Deep hypothermic circulatory arrest

Deep hypothermic circulatory arrest (DHCA) is a surgical technique that involves cooling the body to temperatures below 20°C (68°F), and stopping blood circulation and brain function for up to one hour. It is used when blood circulation to the brain must be stopped because of delicate surgery within the brain, or because of surgery on large blood vessels that lead to or from the brain. DHCA is a form of carefully managed clinical death in which heartbeat and all brain activity cease.

At normal body temperature of 37°C only several minutes of stopped blood circulation causes changes within the brain leading to permanent damage after circulation is restored. Reducing body temperature extends the time interval that such stoppage can be survived. At a brain temperature of 14°C , blood circulation can be safely stopped for 30 to 40 minutes. There is an increased incidence of brain injury at times longer than 40 minutes, but sometimes circulatory arrest for up to 60 minutes is used if life-saving surgery requires it. Infants tolerate longer periods of DHCA than adults.

Applications of DHCA include repairs of the aortic arch, repairs to head and neck great vessels, repair of large cerebral aneurysms, repair of cerebral arteriovenous malformations, pulmonary thromboendarterectomy, and resection of tumors that have invaded the vena cava.

Cells require energy to operate membrane ion pumps and other mechanisms of cellular homeostasis. Cold reduces the metabolic rate of cells, which conserves energy stores (ATP) and oxygen needed to produce energy. Cold therefore extends the length of time that cells can maintain homoestasis and avoid damaging hypoxia and anaerobic glycolysis by conserving local resources when blood circulation is stopped and unable to deliver fresh oxygen and glucose to make more energy.

...
Wikipedia