Microfluidics as a Powerful Tool to Investigate Microvascular Dysfunction in Trauma Conditions: A Review of the State-of-the-Art

Skeletal muscle trauma such as fracture or crush injury can result in a life-threatening condition called acute compartment syndrome (ACS), which involves elevated compartmental pressure within a closed osteo-fascial compartment, leading to collapse of the microvasculature and resulting in necrosis of the tissue due to ischemia. Diagnosis of ACS is complex and controversial due to the lack of standardized objective methods, which results in high rates of misdiagnosis/late diagnosis, leading to permanent neuro-muscular damage. ACS pathophysiology is poorly understood at a cellular level due to the lack of physiologically relevant models. In this context, microfluidics organ-on-chip systems (OOCs) provide an exciting opportunity to investigate the cellular mechanisms of microvascular dysfunction that leads to ACS. In this article, the state-of-the-art OOCs designs and strategies used to investigate microvasculature dysfunction mechanisms is reviewed. The differential effects of hemodynamic shear stress on endothelial cell characteristics such as morphology, permeability, and inflammation, all of which are altered during microvascular dysfunction is highlighted. The article then critically reviews the importance of microfluidics to investigate closely related microvascular pathologies that cause ACS. The article concludes by discussing potential biomarkers of ACS with a special emphasis on glycocalyx and providing a future perspective.

Capillary leak and endothelial permeability in critically ill patients: a current overview

Capillary leak syndrome (CLS) represents a phenotype of increased fluid extravasation, resulting in intravascular hypovolemia, extravascular edema formation and ultimately hypoperfusion. While endothelial permeability is an evolutionary preserved physiological process needed to sustain life, excessive fluid leak-often caused by systemic inflammation-can have detrimental effects on patients' outcomes. This article delves into the current understanding of CLS pathophysiology, diagnosis and potential treatments. Systemic inflammation leading to a compromise of endothelial cell interactions through various signaling cues (e.g., the angiopoietin-Tie2 pathway), and shedding of the glycocalyx collectively contribute to the manifestation of CLS. Capillary permeability subsequently leads to the seepage of protein-rich fluid into the interstitial space. Recent insights into the importance of the sub-glycocalyx space and preserving lymphatic flow are highlighted for an in-depth understanding. While no established diagnostic criteria exist and CLS is frequently diagnosed by clinical characteristics only, we highlight more objective serological and (non)-invasive measurements that hint towards a CLS phenotype. While currently available treatment options are limited, we further review understanding of fluid resuscitation and experimental approaches to target endothelial permeability. Despite the improved understanding of CLS pathophysiology, efforts are needed to develop uniform diagnostic criteria, associate clinical consequences to these criteria, and delineate treatment options.

The potential mechanism of histamine-inducing cardiopulmonary inflammation and apoptosis in a novel oral model of rat intoxication

Histamine (HIS) is a potent vasodilator that contributes to anaphylactic reactions. Our investigation aims to study the possible toxic impact of repeated oral administration of histamine on the target organs of HIS poisoning (lung & heart) in rats as a model of scombroid poisoning. We used 15 rats that were separated into three groups with 5 rats in each. All rats received the treatments orally for 14 days as follows; (1): distilled water, (2) HIS at a dosage level of 250 mg/kg BWT daily and (3) HIS at a dosage level of 1750 mg/kg BWT weekly. Our results revealed that the consumption of HIS either daily or weekly could cause marked cardiopulmonary toxicity in rats. HIS can trigger inflammatory reactions in the cardiopulmonary tissues and induce oxidative stress damage along with apoptosis of such organs. HIS was markedly increase the MDA levels and decrease the CAT and GSH activity in both lung and heart tissues. The main pathological lesion observed is inflammation which was confirmed by immunohistochemistry and demonstrated strong iNOS and TNF-α protein expressions. Cardiac muscles showed extensive degeneration and necrosis and displayed strong casp-3 protein expression. Additionally, all HIS receiving groups noticed marked elevation of the pulmonary transcription levels of Cox2, TNF-α, and IL1β along with substantial elevation of casp-3 and bax genes and downregulation of Bcl2 gene in the cardiac tissue. We concluded that the oral administration of HIS either daily or weekly can induce cardiopulmonary toxicity via the upregulation of proinflammatory cytokines resulting in ROS overgeneration and inducing both oxidative stress and apoptosis.

A Study to Evaluate Changes in Modified Mallampati Class in Patients Undergoing Spine Surgery in Prone Position

Background: Perioperative airway changes due to anesthesia and surgery could change a normal airway at induction to a risky airway at extubation.

Objectives: The objective is to evaluate primarily the degree of airway changes, as quantified by the modified Mallampati (MMP) class, after spine surgery in the prone position. Secondary to assess the time required for these changes to revert back to the preoperative state and their correlation with other demographic and surgical variables.

Methods: The present prospective observational study was conducted in a tertiary care hospital after ethical approval and trial registration. Fifty ASA I and II patients aged 18-65 years of both sex and undergoing spine surgery in prone positions were included. Supine MMP grade was observed preoperatively and at one, two, four, 24, and 48 hours postoperatively.

Statistical analysis: IBM SPSS version 22 (IBM Corp, Armonk, NY) was used.Mean values were compared using paired t-tests and medians by the Wilcoxon test. The Spearman correlation was used to assess a relationship. The time for recovery was analyzed by Kaplan-Meir analysis.

Results: An increase in MMP grade was observed at one hour postoperatively in 46 (92%) patients. Changes reverted back in 45 (98%) patients by 24 hours postoperatively. A weak positive correlation with age, weight, body mass index, duration of surgery, perioperative drop in hemoglobin, and a moderate positive correlation with fluid administered and estimated blood loss was recorded.

Conclusions: An increase in postoperative MMP occurs in the majority of patients undergoing prone position spine surgery which may persist up to 48 hours. So, more vigilance and caution are warranted should reintubation be needed postoperatively.

Comparison of ANP and BNP Granular Density in Atria of Rats After Physiological and Pathological Hypertrophy

Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are cardiac hormones located in atria granules. Both peptides respond to cardiac pressure and volume dynamics and accordingly serve as translation biomarkers for the clinical treatment of heart failure. Serum ANP and BNP play central secretary roles in blood pressure and cardiac output regulation and have proven utility as differential biomarkers of cardiovascular proficiency and drug-induced maladaptation, yet both peptides are impervious to exercise-induced hypertrophy. We employed immunoelectron microscopy to examine the effects of 28 days of chronic swim exercise or administration of a PPARγ agonist on atrial granules and their stored natriuretic peptides in Sprague Dawley rats. Chronic swimming and drug treatment both resulted in a 15% increase in heart weight compared with controls, with no treatment effects on perinuclear granule area in the left atria (LAs). Drug treatment resulted in larger size granules with greater BNP density in the right atria. Comparing swimming and PPARγ agonist treatment effects on ANP:BNP granule density ratios between atrial chambers revealed a shift toward a greater proportion of ANP than BNP in LAs of swim-trained rats. These data suggest a distinction in the population of ANP and BNP after chronic swim or PPARγ that makes it a novel metric for the differentiation of pathological and physiological hypertrophy.

Diagnosing capillary leak in critically ill patients: development of an innovative scoring instrument for non-invasive detection

BACKGROUND

The concomitant occurrence of the symptoms intravascular hypovolemia, peripheral edema and hemodynamic instability is typically named Capillary Leak Syndrome (CLS) and often occurs in surgical critical ill patients. However, neither a unitary definition nor standardized diagnostic criteria exist so far. We aimed to investigate common characteristics of this phenomenon with a subsequent scoring system, determining whether CLS contributes to mortality.

METHODS

We conducted this single-center, observational, multidisciplinary, prospective trial in two separately run surgical ICUs of a tertiary academic medical center. 200 surgical patients admitted to the ICU and 30 healthy volunteers were included. Patients were clinically diagnosed as CLS or No-CLS group (each N = 100) according to the grade of edema, intravascular hypovolemia, hemodynamic instability, and positive fluid balance by two independent attending physicians with > 10 years of experience in ICU. We performed daily measurements with non-invasive body impedance electrical analysis, ultrasound and analysis of serum biomarkers to generate objective diagnostic criteria. Receiver operating characteristics were used, while we developed machine learning models to increase diagnostic specifications for our scoring model.

RESULTS

The 30-day mortility was increased among CLS patients (12 vs. 1%, P = 0.002), while showing higher SOFA-scores. Extracellular water was increased in patients with CLS with higher echogenicity of subcutaneous tissue [29(24-31) vs. 19(16-21), P < 0.001]. Biomarkers showed characteristic alterations, especially with an increased angiopoietin-2 concentration in CLS [9.9(6.2-17.3) vs. 3.7(2.6-5.6)ng/mL, P < 0.001]. We developed a score using seven parameters (echogenicity, SOFA-score, angiopoietin-2, syndecan-1, ICAM-1, lactate and interleukin-6). A Random Forest prediction model boosted its diagnostic characteristics (AUC 0.963, P < 0.001), while a two-parameter decision tree model showed good specifications (AUC 0.865).

CONCLUSIONS

Diagnosis of CLS in critically ill patients is feasible by objective, non-invasive parameters using the CLS-Score. A simplified two-parameter diagnostic approach can enhance clinical utility. CLS contributes to mortality and should, therefore, classified as an independent entity.

TRIAL REGISTRATION

German Clinical Trials Registry (DRKS No. 00012713), Date of registration 10/05/2017, www.drks.de.

Advances in the Starling Principle and Microvascular Fluid Exchange; Consequences and Implications for Fluid Therapy

Ernest Starling first presented a hypothesis about the absorption of tissue fluid to the plasma within tissue capillaries in 1896. In this Chapter we trace the evolution of Starling's hypothesis to a principle and an equation, and then look in more detail at the extension of the Starling principle in recent years. In 2012 Thomas Woodcock and his son proposed that experience and experimental observations surrounding clinical practices involving the administration of intravenous fluids were better explained by the revised Starling principle. In particular, the revised or extended Starling principle can explain why crystalloid resuscitation from the abrupt physiologic insult of hypovolaemia is much more effective than the pre-revision Starling principle had led clinicians to expect. The authors of this chapter have since combined their science and clinical expertise to offer clinicians a better basis for their practice of rational fluid therapy.

Microvascular Fluid Exchange: Implications of the Revised Starling Model for Resuscitation of Dengue Shock Syndrome

Dengue is the most common mosquito-borne viral infection in the world. The most feared complication is a poorly understood vasculopathy that occurs in only a small minority of symptomatic individuals, especially children and young adults, but can result in potentially fatal dengue shock syndrome (DSS). Based mainly on expert opinion, WHO management guidelines for DSS recommend prompt infusion of a crystalloid fluid bolus followed by a tapering crystalloid fluid regimen, supplemented if necessary by boluses of synthetic colloid solutions. However, following publication of a number of major trials undertaken in other, primarily adult, critical care scenarios, use of both synthetic colloid solutions and of fluid boluses for volume expansion have become controversial. Synthetic colloids tend to be used for severe DSS cases in order to boost intravascular oncotic pressure, based on the classic Starling hypothesis in which opposing hydrostatic and oncotic forces determine fluid flow across the microvascular barrier. However, the revised Starling model emphasizes the critical contribution of the endothelial glycocalyx layer (EGL), indicating that it is the effective oncotic pressure gradient across the EGL not endothelial cells per se that opposes filtration. Based on several novel concepts that are integral to the revised Starling model, we review the clinical features of DSS and discuss a number of implications that are relevant for fluid management. We also highlight the need for context-specific clinical trials that address crucially important questions around the management of DSS.

The microcirculation

The microcirculation is responsible for the transfer of oxygen from the red blood cells in the capillaries to the cells to meet cellular energy requirements, support functional activity and remove carbon dioxide and waste. The microcirculation also assists in the regulation of vascular tone, solute exchange, the production of hormones, the inflammatory response and haemostasis. The identification of the endothelial glycocalyx and the assessment of the effects of disease, drugs and fluids on the microcirculation is the subject of ongoing research.

[Essential aspects during the resuscitation of intravascular volume in polytraumatized patients]

Trauma is the leading cause of death in the first four decades of life, responsible for 3.5 million deaths a year and carrying a high economic and social impact. Hemorrhagic shock is the consequence of injuries in these patients. Despite extensive knowledge about its pathophysiology and many replacement drugs and therapies, resuscitation of the intravascular volume sometimes is insufficient and ineffective. Hemorrhagic shock, resulting in macro and microvascular changes that favor the development of anaerobic metabolism, is associated with multiple complications that can lead to the demise of the patient. The purpose of this article is to describe the essential aspects that should be taken into account during the resuscitation of the intravascular volume of multiple trauma patients. We conducted a search and review of the available literature on the resuscitation of trauma patients. Reference searches were conducted in the MEDLINE/PubMed, Cumed, SciELO, EBSCO, Hinari, Cochrane databases. We reviewed the historical evolution of volume replacement in the polytrauma patient, endothelial glycocalyx, changes in the Starling law paradigm, goal-guided resuscitation, the different fluids used during resuscitation, monitoring, and the concepts of damage control resuscitation and damage control surgery.

The role of endothelial glycocalyx in health and disease

The endothelium is the largest organ in the body and recent studies have shown that the endothelial glycocalyx (eGCX) plays a major role in health and disease states. The integrity of eGCX is vital for homoeostasis and disruption of its structure and function plays a major role in several pathologic conditions. An increased understanding of the numerous pathophysiological roles of eGCX may lead to the development of potential surrogate markers for endothelial injury or novel therapeutic targets. This review provides a state-of-the-art update on the structure and function of the eGCX, emphasizing the current understanding of interorgan crosstalk between the eGCX and other organs that might also contribute to the pathogenesis of kidney diseases.

Recent advances in the understanding of endothelial barrier function and fluid therapy

Elucidation of the structural basis of endothelial barrier function and the study of transcapillary fluid exchange dynamics are areas of active research. There has been significant enhancement in our understanding of the ultrastructural basis of endothelial barrier function. The role of glycocalyx has received special attention. Experimental evidence has called for a revision in the classic Starling principle of transcapillary exchange. The glycocalyx model provides a potential structural mechanism for the revised Starling principle. This knowledge can provide the framework for understanding the volume expansion effect of fluid therapy and the physiological basis of fluid therapy.