ABSTRACT
Reduced cerebral perfusion due to high levels of ICP influence CBF and oxygen delivery, a common theme following neurotrauma (Siesjo, 1992). Cerebral ischemia occurs if compensation by increased oxygen extraction is incomplete. Since histological ischemic changes are found in the brains of up to 80 percent of patients dying from head injuries, the provision for monitoring low CBF seems important (Kirkpatrick et al., 1996b). Biochemical processes accompany low CBF states and may contribute to the evolution of cellular injury. These processes are intimately related to derangements in CBF and oxygen delivery, and include glutamate excitotoxicity, freeradical induced damage and excessive production of hydrogen ions and lactate. Secondary cerebral events following the primary injury may account for the poor predictive value of early clinical and radiological findings (Chan et al., 1992a; Gopinath et al., 1994; Kirkpatrick et al., 1995; Miller, 1985; Robertson et al., 1989). Such episodes can now be detected, and some influence prognosis (Bouma and Muizelaar, 1990; Chan et al., 1992a-e; Chan et al., 1993; Cruz et al., 1991; Cruz 1993a; Jones et al., 1993; Kirkpatrick et al., 1994b; Kirkpatrick et al., 1995; Kirkpatrick et al., 1996a; Kirkpatrick et al., 1996b). Low CBF values in the first few hours after injury, and episodes of profound cerebral hypoxia are predictive of a poor outcome (Bouma and Muizelaar, 1990; Chan et al., 1992a; Gopinath et al., 1994).
