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

• MRI of cerebrum [ Time Frame: Baseline prior to surgery and 4 to 5 days postoperatively ] [ Designated as safety issue: No ]
  Standard perfusion-weighed Magnetic Resonance imaging of the cerebrum. The same investigator describes all images. No use of contrast agents.
• Markers of neurological injury [ Time Frame: baseline, postoperative ] [ Designated as safety issue: No ]
  s-100b, Neuron specific enolase
• neurological exam [ Time Frame: baseline, postoperative, after 4 months ] [ Designated as safety issue: No ]
• cognitive test [ Time Frame: baseline, postoperative, after 4 months ] [ Designated as safety issue: No ]
• markers of elevated inflammatory response [ Time Frame: perioperatively ] [ Designated as safety issue: No ]
• Markers of oxidative stress [ Time Frame: perioperatively ] [ Designated as safety issue: No ]
• Coagulation parameters [ Time Frame: perioperatively ] [ Designated as safety issue: No ]

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.

Tertiary care clinic. Patients eligible for planned ascending aorta aneurism repair under deep hypothermic circulatory arrest.

• Gradient cooling group
  Study group receiving gradient cooling during the procedure using extracorporeal circulation (ECC). The procedure is used routinely in the department and is not an experimental procedure. A maximum of 10 degrees celsius is allowed between the measured nasopharyngeal body temperature and the heater-cooler unit of the ECC-machine, when cooling or rewarming.
• Crash cooling group
  Study group receiving rapid cooling using extracorporeal circulation. The protocol for rapid cooling is using routinely in the department and is not an experimental procedure. When cooling, the investigators aim for maximal difference in temperature between the heater-cooler unit of the ECC-machine.

Inclusion Criteria:

• Patients scheduled for surgery on the ascending aorta
• Need for deep hypothermic circulatory arrest during the procedure

Exclusion Criteria:

• Known coagulopathy
• Ejection fraction less than 30 %
• Severe psychiatric or neurological disease
• Severe liver disease
• Severely reduced lung function
• Glomerular filtration rate less than 15 ml/min/1.73 m2