It has been suggested just going thru sacrococcygeal ligament is enough to get into epidural space. Imaging shows it works 68% of time, while advancing up 1 cm works 95.8% of time. However, intravascular injection occurred 25% of time where advanced into canal while 0% when not.
Korean J Pain. 2015 Apr;28(2):122-8. doi: 10.3344/kjp.2015.28.2.122.
A Comparison of Two Techniques for Ultrasound-guided Caudal Injection: The Influence of the Depth of the Inserted Needle on Caudal Block.
Doo AR(1), Kim JW(1), Lee JH(1), Han YJ(1), Son JS(1).
- 49 cases
- Ultrasound for placement and Contrast dyed fluoroscopy for spread
- one group needle just penetrated sacrococcygeal ligament; other needle was advance 1 cm up
- though aspiration of cerebrospinal fluid and blood was done, it obviously was not very effective as 25 % of the needle advanced cases showed intravascular spread. However the non-advanced needle placement showed not intravascular spread.
Comment – Considering 25% of the advanced ones went intravascular, then only 95.8 – 25 = 70.8 were really successful – the same as not advanced. However it is not likely all material went intravascular so… Since switching to just injecting D5W with little B12, I have not had to worry re iv spread but the blocks have to be repeated frequently.