Real-time correlation coefficient between MAP and ICP slow waves.
Autoregulation Probe
Input the calculated PRx value to interpret the current state of cerebral pressure reactivity and autoregulatory capacity.
Guidelines & Evidence
Clinical Details
Section 1
When to Use
When to Use
Advanced neuro-monitoring in severe TBI.
Determining the health of cerebral autoregulation.
Identifying the "Optimal CPP" (CPPopt) for an individual patient.
Prognosticating outcomes based on autoregulatory capacity.
Section 2
Formula & Logic
Pearson Correlation
PRx is a rolling correlation coefficient (calculated over 5-minute windows) between slow oscillations of Mean Arterial Pressure (MAP) and Intracranial Pressure (ICP).
Interpretive Values
PRx Value
Meaning
Vessel State
Negative (-1 to -0.2)
Intact Autoregulation
Vessels constrict when BP rises (Active).
-0.2 to +0.2
Transitional
Fragile or varying reactivity.
Positive (+0.2 to +1)
Impaired Autoregulation
Vessels are passive pipes; follow MAP.
Section 3
Pearls/Pitfalls
The Passive Pipe Danger
A highly positive PRx (> 0.3) is a predictor of mortality. It signifies that any increase in systemic blood pressure will be transmitted directly to the cerebral capillary bed, causing rapid oedema and ICP spikes. Conversely, any drop in MAP will lead to immediate, undefended cerebral ischaemia.
Section 4
Evidence Appraisal
Primary Reference
Continuous assessment of the cerebral vasomotor reactivity in head injury
Czosnyka M et al. • Neurosurgery. 1997;41(1):11-17; discussion 17-19
