Low-frequency sampling for PRx calculation does not reduce prognostication and produces similar CPPopt in intracerebral haemorrhage patients

Abstract

The cerebral pressure reactivity index (PRx) correlates with the outcome in intracerebral haemorrhage (ICH) patients and has been used to define an autoregulation-oriented "optimal cerebral perfusion pressure" (CPPopt). PRx has been calculated as a moving correlation coefficient between mean arterial pressure (MAP) and intracranial pressure (ICP) averaged over 5-10 s, using a 2.5- to 5-min moving time window, in order to reflect changes in MAP and ICP within a time frame of 20 s to 2 min. We compared PRx with a different calculation method [low-frequency PRx (L-PRx)], where rapid fluctuations of MAP and ICP are cancelled (waves with frequencies greater than 0.01 Hz). A total of 548.5 h of artefact-free data (sampling frequency 1 Hz) from 18 patients suffering from non-traumatic ICH were included in the analysis. L-PRx was calculated using minute averages, between both MAP and ICP, in 20-min moving correlation windows. CPPopt was calculated based on PRx and on L-PRx. The averaged PRx values for each patient correlated with L-PRx (P = 0.846, p < 0.001). CPPopt based on standard PRx was identified in eight patients. In contrast, a CPPopt value based on L-PRx could be found in 12 patients. CPPopt values by both methods correlated strongly with each other (P = 0.980, p < 0.001). L-PRx had a similar correlation with the National Institutes of Health Stroke Scale Score (NIHSS) (0.667, p = 0.002) as did PRx (0.563, p = 0.015). L-PRx correlated with the outcome as good as PRx did. CPPopt could be identified in more patients using L-PRx. Slower MAP and ICP changes (in the range of 1-20 min) can be used for autoregulation assessment and contain important prognostic information.