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

This single-center prospective study will enroll adults undergoing elective or urgent ascending aortic surgery with planned axillary artery cannulation. Participants are grouped according to whether release of the aortic cross-clamp is required to construct the distal anastomosis, and therefore whether selective antegrade cerebral perfusion is applied. Group membership follows from the intraoperative surgical requirement and is not assigned by the investigators. All participants receive a single protocol-specified general anesthesia and ventilation regimen, identical in both groups, so that variables known to act on optic nerve sheath diameter, in particular arterial carbon dioxide tension, volatile agent concentration and airway pressure, are held constant. Because this regimen is assigned by the protocol, the study is registered as interventional. Bilateral optic nerve sheath diameter and optic nerve diameter will be measured by ultrasonography, and middle cerebral artery mean flow velocity by transcranial Doppler, at three time points: before anesthesia induction (T0), at the end of surgery after hemodynamic stabilization in the operating room (T1), and at postoperative hour 24 in the intensive care unit (T2). Regional cerebral oxygen saturation by near-infrared spectroscopy and the electroencephalographic suppression ratio derived from bispectral index monitoring will be recorded intraoperatively. Delirium will be screened at postoperative hour 24 using the Nursing Delirium Screening Scale (Nu-DESC), with a total score of 2 or more considered a positive screen. The primary outcome is the change in bilateral mean optic nerve sheath diameter across T0, T1 and T2, evaluated as the group-by-time interaction in a linear mixed-effects model.

• Optic nerve sheath and optic nerve diameter ultrasonography (Diagnostic test): Ocular ultrasonography with a linear probe of approximately 7-13 MHz, participant supine with the head neutral, eyelids closed, sterile transparent dressing and gel, minimal probe pressure. Optic nerve sheath diameter is measured in the transverse plane 3 mm posterior to the entry of the optic nerve into the globe. Three measurements per eye are averaged, and the mean of the two eyes is recorded. Performed at T0, T1 and T2.
• Transcranial Doppler ultrasonography (Diagnostic test): Transcranial Doppler ultrasonography with a 2 MHz pulsed-wave probe. The M1 segment of the middle cerebral artery is insonated through the temporal window at approximately 45-55 mm depth, bilaterally where a window is obtainable. Three consecutive stable mean flow velocity measurements are taken per side and averaged. Performed at T0, T1 and T2, and where technically feasible during selective antegrade cerebral perfusion and/or circulatory arrest.

Primary outcomes

• Change in bilateral mean optic nerve sheath diameter (ONSD) over time [From before anesthesia induction to postoperative hour 24]: 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.

Secondary outcomes

• Change in bilateral mean optic nerve diameter (OND) over time [From before anesthesia induction to postoperative hour 24]: 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.
• Change in middle cerebral artery mean flow velocity measured by transcranial Doppler [From before anesthesia induction to postoperative hour 24]: 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.
• Change in regional cerebral oxygen saturation measured by near-infrared spectroscopy [From before anesthesia induction to the end of surgery]: 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.
• Proportion of participants with a positive delirium screen (Nu-DESC >=2) [At postoperative hour 24]: 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.
• Number of participants with a clinical neurological event [From end of surgery to hospital discharge, up to 30 days]: 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.
• Cumulative intraoperative electroencephalographic suppression time [From before anesthesia induction to the end of surgery]: 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.

Sex: All, ages: 18 Years to any

Inclusion Criteria:

* Age 18 years or older
* Planned or urgent, hemodynamically stable ascending aortic surgery, including supracoronary ascending aortic replacement, aortic root replacement (Bentall procedure) or valve-sparing root surgery (David procedure), limited to cases involving the ascending aortic segment
* Perfusion planned through axillary artery cannulation
* Written informed consent

Exclusion Criteria:

* History of intracranial procedure or intracranial pathology
* Previous carotid intervention, or carotid artery stenosis of 50 percent or more on preoperative Doppler ultrasonography
* Advanced chronic obstructive pulmonary disease, defined clinically as advanced stage disease with long-term oxygen therapy or a history of frequent exacerbations
* Baseline arterial carbon dioxide tension of 55 mmHg or higher on preoperative arterial blood gas analysis
* Ocular pathology, ocular surgery or ocular trauma that could affect measurement of the optic nerve sheath or optic nerve, including glaucoma and retinal detachment or fibrosis
* Severe preoperative neurological deficit, including major stroke or severe dementia, or active psychiatric illness
* Hemodynamic instability, or a requirement for extracorporeal membrane oxygenation or intra-aortic balloon counterpulsation, of a degree that prevents measurements during the first 24 postoperative hours
* Known contraindication to any component of the protocol-specified anesthesia regimen