State of the art in neuroprotection during acute type A aortic dissection repair.

Temporary (TND) or permanent neurologic dysfunctions (PND) represent the main neurological complications following acute aortic dissection repair. The aim of our experimental and clinical research was the improvement and update of the most common neuroprotective strategies which are in present use. HYPOTHERMIC CIRCULATORY ARREST (HCA): Cerebral metabolic suppression at the clinically most used temperatures (18-22°C) is less complete than had been assumed previously. If used as a 'stand-alone' neuroprotective strategy, cooling to 15-20°C with a jugular SO(2) ≥ 95% is needed to provide sufficient metabolic suppression. Regardless of the depth of cooling, the HCA interval should not exceed 25 min. After 40 min of HCA, the incidence of TND and PND increases, after 60 min, the mortality rate increases. ANTEGRADE SELECTIVE CEREBRAL PERFUSION (ASCP): At moderate hypothermia (25-28°C), ASCP should be performed at a pump flow rate of 10ml/kg/min, targeting a cerebral perfusion pressure of 50-60mmHg. Experimental data revealed that these conditions offer an optimal regional blood flow in the cortex (80±27ml/min/100g), the cerebellum (77±32ml/min/100g), the pons (89±5ml/min/100g) and the hippocampus (55±16ml/min/100g) for 25 minutes. If prolonged, does ASCP at 32°C provide the same neuroprotective effect? CANNULATION STRATEGY: Direct axillary artery cannulation ensures the advantage of performing both systemic cooling and ASCP through the same cannula, preventing additional manipulation with the attendant embolic risk. An additional cannulation of the left carotid artery ensures a bi-hemispheric perfusion, with a neurologic outcome of only 6% TND and 1% PND. NEUROMONITORING: Near-infrared spectroscopy and evoked potentials may prove the effectiveness of the neuroprotective strategy used, especially if the trend goes to less radical cooling. CONCLUSION: A short interval of HCA (5 min) followed by a more extended period of ASCP (25 min) at moderate hypothermia (28°C), with a pump flow rate of 10ml/kg/min and a cerebral perfusion pressure of 50 mmHg, represents safe conditions for open arch surgery.

Changes in regional cerebral blood flow under hypothermic selective cerebral perfusion.

OBJECTIVE: Currently the most frequently used perfusion technique during aortic arch surgery to prevent cerebral damage is hypothermic selective cerebral perfusion (SCP). Changes in cerebral blood flow (CBF) are known to occur during these procedures. We investigated regional changes of CBF under conditions of SCP in a porcine model. METHODS: In this blinded study, twenty-three juvenile pigs (20 - 22 kg) were randomized after cooling to 20 degrees C on CPB. Group I (n = 12) underwent SCP for 90 minutes, while group II (n = 11) underwent total body perfusion. Fluorescent microspheres were injected at seven time-points to calculate total and regional CBF. Hemodynamics, intracranial pressure (ICP), cerebrovascular resistance (CVR) and oxygen consumption were assessed. Tissue samples from the neocortex, cerebellum, hippocampus and brain stem were taken for a microsphere count. RESULTS: CBF decreased significantly (p = 0.0001) during cooling, but remained at significantly higher levels with SCP than with CPB throughout perfusion (p < 0.0001) and recovery (p < 0.0001). These findings were similar among all regions of the brain, certainly at different levels. Neocortex CBF decreased 50%, whereas brain stem and hippocampus CBF decreased by only 25 % during total body perfusion. All four regions showed 10 - 20% less CBF in the post-CPB period. CBF during SCP did not fall by more than 20% in any analysed region. The hippocampus turned out to have the lowest CBF, while the neocortex showed the highest CBF. CONCLUSION: SCP improves CBF in all regions of the brain. Our study characterizes the brain specific hierarchy of blood flow during SCP and total body perfusion. These dynamics are highly relevant for clinical strategies of perfusion.