Short period of mild hypothermia improves resuscitation outcome in a porcine model of prolonged ventricular fibrillation

Abstract

Objective To investigate the resuscitation outcome after a short period of mild hypothermia in porcine model of prolonged ventricular fibrillation (VF). Methods Fourteen male healthy domestic swine weighting 34 to 36 kg were used. VF was induced electrically and maintained untreated for 11 mins, followed by manual cardiopulmonary resuscitation (CPR) procedure. Two investigators initiated chest compression and bag-valve mask ventilation in pattern of 2 min rotation. A biphasic wave of 120 J electric defibrillation (ED) was attempted 6 mins after CPR. If there was no return of spontaneous circulation (ROSC), CPR was restored and ED was delivered when necessarily. Resuscitation was considered unsuccessful if absence of ROSC for 12 mins. However, if ROSC occurred, animals were randomly(random number) diveded into normothermia (NT) group and hypothermia treatment (CH) group. Animals in CH group were immediately cooled by using intravenous infusion of ice-cold saline and surface cooling. Core temperature was reduced to 32-34 degrees centigrade within 120 mins and maintained at this level for 2 h. Active rewarming was completed within 2 h until baseline body temperature was reached. Data of hemodynamic variables, blood-gas analysis and blood lactate before VF of two groups were recorded. Meawhile, cardiac output (CO), heart rate and Tc after ROSC were recorded. Neurological defect scores (NDS) were evaluated every 24 h until 96 h after ROSC. Variables were compared using either Fisher test or repeated measures analysis of variance, followed by Bonferroni for multiple comparisons. A two-sided P value<0.05 was regarded statistically significant. Results There was no significant difference in body weight, mean arterial pressure, CO, pH, pressure of end-tidal carbon dioxide (ETCO2) and lactate between groups before VF. In the period of CPR, there were also no significant difference in total resuscitation time, first shock success rate, ROSC rate, shock ROSC rate, total number of shock and doses of epinephrine. However, animals in CH group survived longer time than that in NT groups [（96.00±0.00)h vs (49.71±43.65)h,P=0.031]. Meanwhile, the survival rate of 96 h was significantly higher in CH than that in NT (P<0.05). For neurological function, there was a obviously better NDS in CH group than that in NT group within ROSC 96 h (P<0.05). Conclusion Even a short duration of 2 hour mild hypothermia could improve resuscitation outcome in porcine model of 11 minute VF. Key words: Cardiopulmonary resuscitation; Mild hypothermia; Short duration; Resuscitation outcome