Does Use of Ultrasound Reduce the Rate of Sham Caudal Block in Children

Caudal blocks are one of the most commonly performed regional anesthetics in children and are performed daily for a host of infra-umbilical surgical procedures. A caudal block is an epidural injection, most commonly of local anesthetic into the epidural space as accessed via the sacral hiatus. In children, the sacral hiatus is a normally occurring aperture in which the epidural space may be accessed with extremely minimal risk; as neural tissue ends more proximally. Due to this measure of safety, caudal blocks are preferred in children when compared with standard lumbar epidurals. Caudal blocks are performed blindly using palpation and tactile feedback to assess if the medication is being administered in the correct location. As a result of blind injection, administration of local anesthetic totally or partially outside of the correct site can often be unnoticed or identified after a significant volume has already been injected. With the potential for toxicity of local anesthetic, this may result in either the inability to give a complete dose or an unintentional and often unnoticed sham block "incorrect site of injection".

Use of ultrasound has been proposed for identification of caudal block placement and correct medication spread. However, a recent review of the Pediatric Regional Anesthesia Network database reveals that ultrasound is reportedly only used in less that 3% of blocks. The benefit of ultrasound is safe and real-time confirmation of injection. Ultrasound allows the provider to determine with minimal local anesthetic or even saline injection if the correct space is accessed. Without ultrasound, failed blocks are either identified after significant percentage of the total dose of local anesthetic is incorrectly administered or intra or post operatively when the patient demonstrates a significant opioid requirement. This is problematic given that one of the primary benefits of a caudal block in children is the ability to avoid opioids.

Review of local practice here at Texas Children's Hospital for quality improvement purposes revealed a failure rate of caudal blocks to be 18%. Failure was defined as a heart rate increase with incision of >20% despite a caudal block and >1MAC of gas for the patient age. These patients all required opioids both intra and post operatively in addition to surgical levels of inhaled anesthetic agent.