After severe skull-brain injuries hypoxia occurs not only during the first hours but even for several days during the acute stage. Though the arterial oxygen saturation is mostly normal, cerebral anemia is present more often than it could be expected: owing to the rise of intracranial pressure, the fall of blood pressure and/or respiratory alkalosis, the cerebral circulation is reduced and the oxygen pressure for the brain cells consequently falls; this was proved by measuring the O2 tension of the venous blood of the brain. Therefore after severe brain injury, besides the normalization of the intracranial pressure and maintenance of the blood pressure, it is necessary to prevent hyperventilation by administration of neuroplegic drugs and avoid anemia by means of blood transfusion.