Selective Antegrade Cerebral Perfusion and Perioperative Optic Nerve Sheath Diameter in Ascending Aortic Surgery

Optic nerve sheath diameter in millimetres, measured by ocular ultrasonography 3 mm posterior to the entry of the optic nerve into the globe in the transverse plane. Three measurements are obtained per eye and averaged; the mean of the right and left eye values is the participant value. Higher values indicate a larger sheath diameter and are interpreted as consistent with a higher intracranial pressure. The endpoint is the trajectory across the three time points, evaluated as the group-by-time interaction term in a linear mixed-effects model with a random intercept for participant.

Optic nerve diameter in millimetres, measured at the same level as the sheath diameter between the outer margins of the nerve, excluding the sheath. Three measurements per eye are averaged and the mean of the two eyes is the participant value. The endpoint is the trajectory across the three time points, evaluated as the group-by-time interaction term in a linear mixed-effects model with a random intercept for participant. Measurements are obtained before anesthesia induction, at the end of surgery after hemodynamic stabilization in the operating room, and at postoperative hour 24 in the intensive care unit.

Mean flow velocity in centimetres per second in the M1 segment of the middle cerebral artery, insonated through the temporal window at approximately 45-55 mm depth. Three consecutive stable measurements per side are averaged and the bilateral mean is the participant value. The endpoint is the trajectory across the three time points, evaluated as the group-by-time interaction in a linear mixed-effects model. This analysis is exploratory. Measurements are obtained before anesthesia induction, at the end of surgery after hemodynamic stabilization in the operating room, and at postoperative hour 24 in the intensive care unit.

Bilateral regional cerebral oxygen saturation as a percentage, recorded by near-infrared spectroscopy with adhesive frontal sensors. Baseline value, nadir value, percentage change from baseline, number of desaturation episodes at or beyond a 20 percent relative fall from baseline, and total duration of desaturation in minutes are recorded for each side. Values are recorded before anesthesia induction, before cardiopulmonary bypass, before and after selective antegrade cerebral perfusion, at the end of cardiopulmonary bypass, and at the end of surgery.

Delirium screened with the Nursing Delirium Screening Scale, a five-item observational scale scored 0 to 2 per item for a total range of 0 to 10, where higher scores indicate more delirium features. A total score of 2 or more is a positive screen. Screening is performed once the participant is sufficiently awake and communicative; where deep sedation precludes assessment the screen is repeated at an appropriate time and the delay recorded.

Composite of stroke, transient ischemic attack, seizure, or a new focal neurological deficit, ascertained from clinical records and bedside neurological examination. Each component is reported separately in addition to the composite. Events are recorded from the end of surgery to hospital discharge.

Total time in minutes for which the electroencephalogram is suppressed, derived from continuous bispectral index monitoring with an adhesive frontal sensor. Suppression time is accumulated from anesthesia induction to the end of surgery and reported in total and separately for the period of cardiopulmonary bypass and, where applicable, for the period of selective antegrade cerebral perfusion and systemic circulatory arrest. Higher values indicate a longer cumulative duration of an isoelectric electroencephalogram. The proportion of participants with any recorded suppression is reported alongside the duration.