<Ul> <Li> Edema </Li> <Li> Impaired metabolism </Li> <Li> Altered cerebral blood flow </Li> <Li> Free radical formation </Li> <Li> Excitotoxicity </Li> </Ul> <Li> Altered cerebral blood flow </Li> <Li> Free radical formation </Li> <P> In TBI, primary injuries result immediately from the initial trauma . Primary injury occurs at the moment of trauma and includes contusion, damage to blood vessels, and axonal shearing, in which the axons of neurons are stretched and torn . The blood brain barrier and meninges may be damaged in the primary injury, and neurons may die . Cells are killed in a nonspecific manner in primary injury . Tissues have a deformation threshold: if they are deformed past this threshold they are injured . Different regions in the brain may be more sensitive to mechanical loading due to differences in their properties that result from differences in their makeup; for example, myelinated tissues may have different properties than other tissues . Thus some tissues may experience more force and be more injured in the primary injury . The primary injury leads to the secondary injury . </P>

Which of the following is a preventable cause of secondary brain injury