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Cerebral Perfusion Pressure - Ensuring Blood Flow In The Brain

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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.

Cerebral Perfusion Pressure (CPP) made easy

Brain And Blood Flow

COPYRIGHT_SPINE: Published on https://spinal-injury.net/cerebral-perfusion-pressure/ by Dr. Bill Butcher on 2022-10-24T11:17:12.286Z

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
A model of a human head with eyes closed and the brain out in the open

CPP - Contemporary Brain Injury Therapy

Maintenance of an adequate Cerebral Perfusion Pressure is a cornerstone of modern brain injury therapy.

After brain injury, and especially in the multiply injured patient, cerebral blood flow may be lowered to the ischaemic threshold.

To prevent further neuronal death (the secondary brain injury), this flow of well oxygenated blood must be restored.

There is no class I evidence for the optimum level of CPP, but 70-80mmHg is probably the critical threshold.

Mortality increases approximately 20 percent for each 10mmHg loss of CPP.

In those studies where CPP is maintained above 70mmHg, the reduction in mortality is as much as 35% for those with severe head injury.

A male doctor points at the illustrations of the human brain and red blood cells shown through a projector
A male doctor points at the illustrations of the human brain and red blood cells shown through a projector

CCP And MAP

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
A female doctor shows the formula written on a white board when calculating cerebral perfusion pressure

Key Recommendations

Below are the important things to consider regarding Cerebral Perfusion Pressure:

  • Maintenance of CPP reduces mortality in severe head injury.
  • CPP should be maintained above 70-80mmHg.
  • Systemic hypotension is associated with poor prognosis.
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About The Authors

Dr. Bill Butcher

Dr. Bill Butcher - With more than two decades of experience, Dr. Bill Butcher aims to provide a repository for educational materials, sources of information, details of forthcoming events, and original articles related to the medical field and about health subjects that matter to you. His goal is to help make your life better, to help you find your way when faced with healthcare decisions, and to help you feel better about your health and that of your family. Bill received his medical degree at Boston University School of Medicine and spent his entire career helping people find the health and medical information, support, and services they need. His mission is to help millions of people feel fantastic by restoring them to optimal health.

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