Cerebral Perfusion Pressure - Ensuring Blood Flow In The Brain
Studying cerebral perfusion pressure (CCP) and how to compute will be beneficial in learning about the human brain. A normal blood flow in the brain guarantees that it will function well. Knowledge regarding CCP is also important, particularly when dealing with brain injury therapy.
Dr. Bill ButcherOct 20, 20224 Shares593 Views
Cerebral Perfusion Pressure(CPP) is defined as the difference between the Mean Arterial Pressure (MAP) and the Intracranial Pressure (ICP).
The equation is: CPP = MAP - ICP.
This represents the pressure gradient driving cerebral blood flow (CBF) and hence oxygen and metabolite delivery.
The normal brain autoregulates its blood flow to provide a constant flow regardless of blood pressure by altering the resistance of cerebral blood vessels.
These homeostatic mechanisms are often lost after head trauma(cerebral vascular resistance is usually increased), and the brain becomes susceptible to changes in blood pressure.
Those areas of the brain that are ischaemic, or at risk of ischemia (ischaemia) are critically dependent on and adequate cerebral blood flow, and therefore cerebral perfusion pressure.
A model of a human head with eyes closed and the brain out in the open
Cerebral Perfusion Pressure may be maintained by raising the Mean Arterial Pressure or by lowering the Intracranial Pressure.
In practice, ICP is usually controlled to within normal limits (<20mmHg) and MAP is raised therapeutically. It is unknown whether ICP control is necessary providing CPP is maintained above the critical threshold.
Control of intracranial hypertension is discussed on the pages on intracranial pressure.
There is substantial evidence now that early hypotension (BP < 90mmHg) is associated with increased morbidity and mortality following severe brain injury.
Even patients with one episode of hypotension during their ICU stay have a significantly reduced prognosis.
Maintenance of an adequate MAP requires primarily a normovolaemic patient.
Control of other sites of hemorrhage has the highest priority (with oxygenation).
These patients should NOT be kept “dry” with fluid restriction, but maintained in zero balance.
Further elevation of MAP, once normovolaemia is achieved, is usually accomplished with norepinephrine, though dopamine may be used.
There is little evidence to recommend any one agent over another.
A female doctor shows the formula written on a white board when calculating cerebral perfusion pressure