Fluid therapy in patients with brain injury: what does physiology tell us?

The unique component of the cerebral circulation is the so called blood-brain barrier (BBB). The anatomical structures of the BBB consist of the cerebral vascular endothelial cells, the surrounding pericytes, the basal lamina and the perivascular astrocytes. These form the so-called neurovascular unit. Notably, the endothelial cells are interconnected by tight junctions; thus, any solute transport will be transcellular, as opposed to paracellular, in the peripheral circulation. The specific anatomy of the neurovascular unit allows the brain volume to be kept constant even in the context of marked changes in intravascular volume status.