Chronic cervical and lumbar epidurial catheterization through the atlanto-occipital membrane in rats

We report here an efficient means of epidural catheter placement through atlanto-occipital membrane in rats. [Methods] Male SD rats (n=84) were divided into lumbar (n=48) and cervical (n=36) groups. Under sterile technique, PVC V-1 tubing was inserted and advanced caudally targeted to the C 4 or L 4 level. Analgesic efficacy and duration were measured by injecting increments of 2% lidocaine until a maximum paw withdrawal latency time from a radiant heat thermal stimulator. Rats (n=6 each day) were sacrificed and an autopsy was performed to observe both the laterality of the catheter tip and the proliferation of fibrous tissue around the catheter. [Results] The volume of lidocaine and its duration was 52±17 μl and 27±13 min (mean±SD) in lumbar, 30±10 μl and 26±9 min in cervical group. In lumbar group, two catheters penetrated the dura. The remaining catheters were confirmed to be in the epidural space within L4±1 or C 4±2 segment. Lumbar catheter tips were almost equally distributed between the center, left and right, while cervical catheter tips were distributed between left and center portion of the epidural space. The severity of tissue proliferation was time dependent. The proliferation of fibrotic tissue seemed more rapid in cervical than lumbar group. [Conclusion] Although this approach for epidural catheter placement is efficient and produces excellent drug effects on day 3 after implantation, as reported by others, rapid development of fibrous tissue around the catheter quickly limits the usefulness of the epidural catheter.