Surgical Critical Care

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 energy directly damages neural tissue. This is type of injury is considered a primary brain injury. The initial insult often causes brain edema. If the edema is severe enough, the pressure created by the expansion of injured brain tissue within the confines of the skull, results increased intracranial pressure. It is important to remember that blood flow to the brain is a passive process. Sustained increases of intracranial pressure decrease the amount of blood flow to the whole brain. This decrease in perfusion, if sustained, further damages the primary brain injury AND causes secondary injury to previously viable regions of neural tissue.  

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Assessments in setting of severe TBI​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​

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Glascow Coma Score (GCS) is a tool used to assess a person's level of consciousness

after a brain injury. It's based on three parameters: eye response, verbal response,

and motor response. The GCS score ranges from 3 to 15,

with 3 being the worst and 15 being the best.

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 Patients with severe TBI should have a GCS assessment every hour as part of their ICU care.

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Traumatic Brain Injury in the ICU: Treatment Goals for Severe Traumatic Brain Injury

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▪ Optimize perfusion to the injured area

▪ Optimize oxygen delivery to the injured area

▪ Minimize secondary hypoxemia

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As mentioned above, increased intracranial pressure can result in decreased blood flow to the brain.Therapeutically​

we think of this in terms of "cerebral perfusion" (CPP).  CPP is a calculated pressure and is derived from the Mean Arterial Pressure (i.e. inflow pressure) minus Intracranial Pressure (i.e. resistance pressure to inflow). A normal ICP is considered equal to or less than 22 mmHg.

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CPP = MAP - ICP​​

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Monroe ▪ Kelly Statement

In the unyielding cranial vault, the pressure in the intracranial space increases when the brain, cerebrospinal fluid and blood exceed their usual volumes. This rise in pressure compromises blood flow to brain parenchyma.

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The three entities that occupy space in the intracranial vault: 

1. Neural parenchyma

2. Cerebrospinal fluid

3. Blood and blood vessels

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In neuro-critical care, we can target these entities to decrease intracranial pressure and increase cerebral perfusion pressure. 

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​Blood and Blood vessels

Cerebrovascular tone: Chemoreceptors on the extensive network of cerebrovascularsmooth 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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Cerebrospinal Spinal Fluid​​

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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Neural Parenchyma

Mannitol and Hypertonic Saline have both been used to address neural edema. These therapies can cause increases in plasma osmolality and this needs to be closely monitored when these agents are employed to treat increased ICPs.

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