Fundamental aspects of hypothermia
The research on hemostasis in the setting of hypothermic reveals inconsistent, even conflicting results, ranging from seasonal increase in thromboembolic disease in winter to excessive surgical bleeding in hypothermic patients.
The effects of hypothermia [
20] on coagulation and platelet function is influenced by
the actual body temperature during sampling
the pre-analytical and analytical temperature and sample type (in-vivo, ex-vivo, in-vitro; whole blood, washed platelet preparation)
temperature changes during the sampling time (induction, maintenance, and rewarming)
the moment of sampling in relation to agonist stimulation
the duration of hypothermia
the cause of hypothermia (spontaneous, whether induced externally or internally)
coexisting factors (extracorporeal circulation [
21], comorbidity, drugs)
the modality of induced hypothermia (local, regional, or general) [
2]
Hypothermia can be caused by metabolic dysfunction in association with decreased heat production (hypothyroidism, hypoglycemia, or hypoadrenalism) or disturbed thermoregulation (intracranial tumor or degenerative neurological disorders). Accidental hypothermia is an unintentional decrease of core temperature caused by prolonged exposure to cold [
22]. Hypothermia acts as a natural survival strategy in some animals that hibernate, and actively suppresses metabolism. [
4],[
23],[
24].
In trauma patients, extra precautions are required based on inherent bias due to absolute or relative hypovolemia and acidosis [
25].
Since the early 1950s, active therapeutic cooling has been used during specific surgical procedures to reduce oxygen requirements of organs such as the brain, heart, and kidney [
26],[
27]. The use of hypothermia has recently been extended to post-resuscitation care based on results from more intensive and innovative monitoring techniques [
28]-[
31]. While precluding the current guidelines for platelet storage, research on chilled platelets (at 4°C, ex-vivo) should be differentiated from research on deep hypothermic circulatory arrest at in-vivo temperatures of 15-18°C and from research on cardiopulmonary bypass and post-resuscitation at temperatures > =28°C.
Hypothermia has been shown to result in hemoconcentration, leukopenia and thrombocytopenia, slowing down of coagulation enzymes, disordered fibrinolysis, and disruption of platelet function [
6],[
32]-[
34]. Some hematologic diseases are directly influenced by temperature changes; for example, cold agglutination disease exhibits an increase in cold agglutinin titers [
35].
With more frequent use of hypothermia in clinical practice and concomitant use of platelet-inhibiting drugs, there is a growing need to understand the ramifications of platelet-inhibiting drugs on coagulation and platelet function [
36],[
37].