Abstract 180: Mild Systemic Hypothermia Induced by Preferential Brain Cooling Suppresses Cardiovascular Functions More Significantly Than That Induced by Systemic Cooling in a Rabbit Model
Introduction: The optimal target temperature for preferential brain cooling is unclear.
Hypothesis: Preferential brain cooling suppresses cardiovascular functions more significantly than systemic cooling with the same core body temperature (Tc) target of therapeutic mild hypothermia (TMH).
Methods: After anesthesia and instrumentation, five rabbits first received preferential brain cooling by using a semiconductor neck cooling collar starting from 37°C of Tc to the target of 34°C. Then after rewarming to 37°C of Tc by warming blanket, the animals received systemic cooling with the same Tc target by ice pads and fan. Another five rabbits first received systemic cooling, and then received neck cooling with the same procedures. Mean arterial pressure (MAP), heart rate (HR), left ventricular systolic pressure (LVSP), LV dp/dt, LV -dp/dt, respiratory rate (RR), PetCO2, brain temperature (Tb) and Tc were continuously monitored and recorded at 0.2°C interval of Tc during hypothermia in all animals. For monitoring Tb and Tc, thermoprobes were placed into brain parenchyma and rectum respectively. Paired t-test were used to compare measurements at 37°C and 34°C of Tc.
Results: During systemic cooling, Tb decreased in parallel with Tc. Only HR decreased significantly from 249±13 bpm at 37°C to 216±14 bpm at 34°C, P<0.001. No significant changes were detected in MAP, dp/dt, -dp/dt, LVSP, RR and PetCO2. In contrast, during neck cooling, Tb decreased 3.1±1.2°C more than Tc at 34°C of Tc. At meantime, MAP decreased significantly from 98±8 mmHg at 37°C to 84±7 mmHg at 34°C, P<0.001. HR, dp/dt, LVSP also decreased significantly, all p<0.01. RR, PetCO2 and -dp/dt did not change significantly. Pearson correlation analysis showed MAP was more closely related to Tb than to Tc, the coefficients were 0.539 (P<0.001) and 0.158 (P=0.002) respectively. Multiple linear regression analysis also showed a higher standardized coefficient of Tb than that of Tc for MAP (0.667 vs. -0.224), indicating that Tb has a greater effect on MAP than Tc.
Conclusions: Preferential brain cooling suppresses cardiovascular functions more significantly than systemic cooling when achieving the same core body temperature target of TMH. Brain temperature has a greater impact on MAP than core body temperature during TMH.
- © 2013 by American Heart Association, Inc.