Targeting Endothelial Dysfunction in Acute Critical Illness to Reduce Organ Failure

Microcirculation: Current Perspective in Diagnostics, Imaging, and Clinical Applications

This review discusses the pivotal role of microcirculation in maintaining tissue oxygenation and waste removal and highlights its significance in various pathological conditions. It delves into the cellular mechanisms underlying hemodynamic coherence, elucidating the roles of the endothelium, glycocalyx, and erythrocytes in sustaining microcirculatory integrity. Furthermore, the review gives comprehensive information about microcirculatory changes observed in cardiac surgery, sepsis, shock, and COVID-19 disease. Through comprehensive exploration, the review underscores the intricate relationship between microcirculation, disease states, and clinical outcomes, emphasizing the importance of understanding and monitoring microvascular dynamics in critical care settings.

Exploring the Impact of Extracorporeal Membrane Oxygenation on the Endothelium: A Systematic Review

Extracorporeal membrane oxygenation (ECMO) is a life-saving intervention for patients with circulatory and/or pulmonary failure; however, the rate of complications remains high. ECMO induces systemic inflammation, which may activate and damage the endothelium, thereby causing edema and organ dysfunction. Advancing our understanding in this area is crucial for improving patient outcomes during ECMO. The goal of this review is to summarize the current evidence of the effects of ECMO on endothelial activation and damage in both animals and patients. PubMed and Embase databases were systematically searched for both clinical and animal studies including ECMO support. The outcome parameters were markers of endothelial activation and damage or (in)direct measurements of endothelial permeability, fluid leakage and edema. In total, 26 studies (patient n = 16, animal n = 10) fulfilled all eligibility criteria, and used VA-ECMO (n = 13) or VV-ECMO (n = 6), or remained undefined (n = 7). The most frequently studied endothelial activation markers were adhesion molecules (ICAM-1) and selectins (E- and P-selectin). The levels of endothelial activation markers were comparable to or higher than in healthy controls. Compared to pre-ECMO or non-ECMO, the majority of studies showed stable or decreased levels. Angiopoietin-2, von Willebrand Factor and extracellular vesicles were the most widely studied circulating markers of endothelial damage. More than half of the included studies showed increased levels when compared to normal ranges, and pre-ECMO or non-ECMO values. In healthy animals, ECMO itself leads to vascular leakage and edema. The effect of ECMO support in critically ill animals showed contradicting results. ECMO support (further) induces endothelial damage, but endothelial activation does not, in the critically ill. Further research is necessary to conclude on the effect of the underlying comorbidity and type of ECMO support applied on endothelial dysfunction.

Fluid bolus increases plasma hyaluronan concentration compared to follow-up strategy without a bolus in oliguric intensive care unit patients

Fluid therapy is a fundamental part of supportive therapy in critical care. However, it is also a suspected risk for endothelial glycocalyx degradation which is associated with poor clinical outcomes. This secondary analysis of RESPONSE randomized trial compares the effect of follow-up strategy (FU) on endothelial biomarkers to that of 500 ml crystalloid fluid bolus (FB) in oliguric, hemodynamically optimized intensive care unit (ICU) patients. 130 adult subjects were enrolled in two Finnish ICUs from January 2017 to November 2020. Blood and urine samples of 63 patients in FU group and 67 patients in FB group were collected before and after the intervention and analyzed using enzyme-linked immunosorbent assays. Single fluid bolus, given after median of 3887 ml (interquartile range 2842; 5359 ml) resuscitation fluids in the preceding 24 h, increased plasma hyaluronan concentration compared to the follow-up strategy (difference in medians 29.2 ng/ml with 95% CI [14.5ng/ml; 55.5ng/ml], P < 0.001). No treatment effect was detected in the plasma levels of syndecan-1, , angiopoietin-2, angiopoietin receptors Tie2 and Tie1, or in soluble thrombomodulin in the adjusted median regression analysis. The increase in hyaluronan was independent of its simultaneous renal clearance but correlated moderately with the increase in endothelium-specific Tie1. The follow-up strategy did not show consistent endothelium-sparing effect but protected against hyaluronan increase. The mechanisms and consequences of hyaluronan fluctuations need further clarification. Trial registration: clinicaltrials.gov, NCT02860572. Registered 1 August 2016, https://www.clinicaltrials.gov/study/NCT02860572?term=NCT02860572&rank=1.

Goal-directed Perioperative Albumin Substitution Versus Standard of Care to Reduce Postoperative Complications: A Randomized Clinical Trial (SuperAdd Trial)

OBJECTIVE

To investigate whether goal-directed albumin substitution during surgery and postanesthesia care to maintain a serum albumin concentration >30 g/L can reduce postoperative complications.

BACKGROUND

Hypoalbuminemia is associated with numerous postoperative complications. Since albumin has important physiological functions, substitution of patients with hypoalbuminemia is worth considering.

METHODS

We conducted a single-center, randomized, controlled, outcome assessor-blinded clinical trial in adult patients, American Society of Anesthesiologists physical status classification 3 to 4 or undergoing high-risk surgery. Patients, whose serum albumin concentration dropped <30 g/L were randomly assigned to goal-directed albumin substitution maintaining serum concentration >30 g/L or to standard care until discharge from the postanesthesia intermediate care unit. Standard of care allowed albumin substitution in hemodynamic instable patients with serum concentration <20 g/L, only. Primary outcome was the incidence of postoperative complications ≥2 according to the Clavien-Dindo Classification in at least 1 of 9 domains (pulmonary, infectious, cardiovascular, neurological, renal, gastrointestinal, wound, pain, and hematological) until postoperative day 15.

RESULTS

Of 2509 included patients, 600 (23.9%) developed serum albumin concentrations <30 g/L. Human albumin 60 g (40-80 g) was substituted to 299 (99.7%) patients in the intervention group and to 54 (18.0%) in the standard care group. At least 1 postoperative complication classified as Clavien-Dindo Classification ≥2 occurred in 254 of 300 patients (84.7%) in the intervention group and in 262 of 300 (87.3%) in the standard treatment group (risk difference -2.7%, 95% CI, -8.3% to 2.9%).

CONCLUSION

Maintaining serum albumin concentration of >30 g/L perioperatively cannot generally be recommended in high-risk noncardiac surgery patients.

Female sex protects against renal edema, but not lung edema, in mice with partial deletion of the endothelial barrier regulator Tie2 compared to male sex

BACKGROUND

The endothelial angiopoietin/Tie2 system is an important regulator of endothelial permeability and targeting Tie2 reduces hemorrhagic shock-induced organ edema in males. However, sexual dimorphism of the endothelium has not been taken into account. This study investigated whether there are sex-related differences in the endothelial angiopoietin/Tie2 system and edema formation.

METHODS

Adult male and female heterozygous Tie2 knockout mice (Tie2+/-) and wild-type controls (Tie2+/+) were included (n = 9 per group). Renal and pulmonary injury were determined by wet/dry weight ratio and H&E staining of tissue sections. Protein levels were studied in plasma by ELISA and pulmonary and renal mRNA expression levels by RT-qPCR.

RESULTS

In Tie2+/+ mice, females had higher circulating angiopoietin-2 (138%, p<0.05) compared to males. Gene expression of angiopoietin-1 (204%, p<0.01), angiopoietin-2 (542%, p<0.001) were higher in females compared to males in kidneys, but not in lungs. Gene expression of Tie2, Tie1 and VE-PTP were similar between males and females in both organs. Renal and pulmonary wet/dry weight ratio did not differ between Tie2+/+ females and males. Tie2+/+ females had lower circulating NGAL (41%, p<0.01) compared to males, whereas renal NGAL and KIM1 gene expression was unaffected. Interestingly, male Tie2+/- mice had 28% higher renal wet/dry weight ratio (p<0.05) compared to Tie2+/+ males, which was not observed in females nor in lungs. Partial deletion of Tie2 did not affect circulating angiopoietin-1 or angiopoietin-2, but soluble Tie2 was 44% and 53% lower in males and females, respectively, compared to Tie2+/+ mice of the same sex. Renal and pulmonary gene expression of angiopoietin-1, angiopoietin-2, estrogen receptors and other endothelial barrier regulators was comparable between Tie2+/- and Tie2+/+ mice in both sexes.

CONCLUSION

Female sex seems to protect against renal, but not pulmonary edema in heterozygous Tie2 knock-out mice. This could not be explained by sex dimorphism in the endothelial angiopoietin/Tie2 system.

A ligand-independent Tie2-activating antibody reduces vascular leakage in models of Clarkson disease

Vascular dysfunction resulting from endothelial hyperpermeability is a common and important feature of critical illness due to sepsis, trauma, and other conditions associated with acute systemic inflammation. Clarkson disease [monoclonal gammopathy-associated idiopathic systemic capillary leak syndrome (ISCLS)] is a rare, orphan disorder marked by spontaneous and recurrent episodes of hypotensive shock and peripheral edema due to widespread vascular leakage in peripheral tissues. Mortality from acute flares approaches 30% due to lack of effective therapies. We evaluated a monoclonal antibody (4E2) specific for the endothelial receptor tyrosine kinase Tie2 in ISCLS models. 4E2 activated Tie2 in ISCLS patient-derived endothelial cells and reduced baseline and proinflammatory mediator-induced barrier dysfunction. 4E2 also reduced mortality and/or vascular leakage associated with systemic histamine challenge or influenza infection in the SJL/J mouse model of ISCLS. These findings support a critical role for Tie2 dysregulation in ISCLS and highlight a viable therapeutic approach to this catastrophic disorder.

Heparanase inhibition leads to improvement in patients with acute gastrointestinal injuries induced by sepsis

BACKGROUND

Patients with sepsis are at high risk for acute gastrointestinal injury (AGI), but the diagnosis and treatment of AGI due to sepsis are unsatisfactory. Heparanase (HPA) plays an important role in septic AGI (S-AGI), but its specific mechanism is not completely understood, and few clinical reports are available.

AIM

To explore the effect and mechanism of HPA inhibition in S-AGI patients.

METHODS

In our prospective clinical trial, 48 patients with S-AGI were randomly assigned to a control group to receive conventional treatment, whereas 47 patients were randomly assigned to an intervention group to receive conventional treatment combined with low molecular weight heparin. AGI grade, sequential organ failure assessment score, acute physiology and chronic health evaluation II score, D-dimer, activated partial thromboplastin time (APTT), anti-Xa factor, interleukin-6, tumour necrosis factor-α, HPA, syndecan-1 (SDC-1), LC3B (autophagy marker), intestinal fatty acid binding protein, D-lactate, motilin, gastrin, CD4/CD8, length of intensive care unit (ICU) stay, length of hospital stay and 28-d survival on the 1st, 3rd and 7th d after treatment were compared. Correlations between HPA and AGI grading as well as LC3B were compared. Receiver operator characteristic (ROC) curves were generated to evaluate the diagnostic value of HPA, intestinal fatty acid binding protein and D-lactate in S-AGI.

RESULTS

Serum HPA and SCD-1 levels were significantly reduced in the intervention group compared with the control group (P < 0.05). In addition, intestinal fatty acid-binding protein, D-lactate, AGI grade, motilin, and gastrin levels and sequential organ failure assessment score were significantly decreased (P < 0.05) in the intervention group. However, LC3B, APTT, anti-Xa factor, and CD4/CD8 were significantly increased (P < 0.05) in the intervention group. No significant differences in interleukin-6, tumour necrosis factor-α, d-dimer, acute physiology and chronic health evaluation II score, length of ICU stay, length of hospital stay, or 28-d survival were noted between the two groups (P > 0.05). Correlation analysis revealed a significant negative correlation between HPA and LC3B and a significant positive correlation between HPA and AGI grade. ROC curve analysis showed that HPA had higher specificity and sensitivity in diagnosis of S-AGI.

CONCLUSION

HPA has great potential as a diagnostic marker for S-AGI. Inhibition of HPA activity reduces SDC-1 shedding and alleviates S-AGI symptoms. The inhibitory effect of HPA in gastrointestinal protection may be achieved by enhanced autophagy.

[Application Value of Novel Coagulation Markers in Predicting Postoperarative Complications in the Early Stage After Liver Transplantation]

Objective

To investigate the relationship between thrombin-antithrombin complex (TAT), plasmin-α 2-plasmininhibitor complex (PIC), soluble thrombomodulin (sTM), and tissue plasminogen activator-inhibitor complex (tPAIC) and postoperative complications in the early stage after liver transplantation (LT).

Methods

We analyzed the perioperative clinical data, including plasma TAT, PIC, sTM, and tPAIC, of 130 post-LT patients admitted to the intensive care unit (ICU), West China Hospital, Sichuan University between December 2021 and November 2022. Patients were divided into two groups, a complication group and a non-complication group, according to whether they experienced complications of Clavien-Dindo (CD) grade Ⅲb and above within 30 days after the surgery. Univariate analysis and binary multivariate logistic regression models were used to determine the risk factors for complications within 30 days post-LT.

Results

The incidence of complications of CD grade Ⅲb and above within 30 days post-LT was 33.1% (43/130). Patients in the complication group had significantly higher scores for the Model for End-Stage Liver Disease (MELD), operative time, intraoperative red blood cell transfusion volume, intraoperative plasma transfusion volume, and plasma TAT, PIC, sTM and tPAIC measured at the time of admission to ICU after the operation than those in the non-complication group did (all P<0.05). Logistic regression showed that for every single U of red blood cells transfused during the transplant surgery, the probabilities of complications within 30 days post-LT increased by 15.1% (95% confidence interval [ C I]: 1.070-1.239, P<0.001) and for the increase of every single TU/mL of plasma sTM measured upon post-LT admission to ICU, the probabilities of complications increased by 13.7% (95% CI: 1.060-1.220, P<0.001).

Conclusion

Plasma sTM measured upon admission to ICU after LT is an independent risk factor for complications within 30 days post-LT, and additional assessment of sTM may help predict complications in the early stage post-LT.

Investigation of Serum Endocan Levels and Age in Critical Inflammatory Conditions

Aging negatively affects the endothelium. Endocan (ESM-1), an endothelium-derived soluble proteoglycan, participates in fundamental biological processes of endothelial cells. We aimed to examine the role of endothelial dysfunction and age in poor outcomes in critical illness. ESM-1 levels were measured in the sera of mechanically ventilated critically ill patients, including COVID-19, non-septic, and septic patients. The 3 patient cohorts were divided based on age (≥65 and <65). Critically ill COVID-19 patients had statistically higher ESM-1 levels compared to critically ill septic and non-septic patients. Only in critically ill septic patients were ESM-1 levels higher in older compared to younger patients. Finally, the age-subgrouped patients were further subdivided based on intensive care unit (ICU) outcome. ESM-1 levels were similar in COVID-19 survivors and non-survivors, irrespective of age. Interestingly, only for the younger critically ill septic patients, non-survivors had higher ESM-1 levels compared to survivors. In the non-septic survivors and non-survivors, ESM-1 levels remained unaltered in the younger patients and tended to be higher in the elderly. Even though endocan has been recognized as an important prognostic biomarker in critically ill patients with sepsis, in our patient cohort, increased age, as well as the extent of endothelial dysfunction, seemed to affect its prognostic ability.

Early Postoperative Volume Overload is a Predictor of 1-Year Post-Transplant Mortality in Pediatric Heart Transplant Recipients

Fluid restriction and diuretic management are mainstays in the postoperative management of cardiac patients, at risk of volume overload and its deleterious effects on primary cardiac function and multi-organ systems. The importance of fluid homeostasis is further emphasized among orthotopic heart transplant recipients (OHT). We sought to investigate the relationship between postoperative volume overload, mortality, and allograft dysfunction among pediatric OHT recipients within 1-year of transplantation. This is a retrospective cohort study from a single pediatric OHT center. Children under 21 years undergoing cardiac transplantation between 2010 and 2018 were included. Cumulative fluid overload (cFO) was assessed as percent fluid accumulation adjusted for preoperative body weight. Greater than 10% cFO defined those with postoperative cFO and a comparison of postoperative cFO vs. no postoperative cFO (< 5%) is reported. 102 pediatric OHT recipients were included. Early cFO at 72 h post-OHT occurred in 14% and overall cFO at 1-week post-OHT occurred in 23% of patients. Risk factors for cFO included younger age, lower weight, and postoperative ECMO. Early cFO was associated with postoperative mortality at 1-year, OR 8.6 (95% CI 1.4, 51.6), p = 0.04, independent of age and weight. There was no significant relationship between cFO and allograft dysfunction, measured by rates of clinical rejection and cardiopulmonary filling pressures within 1-year of transplant. Early postoperative volume overload is prevalent and associated with increased risk of death at 1-year among pediatric OHT recipients. It may be an important postoperative marker of transplant survival, and this relationship warrants further clinical investigation.

Pharmacological Cardioprotection against Ischemia Reperfusion Injury-The Search for a Clinical Effective Therapy

Pharmacological conditioning aims to protect the heart from myocardial ischemia-reperfusion injury (IRI). Despite extensive research in this area, today, a significant gap remains between experimental findings and clinical practice. This review provides an update on recent developments in pharmacological conditioning in the experimental setting and summarizes the clinical evidence of these cardioprotective strategies in the perioperative setting. We start describing the crucial cellular processes during ischemia and reperfusion that drive acute IRI through changes in critical compounds (∆G_ATP, Na⁺, Ca²⁺, pH, glycogen, succinate, glucose-6-phosphate, mitoHKII, acylcarnitines, BH₄, and NAD⁺). These compounds all precipitate common end-effector mechanisms of IRI, such as reactive oxygen species (ROS) generation, Ca²⁺ overload, and mitochondrial permeability transition pore opening (mPTP). We further discuss novel promising interventions targeting these processes, with emphasis on cardiomyocytes and the endothelium. The limited translatability from basic research to clinical practice is likely due to the lack of comorbidities, comedications, and peri-operative treatments in preclinical animal models, employing only monotherapy/monointervention, and the use of no-flow (always in preclinical models) versus low-flow ischemia (often in humans). Future research should focus on improved matching between preclinical models and clinical reality, and on aligning multitarget therapy with optimized dosing and timing towards the human condition.

Non-Invasive Pulsatile Shear Stress Modifies Endothelial Activation; A Narrative Review

The monolayer of cells that line both the heart and the entire vasculature is the endothelial cell (EC). These cells respond to external and internal signals, producing a wide array of primary or secondary messengers involved in coagulation, vascular tone, inflammation, and cell-to-cell signaling. Endothelial cell activation is the process by which EC changes from a quiescent cell phenotype, which maintains cellular integrity, antithrombotic, and anti-inflammatory properties, to a phenotype that is prothrombotic, pro-inflammatory, and permeable, in addition to repair and leukocyte trafficking at the site of injury or infection. Pathological activation of EC leads to increased vascular permeability, thrombosis, and an uncontrolled inflammatory response that leads to endothelial dysfunction. This pathological activation can be observed during ischemia reperfusion injury (IRI) and sepsis. Shear stress (SS) and pulsatile shear stress (PSS) are produced by mechanical frictional forces of blood flow and contraction of the heart, respectively, and are well-known mechanical signals that affect EC function, morphology, and gene expression. PSS promotes EC homeostasis and cardiovascular health. The archetype of inducing PSS is exercise (i.e., jogging, which introduces pulsations to the body as a function of the foot striking the pavement), or mechanical devices which induce external pulsations to the body (Enhanced External Pulsation (EECP), Whole-body vibration (WBV), and Whole-body periodic acceleration (WBPA aka pGz)). The purpose of this narrative review is to focus on the aforementioned noninvasive methods to increase PSS, review how each of these modify specific diseases that have been shown to induce endothelial activation and microcirculatory dysfunction (Ischemia reperfusion injury-myocardial infarction and cardiac arrest and resuscitation), sepsis, and lipopolysaccharide-induced sepsis syndrome (LPS)), and review current evidence and insight into how each may modify endothelial activation and how these may be beneficial in the acute and chronic setting of endothelial activation and microvascular dysfunction.

Wingless-related integration site (WNT) signaling is activated during the inflammatory response upon cardiac surgery: A translational study

Objective

Cardiac surgery and the use of cardiopulmonary bypass initiate a systemic inflammatory response. Wingless-related integration site (WNT) signaling is part of the innate immunity and has been attributed a major role in the regulation of inflammation. In preclinical research, WNT-5a may sustain an inflammatory response and cause endothelial dysfunction. Our aim was to investigate WNT signaling after cardiac surgery and its association with postoperative inflammation (Clinicaltrials.gov, NCT04058496).

Methods

In this prospective, single-center, observational study, 64 consecutive patients for coronary artery bypass grafting (CABG) ± valve surgery were assigned into three groups: off-pump CABG (n = 28), on-pump CABG (n = 16) and combined valve-CABG surgery (n = 20). Blood samples were acquired before surgery, at intensive care unit (ICU) admission and 4, 8, and 48 h thereafter. Plasma concentrations of WNT-5a and its antagonists Secreted frizzled-related protein 1 (sFRP-1), Secreted frizzled-related protein 5 (sFRP-5), and WNT inhibitory factor 1 (WIF-1) were determined by enzyme-linked immunosorbent assay. In addition, plasma concentrations of six inflammatory cytokines were measured by multiplex immunoassay. Parameters were analyzed for evolution of plasma concentration over time, interactions, intergroup differences, and association with clinical outcome parameters.

Results

At baseline, WNT-5a, sFRP-1, and WIF-1 were present in a minimal concentration, while sFRP-5 was elevated. A higher baseline value of WNT-5a, sFRP-5, and WIF-1 resulted in higher subsequent values of the respective parameter. At ICU admission, WNT-5a and sFRP-5 reached their maximum and minimum value, respectively. WIF-1 decreased over time and was lowest 8 h after surgery. sFRP-1 changed minimally over time. While WNT-5a returned to the baseline within 48 h, sFRP-5 and WIF-1 did not reach their baseline value at 48 h. Of the investigated WNT system components, only WIF-1 partially reflected the severity of surgery. WNT-5a and WIF-1 had an impact on postoperative fluid balance and noradrenaline requirement.

Conclusion

WNT-5a, sFRP-5, and WIF-1 are part of the systemic inflammatory response after cardiac surgery. WNT-5a peaks immediately after cardiac surgery and returns to baseline within 48 h, presumably modulated by its antagonist sFRP-5. Based on this translational study, WNT-5a antagonism may be further investigated to assess potentially beneficial effects in patients with a dysregulated inflammation after cardiac surgery.

A Positive Fluid Balance in the First Week Was Associated With Increased Long-Term Mortality in Critically Ill Patients: A Retrospective Cohort Study

Introduction

Early fluid balance has been found to affect short-term mortality in critically ill patients; however, there is little knowledge regarding the association between early cumulative fluid balance (CFB) and long-term mortality. This study aims to determine the distinct association between CFB day 1-3 (CFB 1-3) and day 4-7 (CFB 4-7) and long-term mortality in critically ill patients.

Patients and Methods

This study was conducted at Taichung Veterans General Hospital, a tertiary care referral center in central Taiwan, by linking the hospital critical care data warehouse 2015-2019 and death registry data of the Taiwanese National Health Research Database. The patients followed up until deceased or the end of the study on 31 December 2019. We use the log-rank test to examine the association between CFB 1-3 and CFB 4-7 with long-term mortality and multivariable Cox regression to identify independent predictors during index admission for long-term mortality in critically ill patients.

Results

A total of 4,610 patients were evaluated. The mean age was 66.4 ± 16.4 years, where 63.8% were men. In patients without shock, a positive CFB 4-7, but not CFB 1-3, was associated with 1-year mortality, while a positive CFB 1-3 and CFB 4-7 had a consistent and excess hazard of 1-year mortality among critically ill patients with shock. The multivariate Cox proportional hazard regression model identified that CFB 1-3 and CFB 4-7 (with per 1-liter increment, HR: 1.047 and 1.094; 95% CI 1.037-1.058 and 1.080-1.108, respectively) were independently associated with high long-term mortality in critically ill patients after adjustment of relevant covariates, including disease severity and the presence of shock.

Conclusions

We found that the fluid balance in the first week, especially on days 4-7, appears to be an early predictor for long-term mortality in critically ill patients. More studies are needed to validate our findings and elucidate underlying mechanisms.

Resuscitation fluids as drugs: targeting the endothelial glycocalyx

ABSTRACT

Fluid resuscitation is an essential intervention in critically ill patients, and its ultimate goal is to restore tissue perfusion. Critical illnesses are often accompanied by glycocalyx degradation caused by inflammatory reactions, hypoperfusion, shock, and so forth, leading to disturbed microcirculatory perfusion and organ dysfunction. Therefore, maintaining or even restoring the glycocalyx integrity may be of high priority in the therapeutic strategy. Like drugs, however, different resuscitation fluids may have beneficial or harmful effects on the integrity of the glycocalyx. The purpose of this article is to review the effects of different resuscitation fluids on the glycocalyx. Many animal studies have shown that normal saline might be associated with glycocalyx degradation, but clinical studies have not confirmed this finding. Hydroxyethyl starch (HES), rather than other synthetic colloids, may restore the glycocalyx. However, the use of HES also leads to serious adverse events such as acute kidney injury and bleeding tendencies. Some studies have suggested that albumin may restore the glycocalyx, whereas others have suggested that balanced crystalloids might aggravate glycocalyx degradation. Notably, most studies did not correct the effects of the infusion rate or fluid volume; therefore, the results of using balanced crystalloids remain unclear. Moreover, mainly animal studies have suggested that plasma may protect and restore glycocalyx integrity, and this still requires confirmation by high-quality clinical studies.

Therapeutically Targeting Microvascular Leakage in Experimental Hemorrhagic SHOCK: A Systematic Review and Meta-Analysis

BACKGROUND

Microvascular leakage is proposed as main contributor to disturbed microcirculatory perfusion following hemorrhagic shock and fluid resuscitation, leading to organ dysfunction and unfavorable outcome. Currently, no drugs are available to reduce or prevent microvascular leakage in clinical practice. We therefore aimed to provide an overview of therapeutic agents targeting microvascular leakage following experimental hemorrhagic shock and fluid resuscitation.

METHODS

PubMed, EMBASE.com, and Cochrane Library were searched in January 2021 for preclinical studies of hemorrhagic shock using any therapeutic agent on top of standard fluid resuscitation. Primary outcome was vascular leakage, defined as edema, macromolecule extravasation, or glycocalyx degradation. Drugs were classified by targeting pathways and subgroup analyses were performed per organ.

RESULTS

Forty-five studies, published between 1973 and 2020, fulfilled eligibility criteria. The included studies tested 54 different therapeutics mainly in pulmonary and intestinal vascular beds. Most studies induced trauma besides hemorrhagic shock. Forty-four therapeutics (81%) were found effective to reduce microvascular leakage, edema formation, or glycocalyx degradation in at least one organ. Targeting oxidative stress and apoptosis was the predominantly effective strategy (SMD: -2.18, CI [-3.21, -1.16], P < 0.0001). Vasoactive agents were found noneffective in reducing microvascular leakage (SMD: -0.86, CI [-3.07, 1.36], P = 0.45).

CONCLUSION

Pharmacological modulation of pathways involved in cell metabolism, inflammation, endothelial barrier regulation, sex hormones and especially oxidative stress and apoptosis were effective in reducing microvascular leakage in experimental hemorrhagic shock with fluid resuscitation. Future studies should investigate whether targeting these pathways can restore microcirculatory perfusion and reduce organ injury following hemorrhagic shock.

SYSTEMATIC REVIEW REGISTRATION NUMBER

CRD42018095432.

Targeting Cytokines, Pathogen-Associated Molecular Patterns, and Damage-Associated Molecular Patterns in Sepsis via Blood Purification

Sepsis is characterized by a dysregulated immune response to infections that causes life-threatening organ dysfunction and even death. When infections occur, bacterial cell wall components (endotoxin or lipopolysaccharide), known as pathogen-associated molecular patterns, bind to pattern recognition receptors, such as toll-like receptors, to initiate an inflammatory response for pathogen elimination. However, strong activation of the immune system leads to cellular dysfunction and ultimately organ failure. Damage-associated molecular patterns (DAMPs), which are released by injured host cells, are well-recognized triggers that result in the elevation of inflammatory cytokine levels. A cytokine storm is thus amplified and sustained in this vicious cycle. Interestingly, during sepsis, neutrophils transition from powerful antimicrobial protectors into dangerous mediators of tissue injury and organ dysfunction. Thus, the concept of blood purification has evolved to include inflammatory cells and mediators. In this review, we summarize recent advances in knowledge regarding the role of lipopolysaccharides, cytokines, DAMPs, and neutrophils in the pathogenesis of sepsis. Additionally, we discuss the potential of blood purification, especially the adsorption technology, for removing immune cells and molecular mediators, thereby serving as a therapeutic strategy against sepsis. Finally, we describe the concept of our immune-modulating blood purification system.

Ultrasound and Microbubbles for Targeted Drug Delivery to the Lung Endothelium in ARDS: Cellular Mechanisms and Therapeutic Opportunities

Acute respiratory distress syndrome (ARDS) is characterized by increased permeability of the alveolar–capillary membrane, a thin barrier composed of adjacent monolayers of alveolar epithelial and lung microvascular endothelial cells. This results in pulmonary edema and severe hypoxemia and is a common cause of death after both viral (e.g., SARS-CoV-2) and bacterial pneumonia. The involvement of the lung in ARDS is notoriously heterogeneous, with consolidated and edematous lung abutting aerated, less injured regions. This makes treatment difficult, as most therapeutic approaches preferentially affect the normal lung regions or are distributed indiscriminately to other organs. In this review, we describe the use of thoracic ultrasound and microbubbles (USMB) to deliver therapeutic cargo (drugs, genes) preferentially to severely injured areas of the lung and in particular to the lung endothelium. While USMB has been explored in other organs, it has been under-appreciated in the treatment of lung injury since ultrasound energy is scattered by air. However, this limitation can be harnessed to direct therapy specifically to severely injured lungs. We explore the cellular mechanisms governing USMB and describe various permutations of cargo administration. Lastly, we discuss both the challenges and potential opportunities presented by USMB in the lung as a tool for both therapy and research.

Inhalation Injury is Associated with Endotheliopathy and Abnormal Fibrinolytic Phenotypes in Burn Patients: A Cohort Study

Burn injury is associated with endothelial dysfunction and coagulopathy and concomitant inhalation injury increases morbidity and mortality. The aim of this work is to identify associations between inhalation injury (IHI), coagulation homeostasis, vascular endothelium, and clinical outcomes in burn patients. One-hundred and twelve patients presenting to a regional burn center were included in this retrospective cohort study. Whole blood was collected at set intervals from admission through 24 hours and underwent viscoelastic assay with rapid TEG (rTEG). Syndecan-1 (SDC-1) on admission was quantified by ELISA. Patients were grouped by the presence (n=28) or absence (n=84) of concomitant IHI and rTEG parameters, fibrinolytic phenotypes, SDC-1, and clinical outcomes were compared. Of the 112 thermally injured patients, 28 (25%) had IHI. Most patients were male (68.8%) with a median age of 40 (IQR, 29-57) years. Patients with IHI had higher overall mortality (42.68% vs. 8.3%; p<0.0001). rTEG LY30 was lower in patients with IHI at hours 4 and 12 (p<0.05). There was a pattern of increased abnormal fibrinolytic phenotypes among IHI patients. There was a greater proportion of IHI patients with endotheliopathy (SDC-1 > 34 ng/mL) (64.7% vs. 26.4%; p=0.008). There was a pattern of increased mortality among patients with inhalation injury and endotheliopathy (0% vs. 72.7%; p=0.004). Significant differences between patients with and without IHI were found in measures assessing fibrinolytic potential and endotheliopathy. Mortality was associated with abnormal fibrinolysis, endotheliopathy, and inhalation injury. However, the extent to which IHI associated dysfunction is independent of TBSA burn size remains to be elucidated.

Divergent trajectories of cellular bioenergetics, intermediary metabolism and systemic redox status in survivors and non-survivors of critical illness

Background

Numerous pathologies result in multiple-organ failure, which is thought to be a direct consequence of compromised cellular bioenergetic status. Neither the nature of this phenotype nor its relevance to survival are well understood, limiting the efficacy of modern life-support.

Methods

To explore the hypothesis that survival from critical illness relates to changes in cellular bioenergetics, we combined assessment of mitochondrial respiration with metabolomic, lipidomic and redox profiling in skeletal muscle and blood, at multiple timepoints, in 21 critically ill patients and 12 reference patients.

Results

We demonstrate an end-organ cellular phenotype in critical illness, characterized by preserved total energetic capacity, greater coupling efficiency and selectively lower capacity for complex I and fatty acid oxidation (FAO)-supported respiration in skeletal muscle, compared to health. In survivors, complex I capacity at 48 h was 27% lower than in non-survivors (p = 0.01), but tended to increase by day 7, with no such recovery observed in non-survivors. By day 7, survivors’ FAO enzyme activity was double that of non-survivors (p = 0.048), in whom plasma triacylglycerol accumulated. Increases in both cellular oxidative stress and reductive drive were evident in early critical illness compared to health. Initially, non-survivors demonstrated greater plasma total antioxidant capacity but ultimately higher lipid peroxidation compared to survivors. These alterations were mirrored by greater levels of circulating total free thiol and nitrosated species, consistent with greater reductive stress and vascular inflammation, in non-survivors compared to survivors. In contrast, no clear differences in systemic inflammatory markers were observed between the two groups.

Conclusion

Critical illness is associated with rapid, specific and coordinated alterations in the cellular respiratory machinery, intermediary metabolism and redox response, with different trajectories in survivors and non-survivors. Unravelling the cellular and molecular foundation of human resilience may enable the development of more effective life-support strategies.