INTRODUCTION

Background

Traumatic brain injury (TBI) is characterized by an alteration in brain function or other evidence of brain pathology resulting from an external force [1]. TBI severity is typically classified based on the Glasgow Coma Scale (GCS) score at presentation. Accurately determining a patient’s state of consciousness is crucial when managing TBI. The bispectral index (BIS) is an objective tool originally designed to assess consciousness in patients under anesthesia [2–4] and has recently been adapted for use in intensive care units (ICUs). Although the GCS is widely used, it has several limitations. For instance, stimulation during assessment may be detrimental, injuries to the eyes, ears, or spinal cord can interfere with results, and patients in a vegetative state might still open their eyes. In addition, the GCS is subject to interobserver variability. Consequently, an objective tool that complements the GCS by providing a numerical measure of consciousness could enhance the assessment of TBI severity and prognosis.

Objectives

The present study was conducted to evaluate the correlation between GCS and BIS values in TBI patients.

METHODS

Ethics statement

The study was approved by the Institutional Review Board of B. J. Government Medical College (No. BJGMC/IEC/Pharmac/D-0221063-063). Written informed consent for publication of the research details and clinical images were obtained from the patient. This study is part of a trial registered in the Clinical Trials Registry-India (No. CTRI/2021/03/031924).

Study design

This prospective observational study was conducted on 60 patients after obtaining approval from the ethical committee. This study was carried out at a tertiary care center (Sassoon General Hospital, Pune, India) between March and September 2021. The primary objective was to evaluate the correlation between the GCS and BIS values in TBI patients, while secondary objectives included determining the range of BIS scores corresponding to different levels of consciousness and assessing the correlation among mild, moderate, and severe TBI.

Patients

Sixty patients with head trauma who met the inclusion criteria and were admitted to the neurotrauma intensive care unit with TBI were enrolled after obtaining written informed consent from the patients or their guardians. Inclusion criteria included the presence of a computed tomography (CT)-detected hemorrhagic lesion—defined as an epidural hematoma, subdural hematoma, cerebral contusion, cerebral hemorrhage, or subarachnoid hemorrhage—and an age between 18 and 70 years. Patients with a BIS signal quality index of less than 50% were also excluded. Exclusion criteria comprised prehospital cardiac arrest, near brain-death clinical findings after resuscitation, abnormal baseline mental status (e.g., dementia, mental retardation), general anesthesia within the previous 24 hours, sedation and/or paralysis, deafness, and inability to tolerate the forehead BIS sensors.

A thorough history and physical examination were performed. Patient details recorded included age, sex, diagnosis, intubation status, past medical history (including comorbidities such as hypertension, diabetes, and previous neurological conditions), past surgical history, and ICU admission details (including duration of stay and need for ventilatory support). CT brain findings and vital signs were also documented. The patients' GCS and BIS values were recorded at 0, 6, 12, 18, and 24 hours.

Statistical analysis

Assuming a 95% confidence level (z), an 80% disease prevalence (p) based on previous studies, and a precision (d) of 5%, the sample size was calculated using the following formula:

n=z2⋅p⋅1−pd2

Since the calculated sample size was 57.8, enrolling 60 patients was deemed sufficient for our investigation [3,4].

Quantitative data were presented as mean and standard deviation, while qualitative data were summarized using frequency and percentage tables. The unpaired t-test was applied to compare research groups based on normality test results, and associations were evaluated using the Fisher test, Student t-test, and chi-squared test. A P-value below 0.05 was considered statistically significant. Where appropriate, results were displayed graphically. Statistical analyses were performed using software including Microsoft Excel (Microsoft Corp) and IBM SPSS ver. 20 (IBM Corp).

RESULTS

The mean age of the patients was 43.02±15.92 years, with the largest proportion (25.0%) in the 31–40 years age group (Fig. 1). The study group was predominantly male (86.7%), with female patients comprising 13.3% of the participants. Eighteen patients (30.0%) were intubated. The most common CT finding was subdural hematoma (SDH) with 37 patients (61.5%), followed by epidural hematoma (13 patients, 21.7%), SDH with multiple hemorrhagic contusions (6 patients, 10.0%), SDH with epidural hematoma (1 patient, 1.7%), intraventricular hemorrhage (1 patient, 1.7%), diffuse axonal injury (1 patient, 1.7%), and acute on chronic SDH (1 patient, 1.7%) (Fig. 2).

Spearman correlation analysis revealed a strong positive relationship between BIS and GCS at 0 hours (r=0.655, P<0.05), 6 hours (r=0.647, P<0.05), 12 hours (r=0.652, P<0.05), 18 hours (r=0.659, P<0.05), and 24 hours (r=0.648, P<0.05) (Table 1).

The mean BIS values for mild head injuries were 85.10±1.05 at 0 hours, 85.50±1.13 at 6 hours, 85.11±1.28 at 12 hours, 85.25±0.77 at 18 hours, and 85.65±1.03 at 24 hours. The mean BIS values for moderate head injuries were 72.98±4.01 at 0 hours, 73.62±3.93 at 6 hours, 73.88±3.98 at 12 hours, 74.43±3.89 at 18 hours, and 74.53±4.07 at 24 hours. The mean BIS values for severe head injuries were 59.55±2.68 at 0 hours, 60.09±3.18 at 6 hours, 60.65±2.62 at 12 hours, 61.33±3.14 at 18 hours, and 61.82±3.15 at 24 hours. The mean BIS value decreased significantly with increasing head injury severity at all time points, as confirmed by the analysis of variance (P<0.05) (Fig. 3).

DISCUSSION

This prospective study involving 60 patients investigated the correlation between the GCS and the BIS in individuals with TBI.

TBI severity was classified according to established neurotrauma guidelines into mild (GCS score, 13–15), moderate (GCS score, 9–12), and severe (GCS score, ≤8). The GCS is a validated tool for grading TBI severity; lower scores indicate greater neurological impairment and a higher risk of poor outcomes. Patients with mild TBI typically present with a GCS score of 13 to 15, whereas those with moderate TBI (GCS score, 9–12) often exhibit prolonged loss of consciousness, abnormal neuroimaging findings, and neurological deficits [5]. A GCS score of 8 or less indicates significant neurological injury and is classified as severe TBI.

Bispectral analysis was introduced in 1960 to analyze electroencephalogram (EEG) waveforms and produce a numerical output ranging from 0 (EEG suppression) to 100 (full consciousness) using an advanced algorithm. During general anesthesia, a BIS score between 40 and 60 indicates an adequate hypnotic effect. BIS values are updated every 0.5 seconds using a 2-second interval with 75% overlap, and the displayed value is refreshed every second. An internal window of change lasting 15 seconds introduces a delay in the displayed information [6]. The association between pathological CT findings and BIS values in head trauma patients underscores the value of BIS as a quantitative measure of consciousness, emphasizing the importance of early detection and intervention in TBI. Its application in the ICU has expanded to include assessment of consciousness in sedated patients and prediction of neurological outcomes in brain-injured patients, alongside auditory-evoked potentials, EEG, and somatosensory-evoked potentials [7].

In our study, a strong positive correlation was observed between GCS and BIS values. Kusken et al. [8] reported a statistically significant positive correlation at a level of 45.6% when analyzing BIS and GCS scores. Senapathi et al. [3] similarly found a strong positive correlation between BIS and GCS using Spearman correlation test, with BIS scores significantly associated with GCS scores. Another analytical study reported mean BIS values that differed significantly among mild, moderate, and severe head injuries (96.2±3.2, 45.5±1.2, and 31.3±2.08, respectively) [9]. Jarineshin et al. [10] found a significant relationship between BIS and GCS scores in TBI patients admitted to the ICU. Furthermore, Paul et al. [11] reported mean BIS values for mild and moderate head injuries of 65.7±16.1 and 85.7±6.1, respectively, with a significant correlation between the two indices in TBI patients undergoing craniotomy. Gill et al. [12] demonstrated a significant correlation between BIS and GCS scores in emergency department patients with reduced levels of consciousness (GCS score, ≤14).

Our study observed that mean BIS values decreased significantly with increasing head injury severity at 0, 6, 12, 18, and 24 hours, consistent with previous findings. For example, Senapathi et al. [3] reported mean BIS values of 84.1±5.6, 72.1±11.1, and 60.4±11.7 for mild, moderate, and severe head injuries, respectively. Additionally, Jarineshin et al. [10] identified an optimal BIS cutoff of 61.70—with a specificity of 83.3% and sensitivity of 71.4%—for distinguishing between mild and moderate brain injuries.

While GCS is subjective, BIS serves as an objective method for regular monitoring of the degree of consciousness. The substantial interobserver variability of GCS is one of its most frequently cited drawbacks [4,13–16]. Two emergency physicians assessed 116 patients; only 55% to 74% of the matched measurements were the same, and 6% to 17% differed by 2 or more points. When asked about the scores they assigned to intubated patients, 4 out of 73 level I trauma centers responded with "T" for the verbal component, 2 out of 3 gave 3 points for the total GCS of intubated patients, and 2 out of 6 gave 1 point [13].

Limitations

This study has several limitations. The small sample size (60 patients) may restrict statistical power and generalizability, necessitating validation in larger, multicenter studies. Surgical interventions, which may influence GCS recovery and thus the BIS–GCS correlation, were not considered. Although sedation and intubation were acknowledged as confounding factors, no statistical adjustments were made, potentially affecting the results. Future studies should employ multivariable analyses to control for these variables. In addition, BIS values may be affected by artifacts from medical instruments (e.g., warming blankets, suction devices, surgical tools, and muscle movements), and severe forehead soft tissue injuries may compromise BIS accuracy. Finally, since the BIS algorithm is calibrated for anesthetized patients rather than for TBI cases, further research is needed to refine its use in this population.

Conclusions

We observed a correlation between BIS and GCS in relation to the severity of head injury. This suggests that BIS may have potential as an adjunct tool alongside GCS in the assessment of patients with TBI. However, the current study's sample size limits the generalizability of this finding. Larger, well-designed studies are necessary to validate the role of BIS in predicting clinical outcomes in TBI patients before it can be recommended for routine prognostication.

ARTICLE INFORMATION

Author contributions

Conceptualization: all authors; Data curation: all authors; Formal analysis: all authors; Investigation: all authors; Methodology: all authors; Visualization: all authors; Writing–original draft: all authors; Writing–review & editing: all authors. All authors read and approved the final manuscript.

Conflicts of interest

The authors have no conflicts of interest to declare.

Funding

The authors received no financial support for this study.

Data availability

Data analyzed in this study are available from the corresponding author upon reasonable request.

Fig. 1.

Distribution of patients according to age.

Fig. 2.

Distribution of patients according to computed tomography (CT) findings. SDH, subdural hematoma; EDH, epidural hematoma; MHC, multiple hemorrhagic contusions; IVH, intraventricular hemorrhage; DAI, diffuse axonal injury.

Fig. 3.

Correlation between bispectral index (BIS) value and severity of head injuries. (A) At 0 hour. (B) At 6 hours. (C) At 12 hours. (D) At 18 hours. (E) At 24 hours.

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Figure & Data

References

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