Secondary
Secondary injury is an indirect result of the insult. It results from processes initiated by the trauma. It occurs in the hours and days following the primary injury and plays a large role in the brain damage and death that results from TBI. Unlike in most forms of trauma a large percentage of the people killed by brain trauma do not die right away but rather days to weeks after the event. In addition, rather than improving after being hospitalized as most patients with other types of injuries do, about 40% of people with TBI deteriorate. This is often a result of secondary injury, which can damage even neurons that were unharmed in the primary injury. It occurs after a variety of brain insults including subarachnoid hemorrhage, stroke, and traumatic brain injury and involves metabolic cascades.
Secondary injury can result from complications of the injury. These include ischemia (insufficient blood flow); cerebral hypoxia (insufficient oxygen in the brain); hypotension (low blood pressure); cerebral edema (swelling of the brain); changes in the blood flow to the brain; and raised intracranial pressure (the pressure within the skull). If intracranial pressure gets too high, it can lead to deadly brain herniation, in which parts of the brain are squeezed past structures in the skull.
Other secondary insults include hypercapnia (excessive carbon dioxide levels in the blood), acidosis (excessively acidic blood), meningitis, and brain abscess. In addition, alterations in the release of neurotransmitters (the chemicals used by brain cells to communicate) can cause secondary injury. Imbalances in some neurotransmitters can lead to excitotoxicity, damage to brain cells that results from overactivation of biochemical receptors for excitatory neurotransmitters (those that increase the likelihood that a neuron will fire). Excitotoxicity can cause a variety of negative effects, including damage to cells by free radicals, potentially leading to neurodegeneration. Another factor in secondary injury is loss of cerebral autoregulation, the ability of the brain's blood vessels to regulate cerebral blood flow. Other factors in secondary damage are breakdown of the blood–brain barrier, edema, ischemia and hypoxia. Ischemia is one of the leading causes of secondary brain damage after head trauma. Similar mechanisms are involved in secondary injury after ischemia, trauma, and injuries resulting when a person does not get enough oxygen. After stroke, an ischemic cascade, a set of biochemical cascades takes place.
Read more about this topic: Primary And Secondary Brain Injury
Famous quotes containing the word secondary:
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—William Butler Yeats (1865–1939)
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—Robert Musil (1880–1942)