Deep hypothermic circulatory arrest (DHCA) is a surgical technique that induces deep medical hypothermia. It involves cooling the body to temperatures between 20 °C (68 °F) to 25 °C (77 °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 used to provide a better visual field during surgery due to the cessation of blood flow. 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.
HCA at 14 °C is also reported to provide at least 30-40 minutes of safe HCA time.
Most patients tolerate 30 min of DHCA without significant neurological dysfunction, but when this is extended to longer than 40 min, there is a marked increase in the incidence of brain injury. Above 60 min, the majority of patients will suffer irreversible brain injury, although there are still a small number of patients who can tolerate this.
45 to 60 minutes is upper limit of safe time period.
At a body temperature of 60 degrees, almost 40 degrees below normal, the brain can survive an hour without blood flow.
Longer periods of DHCA are tolerated in neonates and infants compared with adults.
DHCA is used for open heart procedures where the ability to perfuse the brain through the head vessels is not possible with standard proximal aorta cannulation. Repairs of the aortic arch, congenital repairs involving the aortic arch, repairs to the head and neck great vessels, or neurosurgical and pulmonary endarterectomies may require DHCA. Inability to clamp the distal arch, secondary to severe aortic atheromas, may also require DHCA to minimize stroke risk.