Global cerebral ischemia: Effects of pentastarch after reperfusion

There has been considerable interest in the use of synthetic hydroxyethyl starch macromolecules (e.g., pentastarch, a colloid used for intravascular fluid replacement) to reduce microvascular permeability and reperfusion injury after cerebral ischemia. A recent report found that hemodilution with pentastarch reduced brain injury and cerebral edema after temporary focal ischemia. We compared the effects of pentastarch versus 0.9% saline on brain edema after reperfusion in a model of temporary global ischemia in halothane- anesthetized rabbits. To ensure the validity of our model, we studied an additional group of animals in which we deliberately raised plasma osmolality with hypertonic saline (1.5%) in the expectation of finding a decreased brain water content at the conclusion of the experiment. Animals were hemodiluted to a hematocrit of 20% with normal saline (control group) (n = 9), pentastarch (n = 7), or hypertonic saline (n = 5). After hemodilution, the animals underwent a 25-min period of global cerebral ischemia, followed by 180 min of reperfusion. The animals were then killed and brain water content was assessed by microgravimetry and by the wet-dry weight method. As anticipated, colloid osmotic pressure was maintained in the pentastarch group, and plasma osmolality became significantly increased in the hypertonic saline group. There were no intergroup differences at any time for central venous pressure, mean arterial pressure, intracranial pressure, or PaCO₂. Brain water content was significantly decreased in the hypertonic saline group. No difference in brain water content was detected between the control group and the pentastarch group. In this model of global cerebral ischemia, no decrease in brain water content could be associated with the administration of pentastarch.