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

Abstract

IntroductionCooling 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 (DO2) 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.Materials and MethodsTotal sixteen healthy, anesthetized juvenile (2–3 months) castrated male pigs were randomized in a prospective, open placebo-controlled experimental study to immersion cooling (IMMc, n = 8), or cooling by CPB (CPBc, n = 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.ResultsSurvival rates at 2 h after completed rewarming were 4 out of 8 in the IMMc group, and 8 out of 8 in the CPBc group. Compared with the CPBc-group, IMMc animals showed significant reduction in DO2, 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 CPBc animals only, and brain micro dialysate-data showed a significantly increase in the lactate/pyruvate ratio in IMMc vs. CPBc animals.ConclusionOur data indicate that, although global O2 consumption was independent of DO2, regional ischemic damage may have taken place during cooling in the brain of IMMc 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.

Functional recovery after accidental deep hypothermic cardiac arrest: Comparison of different cardiopulmonary bypass rewarming strategies

“…Extravasation of plasma fluid takes place during normothermic CPB as well as during cooling with intact circulation ( Tveita et al, 1996b ; Hammersborg et al, 2005 ), but increases significantly during hypothermic CPB ( Heltne et al, 2001 ; Farstad et al, 2003 ; Farstad et al, 2005 ; Hammersborg et al, 2005 ). In a recent animal experiment ( Filseth et al, 2022 ), we reported that significantly more fluid volume was needed to achieve adequate perfusion during CPB rewarming from accidental hypothermia over that required in animals after hypothermic cardiac surgery. The results of the present study demonstrated that the need for vascular volume replacement during CPB rewarming was similar between groups, irrespective if terminated during rewarming at 30°C or at 36°C.…”

“…We previously reported the detailed methods for blood flow measurements using this porcine animal model ( Filseth et al, 2022 ). Briefly, a number of 1,000,000, 15 μM diameter fluorescent polystyrene microspheres (Molecular Probes, Eugene, OR, United States) were ultrasonicated, vortex-mixed and injected into the left ventricle (spontaneous circulation) or in the arterial line (cardiopulmonary bypass) four times in different colors (orange [excitation/emission wavelengths: 540/560 nm], yellow-green [505/515 nm], blue-green [430/465 nm], crimson [625/645 nm] and red [580/605 nm]) during the experiment: At baseline, during cooling at 30°C (bladder), during rewarming at 30°C (bladder), and at the end of experiment 2 h after rewarming to 36°C (bladder).…”

Cerebral Hemodynamic Changes Associated with Neuroinflammation under Seawater Immersion Hypothermia

“…The thermal conductivity of seawater is much higher than that of air. Hence, the core body temperature drops rapidly after a sea fall, leading to acute hypothermia and cold shock response, and causing a series of pathophysiological changes, such as rapidly reducing cerebral blood ow rate, increasing the risk of syncope, and aggravating primary injury [7][8][9][10].…”