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; p = 0.025). Across outcome assignments, the difference ranged from 0.237 to 0.248 mm ( p -values ≤ 0.029), whereas the time-by-group interaction was sensitive to assignment ( p -values ranged from <0.001 to 0.094). No point-specific comparison survived Holm correction (smallest adjusted p = 0.078), and the post-closure T6 minus preoperative baseline showed no clear group difference ( p = 0.147). In an exploratory Firth analysis not adjusted for time-point selection, the odds ratio per 1-mm higher T6 ONSD was 3.75 (95% confidence interval 1.44–12.32; p = 0.005). Areas under the receiver operating characteristic curves were 0.654 for Preop, 0.689 for T0, 0.728 for T6, and 0.626 for change, without evidence of superior T6 discrimination. The five-variable model had an apparent area under the curve of 0.839 and a conditional optimism-corrected value of 0.778; predictor and time-point selection were not repeated during validation. The internally selected 4.90-mm operating point was not an intracranial-hypertension threshold. 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.