Non-Invasive Estimation of Intracranial Pressure-Derived Cerebrovascular Reactivity Using Near-Infrared Spectroscopy Sensor Technology in Acute Neural Injury: A Time-Series Analysis

Abstract

The contemporary monitoring of cerebrovascular reactivity (CVR) relies on invasive intracranial pressure (ICP) monitoring which limits its application. Interest is shifting towards near-infrared spectroscopic regional cerebral oxygen saturation (rSO₂)-based indices of CVR which are less invasive and have improved spatial resolution. This study aims to examine and model the relationship between ICP and rSO₂-based indices of CVR. Through a retrospective cohort study of prospectively collected physiologic data in moderate to severe traumatic brain injury (TBI) patients, linear mixed effects modeling techniques, augmented with time-series analysis, were utilized to evaluate the ability of rSO₂-based indices of CVR to model ICP-based indices. It was found that rSO₂-based indices of CVR had a statistically significant linear relationship with ICP-based indices, even when the hierarchical and autocorrelative nature of the data was accounted for. This strengthens the body of literature indicating the validity of rSO₂-based indices of CVR and potential greatly expands the scope of CVR monitoring.

Keywords: cerebrovascular reactivity monitoring; intracranial pressure monitoring; near-infrared spectroscopy; neurotrauma.

Figure 1

From top to bottom can be seen the density plots of the pressure reactivity index (PRx), the arterial blood pressure-based cerebral oxygen index (COx_a), and the cerebral perfusion pressure-based cerebral oxygen index (COx).

Figure 2

The Bland–Altman plot comparing the 30-min-by-30-min pressure reactivity index (PRx) and the cerebral perfusion pressure-based cerebral oxygen index (COx). The dashed blue line represents the mean difference between the two parameters, indicative of fixed bias. The green dashed line represents the +1.96 standard deviation above the mean while the red dashed line represents the −1.96 standard deviation below the mean. The solid blue line is the line of best fit, indicative of proportional bias. The 95% CI surround each line.

Figure 3

The Bland–Altman plot comparing the 30-min-by-30-min pressure reactivity index (PRx) and the arterial blood pressure-based cerebral oxygen index (COx_a). The dashed blue line represents the mean difference between the two parameters, indicative of fixed bias. The green dashed line represents the +1.96 standard deviation above the mean while the red dashed line represents the −1.96 standard deviation below the mean. The solid blue line is the line of best fit, indicative of proportional bias. The 95% CI surround each line.

Figure 4

The Bland–Altman plot comparing the 30-min-by-30-min cerebral perfusion pressure-based cerebral oxygen index (COx) and the arterial blood pressure-based cerebral oxygen index (COx_a). The dashed blue line represents the mean difference between the two parameters, indicative of fixed bias. The green dashed line represents the +1.96 standard deviation above the mean while the red dashed line represents the −1.96 standard deviation below the mean. The solid blue line is the line of best fit, indicative of proportional bias. The 95% CI surround each line.

Figure 5

On the top is the modeled pressure reactivity index (PRx) by the cerebral perfusion pressure-based cerebral oxygen index (COx) versus the actual PRx. On the bottom is the modeled pressure reactivity index (PRx) by the arterial blood pressure-based cerebral oxygen index (COx_a) versus the actual PRx. Line of best fit in blue. All axes are in arbitrary units (AU).

Figure 6

The Bland–Altman plots comparing actual pressure reactivity index (PRx) and modeled PRx by cerebral perfusion pressure-based cerebral oxygen index (COx), top, and by arterial blood pressure-based cerebral oxygen index (COx_a), bottom. The dashed blue line represents the mean difference between the two parameters, indicative of fixed bias. The green dashed line represents the +1.96 standard deviation above the mean while the red dashed line represents the −1.96 standard deviation below the mean. The solid blue line is the line of best fit, indicative of proportional bias. The 95% CI surround each line.