Abstract P110: Exploratory Study on Mechanism by Which Hypothermia Improves Outcomes of Cardiopulmonary Resuscitation

Abstract

Introduction : In an earlier report, our group demonstrated that when head cooling was started during CPR, outcomes were improved. We had also reported in a series of studies the adverse effects on ultimate outcomes of adrenergic amines, both á 1 and âadrenergic agonists and improved outcomes withá 1 and âadrenergic blockades. We therefore hypothesized that the benefits of rapid head cooling may at least in part relate to reduced adrenergic stimulation. In a small exploratory study, we therefore measured endogenous plasma concentration of norepinephrine. Methods: Pilot studies were conducted in 7 domestic male pigs weighing 40±5 kg. After 15 minutes of untreated ventricular fibrillation, in 4 animals head cooling was induced with a Rhino Chill device coincident with start of CPR. An additional 3 animals served as identically treated controls without hypothermia. CPR was continued for 5 minutes in both group prior to defibrillation. Endogenous plasma norepinephrine levels were measured at baseline and 5 minutes after start of CPR. Results: None of the control animals were successfully resuscitated, in contrast to 3 of 4 brain cooled animals. Jugular vein temperature was reduced from 38.0°C to 37.0°C in brain cooled animals ( P <0.001). Endogenous norepinephrine levels were greatly increased in comparing to baseline levels and was significantly less in brain cooled animals (153 vs 381 μg/L, P <0.05) Conclusions: The mechanism by which rapid head cooling improves outcome of resuscitation may, at least in part, relate to inhibition of the adverse effects of endogenous adrenergic stimulation.