Optic Nerve Sheath Diameter and Cognitive Outcomes in Bentall Surgery

Bentall procedure is a complex cardiac surgery involving replacement of the ascending aorta, aortic root, and aortic valve using a mechanical or bioprosthetic valve conduit and vascular graft. It is commonly performed for aortic aneurysm, aortic dissection, or connective tissue disorders such as Marfan syndrome. The procedure carries a mortality rate of 2-10% and a neurological complication rate of 3-8%, including stroke and postoperative cognitive dysfunction (POCD).Postoperative neurological complications in Bentall surgery are influenced by both patient-related and surgery-related factors. Patient-related risk factors include advanced age (>70 years), low educational level, pre-existing cognitive impairment, carotid artery stenosis, and acute type A dissection. Surgery-related risk factors include prolonged CPB and deep hypothermic arrest duration, cerebral perfusion technique, prosthesis type, prolonged mechanical ventilation, postoperative infection, low cardiac output, and anticoagulation compliance.

The optic nerve sheath (ONS) is a continuation of the intracranial dura mater surrounding the subarachnoid space. It expands in response to elevated intracranial pressure (ICP), particularly in the anterior retrobulbar region. Ultrasound measurement of ONSD is a well-validated, non-invasive bedside method for detecting elevated ICP and has been studied in various clinical settings.

Bentall surgeries involving CPB may affect intracranial dynamics through multiple mechanisms including oxygenation fluctuations, electrolyte disturbances, hemodilution, blood transfusion requirements, temperature variations, total circulatory arrest, prolonged surgical duration, and embolic events. Therefore, perioperative monitoring of intracranial status is of particular importance in these patients.

Study Procedures:

All patients will have the following baseline data recorded: age, sex, BMI, ASA classification, comorbidities, smoking and alcohol use, medications, ejection fraction (EF), EuroSCORE, and educational level.Preoperative assessments (T0) will include MoCA test, bilateral NIRS-based cerebral oximetry, and bilateral ONSD measurement by ultrasound while breathing room air.

Following preoxygenation and routine anesthesia induction, a central venous catheter will be placed. Bilateral NIRS and bilateral ONSD measurements will be performed at the following time points:

T0: Preoperative (room air) T1: 5 minutes after anesthesia induction T2: CPB initiation T3: Maximum hypothermic period T4: Aortic cross-clamp removal T5: CPB termination T6: After sternal closure, before ICU transfer

At each time point, mean arterial pressure (MAP), arterial blood gas values including hematocrit, PaO2, PaCO2, lactate, and pH will also be recorded.

Intraoperative data to be recorded include: anesthetic agent doses, total opioid and inhalation agent consumption, analgesic technique (fascial plane block or IV analgesia), surgical duration, CPB duration, cross-clamp duration, methylprednisolone dose if used, mannitol amount if used, cerebral perfusion type, TCA duration and temperature if applicable, surgical technique, prosthesis type, degree of hypothermia, vasopressor type and dose, blood transfusion volume, total urine output, and fluid balance.

Postoperative Follow-up:

Patients will be transferred to the cardiovascular surgery ICU and managed by the ICU team according to their standard protocols. The study team will not interfere with clinical management.

Postoperative assessments will include:

Bilateral ONSD measurement within the first postoperative hour and after extubation if applicable CAM-ICU delirium assessment twice daily during ICU stay and once daily on the ward RASS sedation score during ICU stay MoCA test after extubation and before hospital discharge VAS pain scores at postoperative 0, 6, 12, and 24 hours

Additional outcome data to be collected: extubation time, ICU length of stay, hospital length of stay, postoperative complications, need for mechanical circulatory support, reintubation, reoperation, blood transfusion volume, analgesic consumption, and mortality if applicable.

The observation period begins before anesthesia induction and ends at hospital discharge or mortality.