Central nervous system monitors full into two main groups those that monitor functional end points and those that monitor oxygen supply to the brain The function monitors which have been used are the awake – up test , Electroencephalogram (EEG) and evoked potentials ( EPS) . Xenon measurement of cerebral Blood flow , Doppler assessment of flow velocity , jugular venous oxygen content and now near Infrared spectroscopy ( NIRS) monitor the oxygen supply indirectly.