Alveolar Mitochondrial Quality Control During Acute Respiratory Distress Syndrome.

Acute respiratory distress syndrome (ARDS) is a leading cause of respiratory failure and death in patients in the intensive care unit. Experimentally, acute lung injury resolution depends on the repair of mitochondrial oxidant damage by the mitochondrial quality control (MQC) pathways, mitochondrial biogenesis, and mitophagy, but nothing is known about this in the human lung. In a case-control autopsy study, we compared the lungs of subjects dying of ARDS (n = 8; cases) and age-/gender-matched subjects dying of nonpulmonary causes (n = 7; controls). Slides were examined by light microscopy and immunofluorescence confocal microscopy, randomly probing for co-localization of citrate synthase with markers of oxidant stress, mitochondrial DNA damage, mitophagy, and mitochondrial biogenesis. ARDS lungs showed diffuse alveolar damage with edema, hyaline membranes, and neutrophils. Compared with controls, a high degree of mitochondrial oxidant damage was seen in type 2 epithelial (AT2) cells and alveolar macrophages by 8-hydroxydeoxyguanosine and malondialdehyde co-staining with citrate synthase. In ARDS, antioxidant protein heme oxygenase-1 and DNA repair enzyme N-glycosylase/DNA lyase (Ogg1) were found in alveolar macrophages but not in AT2 cells. Moreover, MAP1 light chain-3 (LC3) and serine/threonine-protein kinase (Pink1) staining were absent in AT2 cells, suggesting a mitophagy failure. Nuclear respiratory factor-1 staining was missing in the alveolar region, suggesting impaired mitochondrial biogenesis. Widespread hyperproliferation of AT2 cells in ARDS could suggest defective differentiation into type 1 cells. ARDS lungs show profuse mitochondrial oxidant DNA damage but little evidence of MQC activity in AT2 epithelium. Because these pathways are important for acute lung injury resolution, our findings support MQC as a novel pharmacologic target for ARDS resolution.

Management of severe acute respiratory distress syndrome: a primer.

This narrative review explores the physiology and evidence-based management of patients with severe acute respiratory distress syndrome (ARDS) and refractory hypoxemia, with a focus on mechanical ventilation, adjunctive therapies, and veno-venous extracorporeal membrane oxygenation (V-V ECMO). Severe ARDS cases increased dramatically worldwide during the Covid-19 pandemic and carry a high mortality. The mainstay of treatment to improve survival and ventilator-free days is proning, conservative fluid management, and lung protective ventilation. Ventilator settings should be individualized when possible to improve patient-ventilator synchrony and reduce ventilator-induced lung injury (VILI). Positive end-expiratory pressure can be individualized by titrating to best respiratory system compliance, or by using advanced methods, such as electrical impedance tomography or esophageal manometry. Adjustments to mitigate high driving pressure and mechanical power, two possible drivers of VILI, may be further beneficial. In patients with refractory hypoxemia, salvage modes of ventilation such as high frequency oscillatory ventilation and airway pressure release ventilation are additional options that may be appropriate in select patients. Adjunctive therapies also may be applied judiciously, such as recruitment maneuvers, inhaled pulmonary vasodilators, neuromuscular blockers, or glucocorticoids, and may improve oxygenation, but do not clearly reduce mortality. In select, refractory cases, the addition of V-V ECMO improves gas exchange and modestly improves survival by allowing for lung rest. In addition to VILI, patients with severe ARDS are at risk for complications including acute cor pulmonale, physical debility, and neurocognitive deficits. Even among the most severe cases, ARDS is a heterogeneous disease, and future studies are needed to identify ARDS subgroups to individualize therapies and advance care.

Suppression of Fibrinolysis and Hypercoagulability, Severity of Hypoxemia, and Mortality in COVID-19 Patients: A Retrospective Cohort Study.

BACKGROUND: COVID-19 causes hypercoagulability, but the association between coagulopathy and hypoxemia in critically ill patients has not been thoroughly explored. This study hypothesized that severity of coagulopathy would be associated with acute respiratory distress syndrome severity, major thrombotic events, and mortality in patients requiring intensive care unit-level care. METHODS: Viscoelastic testing by rotational thromboelastometry and coagulation factor biomarker analyses were performed in this prospective observational cohort study of critically ill COVID-19 patients from April 2020 to October 2020. Statistical analyses were performed to identify significant coagulopathic biomarkers such as fibrinolysis-inhibiting plasminogen activator inhibitor 1 and their associations with clinical outcomes such as mortality, extracorporeal membrane oxygenation requirement, occurrence of major thrombotic events, and severity of hypoxemia (arterial partial pressure of oxygen/fraction of inspired oxygen categorized into mild, moderate, and severe per the Berlin criteria). RESULTS: In total, 53 of 55 (96%) of the cohort required mechanical ventilation and 9 of 55 (16%) required extracorporeal membrane oxygenation. Extracorporeal membrane oxygenation-naïve patients demonstrated lysis indices at 30 min indicative of fibrinolytic suppression on rotational thromboelastometry. Survivors demonstrated fewer procoagulate acute phase reactants, such as microparticle-bound tissue factor levels (odds ratio, 0.14 [0.02, 0.99]; P = 0.049). Those who did not experience significant bleeding events had smaller changes in ADAMTS13 levels compared to those who did (odds ratio, 0.05 [0, 0.7]; P = 0.026). Elevations in plasminogen activator inhibitor 1 (odds ratio, 1.95 [1.21, 3.14]; P = 0.006), d-dimer (odds ratio, 3.52 [0.99, 12.48]; P = 0.05), and factor VIII (no clot, 1.15 ± 0.28 vs. clot, 1.42 ± 0.31; P = 0.003) were also demonstrated in extracorporeal membrane oxygenation-naïve patients who experienced major thrombotic events. Plasminogen activator inhibitor 1 levels were significantly elevated during periods of severe compared to mild and moderate acute respiratory distress syndrome (severe, 44.2 ± 14.9 ng/ml vs. mild, 31.8 ± 14.7 ng/ml and moderate, 33.1 ± 15.9 ng/ml; P = 0.029 and 0.039, respectively). CONCLUSIONS: Increased inflammatory and procoagulant markers such as plasminogen activator inhibitor 1, microparticle-bound tissue factor, and von Willebrand factor levels are associated with severe hypoxemia and major thrombotic events, implicating fibrinolytic suppression in the microcirculatory system and subsequent micro- and macrovascular thrombosis in severe COVID-19.

ABL kinase inhibition promotes lung regeneration through expansion of an SCGB1A1+ SPC+ cell population following bacterial pneumonia.

Current therapeutic interventions for the treatment of respiratory infections are hampered by the evolution of multidrug resistance in pathogens as well as the lack of effective cellular targets. Despite the identification of multiple region-specific lung progenitor cells, the identity of molecules that might be therapeutically targeted in response to infections to promote activation of progenitor cell types remains elusive. Here, we report that loss of Abl1 specifically in SCGB1A1-expressing cells leads to a significant increase in the proliferation and differentiation of bronchiolar epithelial cells, resulting in dramatic expansion of an SCGB1A1+ airway cell population that coexpresses SPC, a marker for type II alveolar cells that promotes alveolar regeneration following bacterial pneumonia. Furthermore, treatment with an Abl-specific allosteric inhibitor enhanced regeneration of the alveolar epithelium and promoted accelerated recovery of mice following pneumonia. These data reveal a potential actionable target that may be exploited for efficient recovery after pathogen-induced infections.

Heparin-based blood purification attenuates organ injury in baboons with Streptococcus pneumoniae pneumonia.

Bacterial pneumonia is a major cause of morbidity and mortality worldwide despite the use of antibiotics, and novel therapies are urgently needed. Building on previous work, we aimed to 1) develop a baboon model of severe pneumococcal pneumonia and sepsis with organ dysfunction and 2) test the safety and efficacy of a novel extracorporeal blood filter to remove proinflammatory molecules and improve organ function. After a dose-finding pilot study, 12 animals were inoculated with Streptococcus pneumoniae [5 × 109 colony-forming units (CFU)], given ceftriaxone at 24 h after inoculation, and randomized to extracorporeal blood purification using a filter coated with surface-immobilized heparin sulfate (n = 6) or sham treatment (n = 6) for 4 h at 30 h after inoculation. For safety analysis, four uninfected animals also underwent purification. At 48 h, necropsy was performed. Inoculated animals developed severe pneumonia and septic shock. Compared with sham-treated animals, septic animals treated with purification displayed significantly less kidney injury, metabolic acidosis, hypoglycemia, and shock (P < 0.05). Purification blocked the rise in peripheral blood S. pneumoniae DNA, attenuated bronchoalveolar lavage (BAL) CCL4, CCL2, and IL-18 levels, and reduced renal oxidative injury and classical NLRP3 inflammasome activation. Purification was safe in both uninfected and infected animals and produced no adverse effects. We demonstrate that heparin-based blood purification significantly attenuates levels of circulating S. pneumoniae DNA and BAL cytokines and is renal protective in baboons with severe pneumococcal pneumonia and septic shock. Purification was associated with less severe acute kidney injury, metabolic derangements, and shock. These results support future clinical studies in critically ill septic patients.

Peripheral Blood Mononuclear Cells Demonstrate Mitochondrial Damage Clearance During Sepsis.

OBJECTIVES: Metabolic derangements in sepsis stem from mitochondrial injury and contribute significantly to organ failure and mortality; however, little is known about mitochondrial recovery in human sepsis. We sought to test markers of mitochondrial injury and recovery (mitochondrial biogenesis) noninvasively in peripheral blood mononuclear cells from patients with sepsis and correlate serial measurements with clinical outcomes. DESIGN: Prospective case-control study. SETTING: Academic Medical Center and Veterans Affairs Hospital. PATIENTS: Uninfected control patients (n = 20) and septic ICU patients (n = 37). INTERVENTIONS: Blood samples were collected once from control patients and serially with clinical data on days 1, 3, and 5 from septic patients. Gene products for HMOX1, NRF1, PPARGC1A, and TFAM, and mitochondrial DNA ND1 and D-loop were measured by quantitative reverse transcriptase-polymerase chain reaction. Proinflammatory cytokines were measured in plasma and neutrophil lysates. MEASUREMENTS AND MAIN RESULTS: Median (interquartile range) Acute Physiology and Chronic Health Evaluation II and Sequential Organ Failure Assessment scores were 21 (8) and 10 (4), respectively, and 90-day mortality was 19%. Transcript levels of all four genes in peripheral blood mononuclear cells were significantly reduced in septic patients on day 1 (p < 0.05), whereas mitochondrial DNA copy number fell and plasma D-loop increased (both p < 0.05), indicative of mitochondrial damage. D-loop content was directly proportional to tumor necrosis factor-α and high-mobility group protein B1 cytokine expression. By day 5, we observed transcriptional activation of mitochondrial biogenesis and restoration of mitochondrial DNA copy number (p < 0.05). Patients with early activation of mitochondrial biogenesis were ICU-free by 1 week. CONCLUSIONS: Our findings support data that sepsis-induced mitochondrial damage is reversed by activation of mitochondrial biogenesis and that gene transcripts measured noninvasively in peripheral blood mononuclear cells can serve as novel biomarkers of sepsis recovery.

Mitochondrial quality control in alveolar epithelial cells damaged by S. aureus pneumonia in mice.

Mitochondrial damage is often overlooked in acute lung injury (ALI), yet most of the lung's physiological processes, such as airway tone, mucociliary clearance, ventilation-perfusion (Va/Q) matching, and immune surveillance require aerobic energy provision. Because the cell's mitochondrial quality control (QC) process regulates the elimination and replacement of damaged mitochondria to maintain cell survival, we serially evaluated mitochondrial biogenesis and mitophagy in the alveolar regions of mice in a validated Staphylococcus aureus pneumonia model. We report that apart from cell lysis by direct contact with microbes, modest epithelial cell death was detected despite significant mitochondrial damage. Cell death by TdT-mediated dUTP nick-end labeling staining occurred on days 1 and 2 postinoculation: apoptosis shown by caspase-3 cleavage was present on days 1 and 2, while necroptosis shown by increased levels of phospho- mixed lineage kinase domain-like protein (MLKL) and receptor-interacting serine/threonine-protein kinase 1 (RIPK1) was present on day 1 Cell death in alveolar type I (AT1) cells assessed by bronchoalveolar lavage fluid receptor for advanced glycation end points (RAGE) levels was high, yet AT2 cell death was limited while both mitochondrial biogenesis and mitophagy were induced. These mitochondrial QC mechanisms were evaluated mainly in AT2 cells by localizing increases in citrate synthase content, increases in nuclear mitochondrial biogenesis regulators nuclear respiratory factor-1 (NRF-1) and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), and increases in light chain 3B protein (LC3-I)/LC3II ratios. Concomitant changes in p62, Pink 1, and Parkin protein levels indicated activation of mitophagy. By confocal microscopy, mitochondrial biogenesis and mitophagy were often observed on day 1 within the same AT2 cells. These findings imply that mitochondrial QC activation in pneumonia-damaged AT2 cells promotes cell survival in support of alveolar function.

Hypoxic Gene Expression of Donor Bronchi Linked to Airway Complications after Lung Transplantation.

RATIONALE: Central airway stenosis (CAS) after lung transplantation has been attributed in part to chronic airway ischemia; however, little is known about the time course or significance of large airway hypoxia early after transplantation. OBJECTIVES: To evaluate large airway oxygenation and hypoxic gene expression during the first month after lung transplantation and their relation to airway complications. METHODS: Subjects who underwent lung transplantation underwent endobronchial tissue oximetry of native and donor bronchi at 0, 3, and 30 days after transplantation (n = 11) and/or endobronchial biopsies (n = 14) at 30 days for real-time polymerase chain reaction of hypoxia-inducible genes. Patients were monitored for 6 months for the development of transplant-related complications. MEASUREMENTS AND MAIN RESULTS: Compared with native endobronchial tissues, donor tissue oxygen saturations (Sto2) were reduced in the upper lobes (74.1 ± 1.8% vs. 68.8 ± 1.7%; P < 0.05) and lower lobes (75.6 ± 1.6% vs. 71.5 ± 1.8%; P = 0.065) at 30 days post-transplantation. Donor upper lobe and subcarina Sto2 levels were also lower than the main carina (difference of -3.9 ± 1.5 and -4.8 ± 2.1, respectively; P < 0.05) at 30 days. Up-regulation of hypoxia-inducible genes VEGFA, FLT1, VEGFC, HMOX1, and TIE2 was significant in donor airways relative to native airways (all P < 0.05). VEGFA, KDR, and HMOX1 were associated with prolonged respiratory failure, prolonged hospitalization, extensive airway necrosis, and CAS (P < 0.05). CONCLUSIONS: These findings implicate donor bronchial hypoxia as a driving factor for post-transplantation airway complications. Strategies to improve airway oxygenation, such as bronchial artery re-anastomosis and hyperbaric oxygen therapy merit clinical investigation.

Safety of hyperbaric oxygen therapy for management of central airway stenosis after lung transplant.

BACKGROUND: Central airway stenosis (CAS) is common after lung transplantation and causes significant post-transplant morbidity. It is often preceded by extensive airway necrosis, related to airway ischemia. Hyperbaric oxygen therapy (HBOT) is useful for ischemic grafts and may reduce the development of CAS. METHODS: The purpose of this study was to determine whether HBOT could be safely administered to lung transplant patients with extensive necrotic airway plaques. Secondarily, we assessed any effects of HBOT on the incidence and severity of CAS. Patients with extensive necrotic airway plaques within 1-2 months after lung transplantation were treated with HBOT along with standard care. These patients were compared with a contemporaneous reference group with similar plaques who did not receive HBOT. RESULTS: Ten patients received HBOT for 18.5 (interquartile range, IQR 11-20) sessions, starting at 40.5 (IQR 34-54) days after transplantation. HBOT was well tolerated. Incidence of CAS was similar between HBOT-treated patients and reference patients (70% vs 87%, respectively; P=.34), but fewer stents were required in HBOT patients (10% vs 56%, respectively; P=.03). CONCLUSIONS: This pilot study is the first to demonstrate HBOT safety in patients who develop necrotic airway plaques after lung transplantation. HBOT may reduce the need for airway stent placement in patients with CAS.

The Regulation of Proresolving Lipid Mediator Profiles in Baboon Pneumonia by Inhaled Carbon Monoxide.

Strategies for the treatment of bacterial pneumonia beyond traditional antimicrobial therapy have been limited. The recently discovered novel genus of lipid mediators, coined "specialized proresolving mediators" (SPMs), which orchestrate clearance of recruited leukocytes and restore epithelial barrier integrity, have offered new insight into the resolution of inflammation. We performed lipid mediator (LM) metabololipidomic profiling and identification of LMs on peripheral blood leukocytes and plasma from a baboon model of Streptococcus pneumoniae pneumonia. Leukocytes and plasma were isolated from whole blood of S. pneumoniae-infected (n = 5-6 per time point) and control, uninfected baboons (n = 4 per time point) at 0, 24, 48, and 168 hours. In a subset of baboons with pneumonia (n = 3), we administered inhaled carbon monoxide (CO) at 48 hours (200-300 ppm for 60-90 min). Unstimulated leukocytes from control animals produced a proresolving LM signature with elevated resolvins and lipoxins. In contrast, serum-treated, zymosan-stimulated leukocytes and leukocytes from baboons with S. pneumoniae pneumonia produced a proinflammatory LM signature profile with elevated leukotriene B4 and prostaglandins. Plasma from baboons with S. pneumoniae pneumonia also displayed significantly reduced LM-SPM levels, including eicosapentaenoic acid-derived E-series resolvins (RvE) and lipoxins. CO inhalation increased levels of plasma RvE and lipoxins relative to preexposure levels. These results establish the leukocyte and plasma LM profiles biosynthesized during S. pneumoniae pneumonia in baboons and provide evidence for pneumonia-induced dysregulation of these proresolution programs. Moreover, these SPM profiles are partially restored with inhaled low-dose CO and SPM, which may shorten the time to pneumonia resolution.

Effects of inhaled CO administration on acute lung injury in baboons with pneumococcal pneumonia.

Inhaled carbon monoxide (CO) gas has therapeutic potential for patients with acute respiratory distress syndrome if a safe, evidence-based dosing strategy and a ventilator-compatible CO delivery system can be developed. In this study, we used a clinically relevant baboon model of Streptococcus pneumoniae pneumonia to 1) test a novel, ventilator-compatible CO delivery system; 2) establish a safe and effective CO dosing regimen; and 3) investigate the local and systemic effects of CO therapy on inflammation and acute lung injury (ALI). Animals were inoculated with S. pneumoniae (10(8)-10(9) CFU) (n = 14) or saline vehicle (n = 5); in a subset with pneumonia (n = 5), we administered low-dose, inhaled CO gas (100-300 ppm × 60-90 min) at 0, 6, 24, and/or 48 h postinoculation and serially measured blood carboxyhemoglobin (COHb) levels. We found that CO inhalation at 200 ppm for 60 min is well tolerated and achieves a COHb of 6-8% with ambient CO levels ≤ 1 ppm. The COHb level measured at 20 min predicted the 60-min COHb level by the Coburn-Forster-Kane equation with high accuracy. Animals given inhaled CO + antibiotics displayed significantly less ALI at 8 days postinoculation compared with antibiotics alone. Inhaled CO was associated with activation of mitochondrial biogenesis in the lung and with augmentation of renal antioxidative programs. These data support the feasibility of safely delivering inhaled CO gas during mechanical ventilation and provide preliminary evidence that CO may accelerate the resolution of ALI in a clinically relevant nonhuman primate pneumonia model.

Development of a novel preclinical model of pneumococcal pneumonia in nonhuman primates.

Pneumococcal pneumonia is a leading cause of bacterial infection and death worldwide. Current diagnostic tests for detecting Streptococcus pneumoniae can be unreliable and can mislead clinical decision-making and treatment. To address this concern, we developed a preclinical model of pneumococcal pneumonia in nonhuman primates useful for identifying novel biomarkers, diagnostic tests, and therapies for human S. pneumoniae infection. Adult colony-bred baboons (n = 15) were infected with escalating doses of S. pneumoniae (Serotype 19A-7). We characterized the pathophysiological and serological profiles of healthy and infected animals over 7 days. Pneumonia was prospectively defined by the presence of three criteria: (1) change in white blood cell count, (2) isolation of S. pneumoniae from bronchoalveolar lavage fluid (BALF) or blood, and (3) concurrent signs/symptoms of infection. Animals given 10(9) CFU consistently met our definition and developed a phenotype of tachypnea, tachycardia, fever, hypoxemia, and radiographic lobar infiltrates at 48 hours. BALF and plasma cytokines, including granulocyte colony-stimulating factor, IL-6, IL-10, and IL-1ra, peaked at 24 to 48 hours. At necropsy, there was lobar consolidation with frequent pleural involvement. Lung histopathology showed alveolar edema and macrophage influx in areas of organizing pneumonia. Hierarchical clustering of peripheral blood RNA data at 48 hours correctly identified animals with and without pneumonia. Dose-dependent inoculation of baboons with S. pneumoniae produces a host response ranging from spontaneous clearance (10(6) CFU) to severe pneumonia (10(9) CFU). Selected BALF and plasma cytokine levels and RNA profiles were associated with severe pneumonia and may provide clinically useful parameters after validation.

Cell-cell interactions and bronchoconstrictor eicosanoid reduction with inhaled carbon monoxide and resolvin D1.

Polymorphonuclear leukocyte (PMN)-mediated acute lung injury from ischemia/reperfusion (I/R) remains a major cause of morbidity and mortality in critical care medicine. Here, we report that inhaled low-dose carbon monoxide (CO) and intravenous resolvin D1 (RvD1) in mice each reduced PMN-mediated acute lung injury from I/R. Inhaled CO (125-250 ppm) and RvD1 (250-500 ng) each reduced PMN lung infiltration and gave additive lung protection. In mouse whole blood, CO and RvD1 attenuated PMN-platelet aggregates, reducing leukotrienes (LTs) and thromboxane B2 (TxB2) in I/R lungs. With human whole blood, CO (125-250 ppm) decreased PMN-platelet aggregates, expression of adhesion molecules, and cysteinyl LTs, as well as TxB2. RvD1 (1-100 nM) also dose dependently reduced platelet activating factor-stimulated PMN-platelet aggregates in human whole blood. In nonhuman primate (baboon) lung infection with Streptococcus pneumoniae, inhaled CO reduced urinary cysteinyl LTs. These results demonstrate lung protection by low-dose inhaled CO as well as RvD1 that each reduced PMN-mediated acute tissue injury, PMN-platelet interactions, and production of both cysteinyl LTs and TxB2. Together they suggest a potential therapeutic role of low-dose inhaled CO in organ protection, as demonstrated using mouse I/R-initiated lung injury, baboon infections, and human whole blood.

Advanced Respiratory Support Days as a Novel Marker of Mortality in COVID-19 Acute Respiratory Distress Syndrome Requiring Extracorporeal Membrane Oxygenation.

Emerging evidence suggests prolonged use of noninvasive respiratory support may increase mortality of patients with coronavirus disease 2019 (COVID-19)-associated acute respiratory distress syndrome who require extracorporeal membrane oxygenation (ECMO). Using a database of adults receiving ECMO for COVID-19, we calculated survival curves and multivariable Cox regression to determine the risk of death associated with pre-ECMO use of high-flow nasal oxygen (HFNO), noninvasive ventilation (NIV), and invasive mechanical ventilation (IMV) days. We investigated the performance of a novel variable, advanced respiratory support days (composite of HFNO, NIV, and IMV days), on Respiratory ECMO Survival Prediction (RESP) score. Subjects (N = 146) with increasing advanced respiratory support days (<5, 5-9, and ≥10) had a stepwise increase in 90 day mortality (32.2%, 57.7%, and 75.4%, respectively; p = 0.002). Ninety-day mortality was significantly higher in subjects (N = 121) receiving NIV >4 days (81.8% vs. 52.4%, p < 0.001). Each additional pre-ECMO advanced respiratory support day increased the odds of right ventricular failure (odds ratio [OR]: 1.066, 95% confidence interval [CI]: 1.002-1.135) and in-hospital mortality (1.17, 95% CI: 1.08-1.27). Substituting advanced respiratory support days for IMV days improved RESP score mortality prediction (area under the curve (AUC) or: 0.64 vs. 0.71). Pre-ECMO advanced respiratory support days were associated with increased 90 day mortality compared with IMV days alone. Adjusting the RESP score for advanced respiratory support days improved mortality prediction.

T-cell count and T-cell telomere length in patients with severe COVID-19.

Lymphocyte telomere length (TL) is highly variable and shortens with age. Short telomeres may impede TL-dependent T-cell clonal expansion with viral infection. As SARS-CoV-2 infection can induce prolonged and severe T-cell lymphopenia, infected adults, and particularly older adults with short telomeres, may display severe T-cell lymphopenia. To examine the relationship between T-cell TL parameters and T-cell counts, we studied 40 patients hospitalized with severe COVID-19. T-cells were isolated from lymphocytes, counted using flow cytometry, and their TL parameters were measured using the Telomere Shortest Length Assay. The cohort (median age = 62 years, 27% female) was racially and ethnically diverse (33% White, 35% Black, and 33% Other). On intensive care unit study day 1, T-cell count (mean=1.03 x109/L) was inversely related to age (p=0.007) and higher in females than males (p=0.025). Mean TL was 3.88 kilobases (kb), and 45.3% of telomeres were shorter than 3 kb. Using multiple regression analysis and adjusting for age and sex, T-cell count decreased with increased proportion of T-cell telomeres shorter than 3 kb (p=0.033) and increased with mean TL (p=0.052). Our findings suggest an association between the buildup of short telomeres within T-cells and explain in part reduced peripheral blood T-cell counts in patients with severe COVID-19. Shortened T-cell telomeres may be a risk factor for COVID-19-associated T-cell lymphopenia.

Timing of Intubation in COVID-19: When It Is Too Early and When It Is Too Late.

The timing of initiating mechanical ventilation in patients with acute respiratory distress syndrome due to COVID-19 remains controversial. At the outset of the pandemic, "very early" intubation was recommended in patients requiring oxygen flows above 6 L per minute but was followed closely thereafter by avoidance of invasive mechanical ventilation (IMV) due to a perceived (yet over-estimated) risk of mortality after intubation. While the use of noninvasive methods of oxygen delivery, such as high-flow nasal oxygen (HFNO) or noninvasive positive pressure ventilation (NIV), can avert the need for mechanical ventilation in some, accumulating evidence suggests delayed intubation is also associated with an increased mortality in a subset of COVID-19 patients. Close monitoring is necessary in COVID-19 patients on HFNO or NIV to identify signs of noninvasive failure and ensure appropriate provision of IMV.

U-Shaped Association Between Carboxyhemoglobin and Mortality in Patients With Acute Respiratory Distress Syndrome on Venovenous Extracorporeal Membrane Oxygenation.

Background: Carbon monoxide (CO) is an endogenous signaling molecule that activates cytoprotective programs implicated in the resolution of acute respiratory distress syndrome (ARDS) and survival of critical illness. Because CO levels can be measured in blood as carboxyhemoglobin, we hypothesized that carboxyhemoglobin percent (COHb%) may associate with mortality. OBJECTIVES: To examine the relationship between COHb% and outcomes in patients with ARDS requiring venovenous extracorporeal membrane oxygenation (ECMO), a condition where elevated COHb% is commonly observed. DESIGN: Retrospective cohort study. SETTING: Academic medical center ICU. PATIENTS: Patients were included that had ARDS on venovenous ECMO. MEASUREMENTS AND MAIN RESULTS: We examined the association between COHb% and mortality using a Cox proportional hazards model. Secondary outcomes including ECMO duration, ventilator weaning, and hospital and ICU length of stay were examined using both subdistribution and causal-specific hazard models for competing risks. We identified 109 consecutive patients for analysis. Mortality significantly decreased per 1 U increase in COHb% below 3.25% (hazard ratio [HR], 0.35; 95% CI, 0.15-0.80; p = 0.013) and increased per 1 U increase above 3.25% (HR, 4.7; 95% CI, 1.5-14.7; p = 0.007) reflecting a nonlinear association (p = 0.006). Each unit increase in COHb% was associated with reduced likelihood of liberation from ECMO and mechanical ventilation, and increased time to hospital and ICU discharge (all p < 0.05). COHb% was significantly associated with hemolysis but not with initiation of hemodialysis or blood transfusions. CONCLUSIONS: In patients with ARDS on venovenous ECMO, COHb% is a novel biomarker for mortality exhibiting a U-shaped pattern. Our findings suggest that too little CO (perhaps due to impaired host signaling) or excess CO (perhaps due to hemolysis) is associated with higher mortality. Patients with low COHb% may exhibit the most benefit from future therapies targeting anti-oxidant and anti-inflammatory pathways such as low-dose inhaled CO gas.

Feasibility Study of Cord Tissue Derived Mesenchymal Stromal Cells in COVID-19-Related Acute Respiratory Distress Syndrome.

BACKGROUND: Treatment options for patients with COVID-19-related acute respiratory distress syndrome (ARDS) are desperately needed. Allogeneic human umbilical cord derived mesenchymal stromal cells (hCT-MSCs) have potential therapeutic benefits in these critically ill patients, but feasibility and safety data are lacking. MATERIALS AND METHODS: In this phase I multisite study, 10 patients with COVID-19-related ARDS were treated with 3 daily intravenous infusions of hCT-MSCs (1 million cells/kg, maximum dose 100 million cells). The primary endpoint assessed safety. RESULTS: Ten patients (7 females, 3 males; median age 62 years (range 39-79)) were enrolled at 2 sites and received a total of 30 doses of study product. The average cell dose was 0.93 cells/kg (range 0.56-1.45 cells/kg and total dose range 55-117 million cells) with 5/30 (17%) of doses lower than intended dose. Average cell viability was 85% (range 63%-99%) with all but one meeting the >70% release criteria. There were no infusion-related reactions or study-related adverse events, 28 non-serious adverse events in 3 unique patients, and 2 serious adverse events in 2 unique patients, which were expected and unrelated to the study product. Five patients died: 3 by day 28 and 5 by day 90 of the study (median 27 days, range 7-76 days). All deaths were determined to be unrelated to the hCT-MSCs. CONCLUSION: We were able to collect relevant safety outcomes for the use of hCT-MSCs in patients with COVID-19-related ARDS. Future studies to explore their safety and efficacy are warranted.

Use of Inhaled Epoprostenol in Patients With COVID-19 Receiving Humidified, High-Flow Nasal Oxygen Is Associated With Progressive Respiratory Failure.

BACKGROUND: The clinical benefit of using inhaled epoprostenol (iEpo) through a humidified high-flow nasal cannula (HHFNC) remains unknown for patients with COVID-19. RESEARCH QUESTION: Can iEpo prevent respiratory deterioration for patients with positive SARS-CoV-2 findings receiving HHFNC? STUDY DESIGN AND METHODS: This multicenter retrospective cohort analysis included patients aged 18 years or older with COVID-19 pneumonia who required HHFNC treatment. Patients who received iEpo were propensity score matched to patients who did not receive iEpo. The primary outcome was time to mechanical ventilation or death without mechanical ventilation and was assessed using Kaplan-Meier curves and Cox proportional hazard ratios. The effects of residual confounding were assessed using a multilevel analysis, and a secondary analysis adjusted for outcome propensity also was performed in a multivariable model that included the entire (unmatched) patient cohort. RESULTS: Among 954 patients with positive SARS-CoV-2 findings receiving HHFNC therapy, 133 patients (13.9%) received iEpo. After propensity score matching, the median number of days until the composite outcome was similar between treatment groups (iEpo: 5.0 days [interquartile range, 2.0-10.0 days] vs no-iEpo: 6.5 days [interquartile range, 2.0-11.0 days]; P = .26), but patients who received iEpo were more likely to meet the composite outcome in the propensity score-matched, multilevel, and multivariable unmatched analyses (hazard ratio, 2.08 [95% CI, 1.73-2.50]; OR, 4.72 [95% CI, 3.01-7.41]; and OR, 1.35 [95% CI, 1.23-1.49]; respectively). INTERPRETATION: In patients with COVID-19 receiving HHFNC therapy, use of iEpo was associated with the need for invasive mechanical ventilation.