Abstract 48: Reduction of Histological Damage with Mild Therapeutic Hypothermia after Prolonged Cardiac Arrest
Purpose: The aim of our study was to assess the effect of hypothermia on histological damage in 19 brain regions after prolonged cardiac arrest in pigs.
Methods: Pigs were anaesthetized and mechanically ventilated. After stabilisation of pulmonary artery temperature (Tpa) at 38.5±0.2 °C, ventricular fibrillation (VF) was induced and 10 min of untreated VF were followed by 8 min of cardiopulmonary resuscitation (mechanical chest compressions, two doses of vasopressin 0.4 IE/kg). At 8 min of CPR, up to 3 countershocks were delivered. Pigs that had return of spontaneous circulation (ROSC) were randomized to one of 2 groups (control, hypothermia). Pigs in the hypothermia group were cooled to Tpa 33.0±1.0 °C with a surface cooling device (LRS Thermosuit™) circulating ice water over most of the skin surface. Pigs in the control group were kept at 38.5±1.0 °C throughout the experiment. After 14 hours of hypothermia, pigs were rewarmed, weaned and brought to the stable. At day 9 of the experiment, final neurologic examination was performed. After that the animals were sacrificed and perfused with 4 liters of saline, followed by 1 liter of paraformaldehyde (3%, pH 7.4). The brain was removed and 19 different regions of the brain were examined by means of lightmicroscopy using a histopathologic damage score that was used in previous studies. Following damage qualities were considered: edema, eosinophilic necrosis (oncosis), vacuolar degeneration and malacia. The total numeric histological damage score (HDS) was the sum of all area scores. Data are presented as median and interquartile range, group comparison was done with a Mann-Whitney-U test.
Results: 16 (29 –35 kg) pigs were randomized. The time to reach target temperature in the hypothermia group (n = 8) was 9.0 (5.3; 11.9) min. Total HDS in the hypothermia group was 71 (61; 84), in the control group 132 (124; 174; p<0.001). Significant (p<0.05) improvements in damage were found in hippocampus, temporal, parietal, frontal and occipital cortex.
Conclusions: Histological damage after prolonged cardiac arrest was improved significantly in cooled animals compared to control animals. Not all brain regions could benefit to the same extent.