Deep hypothermic circulatory arrest

Deep hypothermic circulatory arrest (DHCA) is a surgical technique that 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. Deep hypothermic circulatory arrest (DHCA) is a surgical technique that 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. The use of hypothermia for medical purposes can date back to the Hippocrates, where they advocated packing snow and ice into wounds to reduce hemorrhage. The origin of hypothermia and neuroprotection was also observed in infants were exposed to cold due to abandonment and the prolonged viability of these infants. In the 1940s and 1950s, Canadian surgeon Wilfred Bigelow demonstrated in animal models that the length of time the brain could survive stopped blood circulation could be extended from 3 minutes to 10 minutes by cooling to 30 °C before circulation was stopped. He found that this time could be extended to 15 to 24 minutes at temperatures below 20 °C. He further found that at a temperature of 5 °C, groundhogs could endure two hours of stopped blood circulation without ill effects. This research was motivated by a desire to stop the heart from beating long enough to do surgery on the heart while it remained still. Since heart-lung machines, also known as cardiopulmonary bypass (CPB), hadn't been invented yet, stopping the heart meant stopping blood circulation to the whole body, including the brain. The first heart surgery using hypothermia to provide a longer time that blood circulation through the whole body could be safely stopped was performed by F. John Lewis and Mansur Taufic at the University of Minnesota in 1952. In this procedure, the first successful open heart surgery, Lewis repaired an atrial septal defect in a 5-year-old girl during 5 minutes of total circulatory arrest at 28 °C. Many similar procedures were performed by Soviet heart surgeon, Eugene Meshalkin, in Novosibirsk during the 1960s. In these procedures, cooling was accomplished externally by applying cold water or melting ice to the surface of the body. The advent of cardiopulmonary bypass in the United States during the 1950s allowed the heart to be stopped for surgery without having to stop circulation to the rest of the body. Cooling more than a few degrees was no longer needed for heart surgery. Thereafter, the only surgeries that required stopping blood circulation to the whole body ('total circulatory arrest') were surgeries involving blood supply to the brain. The only heart surgeries that continued to require total circulatory arrest were repairs to the aortic arch. Cardiopulmonary bypass machines were essential to the development of deep hypothermic circulatory arrest (DHCA) in humans. By 1959, it was known from the animal experiments of Bigelow, Andjus and Smith, Gollan, Lewis's colleague, Niazi, and others that temperatures near 0 °C could be survived by mammals, and that colder temperature permitted the brain to survive longer circulatory arrest times, even beyond one hour. Humans had survived cooling to 9 °C, and circulatory arrest of 45 minutes, using external cooling only. However, reaching such low temperatures by external cooling was difficult and hazardous. At temperatures below 24 °C, the human heart is prone to fibrillation and stopping. This can begin circulatory arrest before the brain has reached a safe temperature. Cardiopulmonary bypass machines allow blood circulation and cooling to continue below the temperature at which the heart stops working. By cooling blood directly, cardiopulmonary bypass also cools people faster than surface cooling, even if the heart is not functioning. In 1959, using cardiopulmonary bypass (CPB), Barnes Woodhall and colleagues at Duke Medical Center performed the first brain surgery using DHCA, a tumor resection, at a brain temperature of 11 °C and esophageal temperature of 4 °C. This was quickly followed by use of DHCA by Alfred Uihlein and other surgeons for treatment of large cerebral aneurysms, another neurosurgical procedure, for which DHCA is still used today. In 1963, Christiaan Barnard and Velva Schrire were the first to use DHCA to repair an aortic aneurysm, cooling the patient to 10 °C. Randall B. Griepp, in 1975, is generally credited with demonstrating DHCA as a safe and practical approach for aortic arch surgery.