Effects of Extracorporeal Circulation Techniques on Cerebral Perfusion in CABG Surgery

Introduction

Despite advances in minimally invasive approaches and technical improvements in extracorporeal circulation systems in cardiac surgery, postoperative morbidity and mortality remain clinically significant. One of the main contributors to these adverse outcomes is the non-physiological nature of cardiopulmonary bypass, which disrupts circulatory dynamics and may negatively affect cerebral perfusion and oxygenation. Impairment of cerebral perfusion is closely associated with postoperative neurological complications, prolonged awakening time, and extended intensive care unit stay.

Early and reliable monitoring of cerebral perfusion during cardiac surgery is critical for preventing potential neurological injury. Although changes in intracranial pressure are an important determinant of cerebral perfusion, invasive monitoring methods have limited routine clinical use. Ultrasonographic measurement of optic nerve sheath diameter has emerged as a non-invasive, rapid, and repeatable method reflecting changes in intracranial pressure. However, the use of optic nerve sheath diameter measurement in cardiac surgery, particularly for evaluating the cerebral effects of different extracorporeal circulation techniques, has not been sufficiently investigated.

Minimal invasive extracorporeal circulation systems, with their closed-circuit design, reduced hemodilution, and better preservation of hemodynamic stability, may offer potential advantages in maintaining cerebral perfusion compared with conventional reservoir-based extracorporeal circulation. While these potential benefits have been evaluated mainly through clinical outcomes, clear evidence examining cerebral perfusion, oxygenation, and their relationship with intracranial pressure changes is lacking. Near-infrared spectroscopy allows non-invasive monitoring of cerebral oxygenation, and its combined use with optic nerve sheath diameter measurement may enable simultaneous assessment of both functional and pressure-related components of cerebral perfusion.

The present study aims to compare the effects of minimal invasive extracorporeal circulation and conventional reservoir-based extracorporeal circulation techniques on cerebral perfusion in patients undergoing elective coronary artery bypass graft surgery, using ultrasonographic optic nerve sheath diameter measurements. The primary hypothesis is that minimal invasive extracorporeal circulation limits increases in intracranial pressure and provides better preservation of cerebral perfusion and oxygenation compared with conventional extracorporeal circulation. The primary objective is to compare the effects of the two circulation techniques on optic nerve sheath diameter. Secondary objectives include evaluation of the relationship between optic nerve sheath diameter and near-infrared spectroscopy measurements, incidence of cerebrovascular events, extubation time, duration of intensive care unit and hospital stay, perioperative hemodynamic parameters, and postoperative complication rates.

Materials and Methods

This prospective study is planned to be conducted between February 2026 and February 2027 at Kartal Koşuyolu High Specialization Training and Research Hospital. A total of 70 patients aged 18 years or older, classified as ASA physical status II-III, scheduled for elective coronary artery bypass graft surgery will be included.

Patients younger than 18 years, those with ASA status other than II-III, pregnant patients, emergency cases, patients with a history of trauma within the previous 24 hours, neurological diseases affecting consciousness or decision-making capacity, carotid artery lesions, psychiatric disorders affecting decision-making capacity, coagulation disorders (international normalized ratio >1.25, activated partial thromboplastin time >35 s, or platelet count \<100,000/μL), reoperations, congestive heart failure, chronic kidney failure, sepsis, hypoxia, ocular trauma, or optic nerve pathology will be excluded from the study.

All patients will be informed about the study before enrollment, and written informed consent will be obtained after providing detailed information regarding extracorporeal circulation.

In the operating room, routine monitoring including electrocardiography, peripheral oxygen saturation, and invasive arterial blood pressure monitoring will be applied. Near-infrared spectroscopy and bispectral index monitoring will also be performed.

The type of perfusion technique will be determined based on the patient's clinical condition and the surgeon's preference.

After monitoring, vascular access will be established using a 20-gauge cannula, and premedication will be administered with intravenous midazolam 0.03 mg/kg and fentanyl 1 μg/kg.

In both groups, anesthesia induction will be achieved using propofol 1.5-2.5 mg/kg and rocuronium 1 mg/kg. Anesthesia maintenance will be provided with sevoflurane 0.8-1 minimum alveolar concentration in a mixture of 50% oxygen and 50% air, along with remifentanil infusion at 0.01-0.1 μg/kg/min. Mechanical ventilation will be set with a tidal volume of 6 mL/kg, maintaining end-tidal CO₂ between 30 and 35 mmHg. Anesthetic depth will be monitored to maintain a bispectral index value between 40 and 60. A standard jugular central venous catheter will be inserted in all patients, allowing measurement of central venous oxygen saturation when required. If heart rate or arterial blood pressure increases by more than 20% from baseline values, the remifentanil dose will be increased to 0.1-2 μg/kg/min. Cold Del Nido cardioplegia will be administered every 45 minutes.

All optic nerve sheath diameter measurements will be performed by a single anesthesiologist experienced in ultrasonographic neuromonitoring and blinded to the perfusion technique used. With patients in the supine position, a linear 7.5 MHz ultrasound probe will be gently placed on the closed upper eyelid in transverse and sagittal planes without applying pressure to the eye. Optic nerve sheath diameter will be measured 3 mm posterior to the globe, from the inner borders of the dura mater, using electronic calipers after clear visualization of the optic nerve. Two measurements will be obtained for each optic nerve, one in the transverse and one in the sagittal plane. The final optic nerve sheath diameter will be calculated as the mean of four measurements obtained from both eyes.

Demographic and perioperative data including sex, age, ASA status, body mass index, right and left jugular vein and carotid artery diameters, ejection fraction, extracorporeal circulation type, number of grafts, anesthesia and surgical duration, peripheral oxygen saturation, mean arterial pressure, fraction of inspired oxygen, near-infrared spectroscopy and bispectral index values, hematocrit, lactate levels, cross-clamp and pump times, fluid balance, blood product use, and right and left optic nerve sheath diameter measurements will be recorded. Postoperative outcomes including duration of mechanical ventilation, intensive care unit stay, incidence of cerebrovascular events, need for reoperation, atrial fibrillation, and length of hospital stay will also be documented.

Sample Size and Statistical Analysis

Sample size calculation will be performed using G*Power version 3.1.9.4 based on data from a similar study evaluating optic nerve sheath diameter in cardiac surgery. With an effect size of 0.80, a significance level of 0.05, and a power of 90%, at least 34 patients per group are required. To account for potential data loss, 35 patients will be included in each group, resulting in a total sample size of 70 patients.

Statistical analyses will be conducted using SPSS version 27.0. Quantitative variables will be presented as mean ± standard deviation, median, minimum, and maximum values, while categorical variables will be expressed as frequency and percentage. Normality of data distribution will be assessed using the Shapiro-Wilk test and box-plot graphs. Comparisons between two groups will be performed using the Student's t-test for normally distributed variables and the Mann-Whitney U test for non-normally distributed variables. Relationships between categorical variables will be analyzed using the chi-square test, Fisher's exact test, or Fisher-Freeman-Halton test as appropriate. Receiver operating characteristic analysis will be used to determine cut-off values. Logistic regression analysis will be performed to assess relationships between parameters. Time-dependent changes will be evaluated using Pearson correlation analysis. A p-value \<0.05 will be considered statistically significant.

Both techniques are routinely used in clinical practice, and no procedures outside standard care will be applied. No additional budget will be required, as all parameters will be obtained from routine preoperative assessments and standard perioperative monitoring.

Endpoints

Primary endpoint:

Perioperative evaluation of optic nerve sheath diameter.

Secondary endpoints:

Assessment of the correlation between preoperative and postoperative optic nerve sheath diameter and near-infrared spectroscopy measurements, incidence of cerebrovascular events, extubation time, duration of intensive care unit and hospital stay, perioperative hemodynamic parameters including mean arterial pressure, peripheral oxygen saturation, and postoperative complication rates such as nausea, vomiting, and atrial fibrillation.