Cerebral protection during surgery of the thoracic aorta

Abstract

The brain is an organ with a high energy demand. Over 90% of the energy produced by mitochondria in the brain is derived from oxygen and glucose carried by the circulation. Any decrease in oxygen causes a prompt fall in energy production and results in severe ischemic brain damage. Since surgery of the aortic arch requires manipulation and exclusion of the cerebral vascularization the utilisation of optimal methods of cerebral function preservation is necessary to avoid ischemic brain injuries. Current brain protection strategies, involving reduction of cerebral oxygen consumption and/or maintenance of cerebral blood flow, include: Deep Hypothermic Circulatory Arrest (DHCA), Retrograde Cerebral Perfusion (RCP), Antegrade Selective Cerebral Perfusion (ASCP). Since 1995, at the St Antonius Hospital (Nieuwegein, Netherlands), ASCP is, for the following reasons the method of choice for brain protection when aortic reconstruction is anticipated to require a period of circulatory arrest longer than 30 minutes:

? As compared to DHCA with or without RCP, ASCP provides a much longer period of safe circulatory arrest. We have demonstrated that the extent of the aortic replacement and an ASCP time of longer than 90 minutes are not associated with an increased risk of hospital mortality and adverse neurologic outcome intended as the postoperative occurrence of permanent and transient neurologic dysfunctions ? ASCP can be used with moderate (instead of deep) hypothermia. Cooling down the patient’s core temperature to only 22°-25°C instead of 10°-18°C, is supposed to have various advantages such as the reduction of the duration of extracorporeal circulation with improved survival and reduced coagulative complications. ? the entire experimental literature, comparatively investigating the effects of ASCP, DHCA and RCP on brain energy metabolism, supports the idea that ASCP is superior to the other methods in maintaining an aerobic brain metabolism even after a prolonged period of circulatory arrest as demonstrated by morphologic, histopathologic and biochemical findings as well as by behavioural and clinical examinations

Aim of the present thesis was: 1) to review our experience with ASCP during surgery of the thoracic aorta, 2) to determine the predictive risk factors for hospital mortality and adverse neurologic outcome, 3) to compare survival, neurologic outcome and systemic morbidity in patients undergoing aortic procedures requiring short periods of circulatory arrest with ASCP and DHCA, 4) to compare survival and neurologic outcome in patients receiving 2 different technique for arch vessels reimplantation to the aortic arch: the separated graft technique and the en bloc technique. Our findings were as follows: The hospital mortality rate ranged from to, permanent and transient neurological dysfunction occurred in of patients. Duration of cerebral perfusion and the extent of the aortic replacement were not indicated as predictive risk factor for hospital mortality and adverse neurologic outcome. Among the preoperative variables, type A dissection, urgency and history of stroke/TIA, emerged as the most important risk factors for hospital mortality and adverse neurologic outcome. The duration of CPB was the only intraoperative factor indicated as a risk factor for hospital mortality and neurologic outcome by our statistical analysis. Patients undergoing ascending aorta/hemiarch replacement with ASCP had similar survival and neurological outcome of those receiving DHCA as a method of brain protection but presented a better postoperative pulmonary and renal function recovery. As compared to the en bloc technique , the separated graft technique may result in several technical advantages and in reduced durations of extracorporeal circulation and myocardial ischemia.

In our experience, ASCP has been demonstrated to be a safe and reliable method of brain protection allowing complex aortic procedures to be performed with acceptable results in terms of hospital mortality and adverse neurologic outcome.