In the current prospective cohort study, the investigators will describe the incidence of mitochondrial dysfunction in a patients admitted to the NICU with severe subarachnoid haemorrhage (SAH). As patients suffering from SAH often have a non-ischemic cerebral metabolic affliction, a global cerebral measurement would presumably be as useful or more so than a focal measurement from only a very small regional brain volume. The investigators wish to evaluate a new method of monitoring, namely microdialysis of cerebral venous blood drainage. The cerebral venous drainage passes almost without exception through the jugular bulbs, left or right sided majority depending on dominance. The investigators will compare results of regional cerebral and venous measurements in order to confirm the hypothesis that metabolic disturbances of the brain are mirrored in the venous blood drainage in the jugular bulb. A pilot study of patients undergoing open heart surgery has confirmed significant differences in lactate and pyruvate in arterial systemic vs jugular venous blood. Yet unpublished data from this groups porcine experimental model supports the possibility of global metabolic venous monitoring.