Abstract
Background: Therapeutic Hypothermia has been recommended by AHA to treat Out of Hospital Cardiac Arrest (OHCA) patients. Animal studies shown that the less time to reach target temperature (TT), the better the clinical outcome. Some animal experiments even suggested that there is an optimal time window that within which the TT should be reached for optimal outcome. In this pilot study, we developed a medical device to infuse a novel medical coolant, ice slurry which is a partially frozen saline, into the blood vessel to rapidly cool the brain. We aimed to evaluate the time to cool the brain temperature down to TT, which is 3°C below normal body temperature, in a swine model of OHCA protocol. Methods: Three Yorkshire swine between 40-50 kg were anesthetized. Bilateral temporal craniotomies were performed for placement of thermocouples at a depth of 1.25 cm for recording cortical temperatures. Two additional thermocouples were placed in esophageal and rectal for measuring the body temperature. A 9.5 French catheter was placed in the right femoral vein for ice slurry infusion. Ventricular fibrillation (VF) was induced by the occlusion of left anterior descending artery. After the onset of VF, there was a 3-minute stand-by followed by a 7-minute chest compression. Ice slurry infusion started at 10 minutes after the onset of VF. Ice slurry with a dosage of 50mL/kg body weight (up to 2L) was infused at constant flow rate while chest compression continues. Chest compressions continued throughout the slurry administration and for 3 minutes post infusion. Thermocouple data were recorded every second for offline processing. Results: In swine 1, 1970mL of ice slurry with 13% of ice fraction was infused into a 40kg pig at a flow rate of 120mL/min. The TT was reached at 22 minutes after the start of infusion. In swine 2 and 3, 2000mL of ice slurry with 25% of ice fraction was infused at 150mL/min into pigs with 49.7 kg and 41.7kg body weight, respectively. The TT were reached at 13min and 15min, respectively. Conclusions: Ice slurry infusion rapidly lowered the cortical temperature of young swine model in cardiac arrest. This rapid cooling method may meet the optimal time window suggested by animal experiment for dramatically improve the survival rate and neurologic outcome of OHCA.
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