British journal of anaesthesia
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In two groups of anaesthetized dogs, with (n = 28) or without (n = 28) induced intracranial hypertension, we compared the effects on intracranial pressure (ICP) of the rapid administration of mannitol 2 g kg-1 i.v. at PaCO2 2.7, 4.0, 5.3, and 6.7 kPa (n = 7). In dogs with no induced intracranial hypertension, ICP increased during the administration of mannitol, reached a peak at 2 min after infusion, and then gradually decreased (P less than 0.05). More marked changes in ICP were observed in response to higher values of PaCO2 (P less than 0.05). ⋯ This was followed by a more gradual decrease which achieved pre-balloon inflation values 10 min after infusion. We postulate that the absence of the initial increase in ICP is the result of a concomitant decrease in arterial pressure, a reduction in the volume-pressure response of the brain, the failure of mannitol to dilate further the cerebral arterial vascular bed and a hitherto unnoticed early water-drawing effect. Our study confirmed the safety of rapidly expanding the circulating blood volume with mannitol in circumstances of increased ICP in dogs.