The effect of mannitol on cerebral blood flow

Abstract

✓ The effect of mannitol on cerebral blood flow was studied in anesthetized baboons, both at normal and raised intracranial pressure. At normal intracranial pressure, rapid intravenous infusion of mannitol (1.5 gm/kg in 10 min) led to a sharp transient rise in cerebral blood flow during and immediately after the period of infusion. This was associated with a reduction in cerebrovascular resistance and a variable change in cerebral metabolic rate (CMRO2). Other parameters measured did not change significantly. A similar response was seen during hypercapnia. Under conditions of raised intracranial pressure (supratentorial subdural balloon) mannitol infusion did not alter cerebral blood flow in three of four animals. In the remaining animal, however, a marked increase in blood flow occurred without any concomitant change in cerebral perfusion pressure. When a further infusion of mannitol was subsequently given to these animals while the intracranial pressure was artificially maintained, there was very little change in cerebral blood flow. The possible causes of the increase in cerebral blood flow at normal intracranial pressure and the clinical implications of these findings are discussed.