How is cerebral perfusion pressure (CPP) related to intracranial pressure (ICP)?

Cerebral perfusion pressure (CPP) is a critical parameter that reflects the pressure gradient driving blood flow to the brain. It is defined as the difference between the mean arterial pressure (MAP) and the intracranial pressure (ICP), articulated mathematically as CPP = MAP - ICP.

When the ICP increases, it directly affects the net pressure available for cerebral perfusion. Because the cerebral perfusion pressure is derived from subtracting ICP from MAP, an elevation in ICP results in a lower CPP, assuming MAP remains constant. This reduction in CPP means there is less effective blood flow to the brain, which can lead to inadequate oxygen and nutrient delivery, and potentially result in cellular injury or death.

Thus, the relationship between CPP and ICP is such that as ICP goes up, CPP goes down, highlighting a crucial aspect of maintaining adequate cerebral blood flow in clinical settings.