Plasma angiopoietin-2 predicts the onset of acute lung injury in critically ill patients

Treating the host response to emerging virus diseases: lessons learned from sepsis, pneumonia, influenza and Ebola

There is an ongoing threat of epidemic or pandemic diseases that could be caused by influenza, Ebola or other emerging viruses. It will be difficult and costly to develop new drugs that target each of these viruses. Statins and angiotensin receptor blockers (ARBs) have been effective in treating patients with sepsis, pneumonia and influenza, and a statin/ARB combination appeared to dramatically reduce mortality during the recent Ebola outbreak. These drugs target (among other things) the endothelial dysfunction found in all of these diseases. Most scientists work on new drugs that target viruses, and few accept the idea of treating the host response with generic drugs. A great deal of research will be needed to show conclusively that these drugs work, and this will require the support of public agencies and foundations. Investigators in developing countries should take an active role in this research. If the next Public Health Emergency of International Concern is caused by an emerging virus, a "top down" approach to developing specific new drug treatments is unlikely to be effective. However, a "bottom up" approach to treatment that targets the host response to these viruses by using widely available and inexpensive generic drugs could reduce mortality in any country with a basic health care system. In doing so, it would make an immeasurable contribution to global equity and global security.

Biotrauma and Ventilator-Induced Lung Injury: Clinical Implications

The pathophysiological mechanisms by which mechanical ventilation can contribute to lung injury, termed "ventilator-induced lung injury" (VILI), is increasingly well understood. "Biotrauma" describes the release of mediators by injurious ventilatory strategies, which can lead to lung and distal organ injury. Insights from preclinical models demonstrating that traditional high tidal volumes drove the inflammatory response helped lead to clinical trials demonstrating lower mortality in patients who underwent ventilation with a lower-tidal-volume strategy. Other approaches that minimize VILI, such as higher positive end-expiratory pressure, prone positioning, and neuromuscular blockade have each been demonstrated to decrease indices of activation of the inflammatory response. This review examines the evolution of our understanding of the mechanisms underlying VILI, particularly regarding biotrauma. We will assess evidence that ventilatory and other "adjunctive" strategies that decrease biotrauma offer great potential to minimize the adverse consequences of VILI and to improve the outcomes of patients with respiratory failure.

Association of markers of endothelial dysregulation Ang1 and Ang2 with acute kidney injury in critically ill patients

BACKGROUND

The role of endothelial dysregulation with acute kidney injury (AKI) in critically ill patients is unclear.

METHODS

We retrospectively assessed the associations of AKI with biomarkers of endothelial function and inflammation among 948 subjects admitted to the intensive care unit (ICU) at Harborview Medical Center (Seattle, WA, USA). From plasma obtained within 24 h of enrollment, we measured angiopoietin (Ang)-1 and Ang-2 alongside biomarkers of inflammation, including interleukin (IL)-6, IL-17 and granulocyte colony-stimulating factor. We tested for associations between standardized concentrations of biomarkers and AKI, defined by serum creatinine, from ICU admission to up to 7 days later.

RESULTS

All biomarkers of inflammation and endothelial dysfunction were associated with AKI. After adjustment for demographics, comorbidities, and IL-6 concentration, every standard deviation of Ang-1 concentration was associated with a 19 % lower risk of AKI (relative risk (RR) = 0.85, 95 % confidence interval (CI) 0.77-0.93, p < 0.001). Conversely, higher Ang-2 concentration was associated with higher risk of AKI (RR per standard deviation = 1.17, 95 % CI 1.13-1.22, p < 0.001).

CONCLUSIONS

In critically ill patients, plasma concentration of the endothelial growth factors Ang-1 and Ang-2 are associated with AKI, independently of inflammation.

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

PURPOSE

Angiopoietin 2 (Ang2) and soluble receptor for advanced glycation end products (sRAGE) are markers of endothelial and pulmonary epithelial damage with prognostic implications in adult acute respiratory distress syndrome (ARDS), but unclear significance in pediatric ARDS (PARDS).

METHODS

This was a prospective, observational study in children with PARDS (2012 Berlin and 2015 PALICC definitions) at the Children's Hospital of Philadelphia. Plasma was collected within 48 h of PARDS onset and biomarkers quantified by enzyme-linked immunosorbent assay.

RESULTS

In 82 children with PARDS (12 deaths, 15 %), Ang2 and sRAGE were higher in non-survivors than survivors (p < 0.01 for both). Mortality was highest in patients with Ang2 and sRAGE levels both above median values. Ang2 and sRAGE correlated with the number of non-pulmonary organ failures (both p < 0.001). Ang2 was higher in indirect lung injury and in immunocompromised children. In stratified analysis, both Ang2 and sRAGE were associated with mortality only in direct lung injury and in immunocompetent children, with no association evident in indirect lung injury or in immunocompromised children.

CONCLUSIONS

Ang2 and sRAGE in early PARDS were higher in non-survivors than survivors and strongly correlated with number of non-pulmonary organ failures. When stratified by type of lung injury, Ang2 and sRAGE were associated with mortality only in direct lung injury. Similarly, when stratified by immunocompromised status, Ang2 and sRAGE were associated with mortality only in immunocompetent children. The utility of these biomarkers for prognostication and risk stratification requires investigation.

Biomarkers in Pediatric ARDS: Future Directions

Acute respiratory distress syndrome (ARDS) is common among mechanically ventilated children and accompanies up to 30% of all pediatric intensive care unit deaths. Though ARDS diagnosis is based on clinical criteria, biological markers of acute lung damage have been extensively studied in adults and children. Biomarkers of inflammation, alveolar epithelial and capillary endothelial disruption, disordered coagulation, and associated derangements measured in the circulation and other body fluids, such as bronchoalveolar lavage, have improved our understanding of pathobiology of ARDS. The biochemical signature of ARDS has been increasingly well described in adult populations, and this has led to the identification of molecular phenotypes to augment clinical classifications. However, there is a paucity of data from pediatric ARDS (pARDS) patients. Biomarkers and molecular phenotypes have the potential to identify patients at high risk of poor outcomes, and perhaps inform the development of targeted therapies for specific groups of patients. Additionally, because of the lower incidence of and mortality from ARDS in pediatric patients relative to adults and lack of robust clinical predictors of outcome, there is an ongoing interest in biological markers as surrogate outcome measures. The recent definition of pARDS provides additional impetus for the measurement of established and novel biomarkers in future pediatric studies in order to further characterize this disease process. This chapter will review the currently available literature and discuss potential future directions for investigation into biomarkers in ARDS among children.

Could Biomarkers Direct Therapy for the Septic Patient?

Sepsis is a serious medical condition caused by a severe systemic inflammatory response to a bacterial, fungal, or viral infection that most commonly affects neonates and the elderly. Advances in understanding the pathophysiology of sepsis have resulted in guidelines for care that have helped reduce the risk of dying from sepsis for both children and older adults. Still, over the past three decades, a large number of clinical trials have been undertaken to evaluate pharmacological agents for sepsis. Unfortunately, all of these trials have failed, with the use of some agents even shown to be harmful. One key issue in these trials was the heterogeneity of the patient population that participated. What has emerged is the need to target therapeutic interventions to the specific patient's underlying pathophysiological processes, rather than looking for a universal therapy that would be effective in a "typical" septic patient, who does not exist. This review supports the concept that identification of the right biomarkers that can direct therapy and provide timely feedback on its effectiveness will enable critical care physicians to decrease mortality of patients with sepsis and improve the quality of life of survivors.

Proteomic study of acute respiratory distress syndrome: current knowledge and implications for drug development

The acute respiratory distress syndrome (ARDS) is a common cause of acute respiratory failure, and is associated with substantial mortality and morbidity. Dozens of clinical trials targeting ARDS have failed, with no drug specifically targeting lung injury in widespread clinical use. Thus, the need for drug development in ARDS is great. Targeted proteomic studies in ARDS have identified many key pathways in the disease, including inflammation, epithelial injury, endothelial injury or activation, and disordered coagulation and repair. Recent studies reveal the potential for proteomic changes to identify novel subphenotypes of ARDS patients who may be most likely to respond to therapy and could thus be targeted for enrollment in clinical trials. Nontargeted studies of proteomics in ARDS are just beginning and have the potential to identify novel drug targets and key pathways in the disease. Proteomics will play an important role in phenotyping of patients and developing novel therapies for ARDS in the future.

Personalized medicine for ARDS: the 2035 research agenda

In the last 20 years, survival among patients with acute respiratory distress syndrome (ARDS) has increased substantially with advances in lung-protective ventilation and resuscitation. Building on this success, personalizing mechanical ventilation to patient-specific physiology for enhanced lung protection will be a top research priority for the years ahead. However, the ARDS research agenda must be broader in scope. Further understanding of the heterogeneous biology, from molecular to mechanical, underlying early ARDS pathogenesis is essential to inform therapeutic discovery and tailor treatment and prevention strategies to the individual patient. The ARDSne(x)t research agenda for the next 20 years calls for bringing personalized medicine to ARDS, asking simultaneously both whether a treatment affords clinically meaningful benefit and for whom. This expanded scope necessitates standard acquisition of highly granular biological, physiological, and clinical data across studies to identify biologically distinct subgroups that may respond differently to a given intervention. Clinical trials will need to consider enrichment strategies and incorporate long-term functional outcomes. Tremendous investment in research infrastructure and global collaboration will be vital to fulfilling this agenda.

Serial inflammatory biomarkers of the severity, course and outcome of late onset acute respiratory distress syndrome in critically ill patients with or at risk for the syndrome after new-onset fever

AIM

Accurate biomarkers of the acute respiratory distress syndrome (ARDS) may help risk stratification and management. We assessed the relation between several biomarkers and the severity, course and outcome of late onset ARDS in 101 consecutive critically ill patients with new onset fever.

MATERIALS AND METHODS

On study days 0, 1, 2 and 7 we measured angiopoietin-2 (ANG2), pentraxin-3 (PTX3), interleukin-6 (IL-6), procalcitonin (PCT) and midregional proadrenomedullin (proADM). ARDS was defined by the Berlin definition and by the lung injury score (LIS).

RESULTS

At baseline, 48% had ARDS according to the Berlin definition and 86% according to the LIS. Baseline markers poorly predicted maximum Berlin categories attained within 7 days, whereas ANG2 best predicted maximum LIS. Depending on the ARDS definition, the day-by-day area under the receiver operating characteristic curves suggested greatest monitoring value for IL-6 and PCT, followed by ANG2. ANG2 and proADM predicted outcome, independently of disease severity.

CONCLUSION

Whereas IL-6 and PCT had some disease monitoring value, ANG2 was the only biomarker capable of both predicting the severity, monitoring the course and predicting the outcome of late onset ARDS in febrile critically ill patients, irrespective of underlying risk factor, thereby yielding the most specific ARDS biomarker among those studied.

Low Plasma Levels of Adiponectin Do Not Explain Acute Respiratory Distress Syndrome Risk: a Prospective Cohort Study of Patients with Severe Sepsis

BACKGROUND

Obesity is associated with the development of acute respiratory distress syndrome (ARDS) in at-risk patients. Low plasma levels of adiponectin, a circulating hormone-like molecule, have been implicated as a possible mechanism for this association. The objective of this study was to determine the association of plasma adiponectin level at ICU admission with ARDS and 30-day mortality in patients with severe sepsis and septic shock.

METHODS

This is a prospective cohort study of patients admitted to the medical ICU at the Hospital of the University of Pennsylvania. Plasma adiponectin was measured at the time of ICU admission. ARDS was defined by Berlin criteria. Multivariable logistic regression was used to determine the association of plasma adiponectin with the development of ARDS and mortality at 30 days.

RESULTS

The study included 164 patients. The incidence of ARDS within 5 days of admission was 45%. The median initial plasma adiponectin level was 7.62 mcg/ml (IQR: 3.87, 14.90) in those without ARDS compared to 8.93 mcg/ml (IQR: 4.60, 18.85) in those developing ARDS. The adjusted odds ratio for ARDS associated with each 5 mcg increase in adiponectin was 1.12 (95% CI 1.01, 1.25), p-value 0.025). A total of 82 patients (51%) of the cohort died within 30 days of ICU admission. There was a statistically significant association between adiponectin and mortality in the unadjusted model (OR 1.11, 95% CI 1.00, 1.23, p-value 0.04) that was no longer significant after adjusting for potential confounders.

CONCLUSIONS

In this study, low levels of adiponectin were not associated with an increased risk of ARDS in patients with severe sepsis and septic shock. This argues against low levels of adiponectin as a mechanism explaining the association of obesity with ARDS. At present, it is unclear whether circulating adiponectin is involved in the pathogenesis of ARDS or simply represents an epiphenomenon of other unknown functions of adipose tissue or metabolic alterations in sepsis.

A Pathophysiologic Approach to Biomarkers in Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is an acute-onset hypoxic condition with radiographic bilateral lung infiltration. It is characterized by an acute exudative phase combining diffuse alveolar damage and lung edema followed by a later fibroproliferative phase. Despite an improved understanding of ARDS pathobiology, our ability to predict the development of ARDS and risk-stratify patients with the disease remains limited. Biomarkers may help to identify patients at the highest risk of developing ARDS, assess response to therapy, predict outcome, and optimize enrollment in clinical trials. After a short description of ARDS pathobiology, here, we review the scientific evidence that supports the value of various ARDS biomarkers with regard to their major biological roles in ARDS-associated lung injury and/or repair. Ongoing research aims at identifying and characterizing novel biomarkers, in order to highlight relevant mechanistic explorations of lung injury and repair, and to ultimately develop innovative therapeutic approaches for ARDS patients. This review will focus on the pathophysiologic, diagnostic, and therapeutic implications of biomarkers in ARDS and on their utility to ultimately improve patient care.

Reverse kinetics of angiopoietin-2 and endotoxins in acute pyelonephritis: Implications for anti-inflammatory treatment?

Based on former studies showing an antagonism between angiopoietin-2 (Ang-2) and bacterial endotoxins (LPS), we investigated the role of Ang-2 as immunomodulatory treatment. At first, kinetics of circulating LPS in Gram-negative pyelonephritis developing after urinary obstruction was studied. Serum LPS, interleukin (IL)-6 and Ang-2 were measured in 25 patients with acute pyelonephritis and sepsis before and after removal of the obstruction performed either with insertion of a pigtail catheter (n=12) or percutaneous drainage (n=13). At a second stage, Ang-2 was given as anti-inflammatory treatment in 40 rabbits one hour after induction of acute pyelonephritis by ligation of the ureter at the level of pelvo-ureteral junction and upstream bacterial inoculation. Survival was recorded; blood mononuclear cells were isolated and stimulated for the production of tumour necrosis factor-alpha (TNFα). The decrease in circulating LPS was significantly greater among patients undergoing drainage than pigtail insertion. This was accompanied by reciprocal changes of Ang-2 and IL-6. Treatment with Ang-2 prolonged survival from Escherichia coli pyelonephritis despite high levels of circulating LPS. When Ang-2 was given as treatment of Pseudomonas aeruginosa pyelonephritis, sepsis-induced decrease of TNFα production by circulating mononuclear cells was reversed without an effect on tissue bacterial overgrowth. It is concluded that Ang-2 and LPS follow reverse kinetics in acute pyelonephritis. When given as experimental treatment, Ang-2 prolongs survival through an effect on mononuclear cells.

Plasma Biomarker Analysis in Pediatric ARDS: Generating Future Framework from a Pilot Randomized Control Trial of Methylprednisolone: A Framework for Identifying Plasma Biomarkers Related to Clinical Outcomes in Pediatric ARDS

OBJECTIVE

Lung injury activates multiple pro-inflammatory pathways, including neutrophils, epithelial, and endothelial injury, and coagulation factors leading to acute respiratory distress syndrome (ARDS). Low-dose methylprednisolone therapy (MPT) improved oxygenation and ventilation in early pediatric ARDS without altering duration of mechanical ventilation or mortality. We evaluated the effects of MPT on biomarkers of endothelial [Ang-2 and soluble intercellular adhesion molecule-1 (sICAM-1)] or epithelial [soluble receptor for activated glycation end products (sRAGE)] injury, neutrophil activation [matrix metalloproteinase-8 (MMP-8)], and coagulation (plasminogen activator inhibitor-1).

DESIGN

Double-blind, placebo-controlled randomized trial.

SETTING

Tertiary-care pediatric intensive care unit (ICU).

PATIENTS

Mechanically ventilated children (0-18 years) with early ARDS.

INTERVENTIONS

Blood samples were collected on days 0 (before MPT), 7, and 14 during low-dose MPT (n = 17) vs. placebo (n = 18) therapy. The MPT group received a 2-mg/kg loading dose followed by 1 mg/kg/day continuous infusions from days 1 to 7, tapered off over 7 days; placebo group received equivalent amounts of 0.9% saline. We analyzed plasma samples using a multiplex assay for five biomarkers of ARDS. Multiple regression models were constructed to predict associations between changes in biomarkers and the clinical outcomes reported earlier, including P/F ratio on days 8 and 9, plateau pressure on days 1 and 2, PaCO2 on days 2 and 3, racemic epinephrine following extubation, and supplemental oxygen at ICU discharge.

RESULTS

No differences occurred in biomarker concentrations between the groups on day 0. On day 7, reduction in MMP-8 levels (p = 0.0016) occurred in the MPT group, whereas increases in sICAM-1 levels (p = 0.0005) occurred in the placebo group (no increases in sICAM-1 in the MPT group). sRAGE levels decreased in both MPT and placebo groups (p < 0.0001) from day 0 to day 7. On day 7, sRAGE levels were positively correlated with MPT group PaO2/FiO2 ratios on day 8 (r = 0.93, p = 0.024). O2 requirements at ICU transfer positively correlated with day 7 MMP-8 (r = 0.85, p = 0.016) and Ang-2 levels (r = 0.79, p = 0.036) in the placebo group and inversely correlated with day 7 sICAM-1 levels (r = -0.91, p = 0.005) in the MPT group.

CONCLUSION

Biomarkers selected from endothelial, epithelial, or intravascular factors can be correlated with clinical endpoints in pediatric ARDS. For example, MPT could reduce neutrophil activation (⇓MMP-8), decrease endothelial injury (⇔sICAM-1), and allow epithelial recovery (⇓sRAGE). Large ARDS clinical trials should develop similar frameworks.

TRIAL REGISTRATION

https://clinicaltrials.gov, NCT01274260.

Plasma angiopoietin-2 outperforms other markers of endothelial injury in prognosticating pediatric ARDS mortality

Angiopoietin-2 (Ang-2) is a key mediator of pulmonary vascular permeability. This study tested the association between plasma Ang-2 and mortality in pediatric acute respiratory distress syndrome (ARDS), with stratification for prior hematopoietic cellular transplantation (HCT), given the severe, yet poorly understood, ARDS phenotype of this subgroup. We enrolled 259 children <18 years of age with ARDS; 25 had prior HCT. Plasma Ang-2, von Willebrand Factor antigen (vWF), and vascular endothelial growth factor (VEGF) were measured on ARDS days 1 and 3 and correlated with patient outcomes. Day 1 and day 3 Ang-2 levels were associated with mortality independent of age, sex, race, and P/F ratio [odds ratio (OR) 3.7, 95% CI 1.1-11.5, P = 0.027; and OR 10.2, 95% confidence interval (CI) 2.2-46.5, P = 0.003, for each log10 increase in Ang-2]. vWF was associated with mortality (P = 0.027), but VEGF was not. The association between day 1 Ang-2 and mortality was independent of levels of both vWF and VEGF (OR 3.6, 95% CI 1.1-12.1, P = 0.039, for each log10 increase in Ang-2). 45% of the cohort had a rising Ang-2 between ARDS day 1 and 3 (adjusted mortality OR 3.3, 95% CI 1.2-9.2, P = 0.026). HCT patients with a rising Ang-2 had 70% mortality compared with 13% mortality for those without (OR 16.3, 95% CI 1.3-197.8, P = 0.028). Elevated plasma levels of Ang-2 were associated with mortality independent of vWF and VEGF. A rising Ang-2 between days 1 and 3 was strongly associated with mortality, particularly in pediatric HCT patients, suggesting vulnerability to ongoing endothelial damage.

Post-operative pulmonary complications after non-cardiothoracic surgery

Post-operative pulmonary complications (PPCs) occur in 5–10% of patients undergoing non-thoracic surgery and in 22% of high risk patients. PPCs are broadly defined as conditions affecting the respiratory tract that can adversely influence clinical course of the patient after surgery. Prior risk stratification, risk reduction strategies, performing short duration and/or minimally invasive surgery and use of anaesthetic technique of combined regional with general anaesthesia can reduce the incidence of PPCs. Atelectasis is the main cause of PPCs. Atelectasis can be prevented or treated by adequate analgesia, incentive spirometry (IS), deep breathing exercises, continuous positive airway pressure, mobilisation of secretions and early ambulation. Pre-operative treatment of IS is more effective. The main reason for post-operative pneumonia is aspiration along the channels formed by longitudinal folds in the high volume, low pressure polyvinyl chloride cuffs of the endotracheal tubes. Use of tapered cuff, polyurethane cuffs and selective rather than the routine use of nasogastric tube can decrease chances of aspiration. Acute lung injury is the most serious PPC which may prove fatal.

A Randomized Dose-Escalation Study of the Safety and Anti-Inflammatory Activity of the p38 Mitogen-Activated Protein Kinase Inhibitor Dilmapimod in Severe Trauma Subjects at Risk for Acute Respiratory Distress Syndrome

OBJECTIVES

There are no current pharmacological therapies for the prevention or treatment of acute respiratory distress syndrome. Early dysregulated inflammation likely plays a role in acute respiratory distress syndrome development and possibly acute respiratory distress syndrome outcomes. p38 mitogen-activated protein kinase is central to the regulation of multiple inflammatory mediators implicated in acute organ dysfunction and is the target for a novel class of cytokine-suppressive anti-inflammatory drugs. In preclinical models, p38 inhibitors reduce lung injury following pancreatitis and burn injury.

DESIGN

We conducted a phase IIa, randomized, double-blind, placebo-controlled, parallel-group study to evaluate the safety and tolerability of dilmapimod, a novel p38 mitogen-activated protein kinase inhibitor, in patients at risk for developing acute respiratory distress syndrome admitted with an Injury Severity Score more than 16, excluding head trauma. Enrolled patients received 4- or 24-hour IV dilmapimod infusions at different doses or placebo, daily for 3 days, in four separate cohorts.

SETTING

Multicenter randomized clinical trial of large, academic trauma centers.

MEASUREMENTS AND MAIN RESULTS

Seventy-seven patients were enrolled. Although adverse events were common in this critically ill population, dilmapimod was well tolerated, with no clinically relevant safety findings. Pharmacokinetic models indicated that the higher dose of 10 mg given as continuous infusion over 24 hours had the most favorable plasma concentration profile. Likewise, measures of soluble inflammatory markers including interleukin-6, C-reactive peptide, interleukin-8, and soluble tumor necrosis factor receptor 1 were most different between this dosing arm and placebo. Although the study was not specifically designed with acute respiratory distress syndrome as an outcome, the number of patients who developed acute respiratory distress syndrome was small (2/77).

CONCLUSIONS

The novel p38 mitogen-activated protein kinase inhibitor dilmapimod appears well tolerated and may merit further evaluation for prevention of acute respiratory distress syndrome and other organ injury in larger clinical trials. Furthermore, results of this early-phase trial may aid in design of future studies aimed at prevention of acute respiratory distress syndrome and other organ injury.

Biomarkers of Endothelial Activation Are Associated with Poor Outcome in Critical Illness

Background

Endothelial activation plays a role in organ dysfunction in the systemic inflammatory response syndrome (SIRS). Angiopoietin-1 (Ang-1) promotes vascular quiescence while angiopoietin-2 (Ang-2) mediates microvascular leak. Circulating levels of Ang-1 and Ang-2 in patients with SIRS could provide insight on risks for organ dysfunction and death distinct from inflammatory proteins. In this study, we determined if biomarkers of endothelial activation and inflammation exhibit independent associations with poor outcomes in SIRS.

Methods

We studied 943 critically ill patients with SIRS admitted to an Intensive Care Unit (ICU) of an academic medical center. We measured plasma levels of endothelial markers (Ang-1, Ang-2, soluble vascular cell adhesion molecule-1 (sVCAM-1)) and inflammatory markers (interleukin-6 (IL-6), interleukin-8 (IL-8), granulocyte-colony stimulating factor (G-CSF), soluble tumor necrosis factor receptor-1 (sTNFR-1)) within 24 hours of enrollment. We tested for associations between each marker and 28 day mortality, shock, and day 3 sequential organ failure assessment (SOFA) score. For 28 day mortality, we performed sensitivity analysis for those subjects with sepsis and those with sterile inflammation. We used multivariate models to adjust for clinical covariates and determine if associations identified with endothelial activation markers were independent of those observed with inflammatory markers.

Results

Higher levels of all biomarkers were associated with increased 28 day mortality except levels of Ang-1 which were associated with lower mortality. After adjustment for comorbidities and sTNFR-1 concentration, a doubling of Ang-1 concentration was associated with lower 28 day mortality (Odds ratio (OR) = 0.81; p<0.01), shock (OR = 0.82; p<0.001), and SOFA score (β = -0.50; p<0.001), while Ang-2 concentration was associated with increased mortality (OR = 1.55; p<0.001), shock (OR = 1.51; p<0.001), and SOFA score (β = +0.63; p<0.001). sVCAM-1 was not independently associated with SIRS outcomes.

Conclusions

In critically ill patients with SIRS, early measurements of Ang-1 and Ang-2 are associated with death and organ dysfunction independently of simultaneously-measured markers of inflammation.

Bolus intravenous 0.9% saline, but not 4% albumin or 5% glucose, causes interstitial pulmonary edema in healthy subjects

Rapid intravenous (iv) infusion of 0.9% saline alters respiratory mechanics in healthy subjects. However, the relative cardiovascular and respiratory effects of bolus iv crystalloid vs. colloid are unknown. Six healthy male volunteers were given 30 ml/kg iv 0.9% saline, 4% albumin, and 5% glucose at a rate of 100 ml/min on 3 separate days in a double-blinded, randomized crossover study. Impulse oscillometry, spirometry, lung volumes, diffusing capacity (DLCO), and blood samples were measured before and after fluid administration. Lung ultrasound B-line score (indicating interstitial pulmonary edema) and Doppler echocardiography indices of cardiac preload were measured before, midway, immediately after, and 1 h after fluid administration. Infusion of 0.9% saline increased small airway resistance at 5 Hz (P = 0.04) and lung ultrasound B-line score (P = 0.01) without changes in Doppler echocardiography measures of preload. In contrast, 4% albumin increased DLCO, decreased lung volumes, and increased the Doppler echocardiography mitral E velocity (P = 0.001) and E-to-lateral/septal e' ratio, estimated blood volume, and N-terminal pro B-type natriuretic peptide (P = 0.01) but not lung ultrasound B-line score, consistent with increased pulmonary blood volume without interstitial pulmonary edema. There were no significant changes with 5% glucose. Plasma angiopoietin-2 concentration increased only after 0.9% saline (P = 0.001), suggesting an inflammatory mechanism associated with edema formation. In healthy subjects, 0.9% saline and 4% albumin have differential pulmonary effects not attributable to passive fluid filtration. This may reflect either different effects of these fluids on active signaling in the pulmonary circulation or a protective effect of albumin.

Targeting normoxemia in acute respiratory distress syndrome may cause worse short-term outcomes because of oxygen toxicity

It was suggested that targeting normoxemia (PaO2 85-110 mm Hg) in patients with acute respiratory distress syndrome (ARDS) might prevent neurocognitive dysfunction in survivors. However, targeting normoxemia may cause detrimental effects to the lungs from oxygen toxicity. Some have suggested that oxygen is not harmful to the lungs at FiO2 (fraction of inspired oxygen) levels less than 0.6-0.7, but contrasting evidence in normal humans suggests that there can be untoward effects of moderate FiO2 levels. Furthermore, in experimental models of the acute respiratory distress syndrome, coexisting lung inflammation increases susceptibility to oxygen toxicity. Coexisting lung inflammation may lower the threshold for oxygen toxicity in patients with ARDS or in other acute illnesses in the lung. Moreover, physicians frequently prescribe higher FiO2 levels than are necessary to achieve their arterial oxygenation goal, further increasing the risk of oxygen toxicity. Targeting normoxemia in patients with ARDS may prevent some long-term neurocognitive deficits in survivors, but it may increase lung inflammation and cause worse short-term clinical outcomes. We advocate for a clinical trial in patients with ARDS to determine more appropriate goals for arterial oxygenation.

Host response biomarkers in the diagnosis of sepsis: a general overview

Critically ill patients who display a systemic inflammatory response syndrome (SIRS) are prone to develop nosocomial infections. The challenge remains to distinguish as early as possible among SIRS patients those who are developing sepsis. Following a sterile insult, damage-associated molecular patterns (DAMPs) released by damaged tissues and necrotic cells initiate an inflammatory response close to that observed during sepsis. During sepsis, pathogen-associated molecular patterns (PAMPs) trigger the release of host mediators involved in innate immunity and inflammation through identical receptors as DAMPs. In both clinical settings, a compensatory anti-inflammatory response syndrome (CARS) is concomitantly initiated. The exacerbated production of pro- or anti-inflammatory mediators allows their detection in biological fluids and particularly within the bloodstream. Some of these mediators can be used as biomarkers to decipher among the patients those who developed sepsis, and eventually they can be used as prognosis markers. In addition to plasma biomarkers, the analysis of some surface markers on circulating leukocytes or the study of mRNA and miRNA can be helpful. While there is no magic marker, a combination of few biomarkers might offer a high accuracy for diagnosis.

Pathobiology of acute respiratory distress syndrome

The unique characteristics of pulmonary circulation and alveolar-epithelial capillary-endothelial barrier allow for maintenance of the air-filled, fluid-free status of the alveoli essential for facilitating gas exchange, maintaining alveolar stability, and defending the lung against inhaled pathogens. The hallmark of pathophysiology in acute respiratory distress syndrome is the loss of the alveolar capillary permeability barrier and the presence of protein-rich edema fluid in the alveoli. This alteration in permeability and accumulation of fluid in the alveoli accompanies damage to the lung epithelium and vascular endothelium along with dysregulated inflammation and inappropriate activity of leukocytes and platelets. In addition, there is uncontrolled activation of coagulation along with suppression of fibrinolysis and loss of surfactant. These pathophysiological changes result in the clinical manifestations of acute respiratory distress syndrome, which include hypoxemia, radiographic opacities, decreased functional residual capacity, increased physiologic deadspace, and decreased lung compliance. Resolution of acute respiratory distress syndrome involves the migration of cells to the site of injury and re-establishment of the epithelium and endothelium with or without the development of fibrosis. Most of the data related to acute respiratory distress syndrome, however, originate from studies in adults or in mature animals with very few studies performed in children or juvenile animals. The lack of studies in children is particularly problematic because the lungs and immune system are still developing during childhood and consequently the pathophysiology of pediatric acute respiratory distress syndrome may differ in significant ways from that seen in acute respiratory distress syndrome in adults. This article describes what is known of the pathophysiologic processes of pediatric acute respiratory distress syndrome as we know it today while also presenting the much greater body of evidence on these processes as elucidated by adult and animal studies. It is also our expressed intent to generate enthusiasm for larger and more in-depth investigations of the mechanisms of disease and repair specific to children in the years to come.

Microvascular obstruction and endothelial activation are independently associated with the clinical manifestations of severe falciparum malaria in adults: an observational study

BACKGROUND

Microvascular obstruction and endothelial dysfunction have both been linked to tissue hypoperfusion in falciparum malaria, but their relative contributions to the disease's pathogenesis and outcome are unknown.

METHODS

Microvascular blood flow was quantified in adults with severe falciparum malaria on their admission to hospital; plasma biomarkers of endothelial function were measured simultaneously. The relationship between these indices and the patients' clinical findings and in-hospital course was examined.

RESULTS

Microvascular obstruction was observed in 119/142 (84 %) patients; a median (interquartile range (IQR)) of 14.9 % (6.6-34.9 %) of capillaries were obstructed in patients that died versus 8.3 % (1.7-26.6 %) in survivors (P = 0.039). The proportion of obstructed capillaries correlated with the estimated parasite biomass (rs = 0.25, P = 0.004) and with plasma lactate (rs = 0.38, P <0.0001), the strongest predictor of death in the series. Plasma angiopoietin-2 (Ang-2) concentrations were markedly elevated suggesting widespread endothelial activation; the median (IQR) Ang-2 concentration was 21.9 ng/mL (13.4-29.4 ng/mL) in patients that died versus 14.9 ng/mL (9.8-29.3 ng/mL) in survivors (P = 0.035). Ang-2 concentrations correlated with estimated parasite biomass (rs = 0.35, P <0.001) and plasma lactate (rs = 0.37, P <0.0001). Microvascular obstruction and Ang-2 concentrations were not significantly correlated with each other (rs = 0.17, P = 0.06), but were independently associated with plasma lactate (P <0.001 and P = 0.002, respectively).

CONCLUSIONS

Microvascular obstruction and systemic endothelial activation are independently associated with plasma lactate, the strongest predictor of death in adults with falciparum malaria. This supports the hypothesis that the two processes make an independent contribution to the pathogenesis and clinical manifestations of the disease.

Extravascular lung water and pulmonary vascular permeability index as markers predictive of postoperative acute respiratory distress syndrome: a prospective cohort investigation

OBJECTIVE

Robust markers of subclinical perioperative lung injury are lacking. Extravascular lung water indexed to predicted body weight and pulmonary vascular permeability index are two promising early markers of lung edema. We aimed to evaluate whether extravascular lung water indexed to predicted body weight and pulmonary vascular permeability index would identify patients at risk for clinically significant postoperative pulmonary edema, particularly resulting from the acute respiratory distress syndrome.

DESIGN

Prospective cohort study.

SETTING

Tertiary care academic medical center.

PATIENTS

Adults undergoing high-risk cardiac or aortic vascular surgery (or both) with risk of acute respiratory distress syndrome.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Extravascular lung water indexed to predicted body weight and pulmonary vascular permeability index measurements were obtained intraoperatively and in the early postoperative period. We assessed the accuracy of peak extravascular lung water indexed to predicted body weight and pulmonary vascular permeability index as predictive markers of clinically significant pulmonary edema (defined as acute respiratory distress syndrome or cardiogenic pulmonary edema) using area under the receiver-operating characteristic curves. Associations between extravascular lung water indexed to predicted body weight and pulmonary vascular permeability patient-important with important outcomes were assessed. Of 150 eligible patients, 132 patients (88%) had extravascular lung water indexed to predicted body weight and pulmonary vascular permeability index measurements. Of these, 13 patients (9.8%) had postoperative acute respiratory distress syndrome and 15 patients (11.4%) had cardiogenic pulmonary edema. Extravascular lung water indexed to predicted body weight effectively predicted development of clinically significant pulmonary edema (area under the receiver-operating characteristic curve, 0.79; 95% CI, 0.70-0.89). Pulmonary vascular permeability index discriminated acute respiratory distress syndrome from cardiogenic pulmonary edema alone or no edema (area under the receiver-operating characteristic curve, 0.77; 95% CI, 0.62-0.93). Extravascular lung water indexed to predicted body weight was associated with the worst postoperative PaO2/FIO2, duration of mechanical ventilation, ICU stay, and hospital stay. Peak values for extravascular lung water indexed to predicted body weight and pulmonary vascular permeability index were obtained within 2 hours of the primary intraoperative insult for the majority of patients (> 80%).

CONCLUSIONS

Perioperative extravascular lung water indexed to predicted body weight is an early marker that predicts risk of clinically significant postoperative pulmonary edema in at-risk surgical patients. Pulmonary vascular permeability index effectively discriminated postoperative acute respiratory distress syndrome from cardiogenic pulmonary edema. These measures will aid in the early detection of subclinical lung injury in at-risk surgical populations.

Increased expression of neutrophil-related genes in patients with early sepsis-induced ARDS

The early sequence of events leading to the development of the acute respiratory distress syndrome (ARDS) in patients with sepsis remains inadequately understood. The purpose of this study was to identify changes in gene expression early in the course of illness, when mechanisms of injury may provide the most relevant treatment and prognostic targets. We collected whole blood RNA in critically ill patients admitted from the Emergency Department to the intensive care unit within 24 h of admission at a tertiary care center. Whole genome expression was compared in patients with sepsis and ARDS to patients with sepsis alone. We selected genes with >1 log2 fold change and false discovery rate <0.25, determined their significance in the literature, and performed pathway analysis. Several genes were upregulated in 29 patients with sepsis with ARDS compared with 28 patients with sepsis alone. The most differentially expressed genes included key mediators of the initial neutrophil response to infection: olfactomedin 4, lipocalin 2, CD24, and bactericidal/permeability-increasing protein. These gene expression differences withstood adjustment for age, sex, study batch, white blood cell count, and presence of pneumonia or aspiration. Pathway analysis demonstrated overrepresentation of genes involved in known respiratory and infection pathways. These data indicate that several neutrophil-related pathways may be involved in the early pathogenesis of sepsis-related ARDS. In addition, identifiable gene expression differences occurring early in the course of sepsis-related ARDS may further elucidate understanding of the neutrophil-related mechanisms in progression to ARDS.

Evaluation of endothelial biomarkers as predictors of organ failures in septic shock patients

BACKGROUND

Endothelial injury is recognized to trigger organ failures during the first 48h of septic shock. We evaluate endothelial biomarkers at ICU admission in their ability to predict severity, outcome, and organ failures in septic shock patients.

METHODS

This prospective observational pilot study was conducted in a medical intensive care unit of a university hospital. Plasma levels of endothelial biomarkers as angiopoietin-2, sE-selectin or endocan were measured at ICU admission of 20 patients presenting with septic shock. Clinical and biological data were recorded at inclusion and each day during the first week.

RESULTS

Significant correlations were found between angiopoietin-2 and severity scores at Day 1: SAPS2 (r(2)=0.620; p=0.004) and LOD score (r(2)=0.681; p=0.001). The angiopoietin-2 level was significantly higher in patients presenting with organ failure such as hemodynamic, renal or hepatic failure. It correlated with catecholamine infusion dose and was higher in non survivors compared with survivors (33.5 [28.9-51.4] vs. 12.4 [6.4-14.7]ng/ml; p=0.001). In contrast, in that population presenting with septic shock, endocan level at inclusion was not related to any organ failure at inclusion or Day 1 but appeared lower in patients presenting with respiratory failure at Day 3 compared to those who do not (1.9 [0.99-3.1] vs 5.2 [3.1-17.2]ng/ml; p=0.032). The endocan level at inclusion was correlated with the decrease in PaO2/FiO2 ratio at Day 2 (r(2)=0.628; p=0.0004) and Day 3 (r(2)=0.645; p=0.005). Endocan level <2.54ng/ml at admission is predictive of a respiratory failure presence at Day 3.

CONCLUSION

In septic shock patients, angiopoietine-2 is related with clinical severity during the first 24h but only endocan is able to predict the presence of respiratory failure at Day 3.

Plasma angiopoietin 2 concentrations are related to impaired lung function and organ failure in a clinical cohort receiving high-dose interleukin 2 therapy

INTRODUCTION

The pathophysiology and therapeutic options in sepsis-induced lung injury remain elusive. High-dose interleukin 2 therapy (HDIL-2) is an important protocol for advanced malignancies but is limited by systemic inflammation and pulmonary edema that is indistinguishable from sepsis. In preclinical models, IL-2 stimulates angiopoietin 2 (AngP-2) secretion, which increases endothelial permeability and causes pulmonary edema. However, these relationships have not been fully elucidated in humans. Furthermore, the relevance of plasma AngP-2 to organ function is not clear. We hypothesized that plasma AngP-2 concentrations increase during HDIL-2 and are relevant to clinical pathophysiology.

METHODS

We enrolled 13 subjects with metastatic melanoma or renal cell carcinoma admitted to receive HDIL-2 and collected blood and spirometry data daily. The plasma concentrations of AngP-2 and IL-6 were measured with enzyme-linked immunosorbent assay.

RESULTS

At baseline, the mean AngP-2 concentration was 2.5 (SD, 1.0) ng/mL. Angiopoietin 2 concentrations increased during treatment: the mean concentration on the penultimate day was 16.0 (SD, 4.5) ng/mL and increased further to 18.6 (SD, 4.9) ng/mL (P < 0.05 vs. penultimate) during the last day of therapy. The forced expiratory volume in 1 s decreased during treatment. Interestingly, plasma AngP-2 concentrations correlated negatively with forced expiratory volume in 1 s (Spearman r = -0.78, P < 0.0001). Plasma AngP-2 concentrations also correlated with plasma IL-6 concentrations (r = 0.61, P < 0.0001) and Sequential Organ Failure Assessment scores (r = 0.68, P < 0.0001).

CONCLUSIONS

Plasma AngP-2 concentrations increase during HDIL-2 administration and correlate with pulmonary dysfunction. High-dose IL-2 may serve as a clinical model of sepsis and acute lung injury. Further investigation is warranted.

Cytokines and clinical predictors in distinguishing pulmonary transfusion reactions

BACKGROUND

Pulmonary transfusion reactions are important complications of blood transfusion, yet differentiating these clinical syndromes is diagnostically challenging. We hypothesized that biologic markers of inflammation could be used in conjunction with clinical predictors to distinguish transfusion-related acute lung injury (TRALI), transfusion-associated circulatory overload (TACO), and possible TRALI.

STUDY DESIGN AND METHODS

In a nested case-control study performed at the University of California at San Francisco and Mayo Clinic, Rochester, we evaluated clinical data and blood samples drawn before and after transfusion in patients with TRALI (n = 70), possible TRALI (n = 48), TACO (n = 29), and controls (n = 147). Cytokines measured included granulocyte-macrophage-colony-stimulating factor, interleukin (IL)-6, IL-8, IL-10, and tumor necrosis factor-α. Logistic regression and receiver operating characteristics curve analyses were used to determine the accuracy of clinical predictors and laboratory markers in differentiating TACO, TRALI, and possible TRALI.

RESULTS

Before and after transfusion, IL-6 and IL-8 were elevated in patients with TRALI and possible TRALI relative to controls, and IL-10 was elevated in patients with TACO and possible TRALI relative to that of TRALI and controls. For all pulmonary transfusion reactions, the combination of clinical variables and cytokine measurements displayed optimal diagnostic performance, and the model comparing TACO and TRALI correctly classified 92% of cases relative to expert panel diagnoses.

CONCLUSIONS

Before transfusion, there is evidence of systemic inflammation in patients who develop TRALI and possible TRALI but not TACO. A predictive model incorporating readily available clinical and cytokine data effectively differentiated transfusion-related respiratory complications such as TRALI and TACO.

Heterogeneous phenotypes of acute respiratory distress syndrome after major trauma

RATIONALE

Acute respiratory distress syndrome (ARDS) is a heterogeneous syndrome that can develop at various times after major trauma.

OBJECTIVES

To identify and characterize distinct phenotypes of ARDS after trauma, based on timing of syndrome onset.

METHODS

Latent class analyses were used to identify patterns of ARDS onset in a cohort of critically ill trauma patients. Identified patterns were tested for associations with known ARDS risk factors and associations were externally validated at a separate institution. Eleven plasma biomarkers representing pathophysiologic domains were compared between identified patterns in the validation cohort.

MEASUREMENTS AND MAIN RESULTS

Three patterns of ARDS were identified; class I (52%) early onset on Day 1 or 2, class II (40%) onset on Days 3 and 4, and class III (8%) later onset on Days 4 and 5. Early-onset ARDS was associated with higher Abbreviated Injury Scale scores for the thorax (P < 0.001), lower lowest systolic blood pressure before intensive care unit admission (P = 0.003), and a greater red blood cell transfusion requirement during resuscitation (P = 0.030). In the external validation cohort, early-onset ARDS was also associated with a higher Abbreviated Injury Scale score for the thorax (P = 0.001) and a lower lowest systolic blood pressure before intensive care unit enrollment (P = 0.006). In addition, the early-onset phenotype demonstrated higher plasma levels of soluble receptor for advanced glycation end-products and angiopoietin-2.

CONCLUSIONS

Degree of hemorrhagic shock and severity of thoracic trauma are associated with an early-onset phenotype of ARDS after major trauma. Lung injury biomarkers suggest a dominant alveolar-capillary barrier injury pattern in this phenotype.

Preventing ARDS: progress, promise, and pitfalls

Advances in critical care practice have led to a substantial decline in the incidence of ARDS over the past several years. Low tidal volume ventilation, timely resuscitation and antimicrobial administration, restrictive transfusion practices, and primary prevention of aspiration and nosocomial pneumonia have likely contributed to this reduction. Despite decades of research, there is no proven pharmacologic treatment of ARDS, and mortality from ARDS remains high. Consequently, recent initiatives have broadened the scope of lung injury research to include targeted prevention of ARDS. Prediction scores have been developed to identify patients at risk for ARDS, and clinical trials testing aspirin and inhaled budesonide/formoterol for ARDS prevention are ongoing. Future trials aimed at preventing ARDS face several key challenges. ARDS has not been validated as an end point for pivotal clinical trials, and caution is needed when testing toxic therapies that may prevent ARDS yet potentially increase mortality.

Biomarkers in acute respiratory distress syndrome

PURPOSE OF REVIEW

The article provides an overview of efforts to identify and validate biomarkers in acute respiratory distress syndrome (ARDS) and a discussion of the challenges confronting researchers in this area.

RECENT FINDINGS

Although various putative biomarkers have been investigated in ARDS, the data have been largely disappointing and the 'troponin' of ARDS remains elusive. Establishing a relationship between measurable biological processes and clinical outcomes is vital to advancing clinical trials in ARDS and expanding our arsenal of treatments for this complex syndrome.

SUMMARY

This article summarizes the current status of ARDS biomarker research and provides a framework for future investigation.

Approach to the patient with the acute respiratory distress syndrome

Given the high incidence and mortality of acute respiratory distress syndrome (ARDS) in critically ill patients, every practitioner needs a bedside approach both for early identification of patients at risk for ARDS and for the appropriate evaluation of patients who meet the diagnostic criteria of ARDS. Recent advances such as the Lung Injury Prediction score, the Early Acute Lung Injury score, and validation of the SpO(2)/Fio(2) ratio for assessing the degree of hypoxemia are all practical tools to aid the practitioner in caring for patients at risk of ARDS.

Prevalence and impact of active and passive cigarette smoking in acute respiratory distress syndrome

OBJECTIVES

Cigarette smoke exposure has recently been found to be associated with increased susceptibility to trauma- and transfusion-associated acute respiratory distress syndrome. We sought to determine 1) the incidence of cigarette smoke exposure in a diverse multicenter sample of acute respiratory distress syndrome patients and 2) whether cigarette smoke exposure is associated with severity of lung injury and mortality in acute respiratory distress syndrome.

DESIGN

Analysis of the Albuterol for the Treatment of Acute Lung Injury and Omega Acute Respiratory Distress Syndrome Network studies.

SETTING

Acute Respiratory Distress Syndrome Network hospitals.

PATIENTS

Three hundred eighty-one patients with acute respiratory distress syndrome.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol, a validated tobacco-specific marker, was measured in urine samples from subjects enrolled in two National Heart, Lung, and Blood Institute Acute Respiratory Distress Syndrome Network randomized controlled trials. Urine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol levels were consistent with active smoking in 36% of acute respiratory distress syndrome patients and with passive smoking in 41% of nonsmokers (vs 20% and 40% in general population, respectively). Patients with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol levels in the active smoking range were younger and had a higher incidence of alcohol misuse, fewer comorbidities, lower severity of illness, and less septic shock at enrollment compared with patients with undetectable 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol levels. Despite this lower severity of illness, the severity of lung injury did not significantly differ based on biomarker-determined smoking status. Cigarette smoke exposure was not significantly associated with death after adjusting for differences in age, alcohol use, comorbidities, and severity of illness.

CONCLUSIONS

In this first multicenter study of biomarker-determined cigarette smoke exposure in acute respiratory distress syndrome patients, we found that active cigarette smoke exposure was significantly more prevalent among acute respiratory distress syndrome patients compared to population averages. Despite their younger age, better overall health, and lower severity of illness, smokers by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol had similar severity of lung injury as patients with undetectable 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol. These findings suggest that active cigarette smoking may increase susceptibility to acute respiratory distress syndrome in younger, healthier patients.

Endocan levels in peripheral blood predict outcomes of acute respiratory distress syndrome

PURPOSE

To investigate the prognostic significance of endocan, compared with procalcitonin (PCT), C-reactive protein (CRP),white blood cells (WBC), neutrophils (N), and clinical severity scores in patients with ARDS.

METHODS

A total of 42 patients with ARDS were initially enrolled, and there were 20 nonsurvivors and 22 survivors based on hospital mortality. Plasma levels of biomarkers were measured and the acute physiology and chronic health evaluation II (APACHE II) was calculated on day 1 after the patient met the defining criteria of ARDS.

RESULTS

Endocan levels significantly correlated with the APACHE II score in the ARDS group (r = 0.676, P = 0.000, n = 42). Of 42 individuals with ARDS, 20 were dead, and endocan was significantly higher in nonsurvivors than in survivors (median (IQR) 5.01 (2.98-8.44) versus 3.01 (2.36-4.36) ng/mL, P = 0.017). According to the results of the ROC-curve analysis and COX proportional hazards models, endocan can predict mortality of ARDS independently with a hazard ratio of 1.374 (95% CI, 1.150-1.641) and an area of receiver operator characteristic curve (AUROC) of 0.715 (P = 0.017). Moreover, endocan can predict the multiple-organ dysfunction of ARDS.

CONCLUSION

Endocan is a promising biomarker to predict the disease severity and mortality in patients with ARDS.

Elevated levels of angiopoietin-2 as a biomarker for respiratory failure after cardiac surgery

OBJECTIVES

Angiopoietin-1 and angiopoietin-2 are important factors in regulating endothelial vascular permeability. This study evaluated perioperative changes in serum levels of angiopoietin-1 and -2 in patients undergoing cardiac surgery.

DESIGN

Measurement of serum levels of angiopoietin-1 and angiopoietin-2 in samples collected during a previously conducted prospective, multicenter, observational study.

SETTING

Three university hospitals.

PARTICIPANTS

Eighty-four adult patients undergoing cardiac surgery.

INTERVENTION

Serum levels of angiopoietins were measured at baseline, immediately after surgery, and the day after surgery (POD-1).

MEASUREMENTS AND MAIN RESULTS

Serum levels of angiopoietin-2 were elevated by POD-1 (median 3.3 ng/mL, interquartile range [IQR] 2.5-4.6 ng/mL) compared with baseline (median 1.6 ng/mL, IQR 1.3-2.1 ng/mL, p < 0.0001), and angiopoietin-1 levels were decreased immediately after surgery (baseline median 23.2 ng/mL, IQR 10.2-32.8 ng/mL; postoperative median 8.0 ng/mL, IQR 1.5-13.2 ng/mL, p<0.0001). Angiopoietin-2 levels on POD-1 in patients undergoing off-pump coronary artery bypass grafting were significantly lower than those in patients undergoing aortic surgery (p = 0.0009) and valve surgery (p = 0.008). Angiopoietin-2 levels on POD-1 had a predictive performance of the area under the curve (AUC) of the receiver operating characteristic curve 0.74 for mechanical ventilation>3 days. Angiopoietin-1 levels and the angiopoietin-2/angiopoietin-1 ratio showed lower predictive performance (AUC values 0.58 and 0.68, respectively).

CONCLUSIONS

Angiopoietin-2 serum levels were elevated after cardiac surgery. Elevated angiopoietin-2 had a good predictive performance for respiratory failure after cardiac surgery, perhaps reflecting the severity of lung dysfunction related to postoperative increases in vascular permeability.

Obstructive sleep apnea, obesity, and the development of acute respiratory distress syndrome

BACKGROUND

Obstructive sleep apnea (OSA) may increase the risk of respiratory complications and acute respiratory distress syndrome (ARDS) among surgical patients. OSA is more prevalent among obese individuals; obesity can predispose to ARDS.

HYPOTHESIS

It is unclear whether OSA independently contributes towards the risk of ARDS among hospitalized patients.

METHODS

This is a pre-planned retrospective subgroup analysis of the prospectively identified cohort of 5,584 patients across 22 hospitals with at least one risk factor for ARDS at the time of hospitalization from a trial by the US Critical Illness and Injury Trials Group designed to validate the Lung Injury Prediction Score. A total of 252 patients (4.5%) had a diagnosis of OSA at the time of hospitalization; of those, 66% were obese. Following multivariate adjustment in the logistic regression model, there was no significant relationship between OSA and development of ARDS (OR = 0.65, 95%CI = 0.32-1.22). However, body mass index (BMI) was associated with subsequent ARDS development (OR = 1.02, 95%CI = 1.00-1.04, p = 0.03). Neither OSA nor BMI affected mechanical ventilation requirement or mortality.

CONCLUSIONS

Prior diagnosis of OSA did not independently affect development of ARDS among patients with at least one predisposing condition, nor the need for mechanical ventilation or hospital mortality. Obesity appeared to independently increase the risk of ARDS.

Intravascular immunity as a key to systemic vasculitis: a work in progress, gaining momentum

Vascular inflammation contributes to the defence against invading microbes and to the repair of injured tissues. In most cases it resolves before becoming apparent. Vasculitis comprises heterogeneous clinical entities that are characterized by the persistence of vascular inflammation after it has served its homeostatic function. Most underlying mechanisms have so far remained elusive. Intravascular immunity refers to the surveillance of the vasculature by leucocytes that sense microbial or sterile threats to vessel integrity and initiate protective responses that entail most events that determine the clinical manifestations of vasculitis, such as end-organ ischaemia, neutrophil extracellular traps generation and thrombosis, leucocyte extravasation and degranulation. Understanding how the resolution of vascular inflammation goes awry in patients with systemic vasculitis will facilitate the identification of novel pharmacological targets and bring us a step closer in each patient to the selection of more effective and less toxic treatments.

The epidemiology of acute respiratory distress syndrome in patients presenting to the emergency department with severe sepsis

BACKGROUND

Acute respiratory distress syndrome (ARDS) is a serious complication of sepsis, and sepsis-associated ARDS is associated with significant morbidity and mortality. To date, no study has directly examined the epidemiology of ARDS in severe sepsis from the earliest presentation to the health care system, the emergency department (ED).

METHODS

This was a single-center retrospective, observational cohort study of 778 adults with severe sepsis presenting to the ED. The primary outcome was the development of ARDS requiring mechanical ventilation during the first 5 hospital days. Acute respiratory distress syndrome was defined using the Berlin definition. We used multivariable logistic regression to identify risk factors associated independently with ARDS development.

RESULTS

The incidence of ARDS was 6.2% (48/778 patients) in the entire cohort. Acute respiratory distress syndrome development varied across the continuum of care: 0.9% of patients fulfilled criteria for ARDS in the ED, 1.4% admitted to the ward developed ARDS, and 8.9% admitted to the intensive care unit developed ARDS. Acute respiratory distress syndrome developed a median of 1 day after admission and was associated with a 4-fold higher risk of in-hospital mortality (14% vs. 60%, P < 0.001). Independent risk factors associated with increased risk of ARDS development included intermediate (2-3.9 mmol/L) (P = 0.04) and high (≥4) serum lactate levels (P = 0.008), Lung Injury Prediction score (P < 0.001), and microbiologically proven infection (P = 0.01).

CONCLUSIONS

In patients presenting to the ED with severe sepsis, the rate of sepsis-associated ARDS development varied across the continuum of care. Acute respiratory distress syndrome developed rapidly and was associated with significant mortality. Elevated serum lactate levels in the ED and a recently validated clinical prediction score were independently associated with the development of ARDS in severe sepsis.

Applying metabolomics to uncover novel biology in ARDS

A better understanding of the pathogenesis and the resolution of the acute respiratory distress syndrome (ARDS) is needed. Although some progress has been made with the use of protein biomarkers and candidate gene studies in understanding the pathobiology of ARDS, we propose that new studies that measure the chemical breakdown products of cellular metabolism (metabolomics) may provide new insights into ARDS, in part because metabolomics targets a later point in the genomics cascade than is possible with studies of DNA, RNA, and protein biomarkers. Technological advances have made large-scale metabolomic profiling increasingly feasible. Metabolomic approaches have already achieved novel insights in nonpulmonary diseases such as diabetes mellitus and malignancy, as well as in sepsis, a major risk factor for developing ARDS. Metabolomic profiling is a promising approach to identify novel pathways in both patients at risk for developing ARDS as well as in the early phase of established ARDS.

Subphenotypes in acute respiratory distress syndrome: latent class analysis of data from two randomised controlled trials

BACKGROUND

Subphenotypes have been identified within heterogeneous diseases such as asthma and breast cancer, with important therapeutic implications. We assessed whether subphenotypes exist within acute respiratory distress syndrome (ARDS), another heterogeneous disorder.

METHODS

We used data from two ARDS randomised controlled trials (ARMA trial and ALVEOLI trial), sponsored by the National Heart, Lung, and Blood Institute. We applied latent class modelling to identify subphenotypes using clinical and biological data. We modelled data from both studies independently. We then tested the association of subphenotypes with clinical outcomes in both cohorts and with the response to positive end-expiratory pressure (PEEP) in the ALVEOLI cohort.

FINDINGS

We analysed data for 1022 patients: 473 in the ARMA cohort and 549 in the ALVEOLI cohort. Independent latent class models indicated that a two-class (ie, two subphenotype) model was the best fit for both cohorts. In both cohorts, we identified a hyperinflammatory subphenotype (phenotype 2) that was characterised by higher plasma concentrations of inflammatory biomarkers, a higher prevalence of vasopressor use, lower serum bicarbonate concentrations, and a higher prevalence of sepsis than phenotype 1. Participants in phenotype 2 had higher mortality and fewer ventilator-free days and organ failure-free days in both cohorts than did those in phenotype 1 (p<0·007 for all). In the ALVEOLI cohort, the effects of ventilation strategy (high PEEP vs low PEEP) on mortality, ventilator-free days and organ failure-free days differed by phenotype (p=0·049 for mortality, p=0·018 for ventilator-free days, p=0·003 for organ-failure-free days).

INTERPRETATION

We have identified two subphenotypes within ARDS, one of which is categorised by more severe inflammation, shock, and metabolic acidosis and by worse clinical outcomes. Response to treatment in a randomised trial of PEEP strategies differed on the basis of subphenotype. Identification of ARDS subphenotypes might be useful in selecting patients for future clinical trials.

FUNDING

National Institutes of Health.

Pathophysiology and biomarkers of acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is defined as an acute-onset, progressive, hypoxic condition with radiographic bilateral lung infiltration, which develops after several diseases or injuries, and is not derived from hydrostatic pulmonary edema. One specific pathological finding of ARDS is diffuse alveolar damage. In 2012, in an effort to increase diagnostic specificity, a revised definition of ARDS was published in JAMA. However, no new parameters or biomarkers were adopted by the revised definition. Discriminating between ARDS and other similar diseases is critically important; however, only a few biomarkers are currently available for diagnostic purposes. Furthermore, predicting the severity, response to therapy, or outcome of the illness is also important for developing treatment strategies for each patient. However, the PaO₂/FIO₂ ratio is currently the sole clinical parameter used for this purpose. In parallel with progress in understanding the pathophysiology of ARDS, various humoral factors induced by inflammation and molecules derived from activated cells or injured tissues have been shown as potential biomarkers that may be applied in clinical practice. In this review, the current understanding of the basic pathophysiology of ARDS and associated candidate biomarkers will be discussed.