A noninvasive method for assessing optimal cerebral perfusion pressure

INTRODUCTION : After acute brain injuries, optimizing cerebral perfusion pressure (CPP) is critical for preventing secondary brain insults, yet current fixed CPP targets may not be ideal for all patients due to individual variability in cerebrovascular autoregulation (CA). The concept of"optimal CPP" (CPPopt) or "optimal mean arterial pressure" (MAPopt) identifies the specific pressure range where CA is most effective. The Pressure-Reactivity Index (PRx), derived from invasive intracranial pressure (ICP) and arterial blood pressure (ABP) monitoring, is a well-established means for assessing CA and MAPopt. This study aimed to investigate the ability of noninvasive surrogate ICP waveforms, specifically the P2/P1 ratio acquired using a cranial deformation sensor (B4C), to determine MAPopt in patients with acute brain injury, and to compare its efficacy with the established invasive PRx method. METHODS: This paper provides a retrospective analysis of data from a multicenter prospective observational study of intensive care patients with severe brain injuries requiring invasive ICP monitoring. Continuous invasive ABP and ICP data were collected alongside noninvasive ICP waveforms using the B4C sensor. MAPopt was determined for each monitoring session using two methods: (1) the nadir of a polynomial regression curve fitted to PRx values (correlation between ICP and ABP) stratified by 1 mmHg MAP intervals, and (2) the nadir of a polynomial regression curve fitted to the noninvasive P2/P1 ratio, also stratified by MAP intervals. Repeated measures correlation was used to analyze their correspondence and P2/P1 ratio ranges within MAPopt limits, whereas Bland-Altman analysis for the methods agreement. RESULTS : A total of 114 patients were included in the study, 68% severe traumatic brain injury and 15% spontaneous subarachnoid hemorrhage. Analysis of optimal MAP for each session revealed a strong linear relationship between the MAPopt derived from the invasive PRx and the noninvasive P2/P1 ratio (r = 0.905, p<0.0001). Bland-Altman analysis demonstrated good agreement between the two methods, with a mean difference of+2.00 mmHg and 95% limits of agreement ranging from −9.87 mmHg to +13.86 mmHg. CONCLUSION : The noninvasive P2/P1 ratio, serving as a marker of intracranial compliance, may effectively and accurately infer the optimal systemic mean arterial pressure. A noninvasive neuromonitoring tool may enable personalized, bedside-guided therapeutic management, significantly widening the assessment of cerebrovascular autoregulation in critical care settings.