If the intracranial pressure (ICP) increases without a change in mean arterial pressure (MAP), what happens to CPP?

Cerebral perfusion pressure (CPP) is calculated using the formula CPP = MAP - ICP. This relationship is crucial in understanding how changes in intracranial pressure impact blood flow to the brain.

When ICP increases while mean arterial pressure (MAP) remains unchanged, the difference (MAP - ICP) diminishes, causing CPP to decrease. This happens because an elevation in ICP exerts more pressure against cerebral blood vessels, leading to reduced perfusion of the brain. A decrease in CPP is significant as it implies that the brain may not be receiving adequate blood flow, which can result in ischemia and subsequent neurological damage if not addressed promptly.

The other potential answers do not accurately reflect the relationship governed by the CPP formula. An increase or fluctuation in CPP would not occur under these circumstances, as they would imply that either the brain is still being adequately perfused despite a rise in ICP or that the dynamics of pressure are changing in a way that compensates for the increase in ICP, which is not the case here.