Brain histology, blood-brain barrier and brain water after normothermic and hypothermic cardiopulmonary bypass in pigs.

The effect of hypothermia during cardiopulmonary bypass (CPB) on cerebral histopathology, blood-brain barrier permeability to serum proteins and water content was evaluated. Pigs were subjected to non-pulsatile CPB for 2 h at either normothermia or hypothermia, and a group of anaesthetised pigs served as normothermic controls. The histopathology was assessed on paraffin embedded sections. The permeability of the cerebral vessels was studied by immunocytochemical demonstration of extravasated serum proteins. The cerebral water content was assessed by specific gravity measurements. The histological studies demonstrated hydropic degeneration of the brain parenchyma and perivascular swelling of the astrocytic endfeet throughout both white and gray matter in the normothermic CPB group. Similar changes were not encountered during hypothermic CPB, which suggests a beneficial effect of decreased temperatures on brain tissue during CPB. Neither normothermic nor hypothermic CPB induced significant changes in the cerebrovascular permeability or in the specific gravities.