Immunoglobulin genes and severity of COVID-19.

There is tremendous interindividual and interracial variability in the outcome of SARS-CoV-2 infection, suggesting the involvement of host genetic factors. Here, we investigated whether IgG allotypes GM (γ marker) 3 and GM 17, genetic markers of IgG1, contributed to the severity of COVID-19. IgG1 plays a pivotal role in response against SARS-CoV-2 infection. We also investigated whether these GM alleles synergistically/epistatically with IGHG3 and FCGR2A alleles-which have been previously implicated in COVID-19-modulated the extent of COVID-19 severity. The study population consisted of 316 COVID-19 patients who needed treatment in the intensive care unit of Hospital Universitario Central de Asturias. All individuals were genotyped for GM 3/17, IGHG3 hinge length, and FCGR2A rs1801274 A/G polymorphisms. Among the 316 critical patients, there were 86 deaths. The risk of death among critical patients was significantly higher in subjects with GM 17 (IgG1) and short hinge length (IgG3). GM 17-carriers were at almost three-fold higher risk of death than non-carriers (p < 0.001; OR = 2.86, CI 1.58-5.16). Subjects with short hinge length of IgG3 had a two-fold higher risk of death than those with medium hinge length (p = 0.01; OR = 2.16, CI 1.19-3.90). GM 3/3 and IGHG3 (MM) genotypes were less frequent among death vs. survivors (9% vs 36%, p < 0.001) and associated with protective effect (OR = 0.18, 95% CI = 0.08-0.39). This is the first report implicating IgG1 allotypes in COVID-19-spurred death. It needs to be replicated in an independent study population.

Chromosome-Y haplogroups in Asturias (Northern Spain) and their association with severe COVID-19.

The main objective of this study was to determine whether the common Y-haplogroups were be associated with the risk of developing severe COVID-19 in Spanish male. We studied 479 patients who required hospitalization due to COVID-19 and 285 population controls from the region of Asturias (northern Spain), They were genotyped for several polymorphisms that define the common European Y-haplogroups. We compared the frequencies between patients and controls aged ≤ 65 and >65 years. There were no different haplogroup frequencies between the two age groups of controls. Haplogroup R1b was less common in patients aged ≤65 years. Haplogroup I was more common in the two patient´s groups compared to controls (p = 0.02). Haplogroup R1b was significantly more frequent among hypertensive patients, without difference between the hypertensive and normotensive controls. This suggested that R1b could increase the risk for severe COVID-19 among male with pre-existing hypertension. In conclusion, we described the Y-haplogroup structure among Asturians. We found an increased risk of severe COVID-19 among haplogroup I carriers, and a significantly higher frequency of R1b among hypertensive patients. These results indicate that Y-chromosome variants could serve as markers to define the risk of developing a severe form of COVID-19.

Calcium-activated potassium channels as amplifiers of TRPV4-mediated pulmonary edema formation in male mice.

BACKGROUND: As a mechanosensitive cation channel and key regulator of vascular barrier function, endothelial transient receptor potential vanilloid-type 4 (TRPV4) contributes critically to ventilator-induced lung injury (VILI) and edema formation. Ca2+ influx via TRPV4 can activate Ca2+-activated K + (KCa) channels, categorized into small (SK1-3), intermediate (IK1), and big (BK) KCa, which may in turn amplify Ca2+ influx by increasing the electrochemical Ca2+ gradient and thus, promote lung injury. We therefore hypothesized that endothelial KCa channels may contribute to the progression of TRPV4-mediated VILI. METHODS: Male C57Bl/6J mice were ventilated for 2 h with low or high tidal volumes in the presence or absence of the non-selective KCa antagonists apamin, charybdotoxin, or the selective IK1 antagonist TRAM34. Lung injury was similarly assessed in overventilated, endothelial-specific TRPV4-deficient mice or TRAM34-treated C57Bl/6J mice challenged with intratracheal acid installation. Changes in endothelial Ca2+ concentration ([Ca2+]i) were monitored by real-time imaging in isolated-perfused lungs in response to airway pressure elevation or in human pulmonary microvascular endothelial cells (HPMECs) in response to TRPV4 activation with or without inhibition of KCa channels. Analogously, changes in intracellular potassium concentration ([K+]i) and membrane potential (Vm) were imaged in vitro. RESULTS: Endothelial TRPV4 deficiency or inhibition of KCa channels, and most prominently inhibition of IK1 by TRAM34 attenuated VILI as demonstrated by reduced lung edema, protein leak, and by quantitative lung histology. All KCa antagonists reduced the [Ca2+]i response to mechanical stimulation or direct TRPV4 activation in isolated lungs. TRAM34 and charybdotoxin, yet not apamin prevented TRPV4-induced K+ efflux and membrane hyperpolarization in HPMECs. TRAM34 also attenuated the TRPV4 agonist-induced Ca2+ influx in vitro and reduced acid-induced lung injury in vivo. CONCLUSIONS: KCa channels, specifically IK1, act as amplifiers of TRPV4-mediated Ca2+ influx and establish a detrimental feedback that promotes barrier failure and drives the progression of VILI.

Flow starvation during square-flow assisted ventilation detected by supervised deep learning techniques.

BACKGROUND: Flow starvation is a type of patient-ventilator asynchrony that occurs when gas delivery does not fully meet the patients' ventilatory demand due to an insufficient airflow and/or a high inspiratory effort, and it is usually identified by visual inspection of airway pressure waveform. Clinical diagnosis is cumbersome and prone to underdiagnosis, being an opportunity for artificial intelligence. Our objective is to develop a supervised artificial intelligence algorithm for identifying airway pressure deformation during square-flow assisted ventilation and patient-triggered breaths. METHODS: Multicenter, observational study. Adult critically ill patients under mechanical ventilation > 24 h on square-flow assisted ventilation were included. As the reference, 5 intensive care experts classified airway pressure deformation severity. Convolutional neural network and recurrent neural network models were trained and evaluated using accuracy, precision, recall and F1 score. In a subgroup of patients with esophageal pressure measurement (ΔPes), we analyzed the association between the intensity of the inspiratory effort and the airway pressure deformation. RESULTS: 6428 breaths from 28 patients were analyzed, 42% were classified as having normal-mild, 23% moderate, and 34% severe airway pressure deformation. The accuracy of recurrent neural network algorithm and convolutional neural network were 87.9% [87.6-88.3], and 86.8% [86.6-87.4], respectively. Double triggering appeared in 8.8% of breaths, always in the presence of severe airway pressure deformation. The subgroup analysis demonstrated that 74.4% of breaths classified as severe airway pressure deformation had a ΔPes > 10 cmH2O and 37.2% a ΔPes > 15 cmH2O. CONCLUSIONS: Recurrent neural network model appears excellent to identify airway pressure deformation due to flow starvation. It could be used as a real-time, 24-h bedside monitoring tool to minimize unrecognized periods of inappropriate patient-ventilator interaction.

Preventing occludin tight-junction disruption via inhibition of microRNA-193b-5p attenuates viral load and influenza-induced lung injury.

Virus-induced lung injury is associated with loss of pulmonary epithelial-endothelial tight junction integrity. While the alveolar-capillary membrane may be an indirect target of injury, viruses may interact directly and/or indirectly with miRs to augment their replication potential and evade the host antiviral defense system. Here, we expose how the influenza virus (H1N1) capitalizes on host-derived interferon-induced, microRNA (miR)-193b-5p to target occludin and compromise antiviral defenses. Lung biopsies from patients infected with H1N1 revealed increased miR-193b-5p levels, marked reduction in occludin protein, and disruption of the alveolar-capillary barrier. In C57BL/6 mice, the expression of miR-193b-5p increased, and occludin decreased, 5-6 days post-infection with influenza (PR8). Inhibition of miR-193b-5p in primary human bronchial, pulmonary microvascular, and nasal epithelial cells enhanced antiviral responses. miR-193b-deficient mice were resistant to PR8. Knockdown of occludin, both in vitro and in vivo, and overexpression of miR-193b-5p reconstituted susceptibility to viral infection. miR-193b-5p inhibitor mitigated loss of occludin, improved viral clearance, reduced lung edema, and augmented survival in infected mice. Our results elucidate how the innate immune system may be exploited by the influenza virus and how strategies that prevent loss of occludin and preserve tight junction function may limit susceptibility to virus-induced lung injury.

Age-dependent effect of the IFIH1/MDA5 gene variants on the risk of critical COVID-19.

MDA5, encoded by the IFIH1gene, is a cytoplasmic sensor of viral RNAs that triggers interferon (IFN) antiviral responses. Common and rare IFIH1 variants have been associated with the risk of type 1 diabetes and other immune-mediated disorders, and with the outcome of viral diseases. Variants associated with reduced IFN expression would increase the risk for severe viral disease. The MDA5/IFN pathway would play a critical role in the response to SARS-CoV-2 infection mediating the extent and severity of COVID-19. Here, we genotyped a cohort of 477 patients with critical ICU COVID-19 (109 death) for three IFIH1 functional variants: rs1990760 (p.Ala946Thr), rs35337543 (splicing variant, intron 8 + 1G > C), and rs35744605 (p.Glu627Stop). The main finding of our study was a significant increased frequency of rs1990760 C-carriers in early-onset patients (< 65 years) (p = 0.01; OR = 1.64, 95%CI = 1.18-2.43). This variant was also increased in critical vs. no-ICU patients and in critical vs. asymptomatic controls. The rs35744605 C variant was associated with increased blood IL6 levels at ICU admission. The rare rs35337543 splicing variant showed a trend toward protection from early-onset critical COVID-19. In conclusion, IFIH1 variants associated with reduced gene expression and lower IFN response might contribute to develop critical COVID-19 with an age-dependent effect.

Transcriptomic clustering of critically ill COVID-19 patients.

BACKGROUND: Infections caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may cause a severe disease, termed coronavirus disease 2019 (COVID-19), with significant mortality. Host responses to this infection, mainly in terms of systemic inflammation, have emerged as key pathogenetic mechanisms and their modulation has shown a mortality benefit. METHODS: In a cohort of 56 critically ill COVID-19 patients, peripheral blood transcriptomes were obtained at admission to an intensive care unit (ICU) and clustered using an unsupervised algorithm. Differences in gene expression, circulating microRNAs (c-miRNAs) and clinical data between clusters were assessed, and circulating cell populations estimated from sequencing data. A transcriptomic signature was defined and applied to an external cohort to validate the findings. RESULTS: We identified two transcriptomic clusters characterised by expression of either interferon-related or immune checkpoint genes, respectively. Steroids have cluster-specific effects, decreasing lymphocyte activation in the former but promoting B-cell activation in the latter. These profiles have different ICU outcomes, despite no major clinical differences at ICU admission. A transcriptomic signature was used to identify these clusters in two external validation cohorts (with 50 and 60 patients), yielding similar results. CONCLUSIONS: These results reveal different underlying pathogenetic mechanisms and illustrate the potential of transcriptomics to identify patient endotypes in severe COVID-19 with the aim to ultimately personalise their therapies.

IGHG3 hinge length variation was associated with the risk of critical disease and death in a Spanish COVID-19 cohort.

IgG3 would play an important role in the immune adaptive response against SARS-CoV-2, and low plasma levels might increase the risk of COVID-19 severity and mortality. The IgG3 hinge sequence has a variable repeat of a 15 amino acid exon with common 4-repeats (M) and 3-repeats (S). This length IGHG3 polymorphism might affect the IgG3 effector functions. The short hinge length would reduce the IgG3 flexibility and impairs the neutralization and phagocytosis compared to larger length-isoforms. We genotyped the IGHG3 length polymorphism in patients with critical COVID-19 (N = 516; 107 death) and 152 moderate-severe but no-critical cases. Carriers of the S allele had an increased risk of critical ICU and mortality (p < 0.001, OR = 2.79, 95% CI = 1.66-4.65). This adverse effect might be explained by a less flexibility and reduced ability to induce phagocytosis or viral neutralization for the short length allele. We concluded that the IgG3 hinge length polymorphism could be a predictor of critical COVID-19 and the risk of death. This study was based on a limited number of patients from a single population, and requires validation in larger cohorts.

Update on the Features and Measurements of Experimental Acute Lung Injury in Animals: An Official American Thoracic Society Workshop Report.

Advancements in methods, technology, and our understanding of the pathobiology of lung injury have created the need to update the definition of experimental acute lung injury (ALI). We queried 50 participants with expertise in ALI and acute respiratory distress syndrome using a Delphi method composed of a series of electronic surveys and a virtual workshop. We propose that ALI presents as a "multidimensional entity" characterized by four "domains" that reflect the key pathophysiologic features and underlying biology of human acute respiratory distress syndrome. These domains are 1) histological evidence of tissue injury, 2) alteration of the alveolar-capillary barrier, 3) presence of an inflammatory response, and 4) physiologic dysfunction. For each domain, we present "relevant measurements," defined as those proposed by at least 30% of respondents. We propose that experimental ALI encompasses a continuum of models ranging from those focusing on gaining specific mechanistic insights to those primarily concerned with preclinical testing of novel therapeutics or interventions. We suggest that mechanistic studies may justifiably focus on a single domain of lung injury, but models must document alterations of at least three of the four domains to qualify as "experimental ALI." Finally, we propose that a time criterion defining "acute" in ALI remains relevant, but the actual time may vary based on the specific model and the aspect of injury being modeled. The continuum concept of ALI increases the flexibility and applicability of the definition to multiple models while increasing the likelihood of translating preclinical findings to critically ill patients.

The FCGR2A rs1801274 polymorphism was associated with the risk of death among COVID-19 patients.

Polymorphisms of Fcγ receptors have been associated with variable responses to infections. We determined the association of functional polymorphisms rs1801274 in the FCGR2A and rs396991 in the FCGR3A with COVID-19 severity. This study involved 453 patients with severe COVID-19, in which the FCGR2A rs1801274 G-allele (131-Arg) was significantly associated with death (p = 0.02, OR = 1.47). This effect was independent of age and increased IL6 and D-Dimer levels. This study suggests that the FCGR2A gene might be associated with the risk of death among COVID-19 patients. Our study has several limitations, mainly the limited number of patients and the inclusion of a single population. It is thus necessary to confirm this result in larger cohorts from different populations.

Mechanical ventilation promotes lung tumour spread by modulation of cholesterol cell content.

BACKGROUND: Mechanical stretch of cancer cells can alter their invasiveness. During mechanical ventilation, lungs may be exposed to an increased amount of stretch, but the consequences on lung tumours have not been explored. METHODS: To characterise the influence of mechanical ventilation on the behaviour of lung tumours, invasiveness assays and transcriptomic analyses were performed in cancer cell lines cultured in static conditions or under cyclic stretch. Mice harbouring lung melanoma implants were submitted to mechanical ventilation and metastatic spread was assessed. Additional in vivo experiments were performed to determine the mechanodependent specificity of the response. Incidence of metastases was studied in a cohort of lung cancer patients that received mechanical ventilation compared with a matched group of nonventilated patients. RESULTS: Stretch increases invasiveness in melanoma B16F10luc2 and lung adenocarcinoma A549 cells. We identified a mechanosensitive upregulation of pathways involved in cholesterol processing in vitro, leading to an increase in pro-protein convertase subtilisin/kexin type 9 (PCSK9) and LDLR expression, a decrease in intracellular cholesterol and preservation of cell stiffness. A course of mechanical ventilation in mice harbouring melanoma implants increased brain and kidney metastases 2 weeks later. Blockade of PCSK9 using a monoclonal antibody increased cell cholesterol and stiffness and decreased cell invasiveness in vitro and metastasis in vivo. In patients, mechanical ventilation increased PCSK9 abundance in lung tumours and the incidence of metastasis, thus decreasing survival. CONCLUSIONS: Our results suggest that mechanical stretch promote invasiveness of cancer cells, which may have clinically relevant consequences. Pharmacological manipulation of cholesterol endocytosis could be a novel therapeutic target in this setting.

FURIN gene variants (rs6224/rs4702) as potential markers of death and cardiovascular traits in severe COVID-19.

Furin is a protease that plays a key role in the infection cycle of SARS-CoV-2 by cleaving the viral proteins during the virus particle assembly. In addition, Furin regulates several physiological processes related to cardio-metabolic traits. DNA variants in the FURIN gene are candidates to regulate the risk of developing these traits as well as the susceptibility to severe COVID-19. We genotyped two functional FURIN variants (rs6224/rs4702) in 428 COVID-19 patients in the intensive care unit. The association with death (N = 106) and hypertension, diabetes, and hyperlipidaemia was statistically evaluated. The risk of death was associated with age, hypertension, and hypercholesterolemia. The two FURIN alleles linked to higher expression (rs6224 T and rs4702 A) were significantly increased in the death cases (odds ratio= 1.40 and 1.43). Homozygosis for the two high expression genotypes (rs6224 TT and rs4702 AA) and for the T-A haplotype was associated with an increased risk of hypercholesterolemia. In the multiple logistic regression both, hypercholesterolemia and the TT + AA genotype were significantly associated with death. In conclusion, besides its association with hypercholesterolemia, FURIN variants might be independent risk factors for the risk of death among COVID-19 patients.

Survival in Immunocompromised Patients Ultimately Requiring Invasive Mechanical Ventilation: A Pooled Individual Patient Data Analysis.

Rationale: Acute respiratory failure (ARF) is associated with high mortality in immunocompromised patients, particularly when invasive mechanical ventilation is needed. Therefore, noninvasive oxygenation/ventilation strategies have been developed to avoid intubation, with uncertain impact on mortality, especially when intubation is delayed. Objectives: We sought to report trends of survival over time in immunocompromised patients receiving invasive mechanical ventilation. The impact of delayed intubation after failure of noninvasive strategies was also assessed. Methods: Systematic review and meta-analysis using individual patient data of studies that focused on immunocompromised adult patients with ARF requiring invasive mechanical ventilation. Studies published in English were identified through PubMed, Web of Science, and Cochrane Central (2008-2018). Individual patient data were requested from corresponding authors for all identified studies. We used mixed-effect models to estimate the effect of delayed intubation on hospital mortality and described mortality rates over time. Measurements and Main Results: A total of 11,087 patients were included (24 studies, three controlled trials, and 21 cohorts), of whom 7,736 (74%) were intubated within 24 hours of ICU admission (early intubation). The crude mortality rate was 53.2%. Adjusted survivals improved over time (from 1995 to 2017, odds ratio [OR] for hospital mortality per year, 0.96 [0.95-0.97]). For each elapsed day between ICU admission and intubation, mortality was higher (OR, 1.38 [1.26-1.52]; P < 0.001). Early intubation was significantly associated with lower mortality (OR, 0.83 [0.72-0.96]), regardless of initial oxygenation strategy. These results persisted after propensity score analysis (matched OR associated with delayed intubation, 1.56 [1.44-1.70]). Conclusions: In immunocompromised intubated patients, survival has improved over time. Time between ICU admission and intubation is a strong predictor of mortality, suggesting a detrimental effect of late initial oxygenation failure.

The Interferon-induced transmembrane protein 3 gene (IFITM3) rs12252 C variant is associated with COVID-19.

BACKGROUND AND AIMS: The interferon-induced transmembrane proteins play an important antiviral role by preventing viruses from traversing the cellular lipid bilayer. IFITM3 gene variants have been associated with the clinical response to influenza and other viruses. Our aim was to determine whether the IFITM3 rs12252 polymorphism was associated with the risk of developing severe symptoms of COVID-19 in our population. METHODS: A total of 288 COVID-19 patients who required hospitalization (81 in the intensive care unit) and 440 age matched controls were genotyped with a Taqman assay. Linear regression models were used to compare allele and genotype frequencies between the groups, correcting for age and sex. RESULTS: Carriers of the minor allele frequency (rs12252 C) were significantly more frequent in the patients compared to controls after correcting by age and sex (p = 0.01, OR = 2.02, 95%CI = 1.19-3.42). This genotype was non-significantly more common among patients who required ICU. CONCLUSIONS: The IFITM3 rs12252 C allele was a risk factor for COVID-19 hospitalization in our Caucasian population. The extent of the association was lower than the reported among Chinese, a population with a much higher frequency of the risk allele.

The central nervous system during lung injury and mechanical ventilation: a narrative review.

Mechanical ventilation induces a number of systemic responses for which the brain plays an essential role. During the last decade, substantial evidence has emerged showing that the brain modifies pulmonary responses to physical and biological stimuli by various mechanisms, including the modulation of neuroinflammatory reflexes and the onset of abnormal breathing patterns. Afferent signals and circulating factors from injured peripheral tissues, including the lung, can induce neuronal reprogramming, potentially contributing to neurocognitive dysfunction and psychological alterations seen in critically ill patients. These impairments are ubiquitous in the presence of positive pressure ventilation. This narrative review summarises current evidence of lung-brain crosstalk in patients receiving mechanical ventilation and describes the clinical implications of this crosstalk. Further, it proposes directions for future research ranging from identifying mechanisms of multiorgan failure to mitigating long-term sequelae after critical illness.

Lung Purinoceptor Activation Triggers Ventilator-Induced Brain Injury.

OBJECTIVES: Mechanical ventilation can cause ventilator-induced brain injury via afferent vagal signaling and hippocampal neurotransmitter imbalances. The triggering mechanisms for vagal signaling during mechanical ventilation are unknown. The objective of this study was to assess whether pulmonary transient receptor potential vanilloid type-4 (TRPV4) mechanoreceptors and vagal afferent purinergic receptors (P2X) act as triggers of ventilator-induced brain injury. DESIGN: Controlled, human in vitro and ex vivo studies, as well as murine in vivo laboratory studies. SETTING: Research laboratory. SUBJECTS: Wild-type, TRPV4-deficient C57BL/6J mice, 8-10 weeks old. Human postmortem lung tissue and human lung epithelial cell line BEAS-2B. INTERVENTION: Mice subjected to mechanical ventilation were studied using functional MRI to assess hippocampal activity. The effects of lidocaine (a nonselective ion-channel inhibitor), P2X-purinoceptor antagonist (iso-PPADS), or genetic TRPV4 deficiency on hippocampal dopamine-dependent pro-apoptotic signaling were studied in mechanically ventilated mice. Human lung epithelial cells (BEAS-2B) were used to study the effects of mechanical stretch on TRPV4 and P2X expression and activation. TRPV4 levels were measured in postmortem lung tissue from ventilated and nonventilated patients. MEASUREMENTS AND MAIN RESULTS: Hippocampus functional MRI analysis revealed considerable changes in response to the increase in tidal volume during mechanical ventilation. Intratracheal lidocaine, iso-PPADS, and TRPV4 genetic deficiency protected mice against ventilationinduced hippocampal pro-apoptotic signaling. Mechanical stretch in both, BEAS-2B cells and ventilated wild-type mice, resulted in TRPV4 activation and reduced Trpv4 and P2x expression. Intratracheal replenishment of adenosine triphosphate in Trpv4 mice abrogated the protective effect of TRPV4 deficiency. Autopsy lung tissue from ventilated patients showed decreased lung TRPV4 levels compared with nonventilated CONCLUSIONS:: TRPV4 mechanosensors and purinergic receptors are involved in the mechanisms of ventilator-induced brain injury. Inhibition of this neural signaling, either using nonspecific or specific inhibitors targeting the TRPV4/adenosine triphosphate/P2X signaling axis, may represent a novel strategy to prevent or treat ventilator-induced brain injury.

Effects of sedatives and opioids on trigger and cycling asynchronies throughout mechanical ventilation: an observational study in a large dataset from critically ill patients.

BACKGROUND: In critically ill patients, poor patient-ventilator interaction may worsen outcomes. Although sedatives are often administered to improve comfort and facilitate ventilation, they can be deleterious. Whether opioids improve asynchronies with fewer negative effects is unknown. We hypothesized that opioids alone would improve asynchronies and result in more wakeful patients than sedatives alone or sedatives-plus-opioids. METHODS: This prospective multicenter observational trial enrolled critically ill adults mechanically ventilated (MV) > 24 h. We compared asynchronies and sedation depth in patients receiving sedatives, opioids, or both. We recorded sedation level and doses of sedatives and opioids. BetterCare™ software continuously registered ineffective inspiratory efforts during expiration (IEE), double cycling (DC), and asynchrony index (AI) as well as MV modes. All variables were averaged per day. We used linear mixed-effects models to analyze the relationships between asynchronies, sedation level, and sedative and opioid doses. RESULTS: In 79 patients, 14,166,469 breaths were recorded during 579 days of MV. Overall asynchronies were not significantly different in days classified as sedatives-only, opioids-only, and sedatives-plus-opioids and were more prevalent in days classified as no-drugs than in those classified as sedatives-plus-opioids, irrespective of the ventilatory mode. Sedative doses were associated with sedation level and with reduced DC (p < 0.0001) in sedatives-only days. However, on days classified as sedatives-plus-opioids, higher sedative doses and deeper sedation had more IEE (p < 0.0001) and higher AI (p = 0.0004). Opioid dosing was inversely associated with overall asynchronies (p < 0.001) without worsening sedation levels into morbid ranges. CONCLUSIONS: Sedatives, whether alone or combined with opioids, do not result in better patient-ventilator interaction than opioids alone, in any ventilatory mode. Higher opioid dose (alone or with sedatives) was associated with lower AI without depressing consciousness. Higher sedative doses administered alone were associated only with less DC. TRIAL REGISTRATION: ClinicalTrial.gov, NCT03451461.

The Emerging Role of Neutrophils in Repair after Acute Lung Injury.

Neutrophils are key players in acute lung injury. Once recruited from the circulation, these cells release cytotoxic molecules that lead to tissue disruption, so their blockade has been advocated to prevent lung damage. However, lung injury also occurs during neutropenia and usually involves a very poor outcome. There is emerging evidence that neutrophils not only contribute to that early damage but also orchestrate later repair. Neutrophils promote epithelial proliferation and are a source of proteases, which are required for the processing of the collagen scar and facilitation of cell migration. This article reviews the effects of neutrophils in repair after acute lung injury, focusing on their role as biovectors for proteases and other molecules involved in tissue remodeling.

Impaired lung repair during neutropenia can be reverted by matrix metalloproteinase-9.

BACKGROUND: Neutrophils may cause tissue disruption during migration and by releasing cytotoxic molecules. However, the benefits of neutrophil depletion observed in experimental models of lung injury do not correspond with the poor outcome of neutropenic patients. METHODS: To clarify the role of neutrophils during repair, mice with ventilator induced lung injury (VILI) were rendered neutropenic after damage, and followed for 48 hours of spontaneous breathing. Lungs were harvested and inflammatory mediators and matrix metalloproteinases measured. Bronchoalveolar lavage fluid (BALF) from ventilated patients with acute respiratory distress syndrome, with or without neutropenia, was collected, the same mediators measured and their effects in an ex vivo model of alveolar repair studied. Finally, neutropenic mice were treated after VILI with exogenous matrix metalloproteinase-9 (MMP-9). RESULTS: Lungs from neutropenic animals showed delayed repair and displayed higher levels of tumour necrosis factor α, interferon γ and macrophage inflammatory protein 2, and absence of MMP-9. BALF from ventilated neutropenic patients with acute respiratory distress syndrome showed similar results. BALFs from neutropenic patients yielded a delayed closure rate of epithelial wounds ex vivo, which was improved by removal of collagen or addition of exogenous MMP-9. Lastly, treatment of neutropenic mice with exogenous MMP-9 after VILI reduced tissue damage without modifying cytokine concentrations. CONCLUSION: Release of MMP-9 from neutrophils is required for adequate matrix processing and lung repair.

Double Cycling During Mechanical Ventilation: Frequency, Mechanisms, and Physiologic Implications.

OBJECTIVES: Double cycling generates larger than expected tidal volumes that contribute to lung injury. We analyzed the incidence, mechanisms, and physiologic implications of double cycling during volume- and pressure-targeted mechanical ventilation in critically ill patients. DESIGN: Prospective, observational study. SETTING: Three general ICUs in Spain. PATIENTS: Sixty-seven continuously monitored adult patients undergoing volume control-continuous mandatory ventilation with constant flow, volume control-continuous mandatory ventilation with decelerated flow, or pressure control-continuous mandatory mechanical ventilation for longer than 24 hours. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: We analyzed 9,251 hours of mechanical ventilation corresponding to 9,694,573 breaths. Double cycling occurred in 0.6%. All patients had double cycling; however, the distribution of double cycling varied over time. The mean percentage (95% CI) of double cycling was higher in pressure control-continuous mandatory ventilation 0.54 (0.34-0.87) than in volume control-continuous mandatory ventilation with constant flow 0.27 (0.19-0.38) or volume control-continuous mandatory ventilation with decelerated flow 0.11 (0.06-0.20). Tidal volume in double-cycled breaths was higher in volume control-continuous mandatory ventilation with constant flow and volume control-continuous mandatory ventilation with decelerated flow than in pressure control-continuous mandatory ventilation. Double-cycled breaths were patient triggered in 65.4% and reverse triggered (diaphragmatic contraction stimulated by a previous passive ventilator breath) in 34.6% of cases; the difference was largest in volume control-continuous mandatory ventilation with decelerated flow (80.7% patient triggered and 19.3% reverse triggered). Peak pressure of the second stacked breath was highest in volume control-continuous mandatory ventilation with constant flow regardless of trigger type. Various physiologic factors, none mutually exclusive, were associated with double cycling. CONCLUSIONS: Double cycling is uncommon but occurs in all patients. Periods without double cycling alternate with periods with clusters of double cycling. The volume of the stacked breaths can double the set tidal volume in volume control-continuous mandatory ventilation with constant flow. Gas delivery must be tailored to neuroventilatory demand because interdependent ventilator setting-related physiologic factors can contribute to double cycling. One third of double-cycled breaths were reverse triggered, suggesting that repeated respiratory muscle activation after time-initiated ventilator breaths occurs more often than expected.