Hypothermic Circulatory Arrest
The potential role of hypothermia as a strategy for organ preservation during cardiac operations was first explored by Bigelow and colleagues in 1950 who successfully recovered dogs after arresting the circulation for 15 minutes at 20°C. Other cardiac surgical pioneers followed suit, employing corporeal hypothermia and systemic circulatory arrest for open cardiac surgical procedures before the widespread use of the cardiopulmonary bypass machine, but it was the report of hypothermic circulatory arrest (HCA) as a means of simplifying the repair of aortic arch aneurysms by Griepp and colleagues in 1975 that marks the advent of its common use in aortic surgery, particularly in aortic arch operations. The most studied and most reliably effective neuroprotective strategy known, hypothermia reduces oxygen consumption by decreasing metabolic rate and prolongs the time to triggering of apoptotic pathways and cellular death in the tissues. Tissue oxygen consumption does not decline in a linear fashion as the temperature falls, and most importantly, does not decrease to zero; there is, therefore, a finite limit to the duration of “safe” circulatory arrest, which varies with the cooling temperature achieved.
Hypothermia extends the safe duration of ischemic tolerance during circulatory arrest and, accordingly, the operating time during which the surgeons can operate in a bloodless field. Although HCA is most frequently used during aortic arch reconstructions, it is also used in thoracoabdominal aortic replacement and to enable other operative procedures, such as repair of complex intracranial vascular abnormalities, pulmonary thromboendarterectomy, or resection of extensive renal cell tumors. As such it is an important tool in the armamentarium of all cardiac surgeons. In this chapter, we will summarize the important underlying principles for the safe conduct of HCA and its current clinical applications.
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