Epileptic Potentials During Cardiac Surgery and Association With Postoperative Neurological Outcome

The investigators will follow the STROBE guidelines to perform this prospective observational study. All patient demographics, co-morbidities and surgical details that are relevant to calculate the EuroSCORE will be recorded using our institutional automatic anesthesia record system. Laboratory tests will be performed according to our clinical standard before cardiac surgery. General anesthesia and surgery will be performed according to attending physician's preferences. Invasive arterial blood pressure, central line and transesophageal echocardiography (TEE) are all standard procedures. Before induction of anesthesia a two channel EEG will be installed on the forehead with reference electrode on FPZ, other electrodes on A1-F3 \& A2-F4. A Narcotrend Compact M Monitor will be connected to evaluate depth of anesthesia continuously during the operation, but also automatically stores EEG data (with a rate of 128Hz) to screen for epileptic activity or/and ischemic episodes. This monitor is standard practice in our cardiovascular division.

Patients at higher risk for intraoperative cerebral ischemic events (stenosis of carotid artery, deep hypothermic cardiac arrest, history of stroke/prind/TIA, severe aortic atherosclerotic disease) do receive bilateral frontal brain oxygenation/perfusion monitoring with Near-infrared spectroscopy (NIRS) as part of standard practice at our institution. After the administration of the anticoagulant heparin for cardiopulmonary bypass, tranexamic acid is given intravenously as our clinical standard according to the BART trial. All other intraoperative administrations of drugs, blood transfusions and hemodynamic management will be according to the responsible cardiac anesthesiologist and cardiac surgeon. Following surgery patients will be transported to the ICU under deep sedation according to the anesthesia team. As standard operation procedure the responsible ICU attending or resident is evaluating cardiac surgery patients every hours while intubated and at least twice per shift if awake (4 times per day) for neurological deficits. A neurological deficit is defined as patient developing a new onset motor, sensory, or cognitive dysfunction (e.g., hemiplegia, hemiparesis, aphasia, sensory deficit, impaired memory) that persists for 24 or more hours due to embolic, thrombotic, or hemorrhagic vascular accident or stroke. Special trained ICU nurses evaluate the Richmond Agitation Sedation Scale (RASS) on an hourly basis. The time from stopping sedation until reaching a RASS of zero will be used to determine (delayed) time to awakening. The appropriateness of timing to stop the sedation is up to the treating ICU team.

Standard practice is, that cardiac enzymes are measured all 6 hours for the first 48 hours, according to clinical judgement thereafter, but at least once daily until discharge from the ICU. New myocardial infarction will be defined as Troponin values >10x99th percentile URL during the first 48 h following cardiac surgery, occurring from a normal baseline Troponin value (≤99th percentile URL). In addition, either (i) new pathological Q waves or new LBBB, or (ii) angiographically documented new graft or new native coronary artery occlusion, or (iii) imaging evidence of new loss of viable myocardium or new regional wall motion abnormality.

Pulmonary and respiratory complications will be noted as (1) pneumonia, (2) prolonged intubation of > 24 hours, (3) re-intubation, (4) TRALI or ARDS, as well as (5) tracheostomy due to weaning failure.

Renal complication is defined as acute renal failure (ARF) requiring dialysis during the postoperative period. The indication for dialysis include uremia, volume overload, or biochemical abnormalities and are based on clinical judgment of the treating ICU team.

The exact time on the ICU and on the ventilator is automatically recorded in the patient data management system (PDMS) and will be recorded on the day of ICU discharge and/or extubation. All postoperative diagnosis of complications will be gathered from the involved intensivist, cardiac surgeon, cardiologist, neurologist, radiologist and other consulted specialists. Mortality will be evaluated for in hospital only.

The postoperative course of all included patients will be followed until discharge from the hospital.