COMPARATIVE HISTOPATHOLOGY OF EPIDURAL HYDROGEL AND SILICONE ELASTOMER CATHETERS FOLLOWING 30 AND 180 DAYS IMPLANT IN THE EWE

New catheter materials, termed Hydrogels, have been developed recently that are stiff until exposed to hydration. The purpose of this study was to compare the 30 and 180 day histopathology of catheters composed of a common silicone elastomer versus a Hydrogel elastomer blend (HEB ). Epidural catheters composed of either silicone or HEB were implante d in 19 yearling ewes for either 30 or 180 days. The degree of fibroti c reaction in the epidural space, muscle and subcutaneous tissue was a ssessed using both histopathology and quantitative imaging analysis. A separate subset of three ewes were implanted with HEB epidural cathet ers connected to subcutaneously implanted ports through which twice we ekly injections of saline were given. There was no evidence of signifi cant neurotoxicology associated with either the silicone or the HEB ca theter materials. However, the silicone elastomer group had a quantifi ably greater degree of fibrosis than the HEB group of both implant dur ations. The mean cross sectional area (sq. mm) of epidural pericathete r fibrosis was significantly smaller in the HEB group compared with th e silicone group (0.491 in the HEB group and 1.585 in the silicone gro up at 30 days [P = 0.02] and 0.28 and 1.401 at 180 days [P = 0.0001]. The HEB catheter was easily inserted with standard epidural needles fa cilitated by the inherent stiffness of the catheter prior to hydration . HEB catheters remained patent throughout 30 days of saline injection s per implanted ports. Silicone catheters demonstrated increased fibro sis relative to the HEB catheter material in the epidural space and in subcutaneous tissue.