Major changes are becoming apparent among neuro-anesthetists and neurosurgeons in their attitude towards hypocarbia, blood volume, mean arterial pressure (MAP), cerebral perfusion pressure (CPP), anesthetic technique, and brain retraction pressure. These changes are related to the transfer from intensive care units to operating theaters of major new physiologic data regarding oxygen delivery to tissues (DO2) and oxygen consumption by tissues (VO2). These fundamental data have progressively, during the last five years, led to the concept of brain homeostasis based on four fundamental therapeutic principles: 1) The use of moderate hypocarbia (as opposed to deep hypocarbia which should stay exceptional). 2) The use of a normal mean arterial pressure (MAP) and thus cerebral perfusion pressure (CPP) by promoting a. normovolemia, b. a hematocrit around 30% and c. a light anesthesia technique allowing rapid recovery. 3) The use of appropriate crystalloids (NaCl 0.9% rather than Ringer-Lactate, and no DW5) taking into account measured osmolality. 4) The optimisation of brain relaxation by combining an appropriate anesthetic technique, mannitol, head up (and head straight) position, together with a lumbar drainage.