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Mild Hypothermia After Cardiac Arrest in Dogs Does Not Affect Postarrest Multifocal Cerebral Hypoperfusion

Background and Purpose Although mild resuscitative hypothermia (34°C) immediately after cardiac arrest improves neurological outcome in dogs, its effects on cerebral blood flow and metabolism are unknown. Methods We used stable xenon-enhanced computed tomography to study local, regional, and global cerebral blood flow patterns up to 4 hours after cardiac arrest in dogs. We compared a normothermic (37.5°C) control group (group I, n=5) with a postarrest mild hypothermic group (group II, n=5). After ventricular fibrillation of 12.5 minutes and reperfusion with brief cardiopulmonary bypass, the ventilation, normotension, normoxia, and mild hypocapnia were controlled to 4 hours after cardiac arrest. Group II received (minimal) head cooling during cardiac arrest, followed by systemic bypass cooling (to 34°C) during the first hour of reperfusion after cardiac arrest. Results The postarrest homogeneous transient hyperemia was followed by global hypoperfusion from 1 to 4 hours after arrest, with increased “no-flow” and “trickle-flow” voxels (compared with baseline), without group differences. At 1 to 4 hours, mean global cerebral blood flow in computed tomographic slices was 55% of baseline in group I and 64% in group II (NS). No flow (local cerebral blood flow < 5 mL/100 cm3 per minute) occurred in 5±2% of the voxels in group I versus 9±5% in group II (NS). Trickle flow (5 to 10 mL/100 cm3 per minute) occurred in 10±3% voxels in group I versus 16±4% in group II (NS). Cerebral blood flow values in eight brain regions followed the same hyperemia-hypoperfusion sequence as global cerebral blood flow, with no significant difference in regional values between groups. The global cerebral metabolic rate of oxygen, which ranged between 2.7 and 4.5 mL/100 cm3 per minute before arrest in both groups, was at 1 hour after arrest 1.8±0.3 mL in normothermic group I (n=3) and 1.9±0.4 mL in still-hypothermic group II (n=5); at 2 and 4 hours after arrest, it ranged between 1.2 and 4.2 mL in group I and between 1.2 and 2.6 mL in group II. Conclusions After cardiac arrest, mild resuscitative hypothermia lasting 1 hour does not significantly affect patterns of cerebral blood flow and oxygen uptake. This suggests that different mechanisms may explain its mitigating effect on brain damage.