Acute Respiratory Distress Syndrome in Nontrauma Surgical Patients: A 6-Year Study

Angiopoietin-Like Protein 2 Is Increased in Obese Mouse Models of Lung Injury

Objective

To investigate the regulatory role of angiopoietin-1ike protein 2 (Angptl 2) in the pathogenesis of acute respiratory distress syndrome (ARDS).

Methods

A high-fat diet (HFD) and tail vein injection of 0.1 ml/kg oleic acid were used to induce acute lung injury (ALI) and ARDS models, and male Kunming mice were randomly divided into four groups: control group (injected with normal saline), ALI group (injected with oleic acid), HFD group (injection of normal saline), and ARDS group (HFD+injection of oleic acid). The degree of lung injury was assessed by lung histopathology score and lung injury index. At the same time, the mRNA and protein expression levels of Angptl 2 in lung tissue were also detected to determine the relationship between Angptl 2 and ARDS.

Results

Lee's index of the HFD group and ARDS group was significantly higher than that of the control group and ALI group (P < 0.05), and the lung injury index of the ARDS group was significantly higher than that of the ALI group. The expression of Angptl 2 in the lung tissue of the ALI group and ARDS group was significantly different, and the Angptl 2 mRNA level was the highest in the ARDS group. Immunohistochemistry showed that the alveolar walls of the ALI group and ARDS group were severely collapsed, and the ARDS group had the greatest Angptl 2 aggregation at the site of edema exudation.

Conclusion

Collectively, obesity might be mediated by Angptl 2 and promotes lung injury. Immunohistochemistry analysis showed that the expression of the receptor on alveolar walls was correlated with Angptl 2, which increased alveolar wall permeability, edema fluid exudation, and alveolar wall collapse. Thus, Angptl 2 might be a target for improving the treatment of ARDS.

Attributable mortality of acute respiratory distress syndrome: a systematic review, meta-analysis and survival analysis using targeted minimum loss-based estimation

BACKGROUND

Although acute respiratory distress syndrome (ARDS) is associated with high mortality, its direct causal link with death is unclear. Clarifying this link is important to justify costly research on prevention of ARDS.

OBJECTIVE

To estimate the attributable mortality, if any, of ARDS.

DESIGN

First, we performed a systematic review and meta-analysis of observational studies reporting mortality of critically ill patients with and without ARDS matched for underlying risk factor. Next, we conducted a survival analysis of prospectively collected patient-level data from subjects enrolled in three intensive care unit (ICU) cohorts to estimate the attributable mortality of critically ill septic patients with and without ARDS using a novel causal inference method.

RESULTS

In the meta-analysis, 44 studies (47 cohorts) involving 56 081 critically ill patients were included. Mortality was higher in patients with versus without ARDS (risk ratio 2.48, 95% CI 1.86 to 3.30; p<0.001) with a numerically stronger association between ARDS and mortality in trauma than sepsis. In the survival analysis of three ICU cohorts enrolling 1203 critically ill patients, 658 septic patients were included. After controlling for confounders, ARDS was found to increase the mortality rate by 15% (95% CI 3% to 26%; p=0.015). Significant increases in mortality were seen for severe (23%, 95% CI 3% to 44%; p=0.028) and moderate (16%, 95% CI 2% to 31%; p=0.031), but not for mild ARDS.

CONCLUSIONS

ARDS has a direct causal link with mortality. Our findings provide information about the extent to which continued funding of ARDS prevention trials has potential to impart survival benefit.

PROSPERO REGISTRATION NUMBER

CRD42017078313.

"Obesity Paradox" in Acute Respiratory Distress Syndrome: Asystematic Review and Meta-Analysis

Background

It is unclear whether an “obesity paradox” exists in the respiratory system, especially in acute respiratory distress syndrome (ARDS) and acute lung injury (ALI). Previous studies have postulated a causal relation between obesity and ARDS/ALI but have lacked power to form a definitive conclusion.

Objective

To investigate the relationships between obesity, ARDS/ALIrisk, and mortality.

Methods

A systematic search current to April 2016 was performed in Pubmed, EMBASE, Medline, Cochrane databases to find relevant studies. All studies that estimate the effect of obesity in the morbidity and mortality of ARDS/ALI were included.

Results

A total of 24 studies including 9,187,248 subjects were analyzed. The combined results from 16 studies that examined the effect of obesity in morbidity of ARDS/ALI showed an89% increase in odds ratio(pooled odds ratios (OR) 1.89, 95% confidence intervals (CI) 1.45 to 2.47). In subgroup analysis, compared to normal weight, obesity was associated with an increased risk of ARDS/ALI (OR1.57, 95% CI 1.30–1.90 for obese (BMI30-39.9kg/m²); OR1.75, 95% CI 1.42–2.15 for obese(BMI≥30kg/m²); OR1.67, 95% CI 1.04–2.68 for morbid obese(BMI≥40kg/m²)). The combined results from 9 studies that examined the effect of obesity in mortality of ARDS/ALI had a pooled odds ratio(pooled OR 0.63, 95% CI 0.41 to 0.98). Inversely, obesity was significantly associated with reduced risk of ARDS/ALI mortality(OR0.88, 95% CI 0.78–1.00 for overweight(BMI≤18.5m²); OR0.74, 95% CI 0.64–0.84 for obese (BMI30-39.9kg/m²);OR0.84, 95% CI 0.75–0.94 for 60days mortality; OR0.38, 95% CI 0.22–0.66 for 90days mortality).

Conclusions

Our data identify obesity as an important risk factor for the development of ARDS/ALI; however, ARDS/ALI outcomes are improved in this population when compared to individuals with a normal body mass index. This meta-analysis results supported ‘‘obesity paradox” in ARDS/ALI.

Obesity, inflammation, and lung injury (OILI): the good

Obesity becomes pandemic, predisposing these individuals to great risk for lung injury. In this review, we focused on the anti-inflammatories and addressed the following aspects: adipocytokines and obesity, inflammation and other mechanisms, adipocytokines and lung injury in obesity bridged by inflammation, and potential therapeutic targets. To sum up, the majority of evidence supported that adiponectin, omentin, and secreted frizzled-related protein 5 (SFRP5) were reduced significantly in obesity, which is associated with increased inflammation, indicated by increase of TNFα and IL-6, through activation of toll-like receptor (TLR4) and nuclear factor light chain κB (NF-κB) signaling pathways. Administration of these adipocytokines promotes weight loss and reduces inflammation. Zinc-α2-glycoprotein (ZAG), vaspin, IL-10, interleukin-1 receptor antagonist (IL-1RA), transforming growth factor β (TGF-β1), and growth differentiation factor 15 (GDF15) are also regarded as anti-inflammatories. There were controversial reports. Furthermore, there is a huge lack of studies for obesity related lung injury. The effects of adiponectin on lung transplantation, asthma, chronic obstructive pulmonary diseases (COPD), and pneumonia were anti-inflammatory and protective in lung injury. Administration of IL-10 agonist reduces mortality of acute lung injury in rabbits with acute necrotizing pancreatitis, possibly through inhibiting proinflammation and strengthening host immunity. Very limited information is available for other adipocytokines.

MicroRNAs are dynamically regulated and play an important role in LPS-induced lung injury

Acute lung injury is characterized by an increase of inflammatory reaction and severe lung edema. Even if there have been great advances in the identification of genes and signaling pathways involved in acute lung injury, the fundamental mechanisms of initiation and propagation of acute lung injury have not been understood completely. A growing amount of evidence indicates that microRNAs (miRNAs) are involved in various human diseases. However, the expression profile and function of miRNAs in acute lung injury have not been investigated. Here, using real-time polymerase chain reaction analysis, we show that a collection of miRNAs is dynamically regulated in lipopolysaccharide (LPS)-induced mouse acute lung injury. Among them, miR-199a and miR-16 are the most significantly down-regulated miRNAs. To study the role of miR-199a and miR-16 in acute lung injury, an over-expression of miR-199a or miR-16 assay was performed in LPS-treated A549 cells, and then the expression of inflammatory factors was analyzed. Over-expression of miR-199a could not alter the expression level of interleukin (IL)-6 and tumor necrosis factor-alpha (TNFα), while up-regulation of miR-16 could significantly down-regulate IL-6 and TNFα expression level. Using bioinformatic analysis, we show that a 3' untranslational region (UTR) of IL-6 and TNFα contains the binding sites of miR-16. Accordingly, over-expression of miR-16 could significantly suppress the luciferase activity of reporter fusion with the binding sites of TNFα in its 3'UTR region, suggesting that miR-16 played its role in LPS-induced lung inflammation by a direct manner. In this study, we show for the first time that miRNAs are dynamically regulated and play an important function in LPS-induced lung injury.

Adiponectin attenuates lipopolysaccharide-induced acute lung injury through suppression of endothelial cell activation

Adiponectin (APN) is an adipose tissue-derived factor with anti-inflammatory and vascular protective properties whose levels paradoxically decrease with increasing body fat. In this study, APN's role in the early development of ALI to LPS was investigated. Intratracheal LPS elicited an exaggerated systemic inflammatory response in APN-deficient (APN(-/-)) mice compared with wild-type (wt) littermates. Increased lung injury and inflammation were observed in APN(-/-) mice as early as 4 h after delivery of LPS. Targeted gene expression profiling performed on immune and endothelial cells isolated from lung digests 4 h after LPS administration showed increased proinflammatory gene expression (e.g., IL-6) only in endothelial cells of APN(-/-) mice when compared with wt mice. Direct effects on lung endothelium were demonstrated by APN's ability to inhibit LPS-induced IL-6 production in primary human endothelial cells in culture. Furthermore, T-cadherin-deficient mice that have significantly reduced lung airspace APN but high serum APN levels had pulmonary inflammatory responses after intratracheal LPS that were similar to those of wt mice. These findings indicate the importance of serum APN in modulating LPS-induced ALI and suggest that conditions leading to hypoadiponectinemia (e.g., obesity) predispose to development of ALI through exaggerated inflammatory response in pulmonary vascular endothelium.

Mortality of patients with respiratory insufficiency and adult respiratory distress syndrome after surgery: the obesity paradox

INTRODUCTION

Obesity has long been considered a risk factor for the development of various pathologies, yet evidence supporting increased risk of perioperative mortality in obese individuals developing postoperative complications is limited. Therefore, we sought to characterize the demographics of obese and nonobese individuals developing postoperative respiratory insufficiency (RI)/adult respiratory distress syndrome (ARDS) and to quantify the impact of obesity on in-hospital mortality among this patient population utilizing data collected for the Nationwide Inpatient Sample (NIS).

METHODS

Nationwide Inpatient Sample data for each year between 1998 and 2007 were accessed. Entries were included if they underwent a surgical procedure and had a diagnosis of RI/ARDS following surgery. Patients fulfilling entry criteria were divided into those with and without obesity. In-hospital mortality was the primary outcome. A logistic regression model was fitted to elucidate if obesity was associated with increased odds for the outcome while controlling for age, gender, admission and procedure type, and comorbidity burden.

RESULTS

We identified 9 149 030 admissions that underwent the included surgical procedures between 1998 and 2007. Of those, 5.48% had a diagnosis of obesity. The incidence of RI/ARDS was 1.82% among obese and 2.01% among nonobese patients. Obese patients whose postoperative course was complicated by RI/ARDS had a significantly lower incidence of the need for mechanical ventilation (50% vs 55%). In-hospital mortality was significantly lower compared to nonobese patients (5.45% vs 18.72%). For those patients with RI/ARDS requiring intubation, the in-hospital mortality rate was 11% for obese and 25% for nonobese patients. In the multivariate regression analysis, obesity was associated with a 69% reduction in the odds of in-hospital mortality in postoperative patients with RI/ARDS.

CONCLUSION

In our analysis, obesity was associated with a decreased incidence and adjusted odds for in-hospital mortality after surgery. Our results support the emerging concept of the "obesity paradox."