Histological changes of the sciatic nerve in dogs after intraneural application of lidocaine--relation to the established application pressure.

Histological changes of sciatic nerve in adult dogs 7 days after single application of 2% lidocaine (4 ml dose, speed of injection 3 ml/min) and measurement of the application pressure was studied, with a goal to investigate structural changes of the nerve in relation to the established pressure values. The application pressure was determined by using Bio Bench software. In intrafascicular puncture an average application pressure of 198.23 +/- 52 kPa was found, and in interfascicular puncture its average value was 53.3 +/- 17.9 kPa, with a note that individual differences are regularly present. Seven days after the injection, a nerve dissection was performed and serial sections covering the region of injection's puncture and bordering proximal and distal zones, in the total length of 3 cm, were prepared. The found changed show the presence of nerves' fibers lesions with a strong reactivity of Schwann's cell, as well as the change of interstitial structure concerning hypercellularity and occurrence of cellular extravasation. The covering system of the nerve in the zone of epineurium manifests changes of inflammatory process and in perineurium a decomposition of lamella layers and the alteration of their tinctorial properties were noticed. A comparison of the found nerve reactivities in intra- and interfascicular application showed their one-way alteration, although the lesions were more noticeable in the conditions of intrafascicular application. The damages were mostly expressed in the zone of local application of anesthetic, than distally from it, while the damage to the structure in the proximal part is of the smallest degree.