Subdural monitoring of ICP during craniotomy: thresholds of cerebral swelling/herniation.

It is possible to define thresholds for cerebral swelling or herniation during craniotomy. In 178 patients subjected to craniotomy for space occupying processes subdural ICP was measured before opening of dura. The subdural ICP was correlated to the degree of cerebral swelling or herniation after opening of dura. At subdural ICP < 7 mm Hg cerebral swelling/herniation after opening of dura rarely occurs, while at ICP > or = 10 mm Hg cerebral swelling/herniation occurs with high probability. These ICP thresholds are independent of the pathophysiology (SAH, cerebral tumor), the anaesthetic agent (isoflurane, propofol) and the PaCO2 level (< or = 4.0 kPa, > 4.0 kPa). Generally, a good correlation between the tactile estimation of dural tension and the tendency to cerebral swelling or herniation after opening of dura was found. However, in 8.5% the surgeons were unable to predict swelling/herniation.