Cerebral Perfusion Pressure (CPP) is the most critical hemodynamic parameter monitored in neuro-intensive care units for patients suffering from traumatic brain injury, massive strokes, or intracranial hemorrhage.
The Physics of Brain Blood Flow
Blood is pushed up into the head by the systemic blood pressure (specifically, the Mean Arterial Pressure, or MAP). However, it faces resistance from the pressure inside the skull (Intracranial Pressure, or ICP). The difference between these two opposing forces is the CPP.
CPP = MAP - ICP
Clinical Management
If a patient has severe brain swelling, their ICP might rise to 30 mmHg (Normal is < 15). If their MAP is 80 mmHg, their CPP is only 50 mmHg. At this level, the brain tissue begins to suffocate (ischemia). The intensivist has two choices to save the brain:
- Lower the ICP: Drain cerebrospinal fluid, surgically remove part of the skull (craniectomy), or give hypertonic saline.
- Raise the MAP: Give the patient powerful vasopressor drugs to artificially drive their blood pressure up, forcing blood into the skull against the high resistance.