If intracranial pressure increases while mean arterial pressure remains the same, what happens to cerebral perfusion pressure?

If intracranial pressure increases while mean arterial pressure remains the same, what happens to cerebral perfusion pressure?

• A. CPP decreases
• B. CPP remains unchanged
• C. CPP becomes negative
• D. CPP increases

Answer: (A)

The key idea is that cerebral perfusion pressure is the pressure gradient that drives blood flow through the brain. It’s calculated as the mean arterial pressure minus the intracranial pressure (CPP = MAP − ICP). When intracranial pressure rises while the mean arterial pressure stays the same, that gradient gets smaller, so cerebral perfusion pressure falls. For example, if MAP is 90 mmHg and ICP is 15 mmHg, CPP is 75 mmHg. If ICP increases to 30 mmHg with the same MAP, CPP drops to 60 mmHg. If ICP nears or exceeds MAP, CPP can approach zero or become negative, risking cerebral ischemia. Clinically, maintaining an adequate CPP (often around 60–70 mmHg in adults with brain injury) is crucial to ensure sufficient cerebral blood flow.

The key idea is that cerebral perfusion pressure is the pressure gradient that drives blood flow through the brain. It’s calculated as the mean arterial pressure minus the intracranial pressure (CPP = MAP − ICP). When intracranial pressure rises while the mean arterial pressure stays the same, that gradient gets smaller, so cerebral perfusion pressure falls.

For example, if MAP is 90 mmHg and ICP is 15 mmHg, CPP is 75 mmHg. If ICP increases to 30 mmHg with the same MAP, CPP drops to 60 mmHg. If ICP nears or exceeds MAP, CPP can approach zero or become negative, risking cerebral ischemia. Clinically, maintaining an adequate CPP (often around 60–70 mmHg in adults with brain injury) is crucial to ensure sufficient cerebral blood flow.