Reconsidering injection volume for caudal epidural block in young pediatric patients: a dynamic flow tracking experimental study

Introduction Caudal epidural block is a commonly used analgesic technique in pediatric patients. Ultrasound could be used to increase the accuracy of the block by visual confirmation of the drug-spreading. Therefore, we aimed to estimate the cephalad spread of injection volume by caudal route using dynamic ultrasound imaging in young pediatric patients. Methods Forty patients, aged 6–24 months, undergoing foot surgery were included. After inducing general anesthesia, an angiocatheter was inserted into the sacral canal under ultrasound guidance. Thereafter, the probe was placed in the paramedian sagittal oblique position, and prepared 0.15% ropivacaine was injected, 1 mL at a time, up to 1.0 mL.kg −1 . The ultrasound probe was moved cranially following the bulk flow of local anesthetics. Our primary outcome was the required volume of local anesthetics to reach each level of interlaminar space. Results The dynamic flow tracking was available in 39 patients, and the required volume of the injectate to reach L5–S1, L4–L5, L3–L4, L2–L3, L1–L2, T12–L1, and T11–T12 was 0.125, 0.223, 0.381, 0.591, 0.797, 0.960, and 1.050 mL.kg −1 , respectively. The required volume to reach the immediate upper spinal level was inconsistent across various spinal levels. Conclusions Local anesthetics of 0.223, 0.591, and 0.797 mL.kg −1 could provide sufficient analgesia for localized foot, knee, and hip surgeries, respectively. However, since the required volume of the local anesthetics could not be calculated linearly, the real-time dynamic flow tracking technique for the caudal epidural block is recommended in young pediatric patients. Trial registrations ClinicalTrials.gov ( NCT04039295 ).