Caudal and epidural blocks in infants and small children: historical perspective and ultrasound-guided approaches.

In infants and small children, ultrasound (US) guidance provides ample anatomical information to perform neuraxial blocks. We can measure the distance from the skin to the epidural space in the US image and can refer to it during needle insertion. We may also visualize the needle or a catheter during real-time US-guided epidural catheterization. In cases where direct needle or catheter visualization is difficult, US allows predicting successful puncture and catheterization using surrogate markers, such as dura mater displacement, epidural space widening due to drug injection, or mass movement of the drug within the caudal space. Although many experienced anesthesiologists still prefer to use conventional techniques, prospective randomized controlled trials using US guidance are providing increasing evidence of its advantages. The use of US-guided regional block will gradually become widespread in infants and children.