Evaluation of the Prognostic Value and Modifiability of Low-Frequency Pressure Reactivity Index in Patients with Traumatic Brain Injury

Background/Objective : Cerebral autoregulation is a critical determinant of traumatic brain injury (TBI) outcomes. Low-frequency pressure reactivity index (LPRx), from routine monitoring, dynamically assesses autoregulation; impairment (elevated LPRx) is linked to poor outcomes. However, the impact of clinical interventions on LPRx and LPRx-derived optimal CPP (CPPopt) utility are unclear. This study evaluated LPRx's prognostic value and therapeutic modifiability in TBI patients, examining its dynamics related to 6-month clinical outcomes (survival, Glasgow Outcome Scale Extended [GOSE]) and common neurocritical care interventions. Methods : We conducted a retrospective analysis of 35 moderate-to-severe TBI patients undergoing neurosurgery and intensive care unit (ICU) monitoring with minute-by-minute recordings at two Taiwanese university hospitals (2022-2024). LPRx (moving Pearson correlation of 1-minute averaged arterial blood pressure/ICP) and CPPopt (nadir of LPRx-CPP curve) were calculated. Patients were stratified by 6-month survival and GOSE (favorable: GOSE 5–8; unfavorable: GOSE 1–4). LPRx relationships with outcomes, ICP, CPPopt, decompressive craniectomy, and mannitol were analyzed using non-parametric tests and generalized estimating equations (GEE). Results : Among 35 patients (26 survivors, 8 favorable outcomes), significantly higher median LPRx and a greater proportion of time with LPRx > thresholds (e.g., >0.2, p=0.013) correlated with unfavorable outcomes. Early impaired LPRx (days 1, 3, 4) was associated with unfavorable function. LPRx showed a U-shaped ICP relationship (nadir ~10 mmHg). CPPopt was derivable in only 32% of monitoring time, with no consistent LPRx relationship. Decompressive craniectomy and mannitol did not significantly alter LPRx (mannitol GEE: p=0.786). Conclusion : Impaired cerebral autoregulation (elevated LPRx) is associated with poor TBI outcomes. While CPPopt is an attractive theoretical target, its limited feasibility and inconsistent physiological correlation pose challenges to its clinical utility. LPRx offers a continuous, practical measure; however, its responsiveness to conventional therapies remains uncertain, warranting further investigation. Registration : The study design was not preregistered.