Intracranial Pressure Variability and Low Cerebral Perfusion Pressure Burden as Prognostic Markers Beyond Mean Pressure in Neurocritically Ill Patients

Background/Objectives: Elevated intracranial pressure (ICP) drives secondary brain injury and poor outcome. The pressure reactivity index (PRx), the reference marker of cerebral autoregulation, requires high-frequency waveforms unavailable in many centers. We examined whether routinely charted hourly ICP and cerebral perfusion pressure (CPP) can stratify prognosis without the PRx. Methods: In a retrospective cohort of 990 adults with invasive ICP monitoring at a tertiary neurosurgical ICU (a predominantly non-traumatic case mix), we derived from hourly ICP the mean, variability (within-patient standard deviation), and peak burden (time above 22 mmHg), and from CPP the low-perfusion burden (time below 60 mmHg). Each metric (per 1 SD) was related to 28-day mortality and poor neurological outcome (Glasgow Outcome Scale 1–3), adjusted for age, sex, APACHE II, GCS, diagnosis, and mean ICP, with incremental value and sensitivity analyses. Results: In total, 86 of 990 patients died within 28 days. ICP variability was associated with both mortality and poor neurological outcome and, unlike peak burden, remained independent after adjustment for mean ICP. Peak burden lost significance once mean and variability were known. For CPP, hypoperfusion burden, but not CPP variability, was associated with mortality. CPP variability did not survive joint modeling with ICP variability. Excess risk was confined to low CPP, with no harm at high CPP. ICP variability added incremental value beyond a clinical model, robust to sensitivity analyses. Conclusions: Routinely available ICP variability and CPP hypoperfusion burden carry prognostic information beyond mean pressure. ICP variability predicted both outcomes, whereas hypoperfusion burden predicted mortality. These summaries may offer a pragmatic alternative where the PRx is unavailable, pending validation.