The "milieu interieur"-a model of brain physiology and pathophysiology.

The "milieu interieur" or "internal environment" of the brain is determined by the glial cells, the cerebrospinal fluid, the blood-brain barrier, the cerebral blood flow, the central regulation of respiration, and the intracranial pressure. Anaesthetic agents and anoxia-ischaemic insult can disrupt this important but vulnerable neuronal environment. Head injury is used as an example of a common insult to the neuronal environment and the principles of management are discussed, using a model of brain physiology and pathophysiology which can be modified to include other clinical situations.