Further Controversies About Brain Tissue Oxygenation Pressure-Reactivity After Traumatic Brain Injury
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ORIGINAL ARTICLE
Further Controversies About Brain Tissue Oxygenation Pressure-Reactivity After Traumatic Brain Injury Morten Andresen1,2 • Joseph Donnelly1 • Marcel Aries1,3 • Marianne Juhler2 David Menon4 • PJA Hutchinson1 • Peter Smielewski1
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Ó Springer Science+Business Media, LLC 2017
Abstract Background Continuous monitoring of cerebral autoregulation is considered clinically useful due to its ability to warn against brain ischemic insults, which may translate to a relationship with adverse outcome. It is typically performed using the pressure reactivity index (PRx) based on mean arterial pressure and intracranial pressure. A new ORx index based on brain tissue oxygenation and cerebral perfusion pressure (CPP) has been proposed that similarly allows for evaluation of cerebrovascular reactivity. Conflicting results exist concerning its clinical utility. Methods Retrospective analysis was performed in 85 patients with traumatic brain injury (TBI). ORx was calculated using three time windows of 5, 20, and 60 min. Correlation coefficients and individual ‘‘optimal CPP’’ (CPPopt) were calculated using both PRx and ORx, and relation to patient outcome investigated. Results Correlation coefficients for all comparisons between PRx and ORx indicated poor association between these indices (range from -0.04 to 0.07). PRx was significantly lower in patients with good outcome (p = 0.01), while none of the ORx indices proved to be significantly
& Morten Andresen [email protected] 1
Division of Neurosurgery, Department of Clinical Neurosciences, Cambridge University Hospital, Cambridge, UK
2
Clinic of Neurosurgery, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark
3
Department of Neurology, University of Groningen, Groningen, The Netherlands
4
Division of Anesthesiology, Cambridge University Hospital, Cambridge, UK
different in the two outcome groups. Higher mortality related to average CPP < CPPopt was found regardless of which index was used to calculate CPPopt. Conclusion In the TBI setting, ORx does not appear to correlate with vascular pressure reactivity as assessed with PRx. Its potential use for individualizing CPP thresholds remains unclear. Keywords ICP PRx ORx Tissue oxygenation CPPopt Cerebral perfusion pressure Cerebral autoregulation
Introduction Continuous monitoring of cerebral autoregulation is clinically useful because correction of failing autoregulation in intensive care may be achieved usually quite easily by modification of cerebral perfusion pressure (CPP), ventilation, regime of anesthesia, etc. It is likely to have a profound impact on the results of treatment, as autoregulation is strongly associated with patient outcome [1, 2]. In contrast to the relatively well-investigated indirect descriptor of autoregulation, the pressure reactivity index (PRx) [3–5], we still lack clarity concerning the clinical utility of a reactivity index based on brain tissue oxygenation (PbtO2), ORx, defined as the moving Pearson correlation coefficient between PbtO2 and CPP. T
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