Identification of Patients With High Mortality Risk and Prediction of Outcomes in Delirium by Bispectral EEG

Abstract

Background: Delirium is common and dangerous, yet underdetected and undertreated. Current screening questionnaires are subjective and ineffectively implemented in busy hospital workflows. Electroencephalography (EEG) can objectively detect the diffuse slowing characteristic of delirium, but it is not suitable for high-throughput screening due to size, cost, and the expertise required for lead placement and interpretation. This study hypothesized that an efficient and reliable point-of-care EEG device for high-throughput screening could be developed.

Methods: This prospective study, which measured bispectral EEG (BSEEG) from elderly inpatients to assess their outcomes, was conducted at the University of Iowa Hospitals and Clinics from January 2016 to October 2017. A BSEEG score was defined based on the distribution of 2,938 EEG recordings from the 428 subjects who were assessed for delirium; primary outcomes measured were hospital length of stay, discharge disposition, and mortality.

Results: A total of 274 patients had BSEEG score data available for analysis. Delirium and BSEEG score had a significant association (P < .001). Higher BSEEG scores were significantly correlated with length of stay (P < .001 unadjusted, P = .001 adjusted for age, sex, and Charlson Comorbidity Index [CCI] score) as well as with discharge not to home (P < .01). Hazard ratio for survival controlling for age, sex, CCI score, and delirium status was 1.35 (95% CI,1.04 to 1.76; P = .025).

Conclusions: In BSEEG, an efficient and reliable device that provides an objective measurement of delirium status was developed. The BSEEG score is significantly associated with pertinent clinical outcomes of mortality, hospital length of stay, and discharge disposition. The BSEEG score better predicts mortality than does clinical delirium status. This study identified a previously unrecognized subpopulation of patients without clinical features of delirium who are at increased mortality risk.

Figure 1.

Survival curve over 360 days based on clinical delirium status (left panel) and BSEEG score (right panel). Patients who were clinically delirious had increased mortality compared to those without clinical delirium (P = 20.0038). BSEEG positive patients showed higher mortality than BSEEG negative patients, regardless of clinical delirium status (P = 0.0032). ”Number at Risk” indicates how many subjects in each stratum are followed at each time point to calculate survival probability as shown in the figure.

Figure 2.

Survival curve over 360 days based on three BSEEG categories. Mortality was directly proportional to the BSEEG score, with higher BSEEG score group associated with higher mortality (P= 0.005). ”Number at Risk” indicates how many subjects in each stratum are followed at each time point to calculate survival probability as shown in the figure.

Figure 3.

Subgroup analysis of mortality based on both clinical delirium status and BSEEG category. Patients who were both clinical delirious and BSEEG positive showed the highest mortality (purple line). Patients who were clinically delirious but BSEEG negative had lower mortality (blue line), almost as low as patients who were both clinically non-delirious and BSEEG negative (orange line). In contrast, patients who were clinically non-delirious, but BSEEG positive, had higher mortality rates (green line), indicating that BSEEG score was a better predictor of mortality than clinical delirium status. ”Number at Risk” indicates how many subjects in each stratum are followed at each time point to calculate survival probability as shown in the figure.