Following TBI, there is an increased risk for the development of secondary cerebral ischaemic
insults. PET studies in humans who suffered TBI revealed brain regions with reduced CBF and increased
oxygen extraction fraction, findings suggestive of an increased vulnerability of these regions to
ischaemic injury.136 Two major mechanisms may contribute to this increased vulnerability to cerebral
ischaemia: (1) direct mechanical trauma and structural damage to intracerebral arteries and (2) local
vasospasms of cerebral arteries secondary to leakage of the BBB and regional extravasation of blood
into the brain parenchyma. In addition to this kind of deterioration in post-traumatic cerebral perfusion,
a cerebrovascular–metabolic uncoupling with reduced local CBF and concomitant increase in local
glucose metabolism has been observed in animals subjected to TBI.137 The increase in glucose
metabolism after TBI has been attributed to higher local metabolic demands as a result of attempts by
brain tissue to compensate for post-traumatic ionic imbalances with increased Naþ/Kþ-ATPase activity.
As a result of higher glucose consumption in brain areas with insufficient oxygen supply due to reduced
CBF, a local lactate acidosis occurs. The cerebrovascular–metabolic uncoupling leads to progression of
ischaemic injury in brain areas which are already damaged by TBI. Ischaemic brain injury itself sets in
motion the post-ischaemic pathophysiological cascade of events as described (quod vide) and has
potentiating effects on the tissue injury