Cerebral effects of HDC.

HDC is commonly used in conditions with a raised intracranial pressure. An effect on cerebral edema was first described in patients with brain tumors, where the intracranial pressure can be lowered following administration of HDC. However, the use of HDC in cerebral edema of other origin is not equally well supported. Apart from effects on brain circulation secondary to the effects of HDC on brain edema, direct effects of HDC on cerebral blood flow and oxygen uptake have been studied mainly in experimental endotoxic shock. Endotoxin given intravenously leads to reduction in the cerebral blood flow and increase in the oxygen uptake. The increased oxygen uptake could be due to circulating catecholamines or other substances affecting the cerebral metabolism following their passage of a damaged blood-brain barrier. Pretreatment with HDC prevents the effects of endotoxin on cerebral blood flow and oxygen uptake. When HDC was given after an intravenous endotoxin injection blood flow was unaffected but the increased cerebral oxygen uptake was reduced transiently. This might hypothetically be explained by either a direct effect on the permeability of the blood-brain barrier or indirectly via a decrease of metabolically active circulatory substances.