Cerebral ischaemia plays a major role in the outcome of brain-injured patients. Because brain oxygenation can be assessed at bedside using intra-parenchymal devices, there has been a growing interest about whether therapeutic hyperoxia could be beneficial for severely head-injured patients. Normobaric hyperoxia increases brain oxygenation and may improve glucose-lactate metabolism in brain regions at risk for ischaemia. However, benefits of normobaric hyperoxia on neurological outcome are not established yet, that hinders the systematic use of therapeutic hyperoxia in head-injured patients. This therapeutic option might be proposed when brain ischemia persists despite the optimization of cerebral blood flow and arterial oxygen blood content.