Changes in cerebral blood flow due to infusion of hyperosmolar solutions are of considerable importance in states of raised intracranial pressure. The present study was aimed to evaluate the effects of
mannitol on the cerebral microcirculation, in a model of
vasogenic brain edema. A right fronto-parietal
craniotomy was performed in 30 adult Sprague-Dawley rats. Vasogenic
edema was produced by placing
dry-ice over the dura for 1 min. The cortical blood flow was monitored for 120 min using a
laser-Doppler
flowmeter (
Perimed, Stockholm, Sweden), and graphics were recorded using a personal computer. Animals were randomly divided into three groups: group 1 (control group) received no
mannitol; group 2 was treated with a bolus injection of 20%
mannitol (1 mg kg-1); group 3 received the same dose over a 30 min infusion. Mean blood pressure, temperature, and respiratory rate were continuously monitored. At the end of the procedure, an
intravenous injection of
Evan's blue 2% was given. Results were compared by using repeated measures of analysis of variance and a two-sample t-test at each time. After the production of a cryogenic injury, we found a marked decrease in the cerebral blood flow, whereas
mannitol partially reversed that effect. There was not significant difference between groups 2 and 3; however, there was a significant difference between
mannitol and control groups after 15 min. During the early phase of vasogenic
edema, early use of
mannitol did not increase the blood flow, but stabilized it, preventing further decrease.
Laser-Doppler flowmetry is a valuable method for continuous estimation of hemodynamic changes in the cerebral microcirculation.