Analysis of the dynamics of experimental epidural bleeding in swine.

The effects on epidural bleeding of two major factors were studied in a swine model. These were detachment of the dura from the skull and an epidural arteriovenous shunt. Firstly the effect of differing degrees of detachment of dura was studied in the absence of a shunt. Secondly the effect of the shunt was examined with a constant degree of dural detachment. Increasing the degree of the detachment of the dural from the skull increased the rate and volume of bleeding. In addition the greater the degree of dural detachment from the skull the easier it was for further dura stripping to take place. The shunt reduced the epidural pressure and increased the bleeding pressure. Sometimes it reduced the force which, acting on the dura would strip more dura free, but never enough to preclude further dura stripping. Larger shunts were associated with a longer bleeding duration. It is concluded that the effects of dura detachment and the epidural shunt acting in concert can explain the delayed expansion of an epidural haematoma and are consistent with the known variability of clinical epidural haematomas.