Transcranial Doppler as a Predictor of Postoperative Cognitive Dysfunction Following Cardiopulmonary Bypass

Patient Selection:

Our study is a single-center, prospective, observational study. The study will include 65 patients scheduled for elective coronary artery bypass grafting (CABG) surgery between 01.04.2025 and 31.03.2026 at the Health Sciences University, Bakırköy Dr. Sadi Konuk Training and Research Hospital. Patients aged 18-70, and those scheduled for isolated elective coronary artery bypass grafting, will be included. Patients with carotid stenosis greater than 50%, a history of cerebrovascular events, those who do not provide consent, those with temporal window failure, ejection fraction (EF) below 40%, a preoperative Mini-Mental State Examination (MMSE) score under 23, those requiring mechanical ventilation for more than 24 hours, or those requiring reintubation will be excluded from the study.

Preoperative Preparation:

Patients eligible for the study will be informed about the study, and a voluntary consent form will be obtained. The demographic characteristics of the patients (age, gender, comorbidities, ASA score, BMI, ejection fraction, kidney function tests, EUROSCORE 2 score) will be recorded. All patients will undergo the Mini-Mental State Examination (MMSE) 24 hours before the operation. All patients will undergo standard cardiovascular surgical monitoring (electrocardiography (ECG), non-invasive blood pressure monitoring, peripheral oxygen saturation (SpO2), bilateral regional cerebral oxygen saturation (rSO2) measured by near-infrared spectroscopy (NIRS), and processed EEG monitoring). At the beginning of anesthesia, two 18-20 G granule peripheral venous access lines will be established. The decision regarding whether to use pulsatile or non-pulsatile pump flow will be made by the surgical team. The preoperative baseline (T1) middle cerebral artery (MCA) flow value will be measured using transcranial Doppler with a low-frequency (2-3.5 MHz) sector/cardiac probe. The trans-temporal window, one of the acoustic windows of the skull, will be identified anatomically by locating the hyperechoic image of the sphenoid and temporal bone petrous part between the upper zygomatic arch, external auditory canal, and orbit. In the color Doppler mode of ultrasound, MCA flow will be observed at a depth of 3-7 cm with the probe approaching, and pulse wave (PW) Doppler will be applied. Peak systolic and end-diastolic measurements will be recorded as the average of the three values shown on the screen and documented. Invasive arterial monitoring will be routinely performed.

Perioperative Process:

During anesthesia induction, patients will receive 0.1-0.2 mg/kg of midazolam, 5-8 µg/kg of fentanyl, and 0.6 mg/kg of rocuronium. Anesthesia depth will be maintained with sevoflurane inhalation, dexmedetomidine, and remifentanil infusion, with a Patient State Index (PSI) general anesthesia level maintained between 25-50. After anesthesia induction (T2), after cross-clamping at the 10th minute (T3), 20th minute (T4), 30th minute (T5), after the cross-clamp is removed (T6), and at the end of surgery (T7), transcranial Doppler measurements, mean arterial pressure (MAP), and cerebral oxygen saturation (rSO2) values will be recorded. Arterial blood gas analyses will be recorded at T2, T3, T6, and T7.

Postoperative Process :

The patient will be admitted to the Postoperative Cardiovascular Surgery Intensive Care Unit. At 24 hours postoperatively, delirium will be assessed using the CAM-ICU (Confusion Assessment Method for the Intensive Care Unit) in the intensive care unit. For patients with prolonged ICU stays, delirium assessments using CAM-ICU will continue. On the 2nd-4th days, delirium evaluation will be conducted in the morning and evening using the 3DCAM test in the service setting. At 24 hours, ventilator time, fluid balance, urine output, inotropic/vasopressor requirements, presence of new arrhythmias, amount of blood products used postoperatively, kidney function tests (AKI), and other recorded data will be evaluated. A repeat Mini-Mental State Examination (MMSE) will be performed on the 5th day of the hospital stay. Cerebrovascular events during the hospital stay will also be recorded.

• Transcranial Doppler measurement of the middle cerebral artery (Procedure): Transcranial Doppler examination was performed using a low-frequency (2-3.5 MHz) sector/cardiac probe through the transtemporal acoustic window. Middle cerebral artery (MCA) flow was identified in color Doppler mode at a depth of 3-7 cm with flow directed toward the probe. Pulsed-wave Doppler was applied, and peak systolic and end-diastolic velocities were recorded as the average of three measurements.

Primary outcomes

• Middle cerebral artery mean flow velocity measured by transcranial Doppler [Perioperative period]: Perioperative transcranial Doppler will be used to measure middle cerebral artery mean flow velocity at predefined time points: before anesthesia induction, after anesthesia induction, at the 10th, 20th, and 30th minutes after aortic cross-clamping, and after removal of the aortic cross-clamp, end of the surgery.
• Postoperative delirium incidence (yes/no) [Postoperative days 1-5]: Postoperative delirium will be assessed as present or absent based on delirium screening (CAM-ICU in ICU; 3D-CAM on the ward) performed twice daily during postoperative days 1-5. Delirium is defined as at least one positive screen.
• Postoperative cognitive dysfunction (MMSE score change) [Postoperative day 5]: The outcome is the change in MMSE score from the preoperative baseline assessment to postoperative day 5.

Secondary outcomes

• Acute kidney injury stage (KDIGO) [Postoperative 24th hour]: Acute kidney injury will be defined and staged according to KDIGO criteria (stages 0-3) based on postoperative changes in serum creatinine and/or urine output
• Duration of mechanical ventilation [Postoperative 24th hour]: The duration of ventilator support withdrawal in the postoperative intensive care unit
• Length of stay in intensive care [within 30 days after surgery]: The time the patient is transferred from intensive care to the ward
• Length of hospital stay [within 60 days after surgery]: The time the patient is discharged home

Sex: All, ages: 18 Years to 70 Years

Inclusion Criteria:

* Patients aged 18-70
* Patients scheduled for isolated elective cardiopulmonary bypass surgery

Exclusion Criteria:

* Patients with carotid stenosis ≥50%
* Emergency patients or those with a history of reoperation
* Patients with a history of cerebrovascular events
* Patients who do not provide consent
* Patients with temporal window failure
* Patients with an ejection fraction (EF) <40%
* Patients with a Mini-Mental State Examination (MMSE) score <23
* Patients who require mechanical ventilation for more than 24 hours or those who are reintubated