OBJECTIVE: This study was undertaken to assess the acute safety and feasibility of rapidly inducing, maintaining, then reversing hypothermia using a novel heat transfer catheter and a closed-loop automatic feedback temperature control system to overcome limitations imposed by current clinical practices used for perioperative cooling and warming.
METHODS : Six swine (mean mass, 53.8 ± 3.6 kg) were studied. The heat transfer catheter was placed in the inferior vena cava via the femoral vein. Hypothermia to 32°C was induced, maintained for 6 hours, then reversed to 36°C. The time needed to induce and reverse hypothermia was recorded via continuous temperature monitoring of the lower esophagus, cerebrum, and rectum. Electrocardiography provided continuous monitoring, and blood draws were made at baseline and at 2-hour intervals. Examination of the catheter in situ was performed after the animals were killed.
RESULTS : Cooling from 36.2 to 32.0°C was rapid and uniform (mean, 7.3 ± 0.7°C/h), with animals reaching the target temperature within 60 minutes. Rewarming was also easily controlled, with animals’ temperatures reaching 36°C within 130 minutes. No arrhythmia was observed, and all hematological variables were within the normal range for swine. There was no evidence of hemolysis or platelet changes. Little to no thrombosis was observed.
CONCLUSION : The data presented here suggest that rapid induction and reversal of hypothermia are technically possible using a core intravenous cooling catheter; this method would provide a safe, rapid, and exquisitely reproducible way to induce hypothermia with subsequent restoration of normothermia.