Proving cortical death after vascular coma: Evoked potentials, EEG and neuroimaging

Multimodal approaches supporting the diagnosis, prognosis and investigation of neural correlates of disorders of consciousness: A systematic review

The limits of the standard, behaviour-based clinical assessment of patients with disorders of consciousness (DoC) prompted the employment of functional neuroimaging, neurometabolic, neurophysiological and neurostimulation techniques, to detect brain-based covert markers of awareness. However, uni-modal approaches, consisting in employing just one of those techniques, are usually not sufficient to provide an exhaustive exploration of the neural underpinnings of residual awareness. This systematic review aimed at collecting the evidence from studies employing a multimodal approach, that is, combining more instruments to complement DoC diagnosis, prognosis and better investigating their neural correlates. Following the PRISMA guidelines, records from PubMed, EMBASE and Scopus were screened to select peer-review original articles in which a multi-modal approach was used for the assessment of adult patients with a diagnosis of DoC. Ninety-two observational studies and 32 case reports or case series met the inclusion criteria. Results highlighted a diagnostic and prognostic advantage of multi-modal approaches that involve electroencephalography-based (EEG-based) measurements together with neuroimaging or neurometabolic data or with neurostimulation. Multimodal assessment deepened the knowledge on the neural networks underlying consciousness, by showing correlations between the integrity of the default mode network and the different clinical diagnosis of DoC. However, except for studies using transcranial magnetic stimulation combined with electroencephalography, the integration of more than one technique in most of the cases occurs without an a priori-designed multi-modal diagnostic approach. Our review supports the feasibility and underlines the advantages of a multimodal approach for the diagnosis, prognosis and for the investigation of neural correlates of DoCs.

Twenty-four-hour rhythmicities in disorders of consciousness are associated with a favourable outcome

Fluctuations of consciousness and their rhythmicities have been rarely studied in patients with a disorder of consciousness after acute brain injuries. 24-h assessment of brain (EEG), behaviour (eye-opening), and circadian (clock-controlled hormones secretion from urine) functions was performed in acute brain-injured patients. The distribution, long-term predictability, and rhythmicity (circadian/ultradian) of various EEG features were compared with the initial clinical status, the functional outcome, and the circadian rhythmicities of behaviour and clock-controlled hormones. Here we show that more physiological and favourable patterns of fluctuations are associated with a higher 24 h predictability and sharp up-and-down shape of EEG switches, reminiscent of the Flip-Flop model of sleep. Multimodal rhythmic analysis shows that patients with simultaneous circadian rhythmicity for brain, behaviour, and hormones had a favourable outcome. Finally, both re-emerging EEG fluctuations and homogeneous 24-h cycles for EEG, eye-opening, and hormones appeared as surrogates for preserved functionality in brainstem and basal forebrain, which are key prognostic factors for later improvement. While the recovery of consciousness has previously been related to a high short-term complexity, we suggest in this exploratory study the importance of the high predictability of the 24 h long-term generation of brain rhythms and highlight the importance of circadian body-brain rhythms in awakening.

The Evoked Potential Score for SSEP and BAEP-A Prognostic Marker for the Long-Term Neurological Outcome in Patients after Poor-Grade Subarachnoid Hemorrhage

Objective: Evoked potentials are widely used in comatose patients to evaluate neurological function; however, prognostic relevance in patients after SAH is barely investigated. Therefore, we aimed to investigate the prognostic value of the proposed Evoked Potential Score (EPS) for somatosensory (SSEP) and brainstem auditory evoked potentials (BAEP) on the neurological outcome in patients after poor-grade SAH. Methods: We retrospectively analyzed patients after poor grade SAH (Hunt and Hess (HH) grade IV and V) that were admitted to the ICU at the Department of Neurosurgery, MUV, between 2014 and 2017. Measurements of SSEP and BAEP were evaluated separately as well as in a combined model, using the EPS at admission and before ventilator weaning and correlated with the grade of the modified ranking scale at the last available follow up. Results: In total, 48 patients after SAH HH IV/V were included in this study. The EPS for SSEP at admission (p = 0.007) and both the EPS for SSEP (p = <0.0001) and BAEP (p = 0.036) before ventilator weaning were significant prognostic markers for neurological improvement at a mean follow-up period of 14.1 months. In addition, the combined model of the EPS for SSEP/BAEP performed as a prognostic marker for neurological improvement (“at admission” p = 0.007; “before ventilator weaning” p < 0.001). Conclusions: In the first series to date we found a high prognostic significance for the EPS as a combined model, as well as a separate analysis for SSEP and BAEP in patients after SAH IV and V. In the future, these findings potentially support physicians in ethically challenging decision-making processes and in advice for patients’ families under consideration of an individual evaluation of each patient.

Changes in Event-Related Potentials Underlying Coma Recovery in Patients with Large Left Hemispheric Infarction

<strong>BACKGROUND</strong> The aim of this study was to investigate changes in event-related potentials (ERPs) between coma and awakening in patients with large left hemispheric infarction (left LHI). <strong>MATERIAL AND METHODS</strong> Ten patients with left LHI who suffered coma and survived to awaken were enrolled in this study. The eye-opening subscore of the Glasgow Coma Scale (GCS) was used to assess the extent of patients' arousal. ERPs elicited by the passive oddball paradigm were collected during coma and awakening states, respectively. Peak latencies, peak amplitudes, topography, and time-frequency information of P1, N1, P2, and mismatch negativity (MMN) were compared between the 2 sessions. <strong>RESULTS</strong> No significant differences in the peak amplitudes and peak latencies of P1 and N1, but significantly greater P2 amplitude with shorter latency in left hemisphere and midline was shown in the awakening state compared with that in coma. A marked shift of P2 topography in response to deviant tones was also seen, from the right centro-parieto-frontal areas during coma to left frontal-midline areas during awakening. MMN waveforms were not detected in 6/10 patients during the coma state, but these 6 patients all recovered to awakening. Evoked oscillations in bilateral hemisphere were profoundly inhibited during the coma state, with poor inter-trial phase synchronization, while obvious activities with broader frequency ranges and consistent inter-trial phase synchronization were observed during awakening state, and different frequency activities were distributed in distinct brain regions. <strong>CONCLUSIONS</strong> P2 may be a central index of coma recovery and a component of the arousal system. Changes in time-frequency information could provide more information during coma recovery, perhaps including some cognitive processing of the sensory stimulus.