Why is hypothermia used in an open heart surgery?

Hypothermia is used widely during open heart surgery due to its cytoprotective effects. In addition to this, other mechanisms of therapeutic hypothermia include suppression of free radicals, inhibition of destructive enzymatic reactions, reduction in metabolic requirements in low-flow regions, and inhibition of the biosynthesis, release, and uptake of excitatory neurotransmitters. Through these mechanisms, hypothermia provides a favorable balance between oxygen supply and demand, slows the onset of ischemic depolarization, decreases the release of ischemic-induced intracellular calcium influx, and suppresses nitric oxide synthase activity.

Hypothermia is widely used in open cardiac surgery not only to protect against perioperative brain ischemia that could potentially develop, but also the myocardium.