During the last decade, with the development of on-line monitoring and waveform analysis, integration of brain signals has increasingly been used in patients with traumatic brain injury (TBI) to guide clinical management and predict outcome.
The goal of this review is to describe current methodology for brain signal integration in TBI patients focusing on ‘reactivity indices’.
We reviewed selected techniques to monitor patients in the acute phase of TBI using the comparison and integration of different physiological signals. The autoregulation indices, Mx and Mxa were defined as the moving correlation between cerebral blood flow velocities (CBFV) and cerebral perfusion pressure (CPP) or arterial blood pressure (ABP), respectively. The cerebrovascular pressure reactivity index PRx was defined as the moving correlation coefficient between ABP and intracranial pressure (ICP). The oxygen reactivity index, Orx, was defined as the moving correlation coefficient between brain tissue oxygenation and CPP. Finally, Tox was defined as the moving correlation coefficient between brain tissue oxygenation measured by Near Infrared Spectroscopy (NIRS) and ABP.
Both Mx > 0.3 and Mxa > 0.45 as well as an asymmetry of Mx between both hemispheres of the brain in the acute phase were associated with poor outcome. PRx may be used to determine the individual optimal CPP and is also a powerful and independent predictor of outcome. Orx showed conflicting results and more studies are need to determine its role in the acute setting of TBI. Studies concerning the role of NIRS in the acute phase of TBI are ongoing.
Multimodal neuromonitoring (MNM) is useful in the neuroICU as it provides valuable insights into the pathophysiological mechanisms occurring in the acute phase of TBI. Furthermore, indices obtained with MNM have been shown to be strong predictors of outcome. Further studies combining current and emergent techniques such as NIRS emphasize on the ability for MNM to continuously evolve.