Secondary injury and acidosis.

Following traumatic brain injury, cells that are not directly, and thereby irreversibly damaged are subjected to ionic fluxes including potassium and calcium. This injury-induced ionic flux is a result of both neuronal firing via direct mechanical stimulation of the neurons as well as the activation of ligand-gated ion channels primarily associated with excitatory amino acids (e.g. glutamate). This ionic destabilization places enormous energy demands on these cells in order to activate pumping mechanisms to reinstate normal ionic balance. The primary fuel used to acquire this energy is glucose, which results in a period of hyperglycolysis leading to the accumulation of lactate. This acute period of increased glucose metabolism lasts only during the acute period, after which these same cells exhibit a state of chronic metabolic depression for both glucose and oxygen. This metabolic derangement may prevent the necessary energy production for maintaining cellular protein synthesis which is inhibited following traumatic brain injury. This injury-induced metabolic derangement is not uniform throughout all regions. Some structures are more or less affected presumably due to their proximity to the site of trauma and/or to the extent to which they have a preponderance to being more vulnerable to insult. Within these affected regions, the metabolic dysfunction indicates that cells are functionally compromised in their ability to respond to both normal physiologic and pathophysiologic challenges. This results in the expression of neurological deficits and an enhanced vulnerability of these cells to a second insult, both of which dissipate as normal metabolic function returns over time.