Neuronal damage after hypothermic circulatory arrest and retrograde cerebral perfusion in the pig

Antegrade and retrograde cerebral perfusion during hypothermic circulatory arrest (HCA) has been reported to provide better brain protection during operation than hypothermic circulatory arrest alone. However, the efficacy of these techniques remains to be fully determined, especially when used for prolonged periods. We used a pig model to evaluate the histopathologic consequences of HCA and the potential benefit of cerebral perfusion during HCA.

Twenty-two pigs were divided into four groups and exposed to either anesthesia alone, 120 minutes of HCA (15 degrees C), 120 minutes of retrograde cerebral perfusion at 15 degrees C during HCA, or 120 minutes of antegrade cerebral perfusion at 15 degrees C during HCA, and then reperfused for 60 minutes under cardiopulmonary bypass at 37 degrees C. The brains were perfusion fixed at the end of the experiments and examined by light microscopy.

There were no morphologic changes in any areas of the brains in the anesthesia group, and very minor changes in some areas of the brains in the antegrade cerebral perfusion. group. Varying severity of neuronal damage was found in the brains of all the pigs in the HCA and retrograde cerebral perfusion groups. The severity of ischemic damage in the brain showed the following descending order: hippocampus (CA4), caudate nucleus, cerebral cortex, putamen, thalamus, Purkinje cells of the cerebellum, pons, and mesencephalic gray matter. In the hippocampus the order of damage was CA4, CA3, polymorphous layer of the dentate gyrus, prosubiculum, CA2, CA1, and granule cell layer of the dentate gyrus. The damage in the retrograde cerebral perfusion group was less severe relative to the HCA group in many areas (no significance except mesencephalic gray matter).

These results demonstrate that the pattern of neuronal damage in pigs subjected to HCA and retrograde cerebral perfusion differs from the traditional pattern in that the caudate nucleus and hippocampal CA4 region are the most vulnerable to ischemia-hypoxia. Our results also suggest that antegrade cerebral perfusion prevented ischemic damage to the brain and retrograde cerebral perfusion provided some protection but moderately severe damage occurred.