A traumatic brain injury (TBI) is caused by force applied to the skull. These forces can be from blunt or penetrating mechanism. The transfer of kinetic injury damages brain tissue and results in an alteration of brain function. The initial insult and subsequent edema within the confines of the skull may cause secondary and tertiary injuries to the brain parenchyma. It is for these reasons that the critical care management of traumatic brain injuries can alter the course and degree of recovery after moderate and severe TBI.

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 Goals of care

▪ Optimize perfusion to the injured area

▪ Optimize oxygen delivery to the injured area

▪ Minimize secondary hypoxemia

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◦ What affects Cerebral Perfusion

◦ CPP = MAP - ICP

The cerebral perfusion pressure is determined by the Mean Arterial Pressure minus the Intracranial pressure

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▪ Inflow

Blood and Cerebrospinal fluid are contained in the intracranial space and are normally a low pressure system. This is why rises in intracranial pressure can compromise perfusion to the brain.

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Cerebrovascular tone: Chemoreceptors on the extensive network of cerebrovascular

smooth muscle respond to systemic CO2 receptors. When CO2

rises, vessels dilate, When CO2 drops vessels constrict. The network of

vessels is so vast, that when they dilate, they take up more space resulting in

an increase in ICP.

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One may think that the solution would be to just let CO2 drop and make that

vascular space smaller... however, it is the cerebrovascular space that also

delivers oxygen to brain tissue. Balance of tone is needed to optimize

perfusion to the tissue.

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▪ Outflow

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Cerebrospinal fluid and Blood both occupy fluid volume within the cranial

space. When acute rises in intracranial pressure occur, small amounts of

cerebrospinal fluid can be drained to lower ICP and allow improved blood

flow to the brain.

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Monroe ▪ Kelly Statement

The skull, while protective, can be constrictive when it's contents, brain,

cerebrospinal fluid and blood exceed their respective usual volumes. In the

face of increasing intracranial volumes and the unyielding cranial vault, the

pressure in the intracranial space increases. The rise in pressure

compromises blood flow to brain parenchyma.