Cerebral Perfusion Pressure (CPP) is calculated as the mean blood pressure (MBP) - mean intracranial pressure (ICP).
= MBP - ICP
Normal CPP = 60-80
Normal MBP is 70-90. Normal ICP is < 10 mmHg. Thus, the blood pressure gradient for perfusing the brain is 60 - 80. A CPP < 50 represents signficant risk for brain ischemia.
Cerebral perfusion can fall if the MBP decreases or if the ICP increases. If the ICP rises, a normal compensatory response is to increase the systemic BP in an attempt to maintain cerebral perfusion pressure. Hypertension in the presence of brain injury may be a life saving response.
If cerebral perfusion
pressure should fall below normal, management strategies may include therapies
aimed at lowering the ICP (e.g. reduction of intracranial volume such as
blood, CSF or tissue mass) or raising the systemic BP.
February 16, 2007