Why does intracranial pressure rise Intracranial pressure (ICP) is the force created brain tissue, blood and cerebrospinal fluid inside a rigid skull that cannot expand. When any one of these increases, bleeding, swelling, tumour growth, impaired venous drainage, high co2 causing vasodilation or CSF obstruction/overproduction, the pressure rises fast. As ICP climbs, the brain loses space to function. That’s when we see headache, vomiting, reduced GCS, asymmetric pupils, limb weakness and in seve