Cooling the newborn after asphyxia - physiological and experimental background and its clinical use

Many years of experimental work on hypoxic-ischaemic injury have supported the hypothesis that cooling the body and brain after the primary injury offers permanent neuroprotection. Clinically, the question of how late cooling can start after the insult and still have a protective effect is important and not fully investigated. Pilot studies in human adults initiated cooling after 10-18 h (trauma, stroke), however animal data suggest cooling is not effective if started later than 6 h. There might be a threshold for 'cooling dose' - by depth or duration - to achieve permanent protection. Hypothermia must be administered with understanding of the extensive physiological effects. Different enzymes have different sensitivity to changes in temperature, hence some effects may be beneficial and some deleterious. Hypothermia and cardiovascular responses and coagulation needs careful monitoring.