Application of normothermic cardiac arrest algorithms to hypothermic cardiac arrest in a canine model

Background: International guidelines (2000) do not recommend vasopressor and antiarrhythmic medications during ventricular fibrillation (VF) with a core temperature below 30 °C. The efficacy of normothermic AHA algorithms using standard doses of epinephrine (EPI) (adrenaline) followed by amiodarone (AMIO) in hypothermic VF is uncertain. Objectives: To determine the effects of EPI followed by the combination of EPI/AMIO in the treatment of VF in a canine model of severe hypothermia. Methods: An un-blinded, placebo controlled experiment using 21 mechanically ventilated dogs. Coronary perfusion pressure (CPP), temperature, and electrocardiogram (ECG) were monitored. Animals were cooled to 22 °C or the onset of spontaneous VF. VF was induced if necessary. Animals in the treatment group received EPI (0.01 mg/kg IV) and defibrillation. This was followed by EPI (0.01 mg/kg IV), AMIO (10 mg/kg IV) and defibrillation if there was no sustained return of spontaneous circulation (ROSC) for 15 min. Results: Mean CPP in the treatment group increased after the administration of EPI/AMIO (24.7 ± 13.3 mmHg to 46.6 ± 7.7 mmHg, p < 0.004). Cumulatively, the administration of EPI followed by EPI/AMIO achieved ROSC after defibrillation in 10 of 11 animals compared to 3 of 10 in the control group (91% versus 30%, n = 21, p = 0.0075). Conclusions: In this model of severe hypothermia, the use of standard 2000 protocols for VF resulted in a significant increase of CPP, and, a higher ROSC rate compared to placebo controls. This study suggests that AHA normothermic algorithms may be beneficial in severe hypothermia.