Elsevier

Clinical Neurophysiology

Volume 129, Issue 8, August 2018, Pages 1534-1543
Clinical Neurophysiology

The prognostic value of discontinuous EEG patterns in postanoxic coma

https://doi.org/10.1016/j.clinph.2018.04.745Get rights and content

Highlights

  • We used quantitative measures of the EEG background to predict outcome of coma after cardiac arrest.

  • A background continuity index of ≥ 0.80 at 12 h or ≥ 0.92 at 24 h predicted a good outcome.

  • A burst-suppression amplitude ratio of ≥ 6.12 at any time predicted a poor outcome.

Abstract

Objective

To assess the value of background continuity and amplitude fluctuations of the EEG for the prediction of outcome of comatose patients after cardiac arrest.

Methods

In a prospective cohort study, we analyzed EEGs recorded in the first 72 h after cardiac arrest. We defined the background continuity index (BCI) as the fraction of EEG not spent in suppressions (amplitudes < 10 µV for ≥ 0.5 s), and the burst-suppression amplitude ratio (BSAR) as the mean amplitude ratio between non-suppressed and suppressed segments. Outcome was assessed at 6 months and categorized as “good” (Cerebral Performance Category 1–2) or “poor” (CPC 3–5).

Results

Of the 559 patients included, 46% had a good outcome. Combinations of BCI and BSAR resulted in the highest prognostic accuracies. Good outcome could be predicted at 24 h with 57% sensitivity (95% confidence interval (CI): 48–67) at 90% specificity (95%-CI: 86–95). Poor outcome could be predicted at 12 h with 50% sensitivity (95%-CI: 42–56) at 100% specificity (95%-CI: 99–100).

Conclusions

EEG background continuity and the amplitude ratio between bursts and suppressions reliably predict the outcome of postanoxic coma.

Significance

The presented features provide an objective, rapid, and reliable tool to assist in EEG interpretation in the Intensive Care Unit.

Introduction

Early outcome prediction of comatose patients after cardiac arrest remains a challenge. The EEG is a sensitive and reliable tool, especially within the first 24 h after cardiac arrest (Hofmeijer and Van Putten, 2016). A timely restoration of continuous, normal amplitude background activity is essential for good neurological recovery. Consistently among various studies, a continuous EEG pattern within 12 h after cardiac arrest predicts a good outcome, whereas a persistent isoelectric or low-voltage EEG at 24 h predicts a poor outcome (Sivaraju et al., 2015, Sondag et al., 2017, Spalletti et al., 2016).

In addition to the EEG background continuity, the degree of amplitude fluctuation seems to be a powerful indicator of the severity of postanoxic encephalopathy. EEG patterns with pronounced alternations in amplitudes, such as burst-suppression with identical bursts (Hofmeijer et al., 2013), and generalized periodic discharges (GPDs) on a suppressed background (Ruijter et al., 2015), have a strong association with poor outcome.

Although both background continuity and amplitude fluctuations play an important role in the visual assessment of the postanoxic EEG, they remain hard to quantify by a human observer. Continuity and relative amplitude are usually treated as categorical variables (Hirsch et al., 2013), for which interrater agreement is far from perfect (Gaspard et al., 2014, Westhall et al., 2015). Therefore, visual analysis alone has probably not been able to elucidate the discriminative power of these features.

The assessment of discontinuous EEG patterns can be improved by the use of quantitative EEG (qEEG). Quantitative measures do not suffer from interrater variability, can be applied by non-experts, and save reviewing time (Swisher and Sinha, 2016, Tjepkema-Cloostermans et al., 2017, Zubler et al., 2016). Quantitative measures for EEG background continuity have proven to be valuable for the prediction of outcome in postanoxic coma, but have only been applied to small case series (Noirhomme et al., 2014, Wennervirta et al., 2009) or selected EEG patterns (Ruijter et al., 2015), so far. The prognostic value of the amplitude ratio between bursts and suppressions has, to the best of our knowledge, never been investigated in any visual or quantitative analysis.

In this study, we relate outcome of postanoxic coma to quantitative measures of EEG background continuity and the amplitude ratio between bursts and suppressions. We will show that these straightforward measures are reliable predictors of outcome, with sensitivities higher than reported for visual EEG analysis. Since the presented features remain closely related to key visual observations, they will also provide insights to be of value in routine EEG assessment.

Section snippets

Patients

This study was designed as a prospective cohort study on continuous EEG monitoring for outcome prediction of comatose patients after cardiac arrest. Data were collected between June 2010 and April 2017 in Medisch Spectrum Twente and Rijnstate, two large teaching hospitals in the Netherlands. All consecutive adult patients that were admitted comatose after cardiac arrest to the Intensive Care Unit (ICU) were included. Parts of the EEG data up to December 2015 were used previously for studies on

Patients

EEG recordings were started in 582 patients. Twenty-three patients were lost to follow-up, leaving 559 patients for the analysis. Outcome was good in 46%. Baseline characteristics are listed in Table 2 and were as expected: patients with good outcome were younger (60 vs. 68 years, p < 0.001), more often had a primary cardiac cause of the arrest (94% vs. 76%, p < 0.001), ventricular fibrillation as initial rhythm (92% vs. 58%, p < 0.001), and required higher doses of propofol (2.95 vs.

Discussion

We show that the background continuity index and the burst-suppression amplitude ratio are straightforward, quantitative EEG-measures that assist in the prediction of outcome after cardiac arrest. Our results confirm that return of EEG background continuity within 24 h indicates a good outcome. Otherwise, a lack of background continuity predicts poor outcome without false positives, except for the first 10 h after cardiac arrest. An amplitude ratio between ‘bursts’ and suppressions of 6.12 and

Acknowledgements

We thank Carin Eertman, Astrid Glimmerveen, Monique Raaijmakers, Saskia Metz, Helene Vogelesang, and Yvonne Teitink for assistance with data aquisition. We thank the ICU staff and all clinical neurophysiology lab technicians from Medisch Spectrum Twente an Rijnstate hospital for the extensive support and constructive collaboration. Barry J. Ruijter was financially supported by the Dutch National Epilepsy Fund (Nationaal Epilepsie Fonds, grant reference NEF 14–18). The funders had no role in

Conflict of interest statement

M.J.A.M. van Putten is co-founder of Clinical Science Systems, which is a supplier of EEG systems for one of the participating sites (Medisch Spectrum Twente). Clinical Science Systems did not provide funding and was not involved in the design, execution, analysis, interpretation or publication of the study. The other authors do not report any conflicts of interest.

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