Abstract 326: Temperature Distribution During Hypothermia Induction Depends on Cooling Method and Blood Flow

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Introduction: Animal research suggests that intra-arrest therapeutic hypothermia, cooling before return of spontaneous circulation (ROSC), may be more protective than inducing hypothermia after ROSC. Reduced blood flow should slow cooling rates, because the amount of blood flow will determine the amount of convective heat transfer. We hypothesize that intra-arrest cooling will result in significant temperature heterogeneity. Methods: 18 temperatures (7 brain, 4 surface, 7 thoracic and abdominal) were monitored in 75 domestic swine (~30 Kg) during hypothermia induction. Cooling technologies included: Control, femoral vein (FV) cold saline infusion, FV ice slurry infusion, carotid (CA) cold saline infusion, CA ice slurry infusion, nasopharyngeal cooling, heat exchange catheter cooling, and blanket cooling. Animals were assigned to three blood flow groups: normal circulation, cardiac arrest treated with mechanical chest compressions (CC), and untreated cardiac arrest. CC and hypothermia induction were started after ten minutes of untreated arrest. CC were performed at a rate of 100 cpm and a depth of 1.25”. For all flow states, the experiments were terminated after 60 min of cooling. Results: 18 Temperatures and cooling rates have been aggregated from 24 experimental groups with six reported time epochs per experiment, resulting in a data set that contains more than 4500 values. Initial analysis indicates that reductions in blood flow led to reduced cooling rates. The highest cooling rate in the right hemisphere of the brain during FV saline induction was -7.83 [[Unable to Display Character: ]]C/hr for normal flow, -4.47 [[Unable to Display Character: ]]C/hr for CPR, and -1.04 [[Unable to Display Character: ]]C/hr during no flow. Compartmentalization of cooling was observed during intra-CPR and intra-arrest cooling. Conclusions: Thermokinetics during intra-arrest cooling, even with ongoing CPR, is significantly different than post ROSC thermokinetics. Temperature heterogeneity increases the challenge of patient temperature monitoring, particularly for over-cooling. These data raise questions about how to optimize intra-arrest cooling.