Abstract 4: Inducing Hypothermia During Resuscitation Improves Return Of Spontaneous Circulation In Prolonged Porcine Ventricular Fibrillation

Abstract

Introduction: Induced hypothermia has been shown to improve survival and neurologic outcomes for ventricular fibrillation (VF) cardiac arrest. Clinical studies have not begun inducing hypothermia until after return of spontaneous circulation (ROSC). The effects of cooling during the resuscitation are not well-studied. Hypothesis: We hypothesized that inducing hypothermia at the start of resuscitation would increase the rates of ROSC and short-term survival (20 minutes) in an established porcine model of prolonged VF. We compared intra-resuscitation hypothermia (IRH) with a normothermic control group (CTL). Methods: We anesthetized and instrumented 28 domestic swine (mean mass 26.5 ±2.4 kgs) with ECG, esophageal temperature, and micromanometer-tipped aortic and right atrial catheters. We then randomly assigned them to IRH and CTL groups (n= 14 each). VF was electrically induced and untreated for 8 minutes. Then resuscitation was begun with mechanical chest compression and ventilation. Hypothermia was induced by rapid IV infusion of ice-cold normal saline (30 mL/kg) at the beginning of resuscitation in the IRH group. The CTL group got 30 mL/kg of body-temperature saline at the start of resuscitation. After 8 minutes of VF, two minutes of CPR was followed by delivery of drugs (epinephrine 0.1 mg/kg, vasopressin 40 U, and propranolol 1.0 mg) and 3 more minutes of CPR (first rescue shock at 13 minutes of VF). ROSC (systolic BP above 80 mmHg for one minute continuously) and survival were recorded, as was total fluid given and hematocrits. Temperatures are reported in degrees C. Rates were compared with 2-tailed Fisher’s exact test, with alpha=0.05. Results: Baseline temperatures at 8 minutes VF did not differ (IRH=37.9° and CTL=37.7°). Post-infusion temperatures at 13 minutes of VF were IRH=34.9° and CTL=37.9°. ROSC occurred in 12/14 (86%) IRH animals and in 6/14 (43%) CTL, with p=0.046. Survival occurred in 8/14 (57%) IRH animals and 4/14 (36%) CTL, with p=0.15. Total fluid volumes given and hematocrits did not differ between groups. Conclusions: IRH doubled the rate of ROSC compared to CTL. There was a non-significant 58% relative improvement in short-term survival. In this porcine model, rapid infusion of ice-cold saline quickly cooled during resuscitation.