An update on the current management of hyponatremia

Hyponatremia is the most common electrolyte disorder in hospitalized patients. According to the Edelman equation, hyponatremia usually develops due to a gain of free water, a loss of serum sodium or a combination of both. Investigating the causes of hyponatremia and consequent correction of the electrolyte disorder can be challenging. In this review we give an overview on the mechanisms leading to hyponatremia and in a further step, the correction of hyponatremia is discussed in detail with sections on: rate of correction, treatment with respect to volume state, risks of correction and a discussion of vasopressin receptor antagonists.

Mapping spikes to sensations

Single-unit recordings conducted during perceptual decision-making tasks have yielded tremendous insights into the neural coding of sensory stimuli. In such experiments, detection or discrimination behavior (the psychometric data) is observed in parallel with spike trains in sensory neurons (the neurometric data). Frequently, candidate neural codes for information read-out are pitted against each other by transforming the neurometric data in some way and asking which code’s performance most closely approximates the psychometric performance. The code that matches the psychometric performance best is retained as a viable candidate and the others are rejected. In following this strategy, psychometric data is often considered to provide an unbiased measure of perceptual sensitivity. It is rarely acknowledged that psychometric data result from a complex interplay of sensory and non-sensory processes and that neglect of these processes may result in misestimating psychophysical sensitivity. This again may lead to erroneous conclusions regarding the adequacy of candidate neural codes. In this review, we first discuss requirements on the neural data for a subsequent neurometric-psychometric comparison. We then focus on different psychophysical tasks for the assessment of detection and discrimination performance and the cognitive processes that may underlie their execution. We discuss further factors that may compromise psychometric performance and how they can be detected or avoided. We believe that these considerations point to shortcomings in our understanding of the processes underlying perceptual decisions, and therefore offer potential for future research.

["Truth at the bedside"]

BACKGROUND AND RESEARCH QUESTION

Discussions with seriously ill patients are part of physicians' tasks. These discussions are very demanding with respect to communication skills. In this paper we present the concept of an obligatory postgraduate course for physicians on breaking bad news and the results of the course evaluation.

RESEARCH PARTICIPANTS AND METHODS

Physicians of 4 German hospitals in which the module was offered as an obligatory inhouse course. An interventional study without control group was carried out in which a questionnaire (closed-ended questions and Likert scales as well as open-ended questions) was distributed before and immediately after the course.

RESULTS

186 physicians (response rate: 88.6 %) participated in the study. 102 respondents (54.8 %) had broken bad news more than five times per month. 75 physicians (40.3 %) indicated that they had never participated in a teaching module on this topic prior to the course. Discussions about the end of life and disclosure about recurrence of the disease were rated most frequently as very difficult communication situations. Compared with the beginning of the course the respondents rated their communication skills significantly better at the end of the course. The course's relevance for clinical practice, teaching methods and the organisation of the course were rated positively.

CONCLUSION

The feedback of the participants indicates the practical relevance of professional training on difficult communication situations such as breaking bad news. The improved rating of communication skills may be interpreted as a positive effect of the course. In our view, observational studies as well as interprofessional teaching modules contribute to improved professional communication with patients about diagnosis, prognosis and treatment options.

Observation and Characterization of the Pseudomorphic to Stable Phase Transitions of Fe1-xSi on Si(111)

Pseudomorphic Fe1-x Si films have been grown on Si(111) by molecular beam epitaxy (MBE) at room temperature (RT). Structural investigations revealed that the phase crystallizes in the cubic CsCl structure with a lattice constant close to half that of Si. Upon annealing, films thicker than 15Å undergo a phase transition to the stable bulk ε-FeSi, either in epitaxial or in polycrystalline form at temperatures around 300°C. Thinner films do not transform to the ε-FeSi phase. Instead they exhibit a continuous increase of the Si content up to the stoichiometry of FeSi2 The CsCl symmetry persists, exept for prolonged annealing close to the transition to βFeSi2, where γ-FeSi2 (CaF2 ) forms as an intermediate phase.

Real-time adaptive microstimulation increases reliability of electrically evoked cortical potentials

Cortical neuroprostheses that employ repeated electrical stimulation of cortical areas with fixed stimulus parameters, are faced with the problem of large trial-by-trial variability of evoked potentials. This variability is caused by the ongoing cortical signal processing, but it is an unwanted phenomenon if one aims at imprinting neural activity as precisely as possible. Here, we use local field potentials measured by one microelectrode, located at a distance of 200 microns from the stimulation site, to drive the electrically evoked potential toward a desired target potential by real-time adaptation of the stimulus intensity. The functional relationship between ongoing cortical activity, evoked potential, and stimulus intensity was estimated by standard machine learning techniques (support vector regression with problem-specific kernel function) from a set of stimulation trials with randomly varied stimulus intensities. The smallest deviation from the target potential was achieved for low stimulus intensities. Further, the observed precision effect proved time sensitive, since it was abolished by introducing a delay between data acquisition and stimulation. These results indicate that local field potentials contain sufficient information about ongoing local signal processing to stabilize electrically evoked potentials. We anticipate that adaptive low intensity microstimulation will play an important role in future cortical prosthetic devices that aim at restoring lost sensory functions.

Mislocalization of near-threshold tactile stimuli in humans: a central or peripheral phenomenon?

Principles of brain function can be disclosed by studying their limits during performance. Tactile stimuli with near-threshold intensities have been used to assess features of somatosensory processing. When stimulating fingers of one hand using near-threshold intensities, localization errors are observed that deviate significantly from responses obtained by guessing - incorrectly located stimuli are attributed more often to fingers neighbouring the stimulated one than to more distant fingers. Two hypotheses to explain the findings are proposed. The 'central hypothesis' posits that the degree of overlap of cortical tactile representations depends on stimulus intensity, with representations less separated for near-threshold stimuli than for suprathreshold stimuli. The 'peripheral hypothesis' assumes that systematic mislocalizations are due to activation of different sets of skin receptors with specific thresholds. The present experiments were designed to decide between the two hypotheses. Taking advantage of the frequency tuning of somatosensory receptors, their contribution to systematic misclocalizations was studied. In the first experiment, mislocalization profiles were investigated using vibratory stimuli with frequencies of 10, 20 and 100 Hz. Unambiguous mislocalization effects were only obtained for the 10-Hz stimulation, precluding the involvement of Pacinian corpuscles in systematic mislocalization. In the second experiment, Pacinian corpuscles were functionally eliminated by applying a constant 100-Hz vibratory masking stimulus together with near-threshold pulses. Despite masking, systematic mislocation patterns were observed rendering the involvement of Pacinian corpuscles unlikely. The results of both experiments are in favor of the 'central hypothesis' assuming that the extent of overlap in somatosensory representations is modulated by stimulus intensity.

The head-fixed behaving rat--procedures and pitfalls

This paper describes experimental techniques with head-fixed, operantly conditioned rodents that allow the control of stimulus presentation and tracking of motor output at hitherto unprecedented levels of spatio-temporal precision. Experimental procedures for the surgery and behavioral training are presented. We place particular emphasis on potential pitfalls using these procedures in order to assist investigators who intend to engage in this type of experiment. We argue that head-fixed rodent models, by allowing the combination of methodologies from molecular manipulations, intracellular electrophysiology, and imaging to behavioral measurements, will be instrumental in combining insights into the functional neuronal organization at different levels of observation. Provided viable behavioral methods are implemented, model systems based on rodents will be complementary to current primate models—the latter providing highest comparability with the human brain, while the former offer hugely advanced methodologies on the lower levels of organization, for example, genetic alterations, intracellular electrophysiology, and imaging.

Cross-approximate entropy of cortical local field potentials quantifies effects of anesthesia--a pilot study in rats

Background

Anesthetics dose-dependently shift electroencephalographic (EEG) activity towards high-amplitude, slow rhythms, indicative of a synchronization of neuronal activity in thalamocortical networks. Additionally, they uncouple brain areas in higher (gamma) frequency ranges possibly underlying conscious perception. It is currently thought that both effects may impair brain function by impeding proper information exchange between cortical areas. But what happens at the local network level? Local networks with strong excitatory interconnections may be more resilient towards global changes in brain rhythms, but depend heavily on locally projecting, inhibitory interneurons. As anesthetics bias cortical networks towards inhibition, we hypothesized that they may cause excessive synchrony and compromise information processing already on a small spatial scale. Using a recently introduced measure of signal independence, cross-approximate entropy (XApEn), we investigated to what degree anesthetics synchronized local cortical network activity. We recorded local field potentials (LFP) from the somatosensory cortex of three rats chronically implanted with multielectrode arrays and compared activity patterns under control (awake state) with those at increasing concentrations of isoflurane, enflurane and halothane.

Results

Cortical LFP signals were more synchronous, as expressed by XApEn, in the presence of anesthetics. Specifically, XApEn was a monotonously declining function of anesthetic concentration. Isoflurane and enflurane were indistinguishable; at a concentration of 1 MAC (the minimum alveolar concentration required to suppress movement in response to noxious stimuli in 50% of subjects) both volatile agents reduced XApEn by about 70%, whereas halothane was less potent (50% reduction).

Conclusions

The results suggest that anesthetics strongly diminish the independence of operation of local cortical neuronal populations, and that the quantification of these effects in terms of XApEn has a similar discriminatory power as changes of spontaneous action potential rates. Thus, XApEn of field potentials recorded from local cortical networks provides valuable information on the anesthetic state of the brain.

Activity patterns in the prefrontal cortex and hippocampus during and after awakening from etomidate anesthesia

BACKGROUND

The anesthetic properties of etomidate are largely mediated by gamma-aminobutyric acid type A receptors. There is evidence for the existence of gamma-aminobutyric acid type A receptor subtypes in the brain, which respond to small concentrations of etomidate. After awakening from anesthesia, these subtypes are expected to cause cognitive dysfunction for a yet unknown period of time. The corresponding patterns of brain electrical activity and the molecular identity of gamma-aminobutyric acid type A receptors contributing to these actions remain to be elucidated.

METHODS

Anesthesia was induced in wild-type and beta3(N265M) knock-in mice by intravenous injection of 10 mg/kg etomidate. Local field potentials were recorded simultaneously in the prefrontal cortex and hippocampus using chronically implanted electrode arrays. Local field potentials were sampled before, during, and after anesthesia.

RESULTS

In the prefrontal cortex and hippocampus of wild-type mice, intravenous bolus injection of etomidate evoked isoelectric baselines and subsequent burst suppression. These effects were largely attenuated by the beta3(N265M) mutation. During emergence from anesthesia, power density in the theta band (5-15 Hz) transiently increased in the hippocampus of wild types, but not in the mutants, indicating that this action was caused by the receptors harboring beta3 subunits. In both genotypes, etomidate produced a long-lasting (> 1 h after recovery of righting reflexes) decrease in theta-peak frequency. Significant slowing of theta activity was apparent in the hippocampus and prefrontal cortex.

CONCLUSIONS

Etomidate-induced patterns of brain activity during deep anesthesia mostly involve actions at beta3 containing gamma-aminobutyric acid type A receptors. During the postanesthesia period, altered theta-band activity indicates ongoing anesthetic action.

[Intramedullary nailing of proximal tibial fractures. Complications and risk factors]

INTRODUCTION

We performed a consecutive study on patients with proximal tibial fractures without joint participation to determine the early clinical and radiological outcome.

PATIENTS

From January 2000 to December 2005, 22 fractures of the proximal and proximal diaphyseal tibia without joint participation were operated on using the new tibia nail. A total of 18 patients (82%) completed full follow-up after 6 weeks and 3 and 6 months.

RESULTS

Two primary and one secondary malalignment were observed Two of them were initially polytraumatised. Furthermore, two patients developed a delayed union, and one non-union occurred. Risk factors for limited bony consolidation were smoking and an open fracture. Screw or nail breakage did not occur, and no infection was observed.

A miniaturized chronic microelectrode drive for awake behaving head restrained mice and rats

The present work introduces an electrode microdrive system small enough to be placed into two distinct brain areas in head-fixed mice. To meet the space constraint imposed by the size of mice and the additional presence of a head post, the size and weight of the components were minimized. In the current version, an individual microdrive moves an array of four Reitboeck type electrodes. We report about successful implantation in rats and mice using one or two microdrives. Using two of these devices in individual mice/rats, the recording of parallel single and multi-unit as well as local field potential from prefrontal, motor, somatosensory cortex and hippocampus is demonstrated. The system can be easily constructed with machinery and equipment present in most neurophysiology labs.