Brain Protection in Aortic Arch Surgery

Protection of the brain during aortic arch surgery has been— and continues to be— the primary consideration in carrying out these complex operations. Cerebral damage occurs primarily due to two mechanisms: global injury secondary to inadequate protection of the brain during interruptions of normal cerebral perfusion, and focal defects resulting from embolization of atheroma and surgical debris into the cerebral vessels. If techniques for cerebral protection are to improve, an integrated approach to address both mechanisms of injury will be required.

Hypothermia is the mainstay of essentially all techniques of global cerebral protection. The principal benefit of hypothermia is a reduction in cerebral metabolic demands. As seen in Fig. 1, cerebral metabolism is reduced 50% when the temperature is reduced to 28°C, and to 19% of its normothermic value at 18°C. If one assumes that cerebral ischemia at normothermia can be tolerated without injury for 5 minutes, then hypothermic circulatory arrest (HCA) at 18°C is theoretically safe for only 25 minutes. In fact, laboratory investigations as well as clinical studies of cognitive function and the incidence of temporary neurological dysfunction strongly suggest that intervals of hypothermic circulatory arrest (HCA) longer than 30 minutes even at esophageal temperatures of 13–15°C may be associated with cerebral injury.