Circulating markers of endothelial and alveolar epithelial dysfunction are associated with mortality in pediatric acute respiratory distress syndrome

Comparison of 16 Pediatric Acute Respiratory Distress Syndrome-Associated Plasma Biomarkers With Changing Lung Injury Severity

OBJECTIVES

Pediatric acute respiratory distress syndrome (PARDS) is a source of substantial morbidity and mortality in the PICU, and different plasma biomarkers have identified different PARDS and ARDS subgroups. We have a poor understanding of how these biomarkers change over time and with changing lung injuries. We sought to determine how biomarker levels change over PARDS course, whether they are correlated, and whether they are different in critically ill non-PARDS patients.

DESIGN

Two-center prospective observational study.

SETTING

Two quaternary care academic children's hospitals.

PATIENTS

Subjects under 18 years of age admitted to the PICU who were intubated and met the Second Pediatric Acute Lung Injury Consensus Conference-2 PARDS diagnostic criteria and nonintubated critically ill subjects without apparent lung disease.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Plasma samples were obtained on study days 1, 3, 7, and 14. The levels of 16 biomarkers were measured using a fluorometric bead-based assay. Compared with non-PARDS subjects, on day 1 PARDS subjects had increased concentrations of tumor necrosis factor-alpha, interleukin (IL)-8, interferon-γ, IL17, granzyme B, soluble intercellular adhesion molecule-1 (sICAM1), surfactant protein D, and IL18 but reduced matrix metalloproteinase 9 (MMP-9) concentrations (all p < 0.05). Day 1 biomarker concentrations and PARDS severity were not correlated. Over PARDS course, changes in 11 of the 16 biomarkers positively correlated with changing lung injury with sICAM1 ( R = 0.69, p = 2.2 × 10 -16 ) having the strongest correlation. By Spearman rank correlation of biomarker concentrations in PARDS subjects, we identified two patterns. One had elevations of plasminogen activator inhibitor-1, MMP-9, and myeloperoxidase, and the other had higher inflammatory cytokines.

CONCLUSIONS

sICAM1 had the strongest positive correlation with worsening lung injury across all study time points suggesting that it is perhaps the most biologically relevant of the 16 analytes. There was no correlation between biomarker concentration on day 1 and day 1 PARDS severity; however, changes in most biomarkers over time positively correlated with changing lung injury. Finally, in day 1 samples, 7 of the 16 biomarkers were not significantly different between PARDS and critically ill non-PARDS subjects. These data highlight the difficulty of using plasma biomarkers to identify organ-specific pathology in critically ill patients.

Rare variants in complement system genes associate with endothelial damage after pediatric allogeneic hematopoietic stem cell transplantation

Introduction

Complement system has a postulated role in endothelial problems after hematopoietic stem cell transplantation (HSCT). In this retrospective, singlecenter study we studied genetic complement system variants in patients with documented endotheliopathy. In our previous study among pediatric patients with an allogeneic HSCT (2001-2013) at the Helsinki University Children´s Hospital, Finland, we identified a total of 19/122 (15.6%) patients with vascular complications, fulfilling the criteria of capillary leak syndrome (CLS), venoocclusive disease/sinusoidal obstruction syndrome (VOD/SOS) or thrombotic microangiopathy (TMA).

Methods

We performed whole exome sequencing (WES) on 109 patients having an adequate pre-transplantation DNA for the analysis to define possible variations and mutations potentially predisposing to functional abnormalities of the complement system. In our data analysis, we focused on 41 genes coding for complement components.

Results

50 patients (45.9%) had one or several, nonsynonymous, rare germline variants in complement genes. 21/66 (31.8%) of the variants were in the terminal pathway. Patients with endotheliopathy had variants in different complement genes: in the terminal pathway (C6 and C9), lectin pathway (MASP1) and receptor ITGAM (CD11b, part of CR3). Four had the same rare missense variant (rs183125896; Thr279Ala) in the C9 gene. Two of these patients were diagnosed with endotheliopathy and one with capillary leak syndrome-like problems. The C9 variant Thr279Ala has no previously known disease associations and is classified by the ACMG guidelines as a variant of uncertain significance (VUS). We conducted a gene burden test with gnomAD Finnish (fin) as the reference population. Complement gene variants seen in our patient population were investigated and Total Frequency Testing (TFT) was used for execution of burden tests. The gene variants seen in our patients with endotheliopathy were all significantly (FDR < 0.05) enriched compared to gnomAD. Overall, 14/25 genes coding for components of the complement system had an increased burden of missense variants among the patients when compared to the gnomAD Finnish population (N=10 816).

Discussion

Injury to the vascular endothelium is relatively common after HSCT with different phenotypic appearances suggesting yet unidentified underlying mechanisms. Variants in complement components may be related to endotheliopathy and poor prognosis in these patients.

Children with single ventricle heart disease have a greater increase in sRAGE after cardiopulmonary bypass

INTRODUCTION

Reducing cardiopulmonary bypass (CPB) induced inflammatory injury is a potentially important strategy for children undergoing multiple operations for single ventricle palliation. We sought to characterize the soluble receptor for advanced glycation end products (sRAGE), a protein involved in acute lung injury and inflammation, in pediatric patients with congenital heart disease and hypothesized that patients undergoing single ventricle palliation would have higher levels of sRAGE following bypass than those with biventricular physiologies.

METHODS

This was a prospective, observational study of children undergoing CPB. Plasma samples were obtained before and after bypass. sRAGE levels were measured and compared between those with biventricular and single ventricle heart disease using descriptive statistics and multivariate analysis for risk factors for lung injury.

RESULTS

sRAGE levels were measured in 40 patients: 19 with biventricular and 21 with single ventricle heart disease. Children undergoing single ventricle palliation had a higher factor and percent increase in sRAGE levels when compared to patients with biventricular circulations (4.6 vs. 2.4, p = 0.002) and (364% vs. 181%, p = 0.014). The factor increase in sRAGE inversely correlated with the patient's preoperative oxygen saturation (Pearson correlation (r) = -0.43, p = 0.005) and was positively associated with red blood cell transfusion (coefficient = 0.011; 95% CI: 0.004, 0.017; p = 0.001).

CONCLUSIONS

Children with single ventricle physiology have greater increase in sRAGE following CPB as compared to children undergoing biventricular repair. Larger studies delineating the role of sRAGE in children undergoing single ventricle palliation may be beneficial in understanding how to prevent complications in this high-risk population.

Fluid Overload Precedes and Masks Cryptic Kidney Injury in Pediatric Acute Respiratory Distress Syndrome

OBJECTIVES

Given the complex interrelatedness of fluid overload (FO), creatinine, acute kidney injury (AKI), and clinical outcomes, the association of AKI with poor outcomes in critically ill children may be underestimated due to definitions used. We aimed to disentangle these temporal relationships in a large cohort of children with acute respiratory distress syndrome (ARDS).

DESIGN

Retrospective cohort study.

SETTING

Quaternary care PICU.

PATIENTS

Seven hundred twenty intubated children with ARDS between 2011 and 2019.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Daily fluid balance, urine output (UOP), and creatinine for days 1-7 of ARDS were retrospectively abstracted. A subset of patients had angiopoietin 2 (ANGPT2) quantified on days 1, 3, and 7. Patients were classified as AKI by Kidney Disease Improving Global Outcomes (KDIGO) stage 2/3 then grouped by timing of AKI onset (early if days 1-3 of ARDS, late if days 4-7 of ARDS, persistent if both) for comparison of PICU mortality and ventilator-free days (VFDs). A final category of "Cryptic AKI" was used to identify subjects who met KDIGO stage 2/3 criteria only when creatinine was adjusted for FO. Outcomes were compared between those who had Cryptic AKI identified by FO-adjusted creatinine versus those who had no AKI. Conventionally defined AKI occurred in 26% of patients (early 10%, late 3%, persistent 13%). AKI was associated with higher mortality and fewer VFDs, with no differences according to timing of onset. The Cryptic AKI group (6% of those labeled no AKI) had higher mortality and fewer VFDs than patients who did not meet AKI with FO-adjusted creatinine. FO, FO-adjusted creatinine, and ANGPT2 increased 1 day prior to meeting AKI criteria in the late AKI group.

CONCLUSIONS

AKI was associated with higher mortality and fewer VFDs in pediatric ARDS, irrespective of timing. FO-adjusted creatinine captures a group of patients with Cryptic AKI with outcomes approaching those who meet AKI by traditional criteria. Increases in FO, FO-adjusted creatinine, and ANGPT2 occur prior to meeting conventional AKI criteria.

Pathobiology, Severity, and Risk Stratification of Pediatric Acute Respiratory Distress Syndrome: From the Second Pediatric Acute Lung Injury Consensus Conference

OBJECTIVES

To review the literature for studies published in children on the pathobiology, severity, and risk stratification of pediatric acute respiratory distress syndrome (PARDS) with the intent of guiding current medical practice and identifying important areas for future research related to severity and risk stratification.

DATA SOURCES

Electronic searches of PubMed and Embase were conducted from 2013 to March 2022 by using a combination of medical subject heading terms and text words to capture the pathobiology, severity, and comorbidities of PARDS.

STUDY SELECTION

We included studies of critically ill patients with PARDS that related to the severity and risk stratification of PARDS using characteristics other than the oxygenation defect. Studies using animal models, adult only, and studies with 10 or fewer children were excluded from our review.

DATA EXTRACTION

Title/abstract review, full-text review, and data extraction using a standardized data collection form.

DATA SYNTHESIS

The Grading of Recommendations Assessment, Development, and Evaluation approach was used to identify and summarize relevant evidence and develop recommendations for clinical practice. There were 192 studies identified for full-text extraction to address the relevant Patient/Intervention/Comparator/Outcome questions. One clinical recommendation was generated related to the use of dead space fraction for risk stratification. In addition, six research statements were generated about the impact of age on acute respiratory distress syndrome pathobiology and outcomes, addressing PARDS heterogeneity using biomarkers to identify subphenotypes and endotypes, and use of standardized ventilator, physiologic, and nonpulmonary organ failure measurements for future research.

CONCLUSIONS

Based on an extensive literature review, we propose clinical management and research recommendations related to characterization and risk stratification of PARDS severity.

Sepsis-related pediatric acute respiratory distress syndrome: A multicenter prospective cohort study

OBJECTIVES

This study aimed to compare the risk factors and outcomes for organ dysfunction between sepsis-related Pediatric acute respiratory distress syndrome (PARDS) and nonsepsis PARDS.

METHODS

We prospective cohort recruited intubated patients with PARDS at four tertiary care centers in Thailand. The baseline characteristics, mechanical ventilation, fluid balance, and clinical outcomes were collected. The primary outcome was organ dysfunction.

RESULTS

One hundred and thirty-two mechanically ventilated children with PARDS were included in the study. The median age was 29 months and 53.8% were male. The mortality rate was 22.7% and organ dysfunction was 45.4%. There were 26 (19.7%) and 106 (80.3%) patients who were classified into sepsis-related PARDS and nonsepsis PARDS, respectively. Sepsis-related PARDS patients had a significantly higher incidence of acute kidney injury (30.8% vs. 13.2%, P = 0.041), septic shock (88.5% vs. 32.1%, P < 0.001), organ dysfunction (84.6% vs. 35.8%, P < 0.001), and death (42.3% vs. 17.9%, P = 0.016) than nonsepsis PARDS group. Multivariate analysis adjusted for clinical variables showed that sepsis-related PARDS and percentage of fluid overload were significantly associated with organ dysfunction (odds ratio [OR] 11.414; 95% confidence interval [CI] 1.40892.557, P = 0.023 and OR 1.169; 95% CI 1.0121.352, P = 0.034).

CONCLUSIONS

Sepsis-related PARDS patients had more severe illness, organ dysfunction, and mortality than nonsepsis PARDS patients. The higher percentage of fluid overload and presentation of sepsis was the independent risk factor of organ dysfunction in PARDS patients.

Identification of a pediatric acute hypoxemic respiratory failure signature in peripheral blood leukocytes at 24 hours post-ICU admission with machine learning

Background

There is no generalizable transcriptomics signature of pediatric acute respiratory distress syndrome. Our goal was to identify a whole blood differential gene expression signature for pediatric acute hypoxemic respiratory failure (AHRF) using transcriptomic microarrays within twenty-four hours of diagnosis. We used publicly available human whole-blood gene expression arrays of a Berlin-defined pediatric acute respiratory distress syndrome (GSE147902) cohort and a sepsis-triggered AHRF (GSE66099) cohort within twenty-four hours of diagnosis and compared those children with a P_aO₂/F_iO₂ < 200 to those with a P_aO₂/F_iO₂ ≥ 200.

Results

We used stability selection, a bootstrapping method of 100 simulations using logistic regression as a classifier, to select differentially expressed genes associated with a P_aO₂/F_iO₂ < 200 vs. P_aO₂/F_iO₂ ≥ 200. The top-ranked genes that contributed to the AHRF signature were selected in each dataset. Genes common to both of the top 1,500 ranked gene lists were selected for pathway analysis. Pathway and network analysis was performed using the Pathway Network Analysis Visualizer (PANEV) and Reactome was used to perform an over-representation gene network analysis of the top-ranked genes common to both cohorts. Changes in metabolic pathways involved in energy balance, fundamental cellular processes such as protein translation, mitochondrial function, oxidative stress, immune signaling, and inflammation are differentially regulated early in pediatric ARDS and sepsis-induced AHRF compared to both healthy controls and to milder acute hypoxemia. Specifically, fundamental pathways related to the severity of hypoxemia emerged and included (1) ribosomal and eukaryotic initiation of factor 2 (eIF2) regulation of protein translation and (2) the nutrient, oxygen, and energy sensing pathway, mTOR, activated via PI3K/AKT signaling.

Conclusions

Cellular energetics and metabolic pathways are important mechanisms to consider to further our understanding of the heterogeneity and underlying pathobiology of moderate and severe pediatric acute respiratory distress syndrome. Our findings are hypothesis generating and support the study of metabolic pathways and cellular energetics to understand heterogeneity and underlying pathobiology of moderate and severe acute hypoxemic respiratory failure in children.

Evolution of multiple omics approaches to define pathophysiology of pediatric acute respiratory distress syndrome

Pediatric acute respiratory distress syndrome (PARDS), though both common and deadly in critically ill children, lacks targeted therapies. The development of effective pharmacotherapies has been limited, in part, by lack of clarity about the pathobiology of pediatric ARDS. Epithelial lung injury, vascular endothelial activation, and systemic immune activation are putative drivers of this complex disease process. Prior studies have used either hypothesis-driven (e.g., candidate genes and proteins, in vitro investigations) or unbiased (e.g., genome-wide association, transcriptomic, metabolomic) approaches to predict clinical outcomes and to define subphenotypes. Advances in multiple omics technologies, including genomics, transcriptomics, proteomics, and metabolomics, have permitted more comprehensive investigation of PARDS pathobiology. However, omics studies have been limited in children compared to adults, and analyses across multiple tissue types are lacking. Here, we synthesized existing literature on the molecular mechanism of PARDS, summarized our interrogation of publicly available genomic databases to determine the association of candidate genes with PARDS phenotypes across multiple tissues and cell types, and integrated recent studies that used single-cell RNA sequencing (scRNA-seq). We conclude that novel profiling methods such as scRNA-seq, which permits more comprehensive, unbiased evaluation of pathophysiological mechanisms across tissue and cell types, should be employed to investigate the molecular mechanisms of PRDS toward the goal of identifying targeted therapies.

Soluble Receptor of Advanced Glycation End-Products (sRAGE) in Pediatric Asthma: A Prospective Study in 68 Children Aged 7 Years

Background: Asthma is a chronic inflammatory disease of the airways common in children. Soluble advanced glycation end-product receptor (sRAGE) is a blood biomarker of lung damage and inflammation. We sought to determine whether it could also be a biomarker in childhood asthma. Methods: We conducted a prospective, observational, analytical study at Clermont-Ferrand University Hospital. We measured plasma sRAGE levels in asthmatic and healthy children aged 7 years. Results: Of the 68 children assessed, 15 (22.05%) presented asthma. All presented normal respiratory function. The mean plasma sRAGE level was 1875 pg/mL in the children with asthma and 1794 pg/mL in the healthy children (p = 0.525). The mean plasma sRAGE level was significantly decreased with tobacco exposure during pregnancy: 1478 pg/mL versus 1870 pg/mL without (p = 0.007). Lower levels were observed in children living in apartments (1557 pg/mL) than in those living in houses (1863 pg/mL) (p = 0.031). Conclusions: No difference was observed in plasma sRAGE levels in children with asthma in our well-treated and controlled population. Environmental exposure may affect these levels. Further studies are required to better characterize the role of sRAGE.

Beyond the Alveolar Epithelium: Plasma Soluble Receptor for Advanced Glycation End Products Is Associated With Oxygenation Impairment, Mortality, and Extrapulmonary Organ Failure in Children With Acute Respiratory Distress Syndrome

OBJECTIVES

Soluble receptor for advanced glycation end products is a known plasma marker of alveolar epithelial injury. However, RAGE is also expressed on cell types beyond the lung, and its activation leads to up-regulation of pro-inflammatory mediators. We sought to examine the relationship between plasma soluble receptor for advanced glycation end products and primary pulmonary dysfunction, extrapulmonary organ dysfunction, and mortality in pediatric acute respiratory distress syndrome patients at two early time points following acute respiratory distress syndrome diagnosis and compare these results to plasma surfactant protein-D, a marker of pure alveolar epithelial injury.

DESIGN

Prospective observational study.

SETTING

Five academic PICUs.

PATIENTS

Two hundred fifty-eight pediatric patients 30 days to 18 years old meeting Berlin Criteria for acute respiratory distress syndrome.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Plasma was collected for soluble receptor for advanced glycation end products and surfactant protein-D measurements within 24 hours (day 1) and 48 to 72 hours (day 3) after acute respiratory distress syndrome diagnosis. Similar to surfactant protein-D, plasma soluble receptor for advanced glycation end products was associated with a higher oxygenation index (p < 0.01) and worse lung injury score (p < 0.001) at the time of acute respiratory distress syndrome diagnosis. However, unlike surfactant protein-D, plasma soluble receptor for advanced glycation end products was associated with worse extrapulmonary Pediatric Logistic Organ Dysfunction score during ICU stay (day 3; p < 0.01) and positively correlated with plasma levels of interleukin-6 (p < 0.01), tumor necrosis factor-α (p < 0.01), and angiopoietin-2 (p < 0.01). Among children with indirect lung injury, plasma soluble receptor for advanced glycation end products was associated with mortality independent of age, sex, race, cancer/bone marrow transplant, and Pediatric Risk of Mortality score (day 3; odds ratio, 3.14; 95% CI, 1.46-6.75; p < 0.01).

CONCLUSIONS

Unlike surfactant protein-D, which is primarily localized to the alveolar epithelium plasma soluble receptor for advanced glycation end products is systemically expressed and correlates with markers of inflammation, extrapulmonary multiple organ dysfunction, and death in pediatric acute respiratory distress syndrome with indirect lung injury. This suggests that unlike surfactant protein-D, soluble receptor for advanced glycation end products is a multifaceted marker of alveolar injury and increased inflammation and that receptor for advanced glycation end products activation may contribute to the pathogenesis of multiple organ failure among children with indirect acute respiratory distress syndrome.

Differentiating children with sepsis with and without acute respiratory distress syndrome using proteomics

Both sepsis and acute respiratory distress syndrome (ARDS) rely on imprecise clinical definitions leading to heterogeneity, which has contributed to negative trials. Because circulating protein/DNA complexes have been implicated in sepsis and ARDS, we aimed to develop a proteomic signature of DNA-bound proteins to discriminate between children with sepsis with and without ARDS. We performed a prospective case-control study in 12 children with sepsis with ARDS matched to 12 children with sepsis without ARDS on age, severity of illness score, and source of infection. We performed co-immunoprecipitation and downstream proteomics in plasma collected ≤ 24 h of intensive care unit admission. Expression profiles were generated, and a random forest classifier was used on differentially expressed proteins to develop a signature which discriminated ARDS. The classifier was tested in six independent blinded samples. Neutrophil and nucleosome proteins were over-represented in ARDS, including two S100A proteins, superoxide dismutase (SOD), and three histones. Random forest produced a 10-protein signature that accurately discriminated between children with sepsis with and without ARDS. This classifier perfectly assigned six independent blinded samples as having ARDS or not. We validated higher expression of the most informative discriminating protein, galectin-3-binding protein, in children with ARDS. Our methodology has applicability to isolation of DNA-bound proteins from plasma. Our results support the premise of a molecular definition of ARDS, and give preliminary insight into why some children with sepsis, but not others, develop ARDS.

Biomarkers associated with mortality in pediatric patients with cardiac arrest and acute respiratory distress syndrome

AIMS

To identify plasma biomarkers associated with cardiac arrest in a cohort of children with acute respiratory distress syndrome (ARDS), and to assess the association of these biomarkers with mortality in children with cardiac arrest and ARDS (ARDS + CA).

METHODS

This was a secondary analysis of a single-center prospective cohort study of children with ARDS from 2014-2019 with 17 biomarkers measured. Clinical characteristics and biomarkers were compared between subjects with ARDS + CA and ARDS with univariate analysis. In a sub-cohort of ARDS + CA subjects, the association between biomarker levels and mortality was tested using univariate and bivariate logistic regression.

RESULTS

Biomarkers were measured in 333 subjects: 301 with ARDS (median age 5.3 years, 55.5% male) and 32 ARDS + CA (median age 8 years, 53.1% male). More arrests (69%) occurred out-of-hospital with a median CPR duration of 11 (IQR 5.5, 25) minutes. ARDS severity, PRISM III score, vasoactive-ionotropic score and extrapulmonary organ failures were worse in the ARDS + CA versus ARDS group. Eight biomarkers were elevated in the ARDS + CA versus ARDS cohort: sRAGE, nucleosomes, SP-D, CCL22, IL-6, HSP70, IL-8, and MIP-1b. sRAGE, SP-D, and CCL22 remained elevated when the cohorts were matched for illness severity. When controlling for severity of ARDS and cardiac arrest characteristics, sRAGE, IL-6 and granzyme B were associated with mortality in the ARDS + CA group.

CONCLUSION

sRAGE, IL-6 and granzyme B were associated with cardiac arrest mortality when controlling for illness severity. sRAGE was consistently higher in the ARDS + CA cohort compared to ARDS and retained independent association with mortality.

The Association Between Alveolar Dead Space Fraction and Mortality in Pediatric Acute Respiratory Distress Syndrome: A Prospective Cohort Study

BACKGROUND

Alveolar dead-space fraction (AVDSF), the volume of alveolar gas that does not participate in gas exchange, has been reported to predict mortality and morbidity in adults with acute respiratory distress syndrome (ARDS). This study aims to characterize AVDSF in patients with pediatric ARDS (PARDS), to determine its association with clinical outcomes and examine the validity of a previously studied cutoff (AVDSF > 0.25).

METHODS

This was a prospective cohort study performed in the setting of a lung protective mechanical ventilation protocol. AVDSF was calculated by the equation: AVDSF = [partial pressure of arterial carbon dioxide (P_aCO₂) - end tidal carbon dioxide (etCO₂)]/P_aCO₂. Receiver operating curve and Youden index were used to identify an AVDSF cutoff associated with mortality, which characterized "high or low AVDSF" groups. Correlation between AVDSF and clinical indices of severity were determined [including daily oxygenation index (OI), admission Pediatric Index of Mortality 2 (PIM 2) and Pediatric Logistic Organ Dysfunction (PELOD) scores]. The primary outcome, mortality in PARDS patients, was compared between the high and low AVDSF groups and analyzed in a multivariable logistic regression adjusting for inotrope use and PIM 2 score. Secondary outcomes included 28-day ventilator-free (VFD) and intensive care unit-free (IFD) days.

RESULTS

Sixty-nine PARDS patients with a median (interquartile range) age of 4.5 (0.8, 10.6) years were included in this analysis. Daily AVDSF correlated with daily OI (R ² = 0.10; p < 0.001). Mean AVDSF over the first 7 days of PARDS correlated with PIM 2 (R ² = 0.10; p = 0.010) and PELOD (R ² = 0.12; p = 0.004) scores. The greatest area under the curve identified an AVDSF cutoff of 0.22, which was close to the previously suggested 0.25. The high AVDSF group had higher mortality [7/19 (36.8%) vs. 5/50 (10.0%); p = 0.009] and lower VFD [2 (0, 18) vs. 21 (15, 24); p = 0.007] and IFD [0 (0, 16) vs. 16 (5, 21); p = 0.013]. In the multivariable model, being in the high AVDSF group [adjusted odds ratio 4.67 (95% CI: 1.12, 19.39)] was significantly associated with mortality.

CONCLUSIONS

High AVDSF was independently associated with increased mortality and decreased VFD and IFD. AVDSF may be complementary to oxygenation indices in risk stratifying PARDS and warrant further study.

Refining the Pediatric Multiple Organ Dysfunction Syndrome

Since its introduction into the medical literature in the 1970s, the term multiple organ dysfunction syndrome (or some variant) has been applied broadly to any patient with >1 concurrent organ dysfunction. However, the epidemiology, mechanisms, time course, and outcomes among children with multiple organ dysfunction vary substantially. We posit that the term pediatric multiple organ dysfunction syndrome (or MODS) should be reserved for patients with a systemic pathologic state resulting from a common mechanism (or mechanisms) that affects numerous organ systems simultaneously. In contrast, children in whom organ injuries are attributable to distinct mechanisms should be considered to have additive organ system dysfunctions but not the syndrome of MODS. Although such differentiation may not always be possible with current scientific knowledge, we make the case for how attempts to differentiate multiple organ dysfunction from other states of additive organ dysfunctions can help to evolve clinical and research priorities in diagnosis, monitoring, and therapy from largely organ-specific to more holistic strategies.

Delayed angiopoietin-2 blockade reduces influenza-induced lung injury and improves survival in mice

Influenza remains a major cause of death and disability with limited treatment options. Studies of acute lung injury have identified angiopoietin-2 (Ang-2) as a key prognostic marker and a potential mediator of Acute respiratory distress syndrome. However, the role of Ang-2 in viral pneumonia remains poorly defined. This study characterized the time course of lung Ang-2 expression in severe influenza pneumonia and tested the therapeutic potential of Ang-2 inhibition. We inoculated adult mice with influenza A (PR8 strain) and measured angiopoietin-1 (Ang-1), Ang-2, and Tie2 expressions during the evolution of inflammatory lung injury over the first 7 days post-infection (dpi). We tested a peptide-antibody inhibitor of Ang-2, L1-7, administered at 2, 4, and 6 dpi and measured arterial oxygen saturation, survival, pulmonary edema, inflammatory cytokines, and viral load. Finally, we infected primary human alveolar type II epithelial (AT2) cells grown in air-liquid interface culture with influenza and measured Ang-2 RNA expression. Influenza caused severe lung injury between 5 and 7 dpi in association with increased Ang-2 lung RNA and a dramatic increase in Ang-2 protein in bronchoalveolar lavage. Inhibition of Ang-2 improved oxygenation and survival and reduced pulmonary edema and alveolar-capillary barrier permeability to protein without major effects on inflammation or viral load. Finally, influenza increased the expression of Ang-2 RNA in human AT2 cells. The increased Ang-2 levels in the airspaces during severe influenza pneumonia and the improvement in clinically relevant outcomes after Ang-2 antagonism suggest that the Ang-1/Ang-2 Tie-2 signaling axis is a promising therapeutic target in influenza and potentially other causes of viral pneumonia.

Timing and Clinical Significance of Fluid Overload in Pediatric Acute Respiratory Distress Syndrome

OBJECTIVES

Fluid overload is associated with worse outcomes in adult and pediatric acute respiratory distress syndrome. However, the time-course of fluid overload and its relationship to outcome has not been described. We aimed to determine the relationship between the timing of fluid overload and outcomes over the first 7 days after acute respiratory distress syndrome onset in children.

DESIGN

Retrospective cohort study.

SETTING

Single tertiary care PICU.

PATIENTS

Intubated children with acute respiratory distress syndrome between 2011 and 2019.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Daily and cumulative total fluid intake, total output, urine output, and fluid balance were collected for each 24-hour period from days 1 to 7 after acute respiratory distress syndrome onset. We tested the association between daily cumulative fluid metrics with PICU mortality and probability of extubation by 28 days using multivariable logistic and competing risk regression, respectively. In a subset of children, plasma was collected on day 1 and day 3 of acute respiratory distress syndrome and angiopoietin-2 quantified. Of 723 children with acute respiratory distress syndrome, 132 died (18%). In unadjusted analysis, nonsurvivors had higher cumulative fluid balance starting on day 3. In multivariable analysis, a positive cumulative fluid balance on days 5 through 7 was associated with increased mortality. Higher cumulative fluid balance on days 4 to 7 was associated with lower probability of extubation. Elevated angiopoietin-2 on day 1 predicted early (within 3 d) fluid overload greater than or equal to 10%, and elevated angiopoietin-2 on day 3 predicted late (between days 4 and 7) fluid overload.

CONCLUSIONS

Fluid overload after day 4 of acute respiratory distress syndrome, but not before, was associated with worse outcomes. Higher angiopoietin-2 predicted subsequent fluid overload. Our results suggest that future interventions aimed at managing fluid overload may have differential efficacy depending on when in the time-course of acute respiratory distress syndrome they are initiated.

Inflammatory Biomarkers Are Associated With a Decline in Functional Status at Discharge in Children With Acute Respiratory Failure: An Exploratory Analysis

Supplemental Digital Content is available in the text.

To evaluate the link between early acute respiratory failure and functional morbidity in survivors using the plasma biomarkers interleukin-8, interleukin-1 receptor antagonist, thrombomodulin, and plasminogen activator inhibitor-1. We hypothesized that children with acute respiratory failure with higher levels of inflammation would have worse functional outcomes at discharge, as measured by Pediatric Overall Performance Category.

Circulating angiopoietin-2 and the risk of mortality in patients with acute respiratory distress syndrome: a systematic review and meta-analysis of 10 prospective cohort studies

BACKGROUND

Angiopoietin-2 (Ang-2), as one of the ligands of endothelial receptor Tie2, is known to be significant for vessel maturation and stabilization after birth. Previous studies showed the relationship between Ang-2 level and the risk of mortality in patients with acute respiratory distress syndrome (ARDS). However, the link between circulating Ang-2 and the risk of mortality in patients with ARDS varied in different investigations.

RESULTS

We performed a systematic review and meta-analysis of all available cohort studies regarding the association between baseline circulating Ang-2 and mortality in patients with ARDS. Among the 10 eligible studies, pooled odds ratio (OR) showed that high Ang-2 level contributed to ARDS mortality [OR = 1.56, 95% confidence interval (CI): 1.30-1.89, I² = 76.2%]. Stratified analysis revealed that higher circulating Ang-2 was related to a 30% higher risk in the high-quality scores group (OR = 1.68, 95% CI: 1.33-2.68, I² = 62.4%). The I² of the bad compliance group decreased from 76.2% to 8.5%, which suggested that compliance is a significant source of heterogeneity. This association may be blunted by potential bias, although the results was not meaningfully changed by omitting only one study at a time. Further subgroup analysis and meta-regression support that compliance of patients also affects the results significantly, compared with the publication year, follow-up duration, the samples, or population characteristics.

CONCLUSION

Participants with higher baseline Ang-2 were at a higher risk for future risk of mortality in patients with ARDS. Higher circulating Ang-2 levels could independently predict the risk of mortality in patients with ARDS. However, further large scale prospective cohorts or even interventional studies are warranted to evaluate the diagnostic power of Ang-2 and its causative role on ARDS outcome. The reviews of this paper are available via the supplemental material section.

A Simple-to-Use Web-Based Calculator for Survival Prediction in Acute Respiratory Distress Syndrome

Background: The aim of this study was to construct and validate a simple-to-use model to predict the survival of patients with acute respiratory distress syndrome.

Methods: A total of 197 patients with acute respiratory distress syndrome were selected from the Dryad Digital Repository. All eligible individuals were randomly stratified into the training set (n=133) and the validation set (n=64) as 2: 1 ratio. LASSO regression analysis was used to select the optimal predictors, and receiver operating characteristic and calibration curves were used to evaluate accuracy and discrimination of the model. Clinical usefulness of the model was also assessed using decision curve analysis and Kaplan-Meier analysis.

Results: Age, albumin, platelet count, PaO₂/FiO₂, lactate dehydrogenase, high-resolution computed tomography score, and etiology were identified as independent prognostic factors based on LASSO regression analysis; these factors were integrated for the construction of the nomogram. Results of calibration plots, decision curve analysis, and receiver operating characteristic analysis showed that this model has good predictive ability of patient survival in acute respiratory distress syndrome. Moreover, a significant difference in the 28-day survival was shown between the patients stratified into different risk groups (P < 0.001). For convenient application, we also established a web-based calculator (https://huangl.shinyapps.io/ARDSprognosis/).

Conclusions: We satisfactorily constructed a simple-to-use model based on seven relevant factors to predict survival and prognosis of patients with acute respiratory distress syndrome. This model can aid personalized treatment and clinical decision-making.

Laboratory Markers in the Management of Pediatric Polytrauma: Current Role and Areas of Future Research

Severe trauma is the most common cause of mortality in children and is associated with a high socioeconomic burden. The most frequently injured organs in children are the head and thorax, followed by the extremities and by abdominal injuries. The efficient and early assessment and management of these injuries is essential to improve patients' outcome. Physical examination as well as imaging techniques like ultrasound, X-ray and computer tomography are crucial for a valid early diagnosis. Furthermore, laboratory analyses constitute additional helpful tools for the detection and monitoring of pediatric injuries. Specific inflammatory markers correlate with post-traumatic complications, including the development of multiple organ failure. Other laboratory parameters, including lactate concentration, coagulation parameters and markers of organ injury, represent further clinical tools to identify trauma-induced disorders. In this review, we outline and evaluate specific biomarkers for inflammation, acid-base balance, blood coagulation and organ damage following pediatric polytrauma. The early use of relevant laboratory markers may assist decision making on imaging tools, thus contributing to minimize radiation-induced long-term consequences, while improving the outcome of children with multiple trauma.

Peripheral blood transcriptomic sub-phenotypes of pediatric acute respiratory distress syndrome

Background

Acute respiratory distress syndrome (ARDS) is heterogeneous and may be amenable to sub-phenotyping to improve enrichment for trials. We aimed to identify subtypes of pediatric ARDS based on whole blood transcriptomics.

Methods

This was a prospective observational study of children with ARDS at the Children’s Hospital of Philadelphia (CHOP) between January 2018 and June 2019. We collected blood within 24 h of ARDS onset, generated expression profiles, and performed k-means clustering to identify sub-phenotypes. We tested the association between sub-phenotypes and PICU mortality and ventilator-free days at 28 days using multivariable logistic and competing risk regression, respectively.

Results

We enrolled 106 subjects, of whom 96 had usable samples. We identified three sub-phenotypes, dubbed CHOP ARDS Transcriptomic Subtypes (CATS) 1, 2, and 3. CATS-1 subjects (n = 31) demonstrated persistent hypoxemia, had ten subjects (32%) with immunocompromising conditions, and 32% mortality. CATS-2 subjects (n = 29) had more immunocompromising diagnoses (48%), rapidly resolving hypoxemia, and 24% mortality. CATS-3 subjects (n = 36) had the fewest comorbidities and also had rapidly resolving hypoxemia and 8% mortality. The CATS-3 subtype was associated with lower mortality (OR 0.18, 95% CI 0.04–0.86) and higher probability of extubation (subdistribution HR 2.39, 95% CI 1.32–4.32), relative to CATS-1 after adjustment for confounders.

Conclusions

We identified three sub-phenotypes of pediatric ARDS using whole blood transcriptomics. The sub-phenotypes had divergent clinical characteristics and prognoses. Further studies should validate these findings and investigate mechanisms underlying differences between sub-phenotypes.

Endothelial Biomarkers Are Associated With Indirect Lung Injury in Sepsis-Associated Pediatric Acute Respiratory Distress Syndrome

Supplemental Digital Content is available in the text.

Objectives:

Acute respiratory distress syndrome occurring in the setting of direct versus indirect lung injury may reflect different pathobiologies amenable to different treatment strategies. We sought to test whether a panel of plasma biomarkers differed between children with sepsis-associated direct versus indirect acute respiratory distress syndrome. We hypothesized that a biomarker profile indicative of endothelial activation would be associated with indirect acute respiratory distress syndrome.

Design:

Observational cohort.

Setting:

Academic PICU.

Subjects:

Patients less than 18 years old with sepsis-associated direct (pneumonia, n = 52) or indirect (extrapulmonary sepsis, n = 46) acute respiratory distress syndrome.

Interventions:

None.

Measurements and Main Results:

Of 58 biomarkers examined, 33 differed by acute respiratory distress syndrome subtype. We used classification and regression tree methodology to examine associations between clinical and biochemical markers and acute respiratory distress syndrome subtype. The classification and regression tree model using only clinical variables (age, sex, race, oncologic comorbidity, and Pediatric Risk of Mortality-III score) performed worse than the classification and regression tree model using five clinical variables and 58 biomarkers. The best classification and regression tree model used only four endothelial biomarkers, including elevated angiopoietin-2/angiopoietin-1 ratio, vascular cell-adhesion molecule, and von Willebrand factor, to identify indirect acute respiratory distress syndrome. Test characteristics were 89% (80–97%) sensitivity, 80% (69–92%) specificity, positive predictive value 84% (74–93%), and negative predictive value 86% (76–96%).

Conclusions:

Indirect lung injury in children with acute respiratory distress syndrome is characterized by a biomarker profile indicative of endothelial activation, excess inflammation, and worse outcomes. A model using four biomarkers has the potential to be useful for more precisely identifying patients with acute respiratory distress syndrome whose pathobiology may respond to endothelial-targeted therapies in future trials.

Perioperative Open-lung Approach, Regional Ventilation, and Lung Injury in Cardiac Surgery

BACKGROUND

In the Protective Ventilation in Cardiac Surgery (PROVECS) randomized, controlled trial, an open-lung ventilation strategy did not improve postoperative respiratory outcomes after on-pump cardiac surgery. In this prespecified subanalysis, the authors aimed to assess the regional distribution of ventilation and plasma biomarkers of lung epithelial and endothelial injury produced by that strategy.

METHODS

Perioperative open-lung ventilation consisted of recruitment maneuvers, positive end-expiratory pressure (PEEP) = 8 cm H2O, and low-tidal volume ventilation including during cardiopulmonary bypass. Control ventilation strategy was a low-PEEP (2 cm H2O) low-tidal volume approach. Electrical impedance tomography was used serially throughout the perioperative period (n = 56) to compute the dorsal fraction of ventilation (defined as the ratio of dorsal tidal impedance variation to global tidal impedance variation). Lung injury was assessed serially using biomarkers of epithelial (soluble form of the receptor for advanced glycation end-products, sRAGE) and endothelial (angiopoietin-2) lung injury (n = 30).

RESULTS

Eighty-six patients (age = 64 ± 12 yr; EuroSCORE II = 1.65 ± 1.57%) undergoing elective on-pump cardiac surgery were studied. Induction of general anesthesia was associated with ventral redistribution of tidal volumes and higher dorsal fraction of ventilation in the open-lung than the control strategy (0.38 ± 0.07 vs. 0.30 ± 0.10; P = 0.004). No effect of the open-lung strategy on the dorsal fraction of ventilation was noted at the end of surgery after median sternotomy closure (open-lung = 0.37 ± 0.09 vs. control = 0.34 ± 0.11; P = 0.743) or in extubated patients at postoperative day 2 (open-lung = 0.63 ± 0.18 vs. control = 0.59 ± 0.11; P > 0.999). Open-lung ventilation was associated with increased intraoperative plasma sRAGE (7,677 ± 3,097 pg/ml vs. 6,125 ± 1,400 pg/ml; P = 0.037) and had no effect on angiopoietin-2 (P > 0.999).

CONCLUSIONS

In cardiac surgery patients, open-lung ventilation provided larger dorsal lung ventilation early during surgery without a maintained benefit as compared with controls at the end of surgery and postoperative day 2 and was associated with higher intraoperative plasma concentration of sRAGE suggesting lung overdistension.

EDITOR’S PERSPECTIVE

sRAGE as severe acute bronchiolitis biomarker, prospective observational study

INTRODUCTION AND OBJECTIVES

Acute bronchiolitis (AB) is the leading cause of hospitalization in infants and around 5% require intensive care treatment. Early identification of children diagnosed with AB at a high risk of severe progression is of great interest. The receptor for advanced glycation end products (RAGE), highly expressed in lung tissue, regulates immune responses and inflammation, and its soluble form, sRAGE, is believed to have an anti-inflammatory role. We hypothesized serum sRAGE might be a major determinant of AB severity and prognosis. This study was conducted to measure serum sRAGE in infants with severe AB and to assess its correlation with clinical severity, immediate complications, and outcome.

METHODS

Single-center, prospective, observational study of hospitalized children with severe bronchiolitis admitted to the Pediatric Intensive Care Unit (PICU), from September 2015 to September 2016.

RESULTS

A total of 52 children and 27 controls were included. The cases age ranged from 11 days to 21 months, resulting in a significant age difference with controls (11.85 vs 4.84 months, P < .01). Serum levels of sRAGE were lower but not significant in severe AB patients than in controls (1350.93 vs 1450.42 pg/mL; P = .399). No correlation was found between serum sRAGE and causative viruses, clinical symptoms, Wood-Downes score (a clinical severity score) on admission, respiratory support, or length of hospital stay. Serum sRAGE was also lower in the cases having had a previous respiratory disease (1463.84 vs 1072.43 pg/mL; P = .049). However, it was higher in patients with any lung consolidation on the chest X-ray (1584.79 vs 1131.62 pg/mL; P = .044) and weakly positively correlated with classical biomarkers (maximum C-reactive protein, +0.295, P = .034; maximum procalcitonin, +0.309; P = .029).

CONCLUSION

This single-center study reveals that sRAGE couldn't predict AB severity or outcome in children hospitalized at PICU. Nevertheless, it significantly increased in the presence of any lung consolidation and had a positive correlation with classical biomarkers. The utility of sRAGE in this population could be probably elucidated with a better understanding of AGE-RAGE axis.

Systemic Endothelial Activation Is Associated With Early Acute Respiratory Distress Syndrome in Children With Extrapulmonary Sepsis

OBJECTIVES

Systemic endothelial activation may contribute to sepsis-associated organ injury, including acute respiratory distress syndrome. We hypothesized that children with extrapulmonary sepsis with versus without acute respiratory distress syndrome would have plasma biomarkers indicative of increased endothelial activation and that persistent biomarker changes would be associated with poor outcome.

DESIGN

Observational cohort.

SETTING

Academic PICU.

PATIENTS

Patients less than 18 years old with sepsis from extrapulmonary infection with (n = 46) or without (n = 54) acute respiratory distress syndrome and noninfected controls (n = 19).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Endothelial (angiopoietin-1, angiopoietin-2, tyrosine kinase with immunoglobulin-like loop epidermal growth factor homology domain 2, vascular endothelial growth factor, soluble fms-like tyrosine kinase, von Willebrand factor, E-selectin, intercellular adhesion molecule, vascular cell adhesion molecule, thrombomodulin) and inflammatory biomarkers (C-reactive protein, interleukin-6, and interleukin-8) were measured from peripheral plasma collected within 3 days (time 1) of sepsis recognition and at 3-6 days (time 2) and 7-14 days (time 3). Time 1 biomarkers and longitudinal measurements were compared for sepsis patients with versus without acute respiratory distress syndrome and in relation to complicated course, defined as greater than or equal to two organ dysfunctions at day 7 or death by day 28. Angiopoietin-2, angiopoietin-2/angiopoietin-1 ratio, tyrosine kinase with immunoglobulin-like loop epidermal growth factor homology domain 2, vascular endothelial growth factor, von Willebrand factor, E-selectin, intercellular adhesion molecule, vascular cell adhesion molecule, thrombomodulin, endocan, C-reactive protein, interleukin-6, and interleukin-8 were different between sepsis and noninfected control patients at time 1. Among patients with sepsis, those with acute respiratory distress syndrome had higher angiopoietin-2/angiopoietin-1 ratio, vascular endothelial growth factor, vascular cell adhesion molecule, thrombomodulin, endocan, interleukin-6, and interleukin-8 than those without acute respiratory distress syndrome (all p < 0.003). Angiopoietin-2 and angiopoietin-2/angiopoietin-1 ratio remained higher in sepsis with versus without acute respiratory distress syndrome after multivariable analyses. Time 1 measures of angiopoietin-2, angiopoietin-2/-1 ratio, von Willebrand factor, and endocan were indicative of complicated course in all sepsis patients (all area under the receiver operating curve ≥ 0.80). In sepsis without acute respiratory distress syndrome, soluble fms-like tyrosine kinase decreased more quickly and von Willebrand factor and thrombomodulin decreased more slowly in those with complicated course.

CONCLUSIONS

Children with extrapulmonary sepsis with acute respiratory distress syndrome had plasma biomarkers indicative of greater systemic endothelial activation than those without acute respiratory distress syndrome. Several endothelial biomarkers measured near sepsis recognition were associated with complicated course, whereas longitudinal biomarker changes yielded prognostic information only in those without sepsis-associated acute respiratory distress syndrome.

Circulating Neurofilament Light Chain Is Associated With Survival After Pediatric Cardiac Arrest

OBJECTIVES

To characterize neurofilament light levels in children who achieved return of spontaneous circulation following cardiac arrest compared with healthy controls and determine an association between neurofilament light levels and clinical outcomes.

DESIGN

Retrospective cohort study.

SETTING

Academic quaternary PICU.

PATIENTS

Children with banked plasma samples from an acute respiratory distress syndrome biomarker study who achieved return of spontaneous circulation after a cardiac arrest and healthy controls.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Neurofilament light levels were determined with a highly sensitive single molecule array digital immunoassay. Patients were categorized into survivors and nonsurvivors and into favorable (Pediatric Cerebral Performance Category score of 1-2 or unchanged from baseline) or unfavorable (Pediatric Cerebral Performance Category score of 3-6 or Pediatric Cerebral Performance Category score change ≥1 from baseline). Associations between neurofilament light level and outcomes were determined using Wilcoxon rank-sum test. We enrolled 32 patients with cardiac arrest and 18 healthy controls. Demographics, severity of illness, and baseline Pediatric Cerebral Performance Category scores were similar between survivors and nonsurvivors. Healthy controls had lower median neurofilament light levels than patients after cardiac arrest (5.5 [interquartile range 5.0-8.2] vs 31.0 [12.0-338.6]; p < 0.001). Neurofilament light levels were higher in nonsurvivors than survivors (78.5 [26.2-509.1] vs 12.4 [10.3-28.2]; p = 0.012) and higher in survivors than healthy controls (p = 0.009). The four patients who survived with a favorable outcome had neurofilament light levels that were not different from patients with unfavorable outcomes (21.9 [8.5--35.7] vs 37.2 [15.4-419.1]; p = 0.60) although two of the four patients who survived with favorable outcomes had progressive encephalopathies with both baseline and postcardiac arrest Pediatric Cerebral Performance Category scores of 4.

CONCLUSIONS

Neurofilament light is a blood biomarker of hypoxic-ischemic brain injury and may help predict survival and neurologic outcome after pediatric cardiac arrest. Further study in a larger, dedicated cardiac arrest cohort with serial longitudinal measurements is warranted.

Biomarker Panels in Critical Care

Biomarker panels have the potential to advance the field of critical care medicine by stratifying patients according to prognosis and/or underlying pathophysiology. This article discusses the discovery and validation of biomarker panels, along with their translation to the clinical setting. The current literature on the use of biomarker panels in sepsis, acute respiratory distress syndrome, and acute kidney injury is reviewed.

Characteristics and trajectory of patients with pediatric acute respiratory distress syndrome

OBJECTIVE

This study delineates the disease trajectory of patients with pediatric acute respiratory distress syndrome (PARDS) defined by the Pediatric Acute Lung Injury Consensus Conference (PALICC) definition, and evaluates the impact of comorbidities on outcomes.

METHODS

This prospective study over November 2017-October 2019 was conducted in a single-center multidisciplinary pediatric intensive care unit (PICU) and included patients <21years of age with PARDS. Clinical history of those requiring mechanical ventilation for <3 days was interrogated and cases in which the diagnosis of PARDS were unlikely, identified. The impact of chronic comorbidities on clinical outcomes, in particular, pulmonary disease and immunosuppression, were analyzed.

RESULTS

Eighty-five of 1272 PICU admissions (6.7%) met the criteria for PARDS and were included. Median age and oxygenation indexes were 2.8 (0.6, 8.3) years and 10.6 (7.6, 15.4), respectively. Overall mortality was 12 out of 85 (14.1%). Despite fulfilling criteria in 6/85 (7.1%), hypoxemia contributed by bronchospasm, mucus plugging, fluid overload, and atelectasis was quickly reversible and PARDS was unlikely in these patients. Comorbidities (57/85 [67.1%]) were not associated with worsened outcomes. However, pre-existing pulmonary disease and immunosuppression were associated with severe PARDS (12/20 [60.0%] vs 19/65 [29.2%]; P = .017), extracorporeal membrane oxygenation use (5/20 [25.0%] vs 3/65 [4.6%]; P = .016) and reduced ventilator free days (VFD) (15 [0, 19] vs 21 [6, 23]; P = .039), compared with those without them.

CONCLUSION

A small percentage of children fulfilling the PALICC definition had quickly reversible hypoxemia with likely alternate pathophysiology to PARDS. Patients with pulmonary comorbidities and immunosuppression had a more severe course of PARDS compared with others.

Risk Factors and Etiologies of Pediatric Acute Respiratory Distress Syndrome

The risk factors for acute respiratory distress syndrome (ARDS) have been a focus for clinicians and researchers from the original description in 1967 to the most recent Pediatric Acute Lung Injury Consensus Conference (PALICC). Indeed, there are many comorbidities and risk factors that predispose a patient to develop pediatric ARDS (PARDS) including, but not limited to, immunodeficiency, weight extremes, genetics, and environmental factors. These are particularly important to investigators because accurate prediction of which patients are at greatest risk of PARDS – both the development of PARDS and worse clinical outcomes after PARDS has been established – is key to identifying the next generation of diagnostic techniques and preventative strategies. In addition to those risk factors, there are specific disease processes that lead to the development of PARDS, often divided into direct or pulmonary insults and indirect or extrapulmonary insults. Finally, beyond the clinically visible risk factors, researchers are attempting to identify novel biomarkers to uncover hidden phenotypes of PARDS and enrich the prognostication and prediction of patient outcomes. This chapter delves into each of these concepts.

Biomarkers in pediatric acute respiratory distress syndrome

Pediatric acute respiratory distress syndrome (PARDS) is a heterogenous process resulting in a severe acute lung injury. A single indicator does not exist for PARDS diagnosis. Rather, current diagnosis requires a combination of clinical and physiologic variables. Similarly, there is little ability to predict the path of disease, identify those at high risk of poor outcomes or target therapies specific to the underlying pathophysiology. Biomarkers, a measured indicator of a pathologic state or response to intervention, have been studied in PARDS due to their potential in diagnosis, prognostication and measurement of therapeutic response. Additionally, PARDS biomarkers show great promise in furthering our understanding of specific subgroups or endotypes in this highly variable disease, and thereby predict which patients may benefit and which may be harmed by PARDS specific therapies. In this chapter, we review the what, when, why and how of biomarkers in PARDS and discuss future directions in this quickly changing landscape.

Lessons learned in acute respiratory distress syndrome from the animal laboratory

Since the description of the acute respiratory distress syndrome (ARDS) in 1967, investigators have struggled to reproduce the syndrome in the animal laboratory. While several different models of experimental acute lung injury (ALI) have been developed, none completely capture the inciting etiologies, initial inflammation, heterogeneity, and resolution of human ARDS. This potentially has contributed to the poor translation of potential therapeutics between animal ALI models and human ARDS. It was only recently that standardized criteria were suggested for what makes an ALI model comparable to human ARDS. Nevertheless, despite model heterogeneity, these models have contributed substantially to our understanding of the syndrome. From the initial studies identifying the risks of mechanical ventilation to the identification of potentially targetable inflammatory mediators, to modern studies focusing on regional heterogeneity and novel molecular pathways, animal models continue to inform our understanding of ARDS. This review will cover several major lessons learned from animal models of ALI, and provide some direction for future studies in this field.

Expression of soluble receptor for advanced glycation end products is associated with disease severity in congenital diaphragmatic hernia

Pulmonary hypertension (PH) and lung hypoplasia are major contributors to morbidity and mortality in newborns with congenital diaphragmatic hernia (CDH). The soluble receptor for advanced glycation end products (sRAGE) is a marker of endothelial function and might be associated with disease severity in CDH newborns. In a cohort of 30 CDH newborns and 20 healthy control newborns, sRAGE concentration was measured at birth and at 6 h, 12 h, 24 h, 48 h, and 7-10 days. In healthy newborns, sRAGE was significantly higher at birth and at 48 h compared with CDH newborns (both P < 0.001). Among CDH newborns, sRAGE was significantly lower at birth (P = 0.033) and at 7-10 days (P = 0.035) in patients receiving extracorporeal membrane oxygenation (ECMO) compared with patients not receiving ECMO. In contrast, CDH newborns receiving ECMO had significantly higher values at 6 h (P = 0.001), 12 h (P = 0.004), and 48 h (0.032). Additionally, sRAGE correlated significantly with PH severity, intensity and duration of mechanical ventilation, and prenatally assessed markers of CDH severity (lung size, liver herniation). The probability to receive ECMO therapy was five times higher in CDH newborns with sRAGE concentrations below the calculated cutoff of 650 pg/ml at birth (P = 0.002) and nine times higher in CDH newborns with sRAGE concentrations above the cutoff of 3,500 pg/ml at 6 h (P = 0.001). These findings suggest a potential involvement of sRAGE in the pathophysiology of CDH and may act as a therapeutic target in future treatment approaches.

Serum soluble receptor for advanced glycation end-products during acute bronchiolitis in infant: Prospective study in 93 cases

INTRODUCTION

Acute bronchiolitis is a major cause of acute respiratory distress in infants. The soluble receptor for advanced glycation end-products (sRAGE) is a biomarker of pulmonary damage processes, with a diagnostic and a prognostic value in acute respiratory distress syndrome (ARDS). The RAGE pathway is also implicated in the pathogenesis of other respiratory diseases like asthma, but the value of sRAGE levels in acute bronchiolitis remains under-investigated.

MATERIAL AND METHODS

A prospective, observational, and analytical study was conducted at Clermont-Ferrand University Hospital. The main objective was to evaluate the correlation between serum sRAGE and clinical severity of bronchiolitis in hospitalized infants aged <1 year. We analyzed correlations between serum sRAGE and Wainwright score, short-term morbidity attributable to bronchiolitis, causal viruses and risk for recurrent wheezing at 1 year.

RESULTS

The study included 93 infants. sRAGE levels were significantly lower in acute bronchiolitis patients (mean 1101 pg/mL) than in controls (2203 pg/mL, P < 0.001) but did not correlate with clinical severity. No correlation was found between serum sRAGE and severity score, respiratory viruses, and recurrent wheezing at 1 year. Serum sRAGE levels were negatively correlated with age (r = -0.45, P < 0.001).

CONCLUSION

Serum sRAGE levels are decreased in acute bronchiolitis but not correlated with disease severity. sRAGE levels should be age-adjusted in infants. Serum sRAGE levels measured in the setting of acute bronchiolitis were not predictive of recurrent wheezing.

Circulating soluble RAGE and cell surface RAGE on peripheral blood mononuclear cells in healthy children

BACKGROUND

The receptor for advanced glycation end products (RAGE) has a critical role in the pathogenesis of inflammation. In healthy children, its basal expression on the peripheral blood mononuclear cell (PBMC) and the basal circulating soluble RAGE (sRAGE) levels are unknown. The aim of this study was to describe both.

METHODS

This is a monocentric, observational and descriptive study of samples obtained from healthy children. The RAGE expression on PBMC was analyzed using flow cytometry. The sRAGE values were determined with a specific sandwich enzyme-linked immunosorbent assay (ELISA) kit, later the relation between cellular RAGE and sRAGE was described.

RESULTS

Forty-three children were included. The median sRAGE level was 849.0±579.0 pg/mL. The RAGE mean fluorescence intensity (MFI) was 1382±506 in monocytes and 792±506 in lymphocytes. There were no differences between genders. A negative correlation was found between sRAGE and RAGE MFI in lymphocytes (r=-0.3; p=0.04).

CONCLUSIONS

We describe for the first time the RAGE surface levels on PBMC in children. It showed a negative correlation with sRAGE. The sRAGE circulating level is lower than the sRAGE level described in adult population or non-healthy children. Our findings should be confirmed in order to apply them as reference values for future investigations.

Endothelial Activation: The Ang/Tie Axis in Sepsis

Sepsis, a dysregulated host response to infection that causes life-threatening organ dysfunction, is a highly heterogeneous syndrome with no specific treatment. Although sepsis can be caused by a wide variety of pathogenic organisms, endothelial dysfunction leading to vascular leak is a common mechanism of injury that contributes to the morbidity and mortality associated with the syndrome. Perturbations to the angiopoietin (Ang)/Tie2 axis cause endothelial cell activation and contribute to the pathogenesis of sepsis. In this review, we summarize how the Ang/Tie2 pathway is implicated in sepsis and describe its prognostic as well as therapeutic utility in life-threatening infections.

Plasma Neutrophil Elastase and Elafin as Prognostic Biomarker for Acute Respiratory Distress Syndrome: A Multicenter Survival and Longitudinal Prospective Observation Study

BACKGROUND

Neutrophil elastase (HNE) is a destructive enzyme and plays crucial roles in the pathophysiology of acute respiratory distress syndrome (ARDS). Endogenous proteinase inhibitors elafin (PI3) is important to protect against lung tissue destruction. We proposed to examine whether HNE and PI3 serve as prognostic biomarkers for ARDS.

METHODS

This study is a survival and longitudinal analysis of plasma profiles of HNE and PI3 in ARDS patients from a multicenter prospective observational cohort in Beijing, China. Plasma samples were collected on day-1, day-3, and day-7 of study enrollment.

RESULTS

HNE levels were higher in ARDS non-survivors than survivors, whereas PI3 showed opposite direction for all three measurements (P < 0.01 for all). Patients with HNE level above median and PI3 level below median values had the lowest survival probability and died the fastest. There was a significant longitudinal effect of HNE levels and PI3 level on mortality. Receiver-operating characteristic analysis demonstrated combination of HNE and PI3 had the discrimination ability for 28-day mortality (area under the receiver-operating characteristic curve [AUC]: 0.76), better than the combination of Berlin categories and APACHE II (AUC: 0.63). The addition of HNE and PI3 to Berlin categories and APACHE II has significantly improved the prognostic discrimination ability (AUC: 0.81, P < 0.0001).

CONCLUSIONS

Imbalance between HNE and PI3 levels in ARDS patients was associated with ARDS mortality. By combining these biomarkers with Berlin categories and APACHE II, prognostic power of ARDS was greatly improved. Circulation levels of HNE and PI3 may have the potential to predict ARDS mortality and better inform clinicians about ARDS mortality risk.

Diagnostic indicator of acute lung injury for pediatric critically ill patients at a tertiary pediatric hospital

Early identification of acute lung injury (ALI) in pediatric patients at risk of mortality is important for improving outcome.Assessment of soluble form of receptor for advanced glycation end products (sRAGE) as a valid biomarker for diagnosis of ALI among critically ill, pediatric patients in addition to correlating levels of sRAGE and different outcomes of those patients.A Hospital-based case-control study was conducted in pediatric intensive care units (PICUs) at Cairo University Hospital, along a period of 6 months. Total of 68 pediatric patients following inclusion criteria were classified into: patients with ALI; with both ALI and sepsis; with sepsis and control patients. They were prospectively followed and their laboratory and immunological workup (at days 1 and 9) was done to measure serum sRAGE levels and detect (sRAGE) genotypes.The age of the included children ranged from 8 to 84 months. Plasma level of sRAGE was significantly higher in plasma from patients with ALI regardless of associated sepsis. Plasma sRAGE levels were positively correlated with lung injury score. When assessing sRAGE genotypes, TA and TT genotypes were significant in most of the ALI with and without sepsis patients.Monitoring levels of sRAGE and genotypes can significantly affect the survival of ALI children.

Association of Response to Inhaled Nitric Oxide and Duration of Mechanical Ventilation in Pediatric Acute Respiratory Distress Syndrome

OBJECTIVES

Literature regarding appropriate use of inhaled nitric oxide for pediatric acute respiratory distress syndrome is sparse. This study aims to determine if positive response to inhaled nitric oxide is associated with decreased mortality and duration of mechanical ventilation in pediatric acute respiratory distress syndrome.

DESIGN

Retrospective cohort study.

SETTING

Large pediatric academic medical center.

PATIENTS OR SUBJECTS

One hundred sixty-one children with pediatric acute respiratory distress syndrome and inhaled nitric oxide exposure for greater than or equal to 1 hour within 3 days of pediatric acute respiratory distress syndrome onset.

INTERVENTIONS

Patients with greater than or equal to 20% improvement in oxygenation index or oxygen saturation index by 6 hours after inhaled nitric oxide initiation were classified as "responders."

MEASUREMENTS AND MAIN RESULTS

Oxygenation index, oxygen saturation index, and ventilator settings were evaluated prior to inhaled nitric oxide initiation and 1, 6, 12, and 24 hours following inhaled nitric oxide initiation. Primary outcomes were mortality and duration of mechanical ventilation. Baseline characteristics, including severity of illness, were similar between responders and nonresponders. Univariate analysis showed no difference in mortality between responders and nonresponders (21% vs 21%; p = 0.999). Ventilator days were significantly lower in responders (10 vs 16; p < 0.001). Competing risk regression (competing risk of death) confirmed association between inhaled nitric oxide response and successful extubation (subdistribution hazard ratio = 2.11; 95% CI, 1.41-3.17; p < 0.001). Response to inhaled nitric oxide was associated with decreased utilization of high-frequency oscillatory ventilation and extracorporeal membrane oxygenation and lower hospital charges (difference in medians of $424,000).

CONCLUSIONS

Positive response to inhaled nitric oxide was associated with fewer ventilator days, without change in mortality, potentially via reduced use of high-frequency oscillatory ventilation and extracorporeal membrane oxygenation. Future studies of inhaled nitric oxide for pediatric acute respiratory distress syndrome should stratify based on oxygenation response, given the association with favorable outcomes.