Hypothermia (core temperature ≤35°C) is a frequent and life-threatening complication after mountain accidents, near-drowning, and intoxications, and can provoke arrhythmia, reduced cardiac contractility, and cardiac arrest. The hypothermic heart may be insensitive to defibrillation with a core temperature <30°C. Also, below <30°C after successful defibrillation, a perfusing rhythm often degenerates to ventricular fibrillation (VF) again. Repeated defibrillation can induce myocardial injury. Thus, the guidelines of the European Resuscitation Council (ERC) suggest delaying further defibrillation attempts until the core temperature is >30°C if VF persists after 3 shocks. Epinephrine should be withheld if core temperature is <30°C. Advanced Life Support (ALS) guidelines of the American Heart Association (AHA) state that it may be reasonable to perform further defibrillation attempts according to the standard algorithm and to consider administration of a vasopressor during cardiac arrest (Table 1). This discrepancy between ERC and AHA guidelines can be explained by the different interpretations of mainly animal data, which show that vasopressors increase the chances of successful defibrillation <30°C, defined as return of spontaneous circulation (ROSC) for at least 30 seconds. The guidelines of the Wilderness and Environmental Medicine Society (WMS) state that a single shock at a maximum power can be given for patients with a temperature <30°C.

The aim of this study is to evaluate clinical course of hypothermic patients(<30°C) undergoing defibrillation. The primary aim is to evaluate the success ratio of defibrillation, defined as ROSC for at least 30 seconds. Secondary aims are the recurrence rate of ventricular fibrillation, the number of defibrillation attempts per patient, the presence of cardiac dysfunction after defibrillation and the cerebral performance category (CPC) score at the end of hospitalization.

Inclusion Criteria:

- patients of the International Hypothermia Registry with a defibrillation while having a body core temperature equal or less than 30°C

Exclusion Criteria:

• patients of the International Hypothermia Registry with a body core temperature >30°C
• patients who refused to participate

Patients with accidental hypothermia and a body core temperature equal or less than 30°C who had one or more defibrillation attempts