Intracranial Pressure Threshold Heuristics in Traumatic Brain Injury: One, None, Many!

  
NCJ_cover.jpgBy Christos Lazaridis, Masoom Desai, George Damoulakis & Frederick A. Zeiler

First Online: 05 March 2020

Critical care of the patient with severe traumatic brain injury (TBI) revolves around strategies to address intracranial hypertension (IHT), and optimizing cerebral perfusion. Strong evidence associates IHT (especially refractory IHT) with mortality, and unfavorable clinical outcomes. However, this association may merely indicate that IHT is a surrogate for severity of injury and not necessarily a modifiable, outcome-altering, treatment target, i.e., some patients die with IHT, not from IHT. Another reason for intracranial pressure (ICP), and derived cerebral perfusion pressure (CPP), to be central tenets of bedside management is the fact that are relatively easily monitored as opposed to other secondary brain injury (SBI) mechanisms such as metabolic and energy crisis, cortical spreading ischemia, diffusion microvascular hypoxia, and mitochondrial failure. Consequently, we may be misled targeting what we can measure, not necessarily what matters. A further concern is that by solely focusing on one pathophysiological aspect we may ignore complex multidimensional cascades leading to SBI, and our treatment interventions run the risk of being counterproductive and harmful. Despite limitations, it is unlikely that ICP-guided management should or will entirely go away in the near future. One telling indication is the concerns, and responses, generated by the Benchmark Evidence from South American Trials: Treatment of Intracranial Pressure (BEST TRIP) trial [1]. This is the only level-1 evidence-producing randomized clinical trial (RCT) on the topic, finding no primary outcome difference among groups of TBI patients managed with ICP monitoring vs. an imaging and clinical exam (ICE) protocol. A consensus-of-experts conference was called to specifically alleviate a “misinterpretation” of the trial toward a nihilistic approach or an abandonment of ICP monitoring and targeted management [2].

In this viewpoint, we address the further issue of how to understand and decide upon the ICP threshold for intervention. We begin by a conceptual discussion of using physiologic thresholds as treatment-triggers in order to expose inherent flaws (and advantages) of threshold-driven protocols, and to contextualize assessment of the different approaches. A review follows, of merits and limitations of contemporary modes to ICP, namely the Brain Trauma Foundation (BTF) guidelines [3], the ICE protocol [4], and using multimodality neuromonitoring in order to individualize physiologic targets (Fig. 1 provides a summary). These perspectives roughly map to accepting a fixed and population-level ICP threshold, having no direct measurement and no ICP threshold, and having multiple, dynamic and individualized thresholds, respectively.

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