This monograph is a review of the key literature supporting the use of the INVOS™ Cerebral/Somatic Oximeter during complex aortic procedures. The monograph discusses cerebral perfusion as a common complication of complex thoracic aortic operations that adversely affect clinical outcome and cost of care, and discusses how monitoring with the INVOS™ system may aid in the early detection of cerebral hypoperfusion or malperfusion.