The pressure reactivity index (PRx) has emerged as a surrogate method for the continuous bedside estimation of global cerebral autoregulation and a significant predictor of unfavorable outcomes. However, calculations require continuous, high-resolution monitoring and are currently limited to specialized ICUs with dedicated software. To overcome this problem, new indices calculated using one-minute average data, instead of 10-second average data as performed by the PRx, have been proposed.

The study aims to test new physiological indices appropriately modified to adapt to the scarcity of output data generated by standard hospital systems (frequency ~0.0033 Hz, approximately a 5-minute period) and to evaluate their association with outcome measures.

Data preparation and index calculations were performed using an in-house algorithm.

Data extracted and processed with the algorithm:

Ultra-low pressure reactivity index (UL-PRx), Intracranial pressure (ICP), Cerebral perfusion pressure (CPP), Arterial blood pressure (ABP), heart rate (HR), respiratory rate (RR), temperature, end-tidal CO2 (EtCO2), saturation (SpO2).

Inclusion Criteria:

• Patients with a clinical diagnosis of acute neurological injury requiring intracranial pressure (ICP) monitoring.
• Availability of continuous intensive care monitoring of physiological data.

Exclusion Criteria:

Patients with less than 8 hours of physiological data monitoring.

Patients with acute neurological injury admitted to ICU of the ASST Papa Giovanni XXIII requiring ICP monitoring during the study period (January 2013 - June 2022). For Traumatic Brain Injury (TBI) it is estimated that medical records from approximately 210 TBI subjects requiring ICP monitoring will be reviewed. The final number of subjects to be included will be determined based on available medical records obtained within the timeframe of the estimated duration of the study.