(S-518) Tsui, B.C., Saturday 9:15
TITLE: A NEW METHOD TO PREDICT PARAMEDIAN THORACIC EPIDURAL DEPTH
AUTHORS: Ban C. Tsui, MSCMD, Kathryne Faccenda, MBChB, Brendan T. Finucane, MBBCh
AFFILIATION: University of Alberta, Edmonton, Alberta, Canada.
INTRODUCTION: We hypothesized that knowledge of the perpendicular depth from the skin to vertebral lamina at any thoracic level allows one to calculate the distance to the epidural space using simple trigonometry (fig 1): angulated needle length x cos (sagittal angulation) x cos (transverse angulation);where the contribution of the 1 cm lateral needle placemen (transverse angulation <15°) is negligible.
METHODS: A differing thickness of plasticine was applied to a thoracic spine model to simulate a varying thickness of subcu- taneous tissue (3,4,5 cm). A Tuohy needle was inserted perpen- dicular to"skin",1 cm lateral from the midline,until the vertebral lamina was contacted. The needle was redirected with sagittal and transverse angulation until the "epidural space" was identified. Multiple level measurements were made including, the perpendicular depth from surface to lamina, the length and angulation of the needle.
RESULTS: In fig 2, the regression line (y=0.72 +0.96x; r=0.88) represents: angulated needle length x cos (sagittal angulation) = 0.7cm + perpendicular needle depth.
DISCUSSION: This study supports the hypothesis that the angulated needle length to the epidural space is predictable based on the perpendicular needle depth. This perpendicular depth allows direct measurements of the anatomical layers, including the most variable soft tissue (subcutaneous tissue).