ORIGINAL ARTICLE Continuous Monitoring of Cerebrovascular Reactivity Using Pulse Waveform of Intracranial Pressure Marcel J. H. Aries • Marek Czosnyka • Karol P. Budohoski • Angelos G. Kolias • Danila K. Radolovich • Andrea Lavinio • John D. Pickard • Peter Smielewski Published online: 3 April 2012 Ó Springer Science+Business Media, LLC 2012 Abstract Background Guidelines for the management of traumatic brain injury (TBI) call for the development of accurate methods for assessment of the relationship between cere- bral perfusion pressure (CPP) and cerebral autoregulation and to determine the influence of quantitative indices of pressure autoregulation on outcome. We investigated the relationship between slow fluctuations of arterial blood pressure (ABP) and intracranial pressure (ICP) pulse amplitude (an index called PAx) using a moving correla- tion technique to reflect the state of cerebral vasoreactivity and compared it to the index of pressure reactivity (PRx) as a moving correlation coefficient between averaged values of ABP and ICP. Methods A retrospective analysis of prospective 327 TBI patients (admitted on neurocritical care unit of a university hospital in the period 2003–2009) with continuous ABP and ICP monitoring. Results PAx was worse in patients who died compared to those who survived (-0.04 ± 0.15 vs. -0.16 ± 0.15, v 2 = 28, p < 0.001). In contrast to PRx, PAx was able to differentiate between fatal and non-fatal outcome in a group of 120 patients with ICP levels below 15 mmHg (-0.04 ± 0.16 vs. -0.14 ± 0.16, v 2 = 6, p = 0.01). Conclusions PAx is a new modified index of cerebro- vascular reactivity which performs equally well as established PRx in long-term monitoring in severe TBI patients, but importantly is potentially more robust at lower values of ICP. In view of establishing an autoregulation- oriented CPP therapy, continuous determination of PAx is feasible but its value has to be evaluated in a prospective controlled trail. Keywords Brain injuries Á Intracranial pressure Á Physiological adaptation Á Outcome assessment Á Wavelet analysis Introduction The latest Brain Trauma Foundation guidelines for the management of traumatic brain injury (TBI) call for the development of ‘minimally invasive, efficient, and accurate methods for determining the relationship between cerebral perfusion pressure (CPP) and cerebral autoregulation’ and conclude ‘there is a need for randomized trials of the influence on outcome of basing optimal CPP […] on quantitative indices of pressure autoregulation’ [1]. Among such indices of cerebral autoregulation, the most commonly used in neurocritical care units (NCCU) is the pressure reactivity index (PRx), which reflects the capa- bility of smooth muscle tone in the wall of cerebral arterioles to react to changes in transmural pressure [2, 3]. M. J. H. Aries Á M. Czosnyka Á K. P. Budohoski Á A. G. Kolias Á J. D. Pickard Á P. Smielewski Academic Neurosurgery Unit, Department of Clinical Neurosciences, University of Cambridge, Cambridge, UK M. J. H. Aries (&) Department of Neurology, University Medical Centre Groningen, Hanzeplein 1, 9700 RB Groningen, The Netherlands e-mail: m.j.h.aries@umcg.nl D. K. Radolovich Department of Intensive Care, University Hospital of Pavia, Pavia, Italy A. Lavinio Neurosciences Critical Care Unit, Addenbrooke’s Hospital, Cambridge, UK 123 Neurocrit Care (2012) 17:67–76 DOI 10.1007/s12028-012-9687-z