Continuous Determination of the Optimal Bispectral Index Value Based on Cerebrovascular Reactivity in Moderate/Severe Traumatic Brain Injury: A Retrospective Observational Cohort Study of a Novel Individualized Sedation Target

Abstract

BACKGROUND:We have sought to develop methodology for deriving optimal bispectral index (BIS) values (BISopt) for patients with moderate/severe traumatic brain injury, using continuous monitoring of cerebrovascular reactivity and bispectral electroencephalography. METHODS:Arterial blood pressure, intracranial pressure, and BIS (a bilateral measure that is associated with sedation state) were continuously recorded. The pressure reactivity index, optimal cerebral perfusion pressure (CPPopt), and BISopt were calculated. Using BIS values and the pressure reactivity index, a curve fitting method was applied to determine the minimum value for the pressure reactivity index thus giving the BISopt. RESULTS AND CONCLUSIONS:Identification of BISopt was possible in all of the patients, with both visual inspection of data and using our method of BISopt determination, demonstrating a similarity of median values of 44.62 (35.03-59.98) versus 48 (39.75-57.50) (p = 0.1949). Furthermore, our method outperformed common CPPopt curve fitting methods applied to BISopt with improved percent (%) yields on both the left side 52.1% (36.3-72.4%) versus 31.2% (23.0-48.9%) (p < 0.0001) and the right side 54.1% (35.95-75.9%) versus 33.5% (12.5-47.9%) (p < 0.0001). The BIS values and BISopt were compared with cerebral perfusion pressure, mean arterial pressure, and CPPopt. The results indicated that BISopt's impact on pressure reactivity was distinct from CPPopt, cerebral perfusion pressure, or mean arterial pressure. Real-time BISopt can be derived from continuous physiologic monitoring of patients with moderate/severe traumatic brain injury. This BISopt value appears to be unassociated with arterial blood pressure or CPPopt, supporting its role as a novel physiologic metric for evaluating cerebral autoregulation. BISopt management to optimize cerebrovascular pressure reactivity should be the subject of future studies in moderate/ severe traumatic brain injury.

Optimal bispectral index level of sedation and cerebral oximetry in traumatic brain injury: a non-invasive individualized approach in critical care?

“…All signals were recorded using digital data transfer or digitized via an A/D converter (DT9803/DT9804/DT9826; Data Translation, Marlboro, MA) and where appropriate sampled at a frequency of 100 Hz, using the ICM+ software (Cambridge Enterprise Ltd., Cambridge, UK, http://icmplus.neurosurg.cam.ac.uk ). Signal artifacts were removed using both manual and automated methods prior to further processing or analysis, identical to past work by our lab [ 13 , 14 , 39 , 40 ].…”

“…To determine BISopt in individual patients, a 60-s median BIS time trend was calculated alongside COx_a. Similar to past work by Aries et al in optimal cerebral perfusion pressure (CPPopt) determination [ 6 ] and our group for BISopt [ 14 ], a custom created automatic quadratic curve-fitting method was applied to the binned BIS data to determine the BIS value with the lowest associated COx_a values (for details see Additional file 1 A). Notably COx_a index ranges from − 1 to 1, with values higher than ~ 0.3 au (arbitrary units) being linked with impaired cerebrovascular reactivity, thus higher COx_a values are considered to worsen autoregulatory status.…”

“…Our group has recently demonstrated an association between individualized depth of sedation (as measured through the bispectral index; BIS) and PRx [ 13 , 14 ]. This indicates that there is potentially an optimal sedation depth, with regard to cerebrovascular reactivity, that can be attained during TBI care.…”

“…This individualized sedation target, called BISopt, offers a potential avenue for true personalized medicine in moderate/severe TBI patients, focusing on the sedation target where cerebrovascular reactivity is the most intact. Our previous work has demonstrated that BISopt, determined using PRx, can be continuously derived at the bedside and varies between patients and over time [ 14 ]. Furthermore, we highlighted the impact of both over-sedation and under-sedation in this population, finding that both lead to worse cerebrovascular reactivity and potentially expose patients to ongoing secondary brain injuries [ 14 ].…”

“…Our previous work has demonstrated that BISopt, determined using PRx, can be continuously derived at the bedside and varies between patients and over time [ 14 ]. Furthermore, we highlighted the impact of both over-sedation and under-sedation in this population, finding that both lead to worse cerebrovascular reactivity and potentially expose patients to ongoing secondary brain injuries [ 14 ].…”