Abstract 323: Intra-arrest Induction of Preferential Brain Cooling With Mild Systemic Hypothermia Does Not Correlate With Favorable Outcome in a Rabbit Model of Ventricular Fibrillation
Introduction: Recent reports suggested that poor clinical outcomes correlate with rapid cooling in cardiac arrest patients. The possible causes are unclear. We have now compared survival between intra-arrest induction of preferential brain cooling with mild systemic hypothermia and conventional surface cooling animals, and focused on the relationship between hemodynamics and brain temperature (Tb).
Methods: Untreated VF of 4 min and CPR of 4min were given to 24 rabbits prior to defibrillation. Animals were randomly assigned to (1) preferential brain cooling by a neck cooling collar initiated at beginning of CPR, (2) body surface cooling by ice pads and fan initiated at 30 min after ROSC, (3) spontaneous normothermia control. Core body temperature (Tc) and Tb were monitored by thermoprobes in rectum and brain parenchyma respectively. Mean aortic pressure (MAP), heart rate (HR), LV dp/dt, LV -dp/dt, and PetCO2 were continuously monitored. During 4 hrs of cooling, Tc was maintained between 33.5°C and 34.5°C by turning on/off the cooling regardless Tb. Cooling would also be paused if MAP is below 60 mmHg. Methods for control animals were identical except for cooling.
Results: Six of 8 animals in each group achieved ROSC and survived to 18±17, 17±18, and 21±23 hrs after ROSC respectively, P=0.921. First time pause of cooling due to low MAP only occurred in all 6 brain cooling animals. At first pause of cooling, Tb and Tc were 34.1±0.8°C and 33.5±0.2°C in body cooling animals, but were 29.2±1.3°C and 35.5±0.9°C in brain cooling animals respectively. MAP and HR in brain cooling animals were significantly lower than those in body cooling and control animals at 30min, and 60 min after ROSC (Table). Linear regression analysis showed that Tb but not Tc was the independent influential factor for MAP after ROSC.
Conclusions: Early induction of preferential brain cooling does not necessarily improve outcome after ROSC. Hypotension correlates with low Tb and warrants close monitoring and management.
- © 2013 by American Heart Association, Inc.