Primary and Secondary Injury Etiology
The primary or initial injury injury to the brain defines the injury as traumatic or non-traumatic. This information helps determine the severity of injury, informs surveillance data, and correlates the injury to an expected long-term outcome. The mechanism of injury is mechanical – for example, neurons damaged from a penetrating injury or stroke. The primary injury causes a cascade of adverse advents leading to secondary aspects which include hypoxia, anemia, metabolic abnormalities, hydrocephalus, intracranial hypertension, and hemorrhagic activity. Other delayed effects include:
- the release of excitatory amino acids (the neurotransmitters of the central nervous system (CNS)
- oxidative free-radical production (oxidative stress alters cell membranes and structure)
- release of arachidonic acid metabolites (intra-cellular messengers causing inflammation, changes in blood flow and cell death)
The injury process extends past the point in time of the initial injury as these delayed effects cause additional cellular injury or cell death and further exacerbate the effects of the injury by extending the amount of damage to the brain.