difficult to identify the sacral hiatus and the caudal space due to variations of anatomical structures or obesity. In these cases, a trans-sacral approach to caudal block, described by Busoni [6], may be used as an alternative method. Although no dural puncture was reported in several trans-sacral approach studies [6][7][8], the risk of dural puncture is a possibility. It is known that the end of the dural sac is located at the S4 level just after birth, then ascends to the S2 level as the child grows [9].The anatomy of the spinal cord and its associated structures have been well defined [10], largely based on post-mortem or imaging studies in the supine or prone positions. Many factors associated with neuraxial anaesthesia have been studied including the structures at the level of the termination of the spinal cord and dural sac [11], vertebral level and shape of the conus medullaris [12], shape of the epidural space [13][14][15], and distance from the skin to the epidural or subarachnoid spaces [16][17][18][19]. However, the effect of body position relevant to neuraxial blockade has not been well studied [20][21][22][23][24], especially in children.Ultrasonography, which is a well-established method of investigating the spinal canal, spinal cord, and meningeal coverings in infants and children, has the advantage of being real time, non invasive and safe [25][26][27]. It allows detection of congenital malformations such as myelocele, myelomeningocele, spinal lipoma, dorsal dermal sinus, tight filum terminale syndrome, diastematomyelia, hydromyelia and syri...

The Myth of the Equiangular Triangle for Identification of Sacral Hiatus in Children Disproved by Ultrasonography

“…Ultrasound can be easily used without radiation exposure and be an effective tool not only in locating the sacral hiatus but also in guiding needle insertion into the caudal space with reducing the risks of the intraosseous, intrathecal, or intravenous injection. 2,15,18,19 Despite these benefits, there are some considerations of using ultrasound for the caudal block such as the cost and extra time of using the high-quality ultrasound equipment or requirement of the sufficient education and experience of the physician. 20,21 In addition, so far there has been no report to prove that the guidance of ultrasound in caudal block is more advantageous than a conventional landmark-based method.…”

“…1,2 The success of a caudal block is dependent on the proper insertion of a needle into the caudal epidural space with knowledge of the exact location of the sacral hiatus. 1 However, anatomical variations and obesity can make it difficult to identify the sacral hiatus.…”

Evidence for the Use of Ultrasound Imaging in Pediatric Regional Anesthesia

“…Although neither was significant, these results suggest that pain is managed equally as well with ultrasound-guided blocks, if not better than the traditional gold standard landmark technique, in patients undergoing circumcision. 36 Koo et al, 33,34 Shin et al, 28 Tachibana et al, 29 Ueda et al 39…”

“…33 In another observational study, ultrasound allowed for visualization of the sacral hiatus, which offers benefits relative to the equiangular triangle landmark technique, because the position of the sacral hiatus can vary based on patient age, weight, and height. 36 One study used ultrasound imaging to examine spinal structures and determine the prevalence of spinal dysraphism in children with urogenital anomalies.…”

25 years of experience, thousands of caudal blocks, and no dural puncture. What happened today?

“…Koo et al. (3) demonstrated that in this position dural sac shifts significantly cephalad providing some safety margin to avoid dural puncture.…”