Cardiovascular Impact of Hypothermia

Abstract

Hypothermia, defined as body temperature equal to or inferior to 35°C is often encountered in the intensive care patients. It can be accidental or therapeutic, in which case it plays a role in certain ischemia-reperfusion processes. Hypothermia has multiple cardiac and vascular effects including initial tachycardia followed by bradycardia; a preservation of myocardial contractility in case of mild or moderate hypothermia, and an initially stable or decreased cardiac index that decreases further during profound hypothermia; a decrease in myocardial and overall metabolic requirements with an increase in SvO₂ resulting in a favorable or stable ratio of oxygen delivery/consumption despite the usual hypoxia-hypocapnia; an increase in overall vascular resistance despite a decrease in sensitivity to exogenous catecholamines; a tendency to hypovolemia essentially due to cold-induced diuresis.

Most of these effects, associated with a possible specific cardioprotection, seem favorable to hypothermia. Nevertheless, hypothermia is associated to a risk of rhythm disturbance (atrial fibrillation then ventricular fibrillation under 30-32°C), metabolic (electrolytes and pharmacokinetics) disturbance, and coagulation abnormalities that may induce deleterious cardiovascular effects. The precise depth of the targeted temperature management -including mild hypothermia-is at present debated in cardiac arrest and neonatal hypoxia. Therapeutic hypothermia remains a promising research topic in the treatment of cardiogenic shock and myocardial revascularization in myocardial infarction.