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 degrees 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 degrees 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.