Objective
Global cerebral edema is an independent risk factor for early mortality and poor outcome after SAH in humans. Little is known about time course and extent of brain edema evolution in the most widely used experimental SAH model, the rat filament model. We therefore investigated cerebral water content and brain swelling at various time points after SAH, investigating the course of CBF, ICP, evolution of cerebral edema and neurological deficits.
Method
42 rats were subjected to SAH by an endovascular filament. ICP and bilateral CBF were continuously recorded by a parenchymal probe and Laser Doppler flowmetry. Animals were randomly assigned to 3 control (1 h, 24 h, 48 h survival) and 3 SAH (1 h, 24 h, 48 h survival) groups (n=7 each). Brain water content was measured at the end of the observation time, neurological deficits at 24 h and 48 h after SAH.
Results
SAH resulted in an immediate increase of ICP up to ∼60 mmHg initially and ∼30 mmHg for the following 30 min without significant differences between these groups. In all groups the bilateral CBF fell by over 80% with partial recovery to 50–60% baseline after 30 min. The brain water content was significantly increased at 24 (SAH: 80.2±0.4% vs. control: 79.2±0.07%) and 48 hours (SAH: 79.8±0.2% vs. control: 79.3±0.07%) after SAH, primarily within the ipsilateral hemisphere. Neuroscore was significantly worse within the SAH groups 24 hours after SAH compared to controls (24 h SAH: 33±15 pts. vs. controls: 5±0 pts.), strongly correlating with extent of brain edema (r=0.96, p<0.001). There was no correlation between brain edema and ICP and bilateral CBF.
Discussion
Experimental SAH in rats, utilizing the filament model with puncture of the internal carotid artery, leads to mainly ipsilateral brain edema peaking 24 h after SAH, comparable with the situation in humans. Extent of brain edema showed strong correlation with resulting neurological deficits. The filament SAH model seems to be well suited to investigate early pathophysiological changes as brain edema formation.