HYPOTHERMIC CIRCULATORY ARREST AND OTHER METHODS OF CEREBRAL PROTECTION DURING OPERATIONS ON THE THORACIC AORTA

Current surgical techniques in operations on the thoracic aorta freque ntly require exclusion of the cerebral circulation for varying periods . During these periods, hypothermic circulatory arrest (HCA), selectiv e cerebral perfusion (SCP), and retrograde cerebral perfusion (RCP) ca n be used for cerebral protection. Hypothermia is the principle compon ent of these methods of protection. The main protective effect of hypo thermia is based on reduction of cerebral energy expenditures and larg ely depends on adequate suppression of cerebral function. It is most e ffective at deep hypothermic levels (13-degrees-C to 15-degrees-C). Me asures that preserve autoregulation of cerebral blood flow help increa se the margin of safety with all methods of protection. There is solid experimental and clinical data indicating the safe limits and outcome following HCA. Current applications of SCP and RCP are fairly recent developments and do not have comparable supporting data. SCP can be us ed without deep hypothermia and allows prolonged periods of cerebral p rotection, but is complex in application. RCP is simpler, but always r equires deep hypothermia. Present clinical data do not allow separatio n of its protective effect from that of HCA alone. Recent modification s in the application of HCA include monitoring of cerebral O2 extracti on, and selective use of supplemental SCP to limit arrest times to les s than 50 minutes, or RCP to prevent embolic strokes, as indicated. Th ese changes appear to have reduced the overall mortality, the severity of embolic strokes, and