Deep Hypothermic Circulatory Arrest

Cardiopulmonary bypass (CPB) and deep ­hypothermic circulatory arrest (DHCA) are techniques, which provide a bloodless field and enable the repair of complex congenital or acquired pathologies in cardiac surgery,1 as well as other conditions that require complete cessation of flow, for example, clipping of giant cerebral aneurysms.2 The protective effects of hypothermia have been known for centuries and possibly millenniums; however, the exact mechanisms that allow the temporary suspension of animation remain to be elucidated. There is extensive evidence that transient periods of no-flow can be tolerated and that the duration of this safe period is related to the level of hypothermia. The practical conduct of CPB and DHCA is dictated by the underlying pathology and has become standardized during recent decades. The compelling clinical success of routine DHCA could be one of the reasons why limited effort has been made to further facilitate the paramount protective effects of hypothermia, to extend the safe period, and to improve organ protection. Selective perfusion of the most vulnerable organs has been introduced into clinical practice only recently. Monitoring of the brain’s metabolism is still limited to experimental settings. Current molecular tools also enable the investigation of the physiologic and biochemical changes that are responsible for the protection. Recently published studies in cardiac arrest showing beneficial effects of hypothermia applied even after ischemic insult have sparked a renewed interest in hypothermia research. We will review the current practice of DHCA, key mechanisms germane to hypothermic protection against ischemia-reperfusion injury, CPB perfusion strategies before and after DHCA, the role of pharmacological adjuncts, and alternative methods of neuroprotection, and discuss future directions in research.