At what body temperature do I start administering epinephrine (Epi) and performing cardioversions in a patient with hypothermic ventricular fibrillation (Vfib)?

From the Guidelines

In hypothermic ventricular fibrillation (VFib), withhold epinephrine (adrenaline) and defibrillation attempts until the patient's core temperature reaches at least 30°C (86°F). This approach is based on the 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care 1. The guidelines suggest that defibrillation should be attempted if VT or VF is present, but the value of deferring subsequent defibrillations until a target temperature is achieved is uncertain.

Key Considerations

• The hypothermic heart may be unresponsive to cardiovascular drugs, pacemaker stimulation, and defibrillation, although recent animal investigations have challenged this conventional wisdom 1.
• Drug metabolism may be reduced, and there is a theoretical concern that medications could accumulate to toxic levels in the peripheral circulation if given repeatedly to the severely hypothermic victim 1.
• A meta-analysis of animal studies found that vasopressor medications, such as epinephrine or vasopressin, increased rates of return of spontaneous circulation (ROSC) when compared with placebo 1.

Management Approach

• Focus on aggressive active core rewarming techniques as the primary therapeutic modality, while providing high-quality CPR.
• Once the patient is warmed to a temperature of at least 30°C, epinephrine may be administered, although at longer intervals than normal (every 6-10 minutes rather than every 3-5 minutes).
• For defibrillation, deliver one shock when the temperature is above 30°C, then focus on continued warming if unsuccessful.
• Additional defibrillation attempts should be limited until the patient reaches 35°C (95°F), as the cold myocardium is more resistant to defibrillation, and repeated unsuccessful shocks may cause further myocardial damage 1.

From the Research

Hypothermic Ventricular Fibrillation Treatment

• The administration of epinephrine (Epi) and performance of cardioversions in patients with hypothermic ventricular fibrillation (Vfib) is a complex topic, with various studies providing insights into the optimal approach 2, 3, 4, 5.
• According to the study by 3, defibrillation can be effective even at low core temperatures, with a reported case of successful defibrillation at a core temperature of 30°C.
• Another study 2 suggests that defibrillation attempts may be reasonable in severely hypothermic patients, despite current guidelines to the contrary, with a reported case of successful defibrillation at a core temperature of 18.2°C.
• The study by 4 found that successful pre-rewarming resuscitation after hypothermic cardiac arrest is possible, with defibrillation being successful in four out of five patients with a shockable rhythm.
• Factors associated with successful resuscitation before rewarming include a higher core body temperature, with a prognostic threshold of 24.6°C, as reported by 5.
• The American Heart Association and European Resuscitation Council guidelines have discrepancies regarding pre-rewarming defibrillation, as noted by 4.
• Overall, the evidence suggests that defibrillation and epinephrine administration can be considered in patients with hypothermic Vfib, even at low core temperatures, but the optimal approach may depend on various factors, including the patient's core temperature and the presence of a shockable rhythm 2, 3, 4, 5.

Core Temperature Thresholds

• A core temperature of 30°C has been reported as a threshold for successful defibrillation in hypothermic patients 3.
• A core temperature of 24.6°C has been identified as a prognostic threshold for successful resuscitation before rewarming 5.
• Defibrillation attempts have been successful at core temperatures as low as 18.2°C, as reported by 2.

Administration of Epinephrine

• The response rate to adrenaline (epinephrine) was reported as normal in six patients with hypothermic cardiac arrest, as noted by 4.
• The effect of epinephrine administration under 30°C was investigated by 4, but no statistically significant differences were found between survivors and non-survivors.