Aspects of experimental cooling and rewarming with special reference to accidental hypothermia

Abstract

Methods and aims We performed open, randomized, placebo-controlled experimental studies in intact, anesthetized pigs with the following main aims: Paper 1 To describe in detail the hemodynamic function with emphasis on left ventricular contractility during surface cooling, steady state severe hypothermia at 25°C, surface rewarming and in the post-hypothermic period of 2 h. Paper 2 1) To investigate the pharmacokinetic properties of DA in normothermia and hypothermia. 2) To carry out a detailed analysis of the cardiovascular response to incrementing dosages of dopamine (DA) at core body temperatures at normothermia, at steady state hypothermia at 25°C, and during rewarming in the temperature span of 30 - 34°C. Paper 3 To compare differences between immersion cooling and cooling by cardiopulmonary bypass (CPB) in cardiovascular function and global delivery and consumption of oxygen i) during cooling until deep hypothermic circulatory arrest; ii) during rewarming by CPB; and iii) during the 2 h post-hypothermic period following weaning from CPB.

Main results and conclusions Surface cooling, followed by surface rewarming, resulted in a mild post-hypothermic systolic cardiac failure that was well compensated for. Diastolic function was unaffected (Paper 1). Pharmacokinetics of DA was seriously altered at 25°C and DA did not increase cardiac output, but had the adverse effects of increased systemic vascular resistance (Paper 2). Immersion cooling to hypothermic circulatory arrest, followed by rewarming taking place on CPB, resulted in severe and uncompensated cardiovascular failure not encountered in CPB-cooled animals (Paper 3).