Hypothermia, defined as unintended drop in core temperature < 35°C, is one of cardiac arrest causes which have been proven to be reversible. Hypothermia is one of “Hs” in universally accepted “4Hs + 4Ts” algorithm. Hypothermia however has one major advantage over the remaining “Hs” and all “Ts.” Not only when early diagnosed and appropriately treated it may change the outcome of resuscitation, but it additionally increases chances of both survival as well as avoidance of ischaemic encephalopathy. Each 1°C of drop of body temperature below norm causes decrease of brain metabolism by 6–10% [1]. Hypothermia affects almost all cell damage mechanisms caused by hypoxia, by preventing their activation or interrupting them on early stage of apoptosis [2]. Intended, induced and controlled hypothermia is increasingly more often used in all these situations in which neuroprotective effect is desired. In emergency care the rule “No one is dead until warm and dead” exists. This phrase, however, proves right under a condition: hypothermia may show its protective action only if it occurs before cardiac arrest. Secondary hypothermia, which develops e.g. during resuscitation in cold environment, not only does not provide neuroprotection, but may be an obstacle in attempts to restore circulation. If however cardiac arrest occurs during cooling of the body or is a direct effect of it, the neurological prognosis is good – provided of course that circulation is restored. The longest reported resuscitation of hypothermic patient resulting in return of spontaneous circulation, restoring of consciousness and full neurological capabilities, endured for over 6.5 hours [3]. This and other reported cases prove that hypothermia may the most optimistic of “4Hs and 4Ts.”

Unfortunately, it happens in practice that all hopes related to hypothermia become ruined. The usual reason for this is lack of diagnostic sensitivity. Hypothermia is one of the least frequent reversible causes of cardiac arrest listed in “4Hs and 4Ts.” What is partially understandable, more attention is given to hypoxia, hypovolaemia or thromboembolisms, while hypothermia is considered a mostly theoretical issue. It also happens that overcome with first impression we consider a hypothermic patient to be dead, after only a superficial, imprecise examination and no resuscitation attempt is made.