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BackgroundThis systematic review and meta-analysis summarizes the safety and efficacy of high flow nasal cannula (HFNC) in patients with acute hypoxemic respiratory failure.MethodsWe performed a comprehensive search of MEDLINE, EMBASE, and Web of Science. We identified randomized controlled trials that compared HFNC to conventional oxygen therapy. We pooled data and report summary estimates of effect using relative risk for dichotomous outcomes and mean difference or standardized mean difference for continuous outcomes, with 95% confidence intervals. We assessed risk of bias of included studies using the Cochrane tool and certainty in pooled effect estimates using GRADE methods.ResultsWe included 9 RCTs (n = 2093 patients). We found no difference in mortality in patients treated with HFNC (relative risk [RR] 0.94, 95% confidence interval [CI] 0.67–1.31, moderate certainty) compared to conventional oxygen therapy. We found a decreased risk of requiring intubation (RR 0.85, 95% CI 0.74–0.99) or escalation of oxygen therapy (defined as crossover to HFNC in the control group, or initiation of non-invasive ventilation or invasive mechanical ventilation in either group) favouring HFNC-treated patients (RR 0.71, 95% CI 0.51–0.98), although certainty in both outcomes was low due to imprecision and issues related to risk of bias. HFNC had no effect on intensive care unit length of stay (mean difference [MD] 1.38 days more, 95% CI 0.90 days fewer to 3.66 days more, low certainty), hospital length of stay (MD 0.85 days fewer, 95% CI 2.07 days fewer to 0.37 days more, moderate certainty), patient reported comfort (SMD 0.12 lower, 95% CI 0.61 lower to 0.37 higher, very low certainty) or patient reported dyspnea (standardized mean difference [SMD] 0.16 lower, 95% CI 1.10 lower to 1.42 higher, low certainty). Complications of treatment were variably reported amongst included studies, but little harm was associated with HFNC use.ConclusionIn patients with acute hypoxemic respiratory failure, HFNC may decrease the need for tracheal intubation without impacting mortality.

Purpose Neurally adjusted ventilatory assist (NAVA) is a ventilatory mode that tailors the level of assistance delivered by the ventilator to the electromyographic activity of the diaphragm. The objective of this study was to compare NAVA and pressure support ventilation (PSV) in the early phase of weaning from mechanical ventilation. Methods A multicentre randomized controlled trial of 128 intubated adults recovering from acute respiratory failure was conducted in 11 intensive care units. Patients were randomly assigned to NAVA or PSV. The primary outcome was the probability of remaining in a partial ventilatory mode (either NAVA or PSV) throughout the first 48 h without any return to assist-control ventilation. Secondary outcomes included asynchrony index, ventilator-free days and mortality. Results In the NAVA and PSV groups respectively, the proportion of patients remaining in partial ventilatory mode throughout the first 48 h was 67.2 vs. 63.3 % ( P  = 0.66), the asynchrony index was 14.7 vs. 26.7 % ( P  < 0.001), the ventilator-free days at day 7 were 1.0 day [1.0–4.0] vs. 0.0 days [0.0–1.0] ( P  < 0.01), the ventilator-free days at day 28 were 21 days [4–25] vs. 17 days [0–23] ( P  = 0.12), the day-28 mortality rate was 15.0 vs. 22.7 % ( P  = 0.21) and the rate of use of post-extubation noninvasive mechanical ventilation was 43.5 vs. 66.6 % ( P  < 0.01). Conclusions NAVA is safe and feasible over a prolonged period of time but does not increase the probability of remaining in a partial ventilatory mode. However, NAVA decreases patient–ventilator asynchrony and is associated with less frequent application of post-extubation noninvasive mechanical ventilation. Trial Registration. clinicaltrials.gov Identifier: NCT02018666.

Le processus décisionnel visant à séparer les patients de la ventilation mécanique repose, entre autres éléments, sur l’interprétation de la tolérance clinique du patient à un test de sevrage, communément désigné comme épreuve de ventilation spontanée. Plusieurs modalités dans la réalisation de l’épreuve de ventilation spontanée s’offrent au clinicien (maintien d’une aide inspiratoire et/ou d’une pression expiratoire positive minimale, aucune aide inspiratoire ni pression expiratoire positive sur le ventilateur, pièce en T). D’un point de vue physiologique, l’épreuve de ventilation spontanée réalisée en pièce en T reproduit le plus fidèlement les conditions de ventilation spontanée en comparaison aux autres modalités, et la situation sans support sur le ventilateur semble être équivalente. Toute addition de support sur les ventilateurs modernes sous-estime le travail respiratoire. Dans la population tout venant ou la probabilité de succès est élevée, le choix du premier test peut prendre en compte plusieurs aspects (faisabilité, choix de ne pas sous-estimer la possibilité de succès, etc.). Dans une population sélectionnée par un premier échec de sevrage, le choix de réaliser les épreuves en pièce en T (ou sans support sur le ventilateur) semble la plus logique dans l’objectif de ne pas sous-estimer le risque d’échec. Decision making process aiming at separate patients from mechanical ventilation relies with others issues, on the interpretation of patient’s clinical tolerance during a weaning attempt, so-called spontaneous breathing trial. Several modalities of spontaneous breathing trial are available for clinicians (T piece, minimal pressure support with/without positive end expiratory pressure, no pressure support, no positive end expiratory pressure). From a physiological point of view, T piece reflects better spontaneous breathing without assistance as compared to others methods and ventilation without any support seems equivalent. Any support provided by modern ventilators underestimates work of breathing. In a non-selected population where the weaning success probability is high, the choice of the first spontaneous breathing trial modality takes into account several issues (feasibility, decision not to underestimate the probability success). In a population selected by a first weaning attempt failure, it is logical to repeat further trial with T piece (or without ventilatory support) in order to avoid underestimation of a potential next failure.

Purpose Lung volumes, especially functional residual capacity (FRC), are decreased in acute respiratory distress syndrome (ARDS). Positive end-expiratory pressure (PEEP) contributes to increased end-expiratory lung volume (EELV) and to improved oxygenation, but differentiating recruitment of previously nonaerated lung units from distension of previously open lung units remains difficult. This study evaluated simple methods derived from bedside EELV measurements to assess PEEP-induced lung recruitment while monitoring strain. Methods Prospective multicenter study in 30 mechanically ventilated patients with ARDS in five university hospital ICUs. Two PEEP levels were studied, each for 45 min, and EELV (nitrogen washout/washin technique) was measured at both levels, with the difference (Δ) reflecting PEEP-induced lung volume changes. Alveolar recruitment was measured using pressure-volume (PV) curves. High and low recruiters were separated based on median recruitment at high PEEP. Minimum predicted increase in lung volume computed as the product of ΔPEEP by static compliance was subtracted from ΔEELV as an independent estimate of recruitment. Estimated and measured recruitments were compared. Strain induced by PEEP was also calculated from the same measurements. Results FRC was 31 ± 11% of predicted. Median [25th–75th percentiles] PEEP-induced recruitment was 272 [187–355] mL. Estimated recruitment correlated with recruited volume measured on PV curves (ρ = 0.68), with a slope close to identity. The ΔEELV/FRC ratio differentiated high from low recruiters (110 [76–135] vs. 55 [23–70]%, p  = 0.001). Strain increase due to PEEP was larger in high recruiters ( p  = 0.002). Conclusion PEEP-induced recruitment and strain can be assessed at the bedside using EELV measurement. We describe two bedside methods for predicting low or high alveolar recruitment during ARDS.

Rationale Lung volume available for ventilation is markedly decreased during acute respiratory distress syndrome. Body positioning may contribute to increase lung volume and partial verticalization is simple to perform. This study evaluated whether verticalization had parallel effects on oxygenation and end expiratory lung volume (EELV). Methods Prospective multicenter study in 40 mechanically ventilated patients with ALI/ARDS in five university hospital MICUs. We evaluated four 45-min successive trunk position epochs (supine slightly elevated at 15°; semi recumbent with trunk elevated at 45°; seated with trunk elevated at 60° and legs down at 45°; back to supine). Arterial blood gases, EELV measured using the nitrogen washin/washout, and static compliance were measured. Responders were defined by a PaO 2 /FiO 2 increase >20 % between supine and seated position. Results are median [25th–75th percentiles]. Results With median PEEP = 10 cmH 2 O, verticalization increased lung volume but only responders (13 patients, 32 %) had a significant increase in EELV/PBW (predicted body weight) compared to baseline. This increase persisted at least partially when patients were positioned back to supine. Responders had a lower EELV/PBW supine [14 mL/kg (13–15) vs. 18 mL/kg (15–27) ( p  = 0.005)] and a lower compliance [30 mL/cmH 2 O (22–38) vs. 42 (30–46) ( p  = 0.01)] than non-responders. Strain decreased with verticalization for responders. EELV/PBW increase and PaO 2 /FiO 2 increase were not correlated. Discussion Verticalization is easily achieved and improves oxygenation in approximately 32 % of the patients together with an increase in EELV. Nonetheless, effect of verticalization on EELV/PBW is not predictable by PaO 2 /FiO 2 increase, its monitoring may be helpful for strain optimization.

Background Delirium (acute brain dysfunction) is a potentially life threatening disturbance in brain function that frequently occurs in critically ill patients. While this area of brain dysfunction in critical care is rapidly advancing, striking limitations in use of terminology related to delirium internationally are hindering cross-talk and collaborative research. In the English literature, synonyms of delirium such as the Intensive Care Unit syndrome, acute brain dysfunction, acute brain failure, psychosis, confusion, and encephalopathy are widely used. This often leads to scientific \"confusion\" regarding published data and methodology within studies, which is further exacerbated by organizational, cultural and language barriers. Objective We undertook this multinational effort to identify conflicts in terminology and phenomenology of delirium to facilitate communication across medical disciplines and languages. Methods The evaluation of the terminology used for acute brain dysfunction was determined conducting communications with 24 authors from academic communities throughout countries/regions that speak the 13 variants of the Romanic languages included into this manuscript. Results In the 13 languages utilizing Romanic characters, included in this report, we identified the following terms used to define major types of acute brain dysfunction: coma , delirium , delirio , delirium tremens , délire , confusion mentale , delir , delier , Durchgangs-Syndrom , acute verwardheid , intensiv-psykose , IVA - psykos , IVA - syndrom , akutt konfusion / forvirring . Interestingly two terms are very consistent: 100 % of the selected languages use the term coma or koma to describe patients unresponsive to verbal and/or physical stimuli, and 100% use delirium tremens to define delirium due to alcohol withdrawal. Conversely, only 54% use the term delirium to indicate the disorder as defined by the DSM-IV as an acute change in mental status, inattention, disorganized thinking and altered level of consciousness. Conclusions Attempts towards standardization in terminology, or at least awareness of differences across languages and specialties, will help cross-talk among clinicians and researchers.

Purpose Pressure preset ventilation (PPV) modes with set inspiratory time can be classified according to their ability to synchronize pressure delivery with patient’s inspiratory efforts (i-synchronization). Non-i-synchronized (like airway pressure release ventilation, APRV), partially i-synchronized (like biphasic airway pressure), and fully i-synchronized modes (like assist-pressure control) can be distinguished. Under identical ventilatory settings across PPV modes, the degree of i-synchronization may affect tidal volume ( V T ), transpulmonary pressure ( P TP ), and their variability. We performed bench and clinical studies. Methods In the bench study, all the PPV modes of five ventilators were tested with an active lung simulator. Spontaneous efforts of −10 cmH 2 O at rates of 20 and 30 breaths/min were simulated. Ventilator settings were high pressure 30 cmH 2 O, positive end-expiratory pressure (PEEP) 15 cmH 2 O, frequency 15 breaths/min, and inspiratory to expiratory ratios (I:E) 1:3 and 3:1. In the clinical studies, data from eight intubated patients suffering from acute respiratory distress syndrome (ARDS) and ventilated with APRV were compared to the bench tests. In four additional ARDS patients, each of the PPV modes was compared. Results As the degree of i-synchronization among the different PPV modes increased, mean V T and P TP swings markedly increased while breathing variability decreased. This was consistent with clinical comparison in four ARDS patients. Observational results in eight ARDS patients show low V T and a high variability with APRV. Conclusion Despite identical ventilator settings, the different PPV modes lead to substantial differences in V T , P TP , and breathing variability in the presence spontaneous efforts. Clinicians should be aware of the possible harmful effects of i-synchronization especially when high V T is undesirable.

Purpose Previous clinical trials suggested that inhaled nitric oxide (iNO) could have beneficial effects in sickle cell disease (SCD) patients with acute chest syndrome (ACS). Methods To determine whether iNO reduces treatment failure rate in adult patients with ACS, we conducted a prospective, double-blind, randomized, placebo-controlled clinical trial. iNO (80 ppm, N  = 50) gas or inhaled nitrogen placebo ( N  = 50) was delivered for 3 days. The primary end point was the number of patients with treatment failure at day 3, defined as any one of the following: (1) death from any cause, (2) need for endotracheal intubation, (3) decrease of PaO 2 /FiO 2  ≥ 15 mmHg between days 1 and 3, (4) augmented therapy defined as new transfusion or phlebotomy. Results The two groups did not differ in age, gender, genotype, or baseline characteristics and biological parameters. iNO was well tolerated, although a transient decrease in nitric oxide concentration was mandated in one patient. There was no significant difference in the primary end point between the iNO and placebo groups [23 (46 %) and 29 (58 %); odds ratio (OR), 0.8; 95 % CI, 0.54–1.16; p  = 0.23]. A post hoc analysis of the 45 patients with hypoxemia showed that those in the iNO group were less likely to experience treatment failure at day 3 [7 (33.3 %) vs 18 (72 %); OR = 0.19; 95 % CI, 0.06–0.68; p  = 0.009]. Conclusions iNO did not reduce the rate of treatment failure in adult SCD patients with mild to moderate ACS. Future trials should target more severely ill ACS patients with hypoxemia. Clinical trial registration NCT00748423.

Purpose Non-invasive ventilation is largely used to treat acute and chronic respiratory failure. This ventilation encounters a non-negligible rate of failure related to the used interface/mask, but the reasons for this failure remain unclear. In order to shed light on this issue and to better understand the effects of the geometrical design of interfaces, we aimed to quantify flow, pressure and gas composition in terms of CO 2 and O 2 at the passage through different types of interface (oronasal mask, integral mask and helmet). In particular, we postulated that due to specific gas flow passing throughout the interface, the effective dead space added by the interface is not always related to the whole gas volume included in the interface. Methods Numerical simulations, using computational fluid dynamics, were used to describe pressure, flow and gas composition during ventilation with the different interfaces. Results Between the different interfaces the effective dead spaces differed only modestly (110–370 ml), whereas their internal volumes were markedly different (110–10,000 ml). Effective dead space was limited to half the tidal volume for the most voluminous interface, whereas it was close to the interface gas volume for the less voluminous interfaces. Pressure variations induced by the flow ventilation throughout the interface were negligible. Conclusions Effective dead space is not related to the internal gas volume included in the interface, suggesting that this internal volume should not be considered as a limiting factor for their efficacy during non-invasive ventilation. Patient’s comfort and synchrony have also to be taken into account.

A remarkable property of cellulose-based materials is that they can absorb huge amounts of water (25% of the dry mass) from ambient vapor, in the form of bound water confined at a nanoscale in the amorphous regions of the cellulose structure. The control of the dynamics of sorption and desorption of bound water is a major stake for the reduction of energy consumption and material or structure damages, but in the absence of direct observations this process is still poorly known. Here we present measurements of bound water transport thanks to Nuclear Magnetic Resonance relaxometry and Magnetic Resonance Imaging measurements. We show that the bound water is transported along the fibers and throughout the network of fibers in contact. For each material a single transport diffusion coefficient value allows to represent the processes over the whole range of saturation. The dependence of the transport diffusion coefficient on the fiber density and orientation is then analyzed to deduce the (elementary) transport diffusion coefficient of bound water along a cellulose fiber axis. This constitutes fundamental physical data which may be compared with molecular simulations, and opens the way to the prediction and control of sorption dynamics of all cellulosic materials or other hygroscopic materials.