Hypothermia and Circulatory Arrest During Surgery on the Ascending Aorta: A Comparison Between Two Cooling Methods

PURPOSE: To compare crash cooling versus gradient cooling methods for patients undergoing planned surgery on the ascending aorta in deep hypothermic circulatory arrest. To investigate the impact of hypothermia and circulatory arrest on the coagulation, stress-response, and cerebral outcome.

BACKGROUND: Cooling to 18 °C using extracorporeal circulation allows for circulatory arrest during surgery on the ascending aorta. Two different methods are used either lowering the temperature of the blood by 10 °C at a time, gradient cooling, or as cold as possible, crash cooling. The distribution of hypothermia is expected to be different for the two methods, the latter predominantly cooling the body core. The influence on the physiological response is expected to vary with the two methods. The surgical procedure and the cooling greatly elicit a stress response and the coagulation is profoundly influenced. There can be adverse effects on the neurological outcome due to the procedure. The two methods are considered equal, but have never been subjected to comparison. The surgery and circulatory changes can have a negative influence on the cerebral outcome .

METHODS: Twenty patients between 18 and 80 yrs randomized either to crash cooling or gradient cooling, ten patients in each group.. Patients with severe comorbidities or known coagulopathy are excluded. Anesthesia and operation as performed routinely in the department. The primary endpoint is duration of cooling, secondary endpoints include coagulation parameters (thromboelastography, clot stability), stress response parameters (adhesion molecule expression on endothelial cells, oxidative stress analysis, inflammatory markers), neuropsychological tests, MRI of the cerebrum, markers of cerebral ischemia, and ultrasound imaging of the great vessels for detection of air bubbles. Baseline values are obtained for all parameters.