Assessment of critical thresholds for cerebral perfusion pressure by performing bedside monitoring of cerebral energy metabolism.

An intractable increase in intracranial pressure (ICP) leading to a progressive decrease in cerebral perfusion pressure (CPP) and cerebral blood flow (CBF) is the dominating cause of death in patients with severe brain trauma. Arterial hypotension may further compromise CPP (and CBF) and significantly contributes to death. In addition, the injured brain is sensitive to raised CPP due to an increased permeability of the blood-brain barrier (BBB) to crystalloids and an impaired pressure autoregulation of the CBF. Given these circumstances, an increase in CPP will cause a net transport of water across the BBB and a further elevation in ICP. Accordingly, the assessment of the lower critical threshold for CPP is important for neurological intensive care. This level varies among different patients and different areas of the brain. In fact, the penumbral zones surrounding focal brain lesions appear to be the most sensitive. In the individual patient, preservation of normal cerebral energy metabolism within areas at risk during a decrease in CPP can be guaranteed by performing intracerebral microdialysis and bedside biochemical analyses.