Patient directed bypass: cooling for aortic surgery--a preliminary concept

No consensus exists as to the temperature to cool to on bypass for surgery involving the aortic arch. Excluding normothermic surgery, which is rarely performed for arch work, circulatory arrest, anterograde, and retrograde cerebral perfusion either in isolation or in combination remain the techniques of "cerebral protection." To date, no account of individual patient body or cerebral function variation is involved. Utilizing an electronic perfusion database we retrospectively analyzed 10 patients undergoing aortic arch work with regard to mixed venous saturations during cooling. Perfusion related variables were registered and uploaded to www.perfsort.net. We regarded a saturation of 100% as being indicative of no oxygen extraction, implying no metabolic activity--the theoretical goal prior to a circulatory arrest period. There is enormous variation in the temperature at which metabolic activity of the body stops. We had a range from 17-25 degrees. Patients were cooled for an average of 6 (SD 3.4) degrees below which oxygen extraction had ceased to occur. Potentially we are adding 111 minutes (SD 62) of unnecessary bypass time. This may imply that excessive cooling is occurring in some individuals undergoing arch surgery. Patient directed cooling for aortic arch surgery may help to reduce the morbidity/physical insult associated with severe hypothermia. This work is very preliminary but may help us to depart from the one size fits all paradigm that exists in current clinical practice. Correlation with bispectral index, electroencephalogram monitoring and neurological outcomes is needed.