The disclosed physiological feedback systems and methods assist with assessing, monitoring and/or treating a patient experiencing a cardiac arrest event. The systems and methods receive multiple inputs and are continuous and/or iterative during a treatment session to provide physiological state trends of the patient. An index of the physiological state of the patient can be derived and confounders, and/or their effects, can be identified, and/or removed, from the index. Additionally, the systems and methods can assist with determining ischemic injury in a patient based on cerebral tissue oxygenation and/or other physiological data.