Prognostication after cardiac arrest: how EEG and evoked potentials may improve the challenge

Abstract

About 80% of patients resuscitated from CA are comatose at ICU admission and nearly 50% of survivors are still unawake at 72 h. Predicting neurological outcome of these patients is important to provide correct information to patient’s relatives, avoid disproportionate care in patients with irreversible hypoxic–ischemic brain injury (HIBI) and inappropriate withdrawal of care in patients with a possible favorable neurological recovery. ERC/ESICM 2021 algorithm allows a classification as “poor outcome likely” in 32%, the outcome remaining “indeterminate” in 68%. The crucial question is to know how we could improve the assessment of both unfavorable but also favorable outcome prediction. Neurophysiological tests, i.e., electroencephalography (EEG) and evoked-potentials (EPs) are a non-invasive bedside investigations. The EEG is the record of brain electrical fields, characterized by a high temporal resolution but a low spatial resolution. EEG is largely available, and represented the most widely tool use in recent survey examining current neuro-prognostication practices. The severity of HIBI is correlated with the predominant frequency and background continuity of EEG leading to “highly malignant” patterns as suppression or burst suppression in the most severe HIBI. EPs differ from EEG signals as they are stimulus induced and represent the summated activities of large populations of neurons firing in synchrony, requiring the average of numerous stimulations. Different EPs (i.e., somato sensory EPs (SSEPs), brainstem auditory EPs (BAEPs), middle latency auditory EPs (MLAEPs) and long latency event-related potentials (ERPs) with mismatch negativity (MMN) and P300 responses) can be assessed in ICU, with different brain generators and prognostic values. In the present review, we summarize EEG and EPs signal generators, recording modalities, interpretation and prognostic values of these different neurophysiological tools. Finally, we assess the perspective for futures neurophysiological investigations, aiming to reduce prognostic uncertainty in comatose and disorders of consciousness (DoC) patients after CA.

Neural complexity and the spectral slope characterise auditory processing in wakefulness and sleep

“…Evidence of the prognostic and diagnostic value of quantification of AEPs and neural information content or the spectral slope for assessing consciousness levels or the integrity of neural functions in reduced consciousness conditions is growing (Aellen et al, 2023;Alnes et al, 2021;Bekinschtein et al, 2009;Benghanem et al, 2022;Colombo et al, 2019Colombo et al, , 2023Comanducci et al, 2020;Liu et al, 2022;Morlet & Fischer, 2014;Pfeiffer et al, 2018). Measures based on information content can differentiate levels of consciousness (Casali et al, 2013), whereas both measures based on information content, spectral slope and AEPs are promising as prognostic tools for patients with disorders of consciousness (Colombo et al, 2023;Fischer et al, 2004;Liu et al, 2022;Pfeiffer et al, 2018;Tzovara et al, 2013).…”

Aberrant brain–heart coupling is associated with the severity of post cardiac arrest brain injury

“…The former are related to prefrontal cortex and limbic system lesions, while the latter are related to a disruption of key systems that support wakefulness and consciousness, such as the ascending reticular system and the hypothalamic and thalamic projections to the frontoparietal cortical network. 4 Two of the most used tools to assess HIBI severity after CA, somatosensory evoked potentials (SSEP) and EEG, 5 , 6 rely on the evaluation of information processing from the brainstem to the cortex and within thalamocortical loops. However, neuroprognosticaion remains challenging due to the diverse conditions in which HIBI presents itself, and our understanding of the multisystem physiological implications caused by severe brain damage is still limited.…”

Aberrant brain-heart coupling is associated with the severity and prognosis of hypoxic-ischemic brain injury after cardiac arrest

“…Methods range from the evaluation of brainstem and cortical integration of peripheral sensory information to the assessment of the complex interplay between subcortical and thalamo-cortical loops. The integration of sensory information can be assessed through pupillometry, auditory evoked potentials, or somatosensory evoked potentials (SSEP) 6 .…”

“…Methods range from the evaluation of brainstem and cortical integration of peripheral sensory information to the assessment of the complex interplay between subcortical and thalamo-cortical loops. The integration of sensory information can be assessed through pupillometry, auditory evoked potentials, or somatosensory evoked potentials (SSEP) 6 . The disrupted interplay between brain structures can be assessed with qualitative 7,8 and quantitative 9–11 analysis of EEG activity, and the analysis of axonal and neuronal injury by quantifying serum biomarkers (neuron-specific enolase, NSE), light-chain neurofilament light 12 , and cerebral MRI 13 .…”