Small-world characteristics of EEG patterns in post-anoxic encephalopathy

Post-anoxic encephalopathy (PAE) has a heterogenous outcome which is difficult to predict. At present, it is possible to predict poor outcome using somatosensory evoked potentials in only a minority of the patients at an early stage. In addition, it remains difficult to predict good outcome at an early stage. Network architecture, as can be quantified with continuous electroencephalography (cEEG), may serve as a candidate measure for predicting neurological outcome. Here, we explore whether cEEG monitoring can be used to detect the integrity of neural network architecture in patients with PAE after cardiac arrest. From 56 patients with PAE treated with mild therapeutic hypothermia, 19-channel cEEG data were recorded starting as soon as possible after cardiac arrest. Adjacency matrices of shared frequencies between 1 and 25Hz of the EEG channels were obtained using Fourier transformations. Number of network nodes and connections, clustering coefficient (C), average path length (L), and small-world index (SWI) were derived. Outcome was quantified by the best cerebral performance category (CPC)-score within 6months. Compared to non-survivors, survivors showed significantly more nodes and connections. L was significantly higher and C and SWI were significantly lower in the survivor group than in the non-survivor group. The number of nodes, connections, and the L were negatively correlated with the CPC-score. C and SWI correlated positively with the CPC-score. The combination of number of nodes, connections, C, and L showed the most significant difference and correlation between survivors and non-survivors and CPC-score. Our data might implicate that non-survivors have insufficient distribution and differentiation of neural activity for regaining normal brain function. These network differences, already present during hypothermia, might be further developed as early prognostic markers. The predictive values are however still inferior to current practice parameters. Keywords: small-world network, continuous EEG, post-anoxic encephalopathy, prognosis, resuscitatio

A Cerebral Recovery Index (CRI) for early prognosis in patients after cardiac arrest

Introduction: Electroencephalogram (EEG) monitoring in patients treated with therapeutic hypothermia after cardiac arrest may assist in early outcome prediction. Quantitative EEG (qEEG) analysis can reduce the time needed to review long-term EEG and makes the analysis more objective. In this study, we evaluated the predictive value of qEEG analysis for neurologic outcome in postanoxic patients.Methods: In total, 109 patients admitted to the ICU for therapeutic hypothermia after cardiac arrest were included, divided over a training and a test set. Continuous EEG was recorded during the first 5 days or until ICU discharge. Neurologic outcomes were based on the best achieved Cerebral Performance Category (CPC) score within 6 months. Of the training set, 27 of 56 patients (48%) and 26 of 53 patients (49%) of the test set achieved good outcome (CPC 1 to 2). In all patients, a 5 minute epoch was selected each hour, and five qEEG features were extracted. We introduced the Cerebral Recovery Index (CRI), which combines these features into a single number.Results: At 24 hours after cardiac arrest, a CRI <0.29 was always associated with poor neurologic outcome, with a sensitivity of 0.55 (95% confidence interval (CI): 0.32 to 0.76) at a specificity of 1.00 (CI, 0.86 to 1.00) in the test set. This results in a positive predictive value (PPV) of 1.00 (CI, 0.73 to 1.00) and a negative predictive value (NPV) of 0.71 (CI, 0.53 to 0.85). At the same time, a CRI >0.69 predicted good outcome, with a sensitivity of 0.25 (CI, 0.10 to 0.14) at a specificity of 1.00 (CI, 0.85 to 1.00) in the test set, and a corresponding NPV of 1.00 (CI, 0.54 to 1.00) and a PPV of 0.55 (CI, 0.38 to 0.70).Conclusions: We introduced a combination of qEEG measures expressed in a single number, the CRI, which can assist in prediction of both poor and good outcomes in postanoxic patients, within 24 hours after cardiac arrest

Forest governance in a changing world: reconciling local and global values

There has been intense international debate on the governance of forests, in particular tropical forests. This has been driven by contrasting pressures from conservation and human rights groups, respectively calling for global values to prevail so as to protect biodiversity and reduce climate change, or for freedom of choice that empowers local people with the right to manage their own forests. Both sides have condemned irresponsible behaviour by forest officials and political actors, and highlighted the harmful impacts of disregard for the law. However, these normative approaches to forest governance have coincided with a fundamental re-examination of the objectives that societies have for their forest resources. The debate is not only about legality, but also about the legitimacy of forest laws and institutions. This review explores the divergence of views on long-term goals for forests and the implications for their governance. It emphasises that the real challenge is to reconcile the management of forests for values that accrue at different spatial and temporal scales. Forest governance needs to adapt, moving away from a framework based upon the neatly defined boundaries beloved of international organisations and treaties, and submitting to a constant process of adaptation and improvisation at a more local scale. The challenge is to find ways to aggregate such approaches into something that recognisably addresses the global values of forests and forest landscapes. Commonwealth countries have a wide range of forest conditions and are innovating with a range of governance options that provide lessons of potentially wide application

Burst-suppression with identical bursts: A distinct EEG pattern with poor outcome in postanoxic coma

OBJECTIVE: To assess the incidence, quantified EEG characteristics, and prognostic significance of "burst-suppression with identical bursts" and to discuss potential pathophysiological mechanisms. METHODS: Burst-suppression EEGs were identified from a cohort of 101 comatose patients after cardiac arrest, and from our complete database of 9600 EEGs, since 2005. Patterns with and without identical bursts were classified visually by two observers. Of patients after cardiac arrest, outcomes were assessed at three and six months. Identical and non-identical burst-suppression patterns were compared for quantified EEG characteristics and clinical outcome. Cross correlation of burstshape was applied to the first 500ms of each burst. RESULTS: Of 9701 EEGs, 240 showed burst-suppression, 22 with identical bursts. Identical bursts were observed in twenty (20%) of 101 comatose patients after cardiac arrest between a median of 12 and 36h after the arrest, but not in the six patients with other pathology than cerebral ischemia, or the 183 with anesthesia induced burst suppression. Inter-observer agreement was 0.8 and disagreement always resulted from sampling error. Burst-suppression with identical bursts was always bilateral synchronous, amplitudes were higher (128 vs. 25μV, p=0.0001) and correlation coefficients of burstshapes were higher (95% >0.75 vs. 0% >0.75, p<0.0001) than in burst-suppression without identical bursts. All twenty patients with identical bursts after cardiac arrest had a poor outcome versus 10 (36%) without identical bursts. CONCLUSION: "Burst-suppression with identical bursts" is a distinct pathological EEG pattern, which in this series only occurred after diffuse cerebral ischemia and was invariably associated with poor outcome. SIGNIFICANCE: In comatose patients after cardiac arrest, "burst-suppression with identical bursts" predicts a poor outcome with a high specificity

The SSEP on the ICU: Current applications and pitfalls

Clinical neurological evaluation of patients in the intensive care unit (ICU) is often limited. Registration of the somatosensory evoked potential (SSEP) can assist in the neurological evaluation in these patients. In this paper, we discuss the principles, applications and limitations of the SSEPs in the ICU with a focus on prognostication in comatose patients. Registration of the SSEP is a very reliable and reproducible method, if it is performed and interpreted correctly. A bilateral absent cortical SSEP response is a reliable predictor for poor neurological outcome in patients with a post-anoxic coma, but not in patients with traumatic brain injury or subarachnoid haemorrhage. During SSEP recordings, great care should be taken in improving the signal to noise ratio. Since the interpreting clinician is often not present during the actual SSEP registration itself, the role of the lab technician is crucial in obtaining reliable SSEP results. If the noise level is too high, the peripheral responses are abnormal, or the response is not reproducible in a second set of stimuli, interpretation of the SSEP cannot be done reliably