UE-CHEUNG HOWei, NathanNathanWeiLU-TING KUO2026-04-212026-04-212026-02-1121938253https://scholars.lib.ntu.edu.tw/handle/123456789/737337Introduction: Aneurysmal subarachnoid hemorrhage (aSAH) disrupts cerebral autoregulation, contributing to secondary brain injury and poor outcomes. The low-frequency pressure reactivity index (LPRx) is an indirect index of autoregulatory function derived from invasive intracranial pressure (ICP) and arterial blood pressure (ABP) monitoring; however, its clinical dynamics in aSAH remain underexplored. This study aimed to characterize the temporal behavior of the LPRx in patients with aSAH, assess its response to standard interventions, and compare it with that in non-injured neurosurgical controls. Methods: This retrospective study included 30 patients with aSAH and 28 controls who underwent tumor resection via external ventricular drain placement. The LPRx was calculated from continuous ICP and ABP recordings over the first 7 days post-admission. Outcomes included survival, functional status (Glasgow Outcome Scale-Extended), and responses to cerebrospinal fluid (CSF) diversion and osmotherapy. The LPRx patterns were compared across groups and analyzed relative to the ICP and optimal cerebral perfusion pressure (CPPopt). Results: The LPRx was significantly higher in patients with aSAH than in controls, particularly among non-survivors. The LPRx showed a consistent U-shaped relationship with ICP, with optimal autoregulation at 5–15 mmHg. No significant changes in the LPRx were observed after CSF diversion, osmotherapy, or different treatment modalities. CPPopt showed no clear association with the LPRx. Conclusion: The LPRx is a feasible and physiologically relevant marker of autoregulatory integrity in aSAH. Its consistent elevation and non-linearity with ICP highlight its potential for individualized ICP management. Conventional interventions do not significantly restore autoregulation, highlighting the need for LPRx-informed treatment strategies. © The Author(s) 2026.entrueAneurysmal subarachnoid hemorrhageCerebral autoregulationIntracranial pressureLumbar drainPressure reactivity indexjournal article10.1007/s40120-025-00883-y2-s2.0-105030076101