Factors for success of awake prone positioning in patients with COVID-19-induced acute hypoxemic respiratory failure: analysis of a randomized controlled trial.

BACKGROUND: Awake prone positioning (APP) improves oxygenation in coronavirus disease (COVID-19) patients and, when successful, may decrease the risk of intubation. However, factors associated with APP success remain unknown. In this secondary analysis, we aimed to assess whether APP can reduce intubation rate in patients with COVID-19 and to focus on the factors associated with success. METHODS: In this multicenter randomized controlled trial, conducted in three high-acuity units, we randomly assigned patients with COVID-19-induced acute hypoxemic respiratory failure (AHRF) requiring high-flow nasal cannula (HFNC) oxygen to APP or standard care. Primary outcome was intubation rate at 28 days. Multivariate analyses were performed to identify the predictors associated to treatment success (survival without intubation). RESULTS: Among 430 patients randomized, 216 were assigned to APP and 214 to standard care. The APP group had a lower intubation rate (30% vs 43%, relative risk [RR] 0.70; CI95 0.54-0.90, P = 0.006) and shorter hospital length of stay (11 interquartile range [IQR, 9-14] vs 13 [IQR, 10-17] days, P = 0.001). A respiratory rate ≤ 25 bpm at enrollment, an increase in ROX index > 1.25 after first APP session, APP duration > 8 h/day, and a decrease in lung ultrasound score ≥ 2 within the first 3 days were significantly associated with treatment success for APP. CONCLUSION: In patients with COVID-19-induced AHRF treated by HFNC, APP reduced intubation rate and improved treatment success. A longer APP duration is associated with APP success, while the increase in ROX index and decrease in lung ultrasound score after APP can also help identify patients most likely to benefit. TRIAL REGISTRATION: This study was retrospectively registered in ClinicalTrials.gov at July 20, 2021. Identification number NCT04477655. https://clinicaltrials.gov/ct2/show/NCT04477655?term=PRO-CARF&draw=2&rank=1.

Detection of different colistin resistance mechanisms among multidrug resistant Klebsiella pneumoniae isolates in Bulgaria.

The more frequent usage of colistin resulted in an increase of colistin resistance due to lipopolysaccharide modifications. The aim of this study was to reveal the prevalence and mechanisms of colistin resistance among multidrug-resistant Klebsiella pneumoniae isolates collected in Bulgaria. One hundred multidrug resistant K. pneumoniae isolates were collected in a period between 2017 and 2018. Among them, 29 colistin resistant and 8 heteroresistant isolates were observed and further investigated. Clonal relatedness was detected by RAPD and MLST. Сarbapenemases, two component system phoQ/phoP, pmrA/B, and mgrB were investigated by PCR amplification and Sanger sequencing. Among 37 colistin nonsusceptible isolates, we detected 25 NDM-1 producers. The isolates belonged mainly to ST11 (80%), and also to ST147, ST35, ST340, ST219 (1-2 members per clone). Nine colistin resistant isolates showed changes in mgrB. IS903B-like elements truncated mgrB in five isolates. In two isolates, premature stopcodon (Q30stopcodon) was observed and another two isolates did not amplify mgrB, possibly due to bigger deletion or insertion. No isolates showed phoQ/phoP and pmrA/B mutations except for pmrB (four isolates had R256G). All isolates with IS903B insertions belonged to ST11 clone. The mgrB alterations play major role in colistin resistance in K. pneumoniae isolates studied in the current work. We report truncation of mgrB by IS903 like element in colistin resistant NDM-1 producing K. pneumoniae ST11 clone in Bulgaria.

Activity Clamp Provides Insights into Paradoxical Effects of the Anti-Seizure Drug Carbamazepine.

A major challenge in experimental epilepsy research is to reconcile the effects of anti-epileptic drugs (AEDs) on individual neurons with their network-level actions. Highlighting this difficulty, it is unclear why carbamazepine (CBZ), a frontline AED with a known molecular mechanism, has been reported to increase epileptiform activity in several clinical and experimental studies. We confirmed in an in vitro mouse model (in both sexes) that the frequency of interictal bursts increased after CBZ perfusion. To address the underlying mechanisms, we developed a method, activity clamp, to distinguish the response of individual neurons from network-level actions of CBZ. We first recorded barrages of synaptic conductances from neurons during epileptiform activity and then replayed them in pharmacologically isolated neurons under control conditions and in the presence of CBZ. CBZ consistently decreased the reliability of the second action potential in each burst of activity. Conventional current-clamp recordings using excitatory ramp or square-step current injections failed to reveal this effect. Network modeling showed that a CBZ-induced decrease of neuron recruitment during epileptic bursts can lead to an increase in burst frequency at the network level by reducing the refractoriness of excitatory transmission. By combining activity clamp with computer simulations, the present study provides a potential explanation for the paradoxical effects of CBZ on epileptiform activity.SIGNIFICANCE STATEMENT The effects of anti-epileptic drugs on individual neurons are difficult to separate from their network-level actions. Although carbamazepine (CBZ) has a known anti-epileptic mechanism, paradoxically, it has also been reported to increase epileptiform activity in clinical and experimental studies. To investigate this paradox during realistic neuronal epileptiform activity, we developed a method, activity clamp, to distinguish the effects of CBZ on individual neurons from network-level actions. We demonstrate that CBZ consistently decreases the reliability of the second action potential in each burst of epileptiform activity. Network modeling shows that this effect on individual neuronal responses could explain the paradoxical effect of CBZ at the network level.

Scytalidium candidum 3C is a new name for the Geotrichum candidum Link 3C strain.

In the 1970s, the strain Geotrichum candidum Link 3C was isolated from rotting rope and since then has been extensively studied as a source of cellulose and xylan-degrading enzymes. The original identification of the strain was based only on morphological characters of the fungal mycelium in culture. Recent comparison of the internal transcribed spacer (ITS) fragments derived from the draft genome published in 2015 did not show its similarity to G. candidum species. Given the value of the strain 3C in lignocellulosic biomass degradation, we performed morphological and molecular studies to find the appropriate taxonomic placement for this fungal strain within the Ascomycota phylum. ITS, 18S rDNA, 28S rDNA sequences, and RPB2 encoding genes were used to construct phylogenetic trees with Maximum likelihood and Bayesian inference methods. Based on sequence comparison and multiple gene sequencing, we conclude that the fungal strain designated as Geotrichum candidum Link 3C should be placed into the genus Scytalidium (Pezizomycotina, Leotiomycetes) and is redescribed herein as Scytalidium candidum 3C comb. nov.

Apneic oxygenation reduces the incidence of hypoxemia during emergency intubation: A systematic review and meta-analysis.

STUDY OBJECTIVE: Apneic oxygenation has been advocated for the prevention of hypoxemia during emergency endotracheal intubation. Because of conflicting results from recent trials, the efficacy of apneic oxygenation remains unclear. We performed a systematic review and meta-analysis to investigate the effect of apneic oxygenation on the incidence of clinically significant hypoxemia during emergency endotracheal intubation. METHODS: MEDLINE, EMBASE, and PubMed databases were searched without language and time restrictions for studies of apneic oxygenation performed in a critical care setting. Meta-analysis was conducted with a random-effect model, and according to intention-to-treat allocation wherever applicable. Subgroup analyses were performed to ensure the robustness of findings across various clinical outcomes. RESULTS: Eight studies (n=1953) were included in the meta-analysis. The pooled absolute risk of clinically significant hypoxemia was 27.6% in the usual care group and 19.1% in the apneic oxygenation group, without any heterogeneity across studies (I2=0%; p=0.42). Apneic oxygenation reduced the relative risk of hypoxemia by 30% (95% confidence interval 0.59 to 0.82). There was a trend toward lower mortality in the apneic oxygenation group (relative risk of death 0.77; 95% confidence interval 0.59 to 1.02). CONCLUSION: Apneic oxygenation significantly reduces the incidence of hypoxemia during emergency endotracheal intubation. These findings support the inclusion of apneic oxygenation in everyday clinical practice.

Tonic GABAA conductance bidirectionally controls interneuron firing pattern and synchronization in the CA3 hippocampal network.

The spiking output of interneurons is key for rhythm generation in the brain. However, what controls interneuronal firing remains incompletely understood. Here we combine dynamic clamp experiments with neural network simulations to understand how tonic GABAA conductance regulates the firing pattern of CA3 interneurons. In baseline conditions, tonic GABAA depolarizes these cells, thus exerting an excitatory action while also reducing the excitatory postsynaptic potential (EPSP) amplitude through shunting. As a result, the emergence of weak tonic GABAA conductance transforms the interneuron firing pattern driven by individual EPSPs into a more regular spiking mode determined by the cell intrinsic properties. The increased regularity of spiking parallels stronger synchronization of the local network. With further increases in tonic GABAA conductance the shunting inhibition starts to dominate over excitatory actions and thus moderates interneuronal firing. The remaining spikes tend to follow the timing of suprathreshold EPSPs and thus become less regular again. The latter parallels a weakening in network synchronization. Thus, our observations suggest that tonic GABAA conductance can bidirectionally control brain rhythms through changes in the excitability of interneurons and in the temporal structure of their firing patterns.

GABA-independent GABAA receptor openings maintain tonic currents.

Activation of GABA(A) receptors (GABA(A)Rs) produces two forms of inhibition: phasic inhibition generated by the rapid, transient activation of synaptic GABA(A)Rs by presynaptic GABA release, and tonic inhibition generated by the persistent activation of perisynaptic or extrasynaptic GABA(A)Rs, which can detect extracellular GABA. Such tonic GABA(A)R-mediated currents are particularly evident in dentate granule cells in which they play a major role in regulating cell excitability. Here we show that in rat dentate granule cells in ex vivo hippocampal slices, tonic currents are predominantly generated by GABA-independent GABA(A) receptor openings. This tonic GABA(A)R conductance is resistant to the competitive GABA(A)R antagonist SR95531 (gabazine), which at high concentrations acts as a partial agonist, but can be blocked by an open channel blocker, picrotoxin. When slices are perfused with 200 nm GABA, a concentration that is comparable to CSF concentrations but is twice that measured by us in the hippocampus in vivo using zero-net-flux microdialysis, negligible GABA is detected by dentate granule cells. Spontaneously opening GABA(A)Rs, therefore, maintain dentate granule cell tonic currents in the face of low extracellular GABA concentrations.

Cortical inhibition, pH and cell excitability in epilepsy: what are optimal targets for antiepileptic interventions?

Epilepsy is characterised by the propensity of the brain to generate spontaneous recurrent bursts of excessive neuronal activity, seizures. GABA-mediated inhibition is critical for restraining neuronal excitation in the brain, and therefore potentiation of GABAergic neurotransmission is commonly used to prevent seizures. However, data obtained in animal models of epilepsy and from human epileptic tissue suggest that GABA-mediated signalling contributes to interictal and ictal activity. Prolonged activation of GABA(A) receptors during epileptiform bursts may even initiate a shift in GABAergic neurotransmission from inhibitory to excitatory and so have a proconvulsant action. Direct targeting of the membrane mechanisms that reduce spiking in glutamatergic neurons may better control neuronal excitability in epileptic tissue. Manipulation of brain pH may be a promising approach and recent advances in gene therapy and optogenetics seem likely to provide further routes to effective therapeutic intervention.

A functional role for both -aminobutyric acid (GABA) transporter-1 and GABA transporter-3 in the modulation of extracellular GABA and GABAergic tonic conductances in the rat hippocampus.

Tonic γ-aminobutyric acid (GABA)A receptor-mediated signalling controls neuronal network excitability in the hippocampus. Although the extracellular concentration of GABA (e[GABA]) is critical in determining tonic conductances, knowledge on how e[GABA] is regulated by different GABA transporters (GATs) in vivo is limited. Therefore, we studied the role of GATs in the regulation of hippocampal e[GABA] using in vivo microdialysis in freely moving rats. Here we show that GAT-1, which is predominantly presynaptically located, is the major GABA transporter under baseline, quiescent conditions. Furthermore, a significant contribution of GAT-3 in regulating e[GABA] was revealed by administration of the GAT-3 inhibitor SNAP-5114 during simultaneous blockade of GAT-1 by NNC-711. Thus, the GABA transporting activity of GAT-3 (the expression of which is confined to astrocytes) is apparent under conditions in which GAT-1 is blocked. However, sustained neuronal activation by K(+)-induced depolarization caused a profound spillover of GABA into the extrasynaptic space and this increase in e[GABA] was significantly potentiated by sole blockade of GAT-3 (i.e. even when uptake of GAT-1 is intact). Furthermore, experiments using tetrodotoxin to block action potentials revealed that GAT-3 regulates extrasynaptic GABA levels from action potential-independent sources when GAT-1 is blocked. Importantly, changes in e[GABA] resulting from both GAT-1 and GAT-3 inhibition directly precipitate changes in tonic conductances in dentate granule cells as measured by whole-cell patch-clamp recording. Thus, astrocytic GAT-3 contributes to the regulation of e[GABA] in the hippocampus in vivo and may play an important role in controlling the excitability of hippocampal cells when network activity is increased.

Photonic bandgap Bragg fiber sensors for bending/displacement detection.

We demonstrate an amplitude-based bending/displacement sensor that uses a plastic photonic bandgap Bragg fiber with one end coated with a silver layer. The reflection intensity of the Bragg fiber is characterized in response to different displacements (or bending curvatures). We note that the Bragg reflector of the fiber acts as an efficient mode stripper for the wavelengths near the edge of the fiber bandgap, which makes the sensor extremely sensitive to bending or displacements at these wavelengths. Besides, by comparison of the Bragg fiber sensor to a sensor based on a standard multimode fiber with similar outer diameter and length, we find that the Bragg fiber sensor is more sensitive to bending due to the presence of a mode stripper in the form of a multilayer reflector. Experimental results show that the minimum detection limit of the Bragg fiber sensor can be as small as 3 µm for displacement sensing.

International Survey of High-Flow Nasal Therapy Use for Respiratory Failure in Adult Patients.

(1) Background: High-flow nasal therapy (HFNT) has shown several benefits in addressing respiratory failure. However, the quality of evidence and the guidance for safe practice are lacking. This survey aimed to understand HFNT practice and the needs of the clinical community to support safe practice. (2) Method: A survey questionnaire was developed and distributed to relevant healthcare professionals through national networks in the UK, USA and Canada; responses were collected between October 2020 and April 2021. (3) Results: In the UK and Canada, HFNT was used in 95% of hospitals, with the highest use being in the emergency department. HNFT was widely used outside of a critical care setting. HFNT was mostly used to treat acute type 1 respiratory failure (98%), followed by acute type 2 respiratory failure and chronic respiratory failure. Guideline development was felt to be important (96%) and urgent (81%). Auditing of practice was lacking in 71% of hospitals. In the USA, HFNT was broadly similar to UK and Canadian practice. (4) Conclusions: The survey results reveal several key points: (a) HFNT is used in clinical conditions with limited evidence; (b) there is a lack of auditing; (c) it is used in wards that may not have the appropriate skill mix; and (d) there is a lack of guidance for HFNT use.

Awake prone positioning in acute hypoxaemic respiratory failure: An international expert guidance.

BACKGROUND: Awake prone positioning (APP) of non-intubated patients with acute hypoxaemic respiratory failure (AHRF) has been inconsistently adopted into routine care of patients with COVID-19, likely due to apparent conflicting evidence from recent trials. This short guideline aims to provide evidence-based recommendations for the use of APP in various clinical scenarios. METHODS: An international multidisciplinary panel, assembled for their expertise and representativeness, and supported by a methodologist, performed a systematic literature search, summarized the available evidence derived from randomized clinical trials, and developed recommendations using GRADE (Grading of Recommendations, Assessment, Development, and Evaluation) methodology. RESULTS: The panel strongly recommends that APP rather than standard supine care be used in patients with COVID-19 receiving advanced respiratory support (high-flow nasal cannula, continuous positive airway pressure or non-invasive ventilation). Due to lack of evidence from randomized controlled trials, the panel provides no recommendation on the use of APP in patients with COVID-19 supported with conventional oxygen therapy, nor in patients with AHRF due to causes other than COVID-19. CONCLUSION: APP should be routinely implemented in patients with COVID-19 receiving advanced respiratory support.

Awake prone positioning in acute hypoxaemic respiratory failure.

Awake prone positioning (APP) of patients with acute hypoxaemic respiratory failure gained considerable attention during the early phases of the coronavirus disease 2019 (COVID-19) pandemic. Prior to the pandemic, reports of APP were limited to case series in patients with influenza and in immunocompromised patients, with encouraging results in terms of tolerance and oxygenation improvement. Prone positioning of awake patients with acute hypoxaemic respiratory failure appears to result in many of the same physiological changes improving oxygenation seen in invasively ventilated patients with moderate-severe acute respiratory distress syndrome. A number of randomised controlled studies published on patients with varying severity of COVID-19 have reported apparently contrasting outcomes. However, there is consistent evidence that more hypoxaemic patients requiring advanced respiratory support, who are managed in higher care environments and who can be prone for several hours, benefit most from APP use. We review the physiological basis by which prone positioning results in changes in lung mechanics and gas exchange and summarise the latest evidence base for APP primarily in COVID-19. We examine the key factors that influence the success of APP, the optimal target populations for APP and the key unknowns that will shape future research.

Volume-transmitted GABA waves pace epileptiform rhythms in the hippocampal network.

Mechanisms that entrain and pace rhythmic epileptiform discharges remain debated. Traditionally, the quest to understand them has focused on interneuronal networks driven by synaptic GABAergic connections. However, synchronized interneuronal discharges could also trigger the transient elevations of extracellular GABA across the tissue volume, thus raising tonic conductance (Gtonic) of synaptic and extrasynaptic GABA receptors in multiple cells. Here, we monitor extracellular GABA in hippocampal slices using patch-clamp GABA "sniffer" and a novel optical GABA sensor, showing that periodic epileptiform discharges are preceded by transient, region-wide waves of extracellular GABA. Neural network simulations that incorporate volume-transmitted GABA signals point to a cycle of GABA-driven network inhibition and disinhibition underpinning this relationship. We test and validate this hypothesis using simultaneous patch-clamp recordings from multiple neurons and selective optogenetic stimulation of fast-spiking interneurons. Critically, reducing GABA uptake in order to decelerate extracellular GABA fluctuations-without affecting synaptic GABAergic transmission or resting GABA levels-slows down rhythmic activity. Our findings thus unveil a key role of extrasynaptic, volume-transmitted GABA in pacing regenerative rhythmic activity in brain networks.

Arginylation regulates myofibrils to maintain heart function and prevent dilated cardiomyopathy.

Protein arginylation mediated by arginyltransferase (ATE1) is essential for heart formation during embryogenesis, however its cell-autonomous role in cardiomyocytes and the differentiated heart muscle has never been investigated. To address this question, we generated cardiac muscle-specific Ate1 knockout mice, in which Ate1 deletion was driven by α-myosin heavy chain promoter (αMHC-Ate1 mouse). These mice were initially viable, but developed severe cardiac contractility defects, dilated cardiomyopathy, and thrombosis over time, resulting in high rates of lethality after 6months of age. These symptoms were accompanied by severe ultrastructural defects in cardiac myofibrils, seen in the newborns and far preceding the onset of cardiomyopathy, suggesting that these defects were primary and likely underlay the development of the future heart defects. Several major sarcomeric proteins were arginylated in vivo. Moreover, Ate1 deletion in the hearts resulted in a significant reduction of active and passive myofibril forces, suggesting that arginylation is critical for both myofibril structural integrity and contractility. Thus, arginylation is essential for maintaining the heart function by regulation of the major myofibril proteins and myofibril forces, and its absence in the heart muscle leads to progressive heart failure through cardiomyocyte-specific defects.

Force produced by isolated sarcomeres and half-sarcomeres after an imposed stretch.

When a stretch is imposed to activated muscles, there is a residual force enhancement that persists after the stretch; the force is higher than that produced during an isometric contraction in the corresponding length. The mechanisms behind the force enhancement remain elusive, and there is disagreement if it represents a sarcomeric property, or if it is associated with length nonuniformities among sarcomeres and half-sarcomeres. The purpose of this study was to investigate the effects of stretch on single sarcomeres and myofibrils with predetermined numbers of sarcomeres (n = 2, 3. . . , 8) isolated from the rabbit psoas muscle. Sarcomeres were attached between two precalibrated microneedles for force measurements, and images of the preparations were projected onto a linear photodiode array for measurements of half-sarcomere length (SL). Fully activated sarcomeres were subjected to a stretch (5-10% of initial SL, at a speed of 0.3 µm·s(-1)·SL(-1)) after which they were maintained isometric for at least 5 s before deactivation. Single sarcomeres showed two patterns: 31 sarcomeres showed a small level of force enhancement after stretch (10.46 ± 0.78%), and 28 sarcomeres did not show force enhancement (-0.54 ± 0.17%). In these preparations, there was not a strong correlation between the force enhancement and half-sarcomere length nonuniformities. When three or more sarcomeres arranged in series were stretched, force enhancement was always observed, and it increased linearly with the degree of half-sarcomere length nonuniformities. The results show that the residual force enhancement has two mechanisms: 1) stretch-induced changes in sarcomeric structure(s); we suggest that titin is responsible for this component, and 2) stretch-induced nonuniformities of half-sarcomere lengths, which significantly increases the level of force enhancement.