EEG for outcome prediction after cardiac arrest: when the quest for optimization needs standardization

Abstract

Early outcome prognostication of comatose patients following cardiac arrest represents a daunting task; several clinical, biochemical, radiological, and neurophysiological parameters have been intensively evaluated recently, in the context of growing popularity of targeted temperature management or therapeutic hypothermia (TH) in the last decade [1,2]. Among these potential predictors, EEG represents a relatively cheap, noninvasive tool available at the bedside, but the assessment of its exact role has to deal with the influence of timing, lingering pharmacological sedation, temperature, and not least the expertise of interpreters and the sometimes confusing taxonomy of the findings.In this issue, Dr. Sivaraju and colleagues report their effort to assess the prognostic significance of continuous EEG (cEEG) data in 100 patients treated with TH at 32-34°C [3]. They reviewed all EEG recordings in the form of 5-min extracts taken at predefined intervals from the acute event (6, 12, 24, 48, and 72 h). Blinded to patients' identity and outcome, they applied the recently published standardized American Clinical Neurophysiology Society (ACNS) critical care EEG terminology [4], correlating their data with those of other clinical investigations.The principal findings are that suppression-burst at any time (but not a discontinuous recording), and a low voltage (\20 lV) background after 24 h, have a false positive rate of 0 % for poor prognosis, defined as a Glasgow outcome scale (GOS) of 1-3 at hospital discharge, suggesting that in this cohort assessment at 24 h heralds the best prognostic value, despite the probable concomitant use of sedation (mostly midazolam, further details not given) and TH. As the authors acknowledge, other groups have reported different results regarding the temporal dynamics of evolution of the cEEG [5]; furthermore, the ACNS terminology puts a threshold between suppression-burst and discontinuous background at 50 % of relative suppression, which could prove tricky to label with certainty in specific borderline situations (in other words: EEG signals represent a continuous, not a discrete variable).Conversely, normal voltage ([20 lV) at any time is related to a good outcome in 71 % of patients, confirming earlier data along the same lines [6]. Considering the delicacy in reliably deciding upon a voltage amplitude around 20 lV in some patients [7], other groups concentrated rather on background reactivity to stimuli, which if present during TH has been reported to herald good prognosis in as much as 86 % [8], while lack of reactivity portended a poor prognosis in a much higher rate (99 % in [9]). This last figure contrasts with a predictive value of 86 % in this study (it was, however, not indicated when reactivity was assessed), pinpointing the lack of standardization of its testing (in this series with auditory and peripheral painful stimuli; in the aforementioned papers applying also vigorous pressure to the nipples) and its scoring [7,10]. In the same context, identical bursts, recently report...

The interrelation between clinical presentation and neurophysiology of posthypoxic myoclonus

“…A different source of uncertainty in this study was that the clinical assessment of PHM might have been challenging due to the dynamic and intermittent character of PHM and the use of video recordings leading to an observation that is less vivid 13, 14, 16. To circumvent this issue, three instead of one experienced neurologist interpreted the clinical videos.…”

“…Despite recent improvements in the specificity of PAE prognostication, there is still a need for more sensitive prognostic parameters in PAE,12, 13 and the clinical subtype of PHM might serve as one. However, one of the challenges for the use of PHM as prognosticator is that the clinical distinction between focal and generalized PHM is complicated; the assessment is hampered by the dynamic and intermittent character of PHM, hypothermia and medication effects 13, 14, 15, 16.…”

“…However, one of the challenges for the use of PHM as prognosticator is that the clinical distinction between focal and generalized PHM is complicated; the assessment is hampered by the dynamic and intermittent character of PHM, hypothermia and medication effects 13, 14, 15, 16. In contrast to the current American guideline for postanoxic coma, the presence of PHM is not included as a criterion for poor prognosis in the European guideline 17.…”