Should we abandon landmark-based technique for caudal anesthesia in neonates and infants?

Caudal anesthesia is a landmark-based technique with ultrasound guidance occasionally used in the absence of landmarks. The current surface landmark remains a popular approach due to its desirable success rate. However, incomplete ossification of the posterior vertebral elements can make this procedure for neonatal caudal anesthesia difficult. The aim of this study was to describe the anatomical relationship of the posterior superior iliac spines (PSISs) to the sacral cornua in infants using ultrasound.

A total of 26 healthy infants (17 female; mean age 13 weeks) were scanned by an experienced radiologist in the prone position with hip and knee joints flexed. The PSISs and sacral cornua were identified clinically then using ultrasound to assess whether these markings corresponded with the clinical markings. The distance between the PSISs and the distance between the tip of the PSIS and tip of the sacral cornu were measured using ultrasound.

The PSISs were clinically identified in all babies, but the sacral cornua were not palpable in four babies (15%). The PSISs and sacral cornua were easily visualized using ultrasound in all participants. The mean distance between the two left and right PSISs was 3.4 ± 0.5 cm; the mean distance between the PSISs and cornu was 2.5 ± 0.5 cm on the left and right.

This study showed that the current landmark (equilateral triangle) for infant caudal anesthesia is unreliable. Importantly, the sacral hiatus is clinically identifiable only if the sacral cornua are palpable; otherwise, using ultrasound is essential.