Elsevier

Resuscitation

Volume 143, October 2019, Pages 17-21
Resuscitation

Short paper
Stratifying comatose postanoxic patients for somatosensory evoked potentials using routine EEG

https://doi.org/10.1016/j.resuscitation.2019.07.027Get rights and content

Abstract

Introduction

Multimodal neurological prognostication is recommended for comatose patients after cardiac arrest. The absence of cortical N20-potentials in a somatosensory evoked potential (SSEP) examination reliably predicts poor outcome, but presence of N20-potentials have limited prognostic value. A benign routine electroencephalogram (EEG) may identify patients with a favourable prognosis who are likely to have present N20-potentials.

Objective

To investigate whether a routine EEG can identify patients where SSEP is unnecessary to perform.

Methods

In a multi-centre trial, comatose patients after cardiac arrest were randomised to a controlled temperature of 33 °C or 36 °C. A routine EEG was protocolised and SSEP performed at the clinicians’ discretion, both during normothermic conditions. EEGs were categorised into benign, malignant or highly malignant based on standardised terminology. A benign EEG was defined as a continuous normal-voltage background without abundant discharges. The N20-potentials were reported as absent (bilaterally) or present (bilaterally or unilaterally).

Results

Both EEG and SSEP were performed in 161 patients. EEG was performed before SSEP in 60%. A benign EEG was seen in 29 patients and 100% (CI 88–100%) had present N20-potentials. For the 69 patients with a malignant EEG and the 63 patients with a highly malignant EEG, 67% (CI 55–77%) and 44% (CI 33–57%) had present N20-potentials, respectively.

Conclusions

All patients with a benign EEG had present N20-potentials, suggesting that SSEP may be omitted in these patients to save resources. SSEP is useful in patients with a malignant or highly malignant EEG since these patterns are associated with both present and absent N20-potentials.

Introduction

EEG is a commonly used tool to assess brain function in comatose patients resuscitated after a cardiac arrest (CA).1 A classification of benign, malignant and highly malignant EEG patterns have previously been proposed.2 A benign EEG may identify patients with a good prognosis.3

Somatosensory evoked potentials (SSEP) is an important method for predicting poor prognosis.4, 5 If cortical N20-potentials are absent bilaterally the prognosis is poor with specificities close to 100%.4, 6 SSEP is less available compared to EEG1 and its sensitivity to predict a poor outcome is limited.7

A clinically relevant question is whether to perform SSEP in all patients or not. Previous studies have evaluated SSEP in addition to EEG to predict poor outcome.6, 8 One study explored if clinical data and EEG could predict absence of N20-potentials,9 but no study has investigated if a benign EEG can be used to anticipate presence of N20-potentials. The aim of this study was to investigate if a routine EEG can identify patients where SSEP is unnecessary to perform.

Section snippets

Methods

In the Targeted Temperature Management (TTM) Trial, 939 adult comatose patients following an out-of-hospital CA were randomised to two different temperature treatments (33 °C or 36 °C). The trial was granted by the ethics committees in each participating country.10

Consecutive patients at the 36 sites were included in the present study if both EEG and SSEP were performed within 10 days after CA. According to the trial protocol11 a routine EEG was mandatory to be performed in patients still

Patients

161 patients from 15 sites had performed both routine EEGs and SSEP and were included in the present study (Fig. 1). The cohort was divided into three EEG categories, benign (n = 29), malignant (n = 69) or highly malignant (n = 63). Patient characteristics and CA related variables are presented in supplementary tables S1 and S2.

EEG and SSEP results

Table 1 presents the SSEP results in each EEG category. A benign EEG defined as a continuous normal-voltage background and absence of abundant discharges was seen in 29

Discussion

Neurophysiological methods are included in algorithms for prognostication following CA,4, 5 but questions remain regarding their most efficient usage. In this cohort, we showed that all patients with a benign EEG had present N20-potentials. Since a benign EEG can predict presence of N20-potentials we suggest that SSEP does not need to be performed in this subgroup of patients. We base this assumption on the traditional view that present N20-potentials is a poor indicator of a good outcome but

Conclusions

In this cohort, benign EEGs were always associated with present N20-potentials. A routine EEG could therefore be used to identify the patients where SSEP is of limited prognostic use.

Funding source

The Swedish Heart and Lung Association; the Skåne University Hospital Foundations; the Gyllenstierna-Krapperup Foundation; the Segerfalk foundation; the Swedish National Health System (ALF); the County Council of Skåne; the Swedish Society of Medicine; the Koch Foundation, The Swedish Heart-Lung Foundation, AFA Insurance, The Swedish Research Council and Hans-Gabriel and Alice Trolle-Wachtmeister Foundation; all in Sweden. The Tryg Foundation; Denmark. EU programme Interreg IV A.

Statistical analysis

Susann Ullén, statistician at our institution, advised the statistical analysis.

Authors’ contributions

All authors contributed to the conceptualization and methodology of the study. AF and EW performed the formal analysis and wrote the first draft of the manuscript. All authors critically reviewed and accepted the final manuscript.

Disclosures

The authors have no disclosures to report.

Declaration of conflicts of interest

None.

Acknowledgements

We would like to acknowledge the 15 sites that contributed data, site investigators (SI) and the contacts of the EEG-laboratories: Copenhagen University Hospital Rigshospitalet (Christian Hassager SI, Jesper Kjaergaard SI, Michael Wanscher SI, Troels Wesenberg Kjaer EEG), Denmark; Santa Maria degli Angeli Hospital Pordenone (Tommaso Pellis SI), Trieste (Vincenzo Campanile SI), Italy; Centre Hospitalier de Luxembourg (Pascal Stammet SI, Stefan Beyenburg EEG), Luxembourg; Academisch Medisch

References (15)

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Cited by (14)

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    However, the same authors [17,19,47,51] stressed that the significance of CA duration in neurological prognostication remains uncertain (mainly because of the variability in its determination), concluding that prognosis of comatose patients after CA cannot be based on this index. The presence of PLR could not be used to predict recovery of consciousness because this index was associated with very high FPR (20.0%), indicating, in agreement with the available data [17,19,47,51], that the inaccuracy in prognosis can be very serious [17,19]. In summary, during the first 6 h following CA, a reliable prognosis of comatose patients after CA cannot be based on PLR.

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