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 implanted in 19 yearling ewes for either 30 or 180 days. The degree of fibrotic reaction in the epidural space, muscle and subcutaneous tissue was assessed using both histopathology and quantitative imaging analysis. A separate subset of three ewes were implanted with HEB epidural catheters connected to subcutaneously implanted ports through which twice weekly injections of saline were given. There was no evidence of significant neurotoxicology associated with either the silicone or the HEB catheter materials. However, the silicone elastomer group had a quantifiably greater degree of fibrosis than the HEB group of both implant durations. The mean cross sectional area (sq. mm) of epidural pericatheter fibrosis was significantly smaller in the HEB group compared with the silicone group (0.491 in the HEB group and 1.585 in the silicone group 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 facilitated by the inherent stiffness of the catheter prior to hydration. HEB catheters remained patent throughout 30 days of saline injections per implanted ports. Silicone catheters demonstrated increased fibrosis relative to the HEB catheter material in the epidural space and in subcutaneous tissue.