Visualizing the pressure and time burden of intracranial hypertension in adult and paediatric traumatic brain injury

Abstract

Take-home message:In adult and paediatric patients suffering from severe traumatic brain injury, an approximately exponential curve describes the relationship between intensity and duration of episodes of increased intracranial pressure (ICP) and worse clinical outcomes. In children, compared to adults, this occurs at lower ICP thresholds of shorter duration. Electronic supplementary materialThe online version of this article (doi:10.1007/s00134-015-3806-1) contains supplementary material, which is available to authorized users. To assess the impact of the duration and intensity of episodes of increased intracranial pressure on 6-month neurological outcome in adult and paediatric traumatic brain injury. Methods:Analysis of prospectively collected minute-by-minute intracranial pressure and mean arterial blood pressure data of 261 adult and 99 paediatric traumatic brain injury patients from multiple European centres. The relationship of episodes of elevated intracranial pressure (defined as a pressure above a certain threshold during a certain time) with 6-month Glasgow Outcome Scale was visualized in a colour-coded plot. Results:The colour-coded plot illustrates the intuitive concept that episodes of higher intracranial pressure can only be tolerated for shorter durations: the curve that delineates the duration and intensity of those intracranial pressure episodes associated with worse outcome is an approximately exponential decay curve. In children, the curve resembles that of adults, but the delineation between episodes associated with worse outcome occurs at lower intracranial pressure thresholds. Intracranial pressures above 20 mmHg lasting longer than 37 minutes in adults, and longer than 8 minutes in children, are associated with worse outcomes. In a multivariate model, together with known baseline risk factors for outcome in severe traumatic brain injury, the cumulative intracranial pressure-time burden is independently associated with mortality. When cerebrovascular autoregulation, assessed with the low-frequency autoregulation index, is impaired, the ability to tolerate elevated intracranial pressures is reduced. When the cerebral perfusion pressure is below 50 mmHg, all intracranial pressure insults, regardless of duration are associated with worse outcome. Conclusions:The intracranial pressure-time burden associated with worse outcome is visualised in a colour-coded plot. In children, secondary injury occurs at lower intracranial pressure thresholds as compared to adults. Impaired cerebrovascular autoregulation reduces the ability to tolerate intracranial pressure insults. Thus, 50 mmHg might be the lower acceptable threshold for cerebral perfusion pressure.

Visualizing secondary brain insults: does the emperor have new clothes?

“…They found a significant relationship between the dose of ICP, patient outcome, and the worst Marshall head CT score. The results of Güiza et al [6] confirm these data by showing that more than a given threshold, the duration of ICP above the treatment goal is probably a critical determinant of patient outcome.…”

“…These individualized doses of intracranial hypertension were stronger predictors of death than doses derived from the standard threshold of 20 mmHg. In the current article by Güiza et al [6], the association between ICP insults and outcome was examined at three different CPP thresholds (50, 60, and 70 mmHg), with elevated ICP no longer tolerated when CPP was below 50 mmHg. Furthermore, there is a suggestion that an ICP threshold of 25 mmHg is not tolerated for more than 10-20 min regardless of the autoregulatory state and thus may be a more appropriate clinical trigger threshold than the more commonly used threshold of 20 mmHg.…”

“…The study by Güiza et al [6] published in this issue of Intensive Care Medicine describes a new way for assessing the consequences of elevated ICP on outcome after TBI. Using color-coded plots the authors correlated the score on the Glasgow Outcome Scale at 6 months with the number, intensity, and duration of ICP elevations.…”

“…A notable finding of the Güiza et al study [6] is the demonstration that when the cerebral perfusion pressure (CPP) was below 50 mmHg, any ICP insult was associated with worse outcome. This strongly suggests that the status of pressure autoregulation in an individual patient plays a key role in how dose-insults of ICP are ''tolerated.''…”

“…It is relevant to note that the observed association does not mean causality, and as acknowledged by the authors, this direct data visualization will not provide a direct modification of the current ICP thresholds. However, the data presented here [6] seems to give some insight into why randomized clinical trials that use a uniform treatment threshold of 20 mmHg to initiate have failed and frankly may continue to do so [2,4].…”