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

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Abstract

Background

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).

Methods

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.

Results

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).

Conclusions

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.

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Conflicts of interest

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Authors and Affiliations

  1. Department of Neurosurgery, University of Heidelberg, Im Neuenheimer Feld 400, 69120, Heidelberg, Germany

    Edgar Santos, Berk Orakcioglu, Modar Kentar, Andreas Unterberg & Oliver W. Sakowitz

  2. Department of Neurology, University of Heidelberg, Heidelberg, Germany

    Jennifer Diedler & Marek Sykora

  3. Department of Clinical Neurosciences, Neurosurgical Unit, University of Cambridge, Addenbrooke’s Hospital, Cambridge, UK

    Marek Czosnyka

Authors
  1. Edgar Santos
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  2. Jennifer Diedler
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  3. Marek Sykora
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  4. Berk Orakcioglu
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  5. Modar Kentar
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  6. Marek Czosnyka
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  7. Andreas Unterberg
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  8. Oliver W. Sakowitz
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Corresponding author

Correspondence to Edgar Santos.

Additional information

Comment

This prospective study demonstrates a different manner of calculating cerebral pressure reactivity in patients with intracerebral hemorrhages and correlates it to optimal cerebral perfusion pressure calculation in this population of patients. As opposed to previously utilized high frequency sampling to generate cerebral reactivity, the authors utilize low-frequency (L-PRx) sampling and show a more reproducible and correlative value to determining optimal perfusion pressure (CPPopt) that appears more prognostic in predicting outcomes.

Although the sample size is small, the L-PRx and CPPopt values can provide prognostic information that will help guide therapy in this patient population. It will be interesting to evaluate brain tissue oxygenation information—via the Licox—and its relationship to L-PRx and CPPopt. I encourage the authors to pursue incorporating the brain oxygenation data with their calculation of CPPopt. We know, for instance, with subarachnoid hemorrhage and traumatic brain injury that increasing CPP to “optimal” values can result in a reduction of brain tissue oxygenation, and poorer outcomes.

Understanding L-PRx, CPPopt and brain tissue oxygenation relationships in the various neuropathologic conditions will direct novel and clinically relevant therapies.

Michael W. Weaver

Christopher M. Loftus

Philadelphia, USA

E. Santos and J. Diedler contributed equally to this study

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Santos, E., Diedler, J., Sykora, M. et al. Low-frequency sampling for PRx calculation does not reduce prognostication and produces similar CPPopt in intracerebral haemorrhage patients. Acta Neurochir 153, 2189–2195 (2011). https://doi.org/10.1007/s00701-011-1148-5

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  • DOI: https://doi.org/10.1007/s00701-011-1148-5

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