Abstract 1777: Intra-Resuscitation Hypothermia Improves Short-Term Survival in Prolonged Porcine Ventricular Fibrillation
Introduction: Two human clinical trials of mild, induced hypothermia demonstrated improved survival and neurologic outcomes for ventricular fibrillation (VF) cardiac arrest. We sought to determine the effects of inducing hypothermia before the induction of VF (PRE group), and during resuscitation (DUR group), compared to normothermic controls (NORM group).
Hypothesis: We hypothesized that PRE and DUR groups would have improved rates of return of spontaneous circulation (ROSC) and short-term survival (20 minutes) when compared to NORM. Our secondary hypothesis was that quantitative ECG changes during VF would be least severe in the PRE group.
Methods: We instrumented 30 swine (23 to 30 kgs) under general anesthesia with ECG, esophageal temperature, and micromanometer-tipped aortic and right atrial catheters, then randomly assigned them to groups (n = 10 each). VF was electrically induced and untreated for 8 minutes. Hypothermia was induced by rapid IV infusion of ice-cold normal saline (30 mL/kg) five minutes before VF in the PRE group and at the start of resuscitation in the DUR group. The NORM group got 30 mL/kg of body-temperature saline at the start of resuscitation. After 8 minutes of VF and in all groups, 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 and post-ROSC norepinephrine use. ROSC and survival were analyzed with Fisher’s exact test.
Results: Pre-infusion temperatures did not differ. Temperatures at 8 and 13 minutes of VF were PRE = 34.8, 35.8, DUR = 38.3, 34.9, and NORM = 37.9, 37.9. ROSC occurred in 5/10 PRE, 7/10 DUR, and 4/10 NORM. Survival occurred in 5/10 PRE, 6/10 DUR and 3/10 NORM (DUR vs. NORM p = 0.30). Total fluid volumes did not differ between groups. Average post-ROSC norepinephrine use in PRE (0.75 mg) and DUR (1.0 mg) was lower than NORM (2.1 mg). PRE slowed the decay of the VF waveform.
Conclusions: Intra-resuscitation cooling doubled short-term survival compared to NORM. Delaying shocks in the PRE group may have worsened their outcomes.