Primary and Secondary Brain Injuries

Primary brain injury:
The result of the initial insult:





  • traumatic (such as a blow to the head received in a motor vehicle accident) 
  • nontraumatic (such as from a stroke, tumor, or infection).






  • is immediate and irreversible.

 Secondary brain injuries:

 consequences of a primary injury

or processes such as:

  1. hypoxia
  2. hypotension
  3. hypercapnia
  4. acidosis
  5. reduced oxygen delivery.


The skull is a closed compartment and can’t expand to compensate for excess blood, cerebrospinal fluid (CSF), swelling brain tissue, or tumor growth.

Intracranial pressure rises as a result of the insult and impedes cerebral blood flow.

 An increase in any one of these components—blood, CSF, brain tissue, or tumor—means that the volume of the others is reduced (compressed) by an equal amount harming those components.




  • This is known as the Monro-Kellie doctrine.
  • Cerebrospinal fluid is the most commonly displaced component;
  • if ICP remains high after CSF has been displaced, cerebral blood volume is altered.
  • When the maximal volume shift is reached, further increases in intracranial volume will markedly increase ICP causing damage to the brain.





 Howard-Fain, Tamara and LeJeune,  Matt. 2002. Caring for patients with increase intracranial pressure. Critical Care. 32. 


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