Hemodynamic changes associated with common EEG patterns in critically ill patients: Pilot results from continuous EEG-fNIRS study

Cortical hemodynamics of electrographic status epilepticus in the critically ill

OBJECTIVES

The pathophysiological mechanisms of status epilepticus (SE) underlying potential brain injury remain largely unclear. This study aims to employ functional near-infrared spectroscopy (fNIRS) combined with video-electroencephalography (vEEG) to monitor brain hemodynamics continuously and non-invasively in critically ill adult patients experiencing electrographic SE. Our primary focus is to investigate neurovascular coupling and cerebrovascular changes associated with seizures, particularly during recurring and/or prolonged episodes.

METHODS

Eleven critically ill adult patients underwent simultaneous vEEG-fNIRS with large cortical coverage. Data from seven patients with identified electrographic SE were analyzed. The timing of recorded seizures was marked using standardized critical care EEG terminology. A general linear model was employed to extract the hemodynamic response to seizures from the fNIRS recordings. Linear mixed-effects models were utilized to correlate hemodynamic responses with seizure characteristics.

RESULTS

A total of >200 h of monitoring and >1000 seizures were recorded. In most patients, an increase in oxyhemoglobin (HbO) and a decrease in deoxyhemoglobin (HbR) were observed during shorter-duration seizures. Although a similar response could also be seen initially for longer-duration seizures, this hemodynamic change was often followed by a progressive decline in HbO concentration and an increase in HbR. At the systemic level, no significant difference in peripheral oxygenation occurred during seizures, and only small changes in mean arterial blood pressure and heart rate occurred in four and two patients, respectively.

SIGNIFICANCE

We demonstrate the feasibility of using multichannel vEEG-fNIRS to measure the hemodynamic changes associated with electrographic seizures in critically ill adult patients. Our findings suggest that disrupted neurovascular coupling is more prevalent during prolonged seizures compared to recurrent short-duration seizures. This research provides valuable insights into the dynamic interplay between neuronal activity and hemodynamics during critical care seizures.

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.

The effect of burst suppression on cerebral blood flow and autoregulation: a scoping review of the human and animal literature

Background: Burst suppression (BS) is an electroencephalography (EEG) pattern in which there are isoelectric periods interspersed with bursts of cortical activity. Targeting BS through anaesthetic administration is used as a tool in the neuro-intensive care unit but its relationship with cerebral blood flow (CBF) and cerebral autoregulation (CA) is unclear. We performed a systematic scoping review investigating the effect of BS on CBF and CA in animals and humans. Methods: We searched MEDLINE, BIOSIS, EMBASE, SCOPUS and Cochrane library from inception to August 2022. The data that were collected included study population, methods to induce and measure BS, and the effect on CBF and CA. Results: Overall, there were 66 studies that were included in the final results, 41 of which examined animals, 24 of which examined humans, and 1 of which examined both. In almost all the studies, BS was induced using an anaesthetic. In most of the animal and human studies, BS was associated with a decrease in CBF and cerebral metabolism, even if the mean arterial pressure remained constant. The effect on CA during periods of stress (hypercapnia, hypothermia, etc.) was variable. Discussion: BS is associated with a reduction in cerebral metabolic demand and CBF, which may explain its usefulness in patients with brain injury. More evidence is needed to elucidate the connection between BS and CA.