Safety and Efficacy of Endovascular Cooling and Rewarming for Induction and Reversal of Hypothermia in Human-Sized Pigs

Abstract

Background and Purpose— Numerous studies indicate that mild hypothermia provides substantial neuroprotection. However, current systems transfer insufficient heat to rapidly vary core temperature. We thus evaluated the safety and efficacy of endovascular cooling and rewarming for the induction and reversal of hypothermia. Methods— In 10 anesthetized pigs (weight, 66±2 kg), a heat-exchange balloon catheter was inserted into the inferior vena cava and used to cool to a core temperature of 32°C and then rewarm to normothermia. Control animals had 38°C saline infused. Venous blood was sampled before, during, and after cooling. Three animals in each group were killed 1 week later, and the lungs and inferior vena cava were removed for gross and microscopic examination. In 5 additional animals, cardiac output was measured during cooling to 32°C. Results— Body temperature in the hypothermic animals decreased at a rate of 4.5±0.4°C/h. Animals were subsequently rewarmed to 36.0±0.04°C at 2.5±0.2°C/h. There was no difference in heart rate between hypothermic and control animals, whereas systolic pressure decreased during cooling. Cardiac output was well maintained during cooling. There were no thermal effects on blood elements or blood vessels. Conclusions— The endovascular heat-exchange system effectively cooled and rewarmed pigs with large thermal mass without producing any adverse effects on blood elements, blood vessel integrity, or cardiovascular function.