Correlation Between Optic Nerve Sheath Diameter Measured by Ultrasound and Delirium in Cardiac Surgery

Delirium is one of the most frequent and serious complications after cardiac surgery, with reported incidence between 15-30% depending on patient population, procedure type, and diagnostic method. It is associated with prolonged ICU and hospital length of stay, increased risk of institutional discharge, higher readmission rates, long-term cognitive impairment, and mortality. Validated delirium screening tools such as the Confusion Assessment Method for the ICU (CAM-ICU) and the Intensive Care Delirium Screening Checklist (ICDSC) are widely used, but their sensitivity in real-world practice can be variable, sometimes missing early cases despite high specificity. This contributes to delayed recognition and potentially worse outcomes.

Ultrasound measurement of the optic nerve sheath diameter (ONSD) has emerged as a non-invasive surrogate marker for intracranial pressure (ICP). Several meta-analyses confirm good diagnostic accuracy of ONSD ultrasound compared to invasive ICP monitoring. Concordance studies also demonstrate strong agreement between ultrasound and MRI ONSD measurements, particularly when standardized measurement protocols are used (e.g., 3 mm posterior to the retina, bilateral averaging). These findings support the reliability of ONSD ultrasound as a bedside monitoring tool.

In critical care, early broadening of ONSD has been associated with delirium, coma, and death within 28 days. Importantly, the first cardiac surgery-specific study that prospectively examined patients undergoing open-heart surgery and found that increased peri-operative ONSD was independently associated with postoperative delirium. Their findings suggest that ONSD may serve not only as a marker of raised ICP but also as a predictive biomarker for delirium in the cardiac surgical population. Taken together, the burden of postoperative delirium in cardiac surgery, the limitations of current screening methods, and the growing evidence supporting ONSD as a surrogate of cerebral dynamics provide the rationale for this study. We hypothesize that perioperative or early ICU ONSD enlargement will be associated with the development of delirium, and that ONSD monitoring may help identify high-risk patients earlier, guiding preventive strategies.

Informed, written consent will be obtained prior to the start of surgery. The participant's surgical plan will not be altered in any way. Participants that are enrolled in this study will have their surgery proceed according to plan and will be placed under general anesthesia using standard of care practices. Cardiopulmonary bypass will be implemented in accordance with standard of care practices.

For the ONSD ultrasound, the ultrasound will be performed using a linear probe 7.5-13 MHz and will follow standard practice for this procedure. Patients will have closed eyelids covered with a Tegaderm adhesive for eye protection. Ultrasound gel will be applied to the patient's eyelids. The ultrasound probe will be gently placed on the patient's eyelids and to locate the optic nerve and measure ONSD. The ultrasound scan will be performed 3 mm posterior to retina with 4 measurements taken at each time point to allow for a mean result to be determined. Average time for each measurement is 1 minute. Each ultrasound will take 10-15 minutes to complete. This ONSD ultrasound will be performed at the following time points: