Isolated experiments suggest that global
cerebral edema is a sequela of large hemispheric ischemic lesions, presumably as an extension of the initial ischemic insult into areas of vital, noninjured tissue.
Diuretics and osmotic agents are controversial and poorly defined therapeutic modalities after large
infarction. By using a rat model of
middle cerebral artery occlusion (MCAO), we tested the hypothesis that significant
edema occurs in the contralateral uninjured hemisphere and that this postischemic complication can be manipulated by hypertonic saline
therapy.
DESIGN: Prospective laboratory animal study.
SETTING: Research laboratory in a teaching hospital.
SUBJECTS: Under controlled conditions of normoxia, normocarbia, and normothermia, rats were subjected to 2 hrs of MCAO.
MEASUREMENTS AND MAIN RESULTS: Adequacy of MCAO and reperfusion was assessed by
laser Doppler flowmetry. All animals except naive rats received continuous infusion of
0.9% saline at 0.5 mL/hr throughout the experiment. Brains were harvested, and tissue water content was estimated by comparing the wet-to-dry weight ratios of ipsilateral and contralateral cerebral hemispheres at 12 hrs, 24 hrs, or 2, 3, or 7 days postischemia. Naive and
sham-operated rats served as control cohorts. In a second series of randomized experiments, wet-to-dry weight ratios were determined in rats treated with continuous
intravenous infusion of 7.5% hypertonic saline (0.5 mL/hr;
acetate/
chloride, 50:50) and were compared with well-studied antiedema
therapy: 20%
mannitol (2.5 g/kg bolus every 6 hrs) or
furosemide (2.5 mg/kg bolus every 6 hrs). Treatments were started at 24 hrs of reperfusion, and brain water was assessed at 2 days of reperfusion. In a third series of experiments, wet-to-dry ratios were determined in brains harvested at 2 days of reperfusion from rats that were subjected to 2 hrs of MCAO and did not receive any intravenous fluids. All values are mean +/- SEM. There were no differences between
sham-operated and naive control cohorts. At 24 hrs of reperfusion, water content was higher in both ipsilateral ischemic (82.80 +/- 0.86%) and contralateral hemispheres (80.53 +/- 0.29%), compared with naive animals (ipsilateral, 79.62 +/- 0.12%; contralateral, 79.53 +/- 0.13%). Maximal
cerebral edema was measured at 2 days in both hemispheres (ipsilateral, 83.94 +/- 0.47%; contralateral, 80.63 +/- 0.13%).
Edema was present for up to 3 days in contralateral tissue (80.27 +/- 0.26%) and persisted to 7 days in the injured hemisphere (81.07 +/- 0.34%). Maximal
edema (as assessed at 2 days postocclusion) was robustly attenuated with hypertonic saline
therapy (ipsilateral, 81.59 +/- 0.52%; contralateral, 78.44 +/- 0.22%). The efficacy of hypertonic saline was equivalent to
furosemide (ipsilateral, 82.09 +/- 0.50%; contralateral, 79.13 +/- 0.17%) but less robust than
mannitol (ipsilateral, 79.89 +/- 0.36%; contralateral, 78.73 +/- 0.17%).
CONCLUSIONS: