Serum Potassium Rate (PR) is a key indicator for medical management of patients with accidental hypothermia particularly for hypothermia related cardiac arrest (CA).

Experts recommend a cut-off value for PR of 12 mmol/l for all hypothermic victims and 8 mmol/l for avalanche casualties. Any patient presenting a PR lower than the cut-off value should be considered for Extracorporeal Rewarming. This therapeutic strategy is vital for patient survival.

However, there is no consensus about what type of vessels should be punctured in order to obtain an accurate potassium rate and what type of measurement technics should be used to measure this potassium rate.

The investigators hypothesize that potassium rate in these patients will differ by 1 mmol/l in blood samples collected from a peripheral vein in contrast to a central vein.

The investigators study is a prospective observational, multicentre study.

Inclusion Criteria:

• Hypothermia related cardiac arrest
• Age > 18 years
• Core temperature < 30° C measured in oesophagus at hospital admission

Exclusion Criteria:

• Age < 18 years
• Known condition of pregnancy or breastfeeding women
• Evidence of trauma-related cardiac arrest
• Cardiac arrest in which reanimation is not justified (frozen body, final stadium of an incurable disease, advance health care directive)