Early dexmedetomidine and postoperative RASS-defined examinability after microsurgical clipping for aneurysmal subarachnoid hemorrhage: a time-resolved 24-h landmark cohort study.

Background: After microsurgical clipping for aneurysmal subarachnoid hemorrhage (aSAH), sedation should preserve neurological examinability without compromising hemodynamics or nimodipine delivery. We examined whether early postoperative dexmedetomidine was associated with a greater post-landmark RASS-defined examinability. Methods: We retrospectively reviewed adults with aSAH treated with clipping at one center from October 2021 to October 2025. Early dexmedetomidine was initiation within 24 h after clipping and continuation for at least 2 h. Exposure was classified during 0-24 h. The primary endpoint was the time-weighted proportion of observed 24-72 h time in RASS-defined examinability defined without reference to the contemporaneous ordered target (Richmond Agitation-Sedation Scale [RASS] -2 to 0). Ordered-target attainment was the key secondary endpoint. Hour-level states were modeled in consecutive 6-h bins using generalized estimating equations (GEE); target-conditional and shared examinable-target-band analyses tested whether easier prescription targets explained the association. The endpoint hierarchy was finalized after data analysis during peer review; the study was not preregistered, no multiplicity adjustment was applied, and all estimates are exploratory. Results: Among 123 eligible patients, 120 were alive and classifiable at 24 h; 41 received early dexmedetomidine and 79 did not. Examinable time during 24-72 h was 68% versus 55% (Hodges-Lehmann location shift, 12 percentage points; 95% CI, 5-19), and the GEE-adjusted marginal difference was 11.8 points (95% CI, 4.1-19.5). Early users had less post-landmark deep-sedation time; post-landmark co-sedative exposure, dose, and duration differences were directionally lower but imprecise. Ordered-target attainment was directionally concordant; the primary association remained after adding ordered-target stratum and in the shared-target restriction. Window-specific differences were 15.2 points (95% CI, 6.0-24.4) and 6.3 points (95% CI, -2.4 to 15.0); the exposure-by-window interaction was imprecise (difference-in-differences, 8.9 points; 95% CI, -3.6 to 21.4; Conclusion: The principal finding was greater post-landmark RASS-defined examinability; related care-process and co-sedative measures were not independent validation. Its descriptive concentration during 24-48 h was not confirmed by the formal interaction test and remains hypothesis-generating, with bradycardia as the principal trade-off. The findings remain vulnerable to confounding by indication and do not establish a drug-specific causal effect or downstream clinical benefit.