Cerebral Oximetry and Neurological Outcomes in Aortic Arch Surgery Patients

Postoperative Cognitive Dysfunction

Aortic Surgeries, Deep Hypothermic Circulatory Arrest

The investigators hypothesize that early intervention to optimize regional cerebral oxygenation detected by cerebral oximetry monitoring during deep hypothermic circulatory arrest (DHCA) for patients undergoing aortic surgery will decrease the incidence of transient and permanent neurological dysfunction and improve neurocognitive impairment.

Permanent or transient neurologic dysfunction is a frequent complication in patients undergoing aortic arch surgery. Two basic methods of brain protection are currently used concomitantly with these complex surgical procedures: deep hypothermic circulatory arrest (DHCA) with or without retrograde cerebral perfusion (RCP)and selective antegrade hypothermic cerebral perfusion. Hypothermic circulatory arrest provides an optimal bloodless operative field, but the incidence of neurological dysfunction increases when the duration of DHCA exceeds 45-50 minutes. Antegrade cerebral perfusion is accomplished by means of direct differential cannulation of the common carotid and right subclavian arteries. Because this technique of brain protection requires a separate perfusion circuit, vigilant monitoring of perfusion pressure and flow rate is of utmost importance. Multiple studies have demonstrated that antegrade selective cerebral perfusion is a well established technique used for cerebral protection during aortic surgery requiring longer periods of DHCA with favorable results in hospital mortality and neurologic outcome. The permanent neurological dysfunction was noted to be 3.8% and the transient neurologic dysfunction to be 7.1% for patients that received antegrade selective cerebral perfusion. Similarly, neurocognitive studies of DHCA with antegrade cerebral perfusion for patients undergoing aortic arch operations demonstrated 9 % transient neurocognitive impairment for 2 days postoperatively that lasted up to 3 weeks thereafter. Consistent with current surgical practice, the University of Michigan uses antegrade selective cerebral perfusion for all patients undergoing aortic arch surgery requiring DHCA with or without RCP. A number of monitoring modalities have been used for detecting cerebral malperfusion during aortic surgery or carotid surgery, including transcranial Doppler ultrasound and near infrared spectroscopy (NIRS). The impact of these monitoring modalities on clinical (neurologic) outcome has not been clearly established. Currently, NIRS has gained considerable attention and acceptance as a non-invasive monitor of cerebral oxygenation. One study showed that a sustained drop in the regional oxygen saturation (rSO2) below 55% for over 5 minutes using cerebral oximetry is closely related to the occurrence of neurological events following aortic surgery. Another study strongly supported that rSO2 should not drop \> 20% from baseline to prevent neurologic compromise. In a cohort of elective coronary artery bypass graph (CABG) patients, intervention for cerebral desaturations did show significantly less major organ morbidity or mortality (death, ventilation \> 48 h, stroke, myocardial infarction, return for re-exploration. Whether NIRS can be used as a monitor to provide rapid detection and prevention of cerebral ischemia by early intervention that may improve neurological outcome in patients undergoing aortic surgery requiring DHCA with or without RCP is currently unknown.

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