AUTHOR=Filseth Ole Magnus , Hermansen Stig Eggen , Kondratiev Timofei , Sieck Gary C. , Tveita Torkjel 

TITLE=Cooling to Hypothermic Circulatory Arrest by Immersion vs. Cardiopulmonary Bypass (CPB): Worse Outcome After Rewarming in Immersion Cooled Pigs

JOURNAL=Frontiers in Physiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2022.862729

DOI=10.3389/fphys.2022.862729

ISSN=1664-042X

ABSTRACT=<sec><title>Introduction</title><p>Cooling by cardiopulmonary bypass (CPB) to deep hypothermic cardiac arrest (HCA) for cardiac surgical interventions, followed by CPB-rewarming is performed on a routine basis with relatively low mortality. In contrast, victims of deep accidental hypothermia rewarmed with CPB generally have a much worse prognosis. Thus, we have developed an intact pig model to compare effects on perfusion pressures and global oxygen delivery (DO<sub>2</sub>) during immersion cooling versus cooling by CPB. Further, we compared the effects of CPB-rewarming between groups, to restitute cardiovascular function, brain blood flow, and brain metabolism.</p></sec><sec><title>Materials and Methods</title><p>Total sixteen healthy, anesthetized juvenile (2–3 months) castrated male pigs were randomized in a prospective, open placebo-controlled experimental study to immersion cooling (IMM<sub><italic>c</italic></sub>, <italic>n</italic> = 8), or cooling by CPB (CPB<sub><italic>c</italic></sub>, <italic>n</italic> = 8). After 75 minutes of deep HCA in both groups, pigs were rewarmed by CPB. After weaning from CPB surviving animals were observed for 2 h before euthanasia.</p></sec><sec><title>Results</title><p>Survival rates at 2 h after completed rewarming were 4 out of 8 in the IMM<sub><italic>c</italic></sub> group, and 8 out of 8 in the CPB<sub><italic>c</italic></sub> group. Compared with the CPB<sub><italic>c</italic></sub>-group, IMM<sub><italic>c</italic></sub> animals showed significant reduction in DO<sub>2</sub>, mean arterial pressure (MAP), cerebral perfusion pressure, and blood flow during cooling below 25°C as well as after weaning from CPB after rewarming. After rewarming, brain blood flow returned to control in CPB<sub><italic>c</italic></sub> animals only, and brain micro dialysate-data showed a significantly increase in the lactate/pyruvate ratio in IMM<sub><italic>c</italic></sub> vs. CPB<sub><italic>c</italic></sub> animals.</p></sec><sec><title>Conclusion</title><p>Our data indicate that, although global O<sub>2</sub> consumption was independent of DO<sub>2</sub>, regional ischemic damage may have taken place during cooling in the brain of IMM<sub><italic>c</italic></sub> animals below 25°C. The need for prolonged extracorporeal membrane oxygenation (ECMO) should be considered in all victims of accidental hypothermic arrest that cannot be weaned from CPB immediately after rewarming.</p></sec>