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Microdialysis enables the chemistry of the extracellular interstitial space to be monitored. Use of this technique in patients with acute brain injury has increased our understanding of the pathophysiology of several acute neurological disorders. In 2004, a consensus document on the clinical application of cerebral microdialysis was published. Since then, there have been significant advances in the clinical use of microdialysis in neurocritical care. The objective of this review is to report on the International Microdialysis Forum held in Cambridge, UK, in April 2014 and to produce a revised and updated consensus statement about its clinical use including technique, data interpretation, relationship with outcome, role in guiding therapy in neurocritical care and research applications.Electronic supplementary materialThe online version of this article (doi:10.1007/s00134-015-3930-y) contains supplementary material, which is available to authorized users.

Metabolic dyslipidemia is characterized by high circulating triglyceride (TG) and low HDL cholesterol levels and is frequently accompanied by hepatic steatosis. Increased hepatic lipogenesis contributes to both of these problems. Because insulin fails to suppress gluconeogenesis but continues to stimulate lipogenesis in both obese and lipodystrophic insulin-resistant mice, it has been proposed that a selective postreceptor defect in hepatic insulin action is central to the pathogenesis of fatty liver and hypertriglyceridemia in these mice. Here we show that humans with generalized insulin resistance caused by either mutations in the insulin receptor gene or inhibitory antibodies specific for the insulin receptor uniformly exhibited low serum TG and normal HDL cholesterol levels. This was due at least in part to surprisingly low rates of de novo lipogenesis and was associated with low liver fat content and the production of TG-depleted VLDL cholesterol particles. In contrast, humans with a selective postreceptor defect in AKT2 manifest increased lipogenesis, elevated liver fat content, TG-enriched VLDL, hypertriglyceridemia, and low HDL cholesterol levels. People with lipodystrophy, a disorder characterized by particularly severe insulin resistance and dyslipidemia, demonstrated similar abnormalities. Collectively these data from humans with molecularly characterized forms of insulin resistance suggest that partial postreceptor hepatic insulin resistance is a key element in the development of metabolic dyslipidemia and hepatic steatosis.

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Increased diffusion barriers may reduce cellular oxygen delivery following head injury and attenuate the ability of the brain to increase oxygen extraction in response to hypoperfusion. Global or regional OEF underestimates tissue hypoxia due to such mechanisms.

Learning depends on surprise and is not engendered by predictable occurrences. In this functional magnetic resonance imaging (fMRI) study of causal associative learning, we show that dorsolateral prefrontal cortex (DLPFC) is associated specifically with the adjustment of inferential learning on the basis of unpredictability. At the outset, when all associations were unpredictable, DLPFC activation was maximal. This response attenuated with learning but, subsequently, activation here was evoked by surprise violations of the learned association. Furthermore, the magnitude of DLPFC response to a surprise event was sensitive to the relationship that had been learned and was predictive of subsequent behavioral change. In short, the physiological response properties of right DLPFC satisfied specific predictions made by associative learning theory.

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