Background: The probability of recovering consciousness in acute brain-injured patients depends on central nervous system damage and complications acquired during their stay in the intensive care unit. The objective of this study was to establish a relation between the Bispectral Index (BIS) and other variables derived from the analysis of the electroencephalographic signal, with the probability of recovering consciousness in patients in a coma state due to severe cerebral damage.
Methods: Twenty-five critically ill, unconscious brain-injured patients from whom sedative drugs were withdrawn at least 24 h before BIS recording were prospectively studied. BIS, 95% spectral edge frequency, burst suppression ratio, and frontal electromyography were recorded for 20 min. The neurologic condition of the patients was measured according to the Glasgow Coma Score (GCS). Patients were followed up for assessment of recovery of consciousness for 6 months after the injury. The studied variables were compared between the group of patients who recovered consciousness and those who did not recover. Their predictive ability was evaluated by means of the Pk statistic. Univariate and multivariate logistic regression was used to model the relation between variables and probability of recovery of consciousness. Cross-validation was used to validate the proposed model.
Results: There were statistically significant differences between the group of patients who recovered consciousness and those who did not with respect to BISmax, BISmin, BISmean, and BISrange, frontal electromyography, signal quality index values, and GCSBIS. The Pk (SE) values were 0.99 (0.01) for electromyelography, 0.96 (0.05) for BISmax, 0.92 (0.05) for BISmean, 0.92 (0.06) for BISrange, and 0.82 (0.09) for GCSBIS. The odds ratio for BISmax in the logistic regression model was 1.17 (95% confidence interval, 1.1-1.35). Cross-validation results reported a high-accuracy median absolute cross-validation performance error of 3.06% (95% confidence interval, 1-22.15%) and a low-bias median cross-validation performance error of 0.84% (0.56-2.12%).
Conclusions: The study BIS and other electrophysiologic and clinical variables has enabled construction and cross-validation of a model relating BIS(max) to the probability of recovery of consciousness in patients in a coma state due to a severe brain injury, after sedation has been withdrawn.