Association between perioperative optic nerve sheath diameter and postoperative delirium after Bentall surgery: a prospective observational study.

Background: Optic nerve sheath diameter (ONSD) is an indirect, technique-dependent marker of intracranial pressure; its association with delirium after Bentall surgery remains uncertain. Therefore, we assessed serial perioperative ONSD and its relationship with delirium. Methods: This prospective single-centre study included 53 adults undergoing elective Bentall surgery. Delirium analyses included 51 participants whose status was assessable with the Confusion Assessment Method for the Intensive Care Unit; two remained unassessable until death. Bilateral ONSD was measured at 10 perioperative time points. Mixed-effects models evaluated serial ONSD, time-point comparisons were Holm-adjusted, and measures underwent Firth regression and receiver operating characteristic analyses. Sensitivity analyses assigned each indeterminate outcome as either delirium present or absent. Results: Documented delirium occurred in 17 of 51 participants with assessable delirium status (33.3%). Average perioperative ONSD was 0.250 mm higher with delirium (95% confidence interval 0.031-0.470; Conclusions: Higher perioperative ONSD was associated with documented delirium, but the temporal interaction was sensitive to unobserved outcomes, and the data did not establish a superior time point or a causal intraoperative change. These findings require external validation. Trial registration: ClinicalTrials.gov NCT07452367; retrospectively registered 5 March 2026.