Intracranial Regulation & Monro-Kellie Doctrine The skull contains brain tissue (78%), blood (12%), and CSF (10%). Under Monro-Kellie, because this volume is constant, an increase in any one component must be offset by displacing another; otherwise, intracranial pressure (ICP) rises. Compensations include displacing CSF, collapsing cerebral veins, and compressing tissue. Decompensation causes ischemia. Normal ICP is 5 to 15 mm Hg; sustained pressure >20 mm Hg is abnormal.

Cerebral Perfusion Pressure (CPP) & Blood Flow CBF requires constant O2 and glucose. Autoregulation maintains constant CBF when MAP is between 70 and 150 mm Hg. CPP = MAP - ICP. Normal CPP is 60 to 100 mm Hg; <50 mm Hg causes ischemia and neuron death, while  ...