Hypervolemia does not cause degradation of the endothelial glycocalyx layer during open hysterectomy performed under sevoflurane or propofol anesthesia

Association between intravenous fluid administration and endothelial glycocalyx shedding in humans: a systematic review

INTRODUCTION

Several studies have demonstrated associations between greater rate/volume of intravenous (IV) fluid administration and poorer clinical outcomes. One postulated mechanism for harm from exogenous fluids is shedding of the endothelial glycocalyx (EG).

METHODS

A systematic review using relevant search terms was performed using Medline, EMBASE and Cochrane databases from inception to October 2023. Included studies involved humans where the exposure was rate or volume of IV fluid administration and the outcome was EG shedding. The protocol was prospectively registered on PROSPERO: CRD42021275133.

RESULTS

The search yielded 450 articles, with 20 articles encompassing 1960 participants included in the review. Eight studies were randomized controlled clinical trials. Half of studies examined patients with sepsis and critical illness; the remainder examined perioperative patients or healthy subjects. Almost all reported blood measurements of soluble EG components; one study used in vivo video-microscopy to estimate EG thickness. Four of 10 sepsis studies, and 9 of 11 non-sepsis studies, found a positive relationship between IV fluid rate/volume and measures of EG shedding.

CONCLUSIONS

A trend toward an association between IV fluid rate/volume and EG shedding was found in studies of stable patients, but was not consistently observed among studies of septic and critically ill patients.

Trajectory of plasma syndecan-1 and heparan sulphate during major surgery: A retrospective observational study

BACKGROUND

Surgical trauma-induced inflammation during major surgery may disrupt endothelial integrity and affect plasma concentrations of glycocalyx constituents, such as syndecan-1 and heparan sulphate. To date, no studies have focused on their perioperative temporal changes.

METHODS

As part of a trial, we obtained plasma and urine specimens sampled during the perioperative period in 72 patients undergoing major abdominal surgery. The plasma concentration of syndecan-1 and heparan sulphate was measured on five occasions, from baseline to the second postoperative day. Plasma and urinary creatinine and urinary syndecan-1 concentrations were measured before surgery and on the first postoperative morning.

RESULTS

We observed three different temporal patterns of plasma syndecan-1 concentration. Group 1 'low' (64% of patients) showed only minor changes from baseline despite a median heparan sulphate increase of 67% (p < .005). Group 2 'increase' (21% of patients) showed a marked increase in median plasma syndecan-1 from 27 μg/L to 118 μg/L during the first postoperative day (p < .001) with a substantial (+670%; p < .005) increase in median plasma heparan sulphate from 279 to 2196 μg/L. Group 3 'high' (14% of patients) showed a constant elevation of plasma syndecan-1 to >100 μg/L, but low heparan sulphate levels. The plasma C-reactive protein concentration did not differ across the three groups and 90% of colon surgeries occurred in Group 1. Treatment with dexamethasone was similar across the three groups. Surgical blood loss, duration of surgery and liver resection were greatest in Group 2.

CONCLUSION

Changes in syndecan-1 and heparan sulphate after surgery appear to show three different patterns, with the greatest increases in those patients with greater blood loss, more liver surgery and longer operations. These observations suggest that increases in syndecan-1 and heparan sulphate reflect the degree of surgical injury.

The effects of female sexual hormones on the endothelial glycocalyx

The glycocalyx is a layer composed of carbohydrate side chains bound to core proteins that lines the vascular endothelium. The integrity of the glycocalyx is essential for endothelial cells' performance and vascular homeostasis. The neuroendocrine and immune systems influence the composition, maintenance, activity and degradation of the endothelial glycocalyx. The female organism has unique characteristics, and estrogen and progesterone, the main female hormones are essential to the development and physiology of the reproductive system and to the ability to develop a fetus. Female sex hormones also exert a wide variety of effects on other organs, including the vascular endothelium. They upregulate nitric oxide synthase expression and activity, decrease oxidative stress, increase vasodilation, and protect from vascular injury. This review will discuss how female hormones and pregnancy, which prompts to high levels of estrogen and progesterone, modulate the endothelial glycocalyx. Diseases prevalent in women that alter the glycocalyx, and therapeutic forms to prevent glycocalyx degradation and potential treatments that can reconstitute its structure and function will also be discussed.

Fast versus slow infusion of 20% albumin: a randomized controlled cross-over trial in volunteers

BACKGROUND

We investigated whether plasma volume (PV) expansion of 20% albumin is larger when the fluid is administered rapidly compared with a slow infusion.

METHODS

In this open-labeled randomized interventional controlled trial, 12 volunteers (mean age, 28 years) received 3 mL/kg of 20% albumin (approximately 225 mL) over 30 min (fast) and 120 min (slow) in a cross-over fashion. Blood hemoglobin and plasma albumin were measured on 15 occasions during 6 h to estimate the PV expansion and the capillary leakage of albumin and fluid.

RESULTS

The largest PV expansion was 16.1% ± 6.5% (mean ± SD) for fast infusion and 12.8% ± 4.0% for slow infusion (p = 0.52). The median area under the curve for the PV expansion was 69% larger for the fast infusion during the first 2 h (p = 0.034), but was then similar for both infusions. The half-life of the PV expansion did not differ significantly (median, 5.6 h versus 5.4 h, p = 0.345), whereas the intravascular half-life of the excess albumin was 8.0 h for fast infusion and 6.3 h for slow infusion (p = 0.028). The measured urine output was almost three times larger than the infused volume. The plasma concentration of atrial natriuretic peptide (MR-proANP) accelerated the capillary leakage of albumin and the urine flow.

CONCLUSIONS

The intravascular persistence of albumin was longer, but the fluid kinetics was the same, when 20% albumin was infused over 30 min compared with 120 min. We found no disadvantages of administering the albumin at the higher rate. Trial registration EU Clinical Trials Register, EudraCT2017-003687-12, registered September 22, 2017, https://www.clinicaltrialsregister.eu/ctr-search/trial/2017-003687-12/SE.

Plasma Volume Expansion and Fluid Kinetics of 20% Albumin During General Anesthesia and Surgery Lasting for More Than 5 Hours

BACKGROUND

Intraoperative administration of crystalloid for plasma volume expansion may be reduced by use of hyperoncotic albumin. However, the degree of plasma volume expansion with administration of 20% albumin is poorly quantitated. We estimated the amount of volume expansion attributable to 20% albumin administration in patients undergoing surgery for more than 5 hours.

METHODS

Twenty percent albumin was delivered at 3 mL/kg by intravenous infusion during 30 minutes to 15 patients (mean ± standard deviation [SD] age; 46 ± 15 years) undergoing surgery. Blood samples and urine were collected for 5 hours. Mass balance calculations and volume kinetics were used to estimate plasma volume expansion and capillary leakage of albumin and fluid.

RESULTS

Administration of 20% albumin was associated with an increase in plasma volume amounting to 1.7 times the infused volume. After correction for hemorrhage, the median (and 25th to 75th percentiles) intravascular half-life for the administered albumin mass was 20.4 (14.2-34.7) hours. The plasma volume decreased with a half-life of 21.7 (16.1-26.8) hours. Urinary excretion was 3 times greater than the infused volume of albumin, but kinetic analysis suggested that other flows of fluid to and from the plasma occurred more slowly than previously found in volunteers. Hemodynamic support with norepinephrine increased urinary excretion and contracted the plasma volume.

CONCLUSIONS

Albumin (20%) increased the plasma volume by 1.7 times the infused volume. Our results do not support that the transcapillary leakage of albumin is accelerated by anesthesia and surgery.

Protective Treatments against Endothelial Glycocalyx Degradation in Surgery: A Systematic Review and Meta-Analysis

The aim was to explore the body of literature focusing on protective treatments against endothelial glycocalyx degradation in surgery. A comprehensive systematic review of relevant articles was conducted across databases. Inclusion criteria: (1) treatments for the protection of the endothelial glycocalyx in surgery; (2) syndecan-1 used as a biomarker for endothelial glycocalyx degradation. Outcomes analysed: (1) mean difference of syndecan-1 (2) correlation between glycocalyx degradation and inflammation; (3) correlation between glycocalyx degradation and extravasation. A meta-analysis was used to present mean differences and 95% confidence intervals. Seven articles with eight randomised controlled trials were included. The greatest change from baseline values in syndecan-1 concentrations was generally from the first timepoint measured post-operatively. Interventions looked to either dampen the inflammatory response or fluid therapy. Methylprednisolone had the highest mean difference in plasma syndecan-1 concentrations. Ulinastatin showed correlations between alleviation of degradation and preserving vascular permeability. In this systematic review of 385 patients, those treated were more likely than those treated with placebo to exhibit less shedding of the endothelial glycocalyx. Methylprednisolone has been shown to specifically target the transient increase of glycocalyx degradation immediately post-operation and has displayed anti-inflammatory effects. We have proposed suggestions for improved uniformity and enhanced confidence for future randomised controlled trials.

The Effects of Resuscitative Fluid Therapy on the Endothelial Surface Layer

The goal of resuscitative fluid therapy is to rapidly expand circulating blood volume in order to restore tissue perfusion. Although this therapy often serves to improve macrohemodynamic parameters, it can be associated with adverse effects on the microcirculation and endothelium. The endothelial surface layer (ESL) provides a protective barrier over the endothelium and is important for regulating transvascular fluid movement, vasomotor tone, coagulation, and inflammation. Shedding or thinning of the ESL can promote interstitial edema and inflammation and may cause microcirculatory dysfunction. The pathophysiologic perturbations of critical illness and rapid, large-volume fluid therapy both cause shedding or thinning of the ESL. Research suggests that restricting the volume of crystalloid, or “clear” fluid, may preserve some ESL integrity and improve outcome based on animal experimental models and preliminary clinical trials in people. This narrative review critically evaluates the evidence for the detrimental effects of resuscitative fluid therapy on the ESL and provides suggestions for future research directions in this field.

Human glycocalyx shedding: Systematic review and critical appraisal

BACKGROUND

The number of studies measuring breakdown products of the glycocalyx in plasma has increased rapidly during the past decade. The purpose of the present systematic review was to assess the current knowledge concerning the association between plasma concentrations of glycocalyx components and structural assessment of the endothelium.

METHODS

We performed a literature review of Pubmed to determine which glycocalyx components change in a wide variety of human diseases and conditions. We also searched for evidence of a relationship between plasma concentrations and the thickness of the endothelial glycocalyx layer as obtained by imaging methods.

RESULTS

Out of 3,454 publications, we identified 228 that met our inclusion criteria. The vast majority demonstrate an increase in plasma glycocalyx products. Sepsis and trauma are most frequently studied, and comprise approximately 40 publications. They usually report 3-4-foldt increased levels of glycocalyx degradation products, most commonly of syndecan-1. Surgery shows a variable picture. Cardiac surgery and transplantations are most likely to involve elevations of glycocalyx degradation products. Structural assessment using imaging methods show thinning of the endothelial glycocalyx layer in cardiovascular conditions and during major surgery, but thinning does not always correlate with the plasma concentrations of glycocalyx products. The few structural assessments performed do not currently support that capillary permeability is increased when the plasma levels of glycocalyx fragments in plasma are increased.

CONCLUSIONS

Shedding of glycocalyx components is a ubiquitous process that occurs during both acute and chronic inflammation with no sensitivity or specificity for a specific disease or condition.

Elevated Plasma Concentrations of Syndecan-1 Do Not Correlate With Increased Capillary Leakage of 20% Albumin

BACKGROUND

Preclinical experiments show that an inflammatory reaction causes degradation of the endothelial glycocalyx layer and accelerated capillary leakage of albumin and fluid. The hypothesis in the present study was that elevated plasma concentrations of glycocalyx degradation products are associated with greater capillary leakage in humans.

METHODS

This open clinical trial involved administration of an intravenous infusion of 20% albumin at 3 mL/kg over 30 minutes to 15 postburn patients who showed an activated inflammatory response. Blood samples and urine were collected for 300 minutes. The plasma concentrations of 2 biomarkers of glycocalyx degradation-syndecan-1 and heparan sulfate-were measured at 0, 60, and 300 minutes and compared to the capillary leakage of albumin and fluid obtained by mass balance calculations and population kinetic analysis.

RESULTS

Patients were studied at 7 days (median) after a burn injury that covered 15% (maximum 48%) of the body surface area. The median plasma syndecan-1 concentration was 71 (25th-75th percentiles, 41-185) ng/mL. The 2 patients with highest values showed 2279 and 2395 ng/mL (normal 15 ng/mL). Heparan sulfate concentrations averaged 915 (673-1539) ng/mL. The infused amount of albumin was 57 (48-62) g, and 6.3 (5.1-7.7)% of that leaked from the plasma per hour.Linear correlation analysis of the relationship between the 10logarithm of the mean syndecan-1 and the albumin leakage showed a slope coefficient of -1.3 (95% confidence interval [CI], -3.6 to 1.0) and a correlation coefficient of -0.33 (P = .24). The kinetic analysis revealed that syndecan-1 served as a statistically significant covariate to the albumin leakage, but the relationship was inverse (power exponent -0.78, 95% CI, -1.50 to -0.05; P < .02). Heparan sulfate levels did not correlate with the capillary leakage of albumin or fluid in any of the analyses.

CONCLUSIONS

A raised plasma concentration of syndecan-1 alone cannot be extrapolated to indicate increased capillary leakage of albumin and fluid.

Effect of peri-operative crystalloid fluid rate on circulating hyaluronan in healthy dogs: A pilot study

Hypervolemia can damage the endothelial glycocalyx, a key regulator of vascular permeability, coagulation and inflammation. A starting peri-operative crystalloid fluid rate of 5mL/kg/h is recommended for healthy dogs undergoing elective procedures but higher rates continue to be commonly used. This study aimed to determine if a higher starting perioperative fluid rate was associated with a greater increase in plasma concentrations of hyaluronan, a marker correlated with glycocalyx damage, in systemically healthy dogs undergoing elective surgical procedures. Based on a sample size calculation, 38 dogs undergoing ovariohysterectomy or castration were randomly assigned to receive lactated Ringer's at a starting perioperative fluid rate of 10mL/kg/h (n=19) or 5mL/kg/h (n=19). Plasma hyaluronan concentrations were measured by ELISA in pre- and post-fluid therapy samples. There were no significant differences between groups in hyaluronan values before (baseline, P=0.52) or after perioperative fluid administration (P=0.62). Compared to respective baseline values, hyaluronan values significantly increased following 5 and 10ml/kg/h fluid administration (P=0.02 for both comparisons). This preliminary study identified an increase in hyaluronan over the course of fluid therapy with both the low and high fluid rate. One possible explanation is that both fluid rates contribute to glycocalyx disruption, but it should be emphasized that hyaluronan is not specific to the glycocalyx. Further studies are needed to determine the origin of the increased circulating hyaluronan and its clinical significance in dogs undergoing elective surgical procedures.

Endothelial cells, neutrophils and platelets: getting to the bottom of an inflammatory triangle

Severe fibrotic and thrombotic events permeate the healthcare system, causing suffering for millions of patients with inflammatory disorders. As late-state consequences of chronic inflammation, fibrosis and thrombosis are the culmination of pathological interactions of activated endothelium, neutrophils and platelets after vessel injury. Coupling of these three cell types ensures a pro-coagulant, cytokine-rich environment that promotes the capture, activation and proliferation of circulating immune cells and recruitment of key pro-fibrotic cell types such as myofibroblasts. As the first responders to sterile inflammatory injury, it is important to understand how endothelial cells, neutrophils and platelets help create this environment. There has been a growing interest in this intersection over the past decade that has helped shape the development of therapeutics to target these processes. Here, we review recent insights into how neutrophils, platelets and endothelial cells guide the development of pathological vessel repair that can also result in underlying tissue fibrosis. We further discuss recent efforts that have been made to translate this knowledge into therapeutics and provide perspective as to how a compound or combination therapeutics may be most efficacious when tackling fibrosis and thrombosis that is brought upon by chronic inflammation.

The Extended Starling principle needs clinical validation

The Revised (or "Extended") Starling principle is based on highly controlled laboratory-based frog and rodent experiments and remains a hypothesis awaiting clinical validation. A key point is that the endothelial glycocalyx layer moves the oncotic gradient from being between the plasma and the interstitium to between the plasma and a virtually protein-free space between the glycocalyx and the endothelial cell membrane, which dramatically changes the prerequisites for fluid absorption from tissue to plasma. However, many experimental and clinical observations in humans agree poorly with the new microcirculatory proposals. The most troubling aspect of the explanation regarding the role of the glycocalyx in the Revised Starling principle is the effective reabsorption of fluid by skeletal muscle when the capillary filtration pressure is acutely reduced. Other issues include the plasma volume effects of hypertonic saline, iso-oncotic and hyper-oncotic albumin, fluid distribution during cardio-pulmonary bypass, and the virtually identical capillary leakage of plasma and albumin despite marked inflammation found in our fluid therapy studies. The Revised Starling principle deals mainly with steady-state conditions, but the circulatory system is highly dynamic. Second to second vasomotion is always operational and must be considered to understand what we observe in humans.

A review on the physiological and pathophysiological role of endothelial glycocalyx

The glycocalyx is a gel-like layer covering the luminal surface of vascular endothelial cells. It comprises of membrane-attached proteoglycans, glycosaminoglycan chains, glycoproteins, and adherent plasma proteins. The glycocalyx maintains homeostasis of the vasculature, which includes controlling vascular permeability and microvascular tone, preventing microvascular thrombosis, and regulating leukocyte adhesion. In the past decades, the number of studies on endothelial glycocalyx has steadily grown. Glycocalyx emerged as an essential part of blood vessels involved in multiple physiological functions. Damage to glycocalyx is associated with many types of diseases. The structure and physiology and pathophysiology of the glycocalyx, as well as the clinical effects of glycocalyx degradation, are addressed throughout this study. We strive in particular to define therapeutic approaches for the survival or reparation of the glycocalyx.

Water content of the endothelial glycocalyx layer estimated by volume kinetic analysis

BACKGROUND

The water volume of the endothelial glycocalyx layer has been estimated at 0.7 to 1.7 L using tracer methods of unclear value. The present study attempts to measure this fluid volume by analyzing the kinetics of a crystalloid fluid load.

METHODS

An intravenous infusion of approximately 1 L of Ringer's acetate was administered to 35 healthy volunteers, and the central volume of distribution of the water volume was calculated from the urinary excretion and frequent measurements of the fluid-induced hemodilution using mixed-effects modeling software. Comparisons were made with the plasma volume derived from three published anthropometric regression equations based on isotope measurements. In a second analysis, up to 2.5 L of Ringer's was administered to 60 volunteers selected from a cohort of 160 to have as similar hematocrits as possible to the volunteers whose data were used to create the anthropometric equations.

RESULTS

Volume kinetics showed that the infused crystalloid fluid occupied a larger central fluid space than was estimated with the isotope measurements. The first analysis of the 35 subjects indicated a mean difference of 0.51 L in males and 0.49 L in females. The second, larger analysis showed a mean excess volume of 0.43 L, which was approximately 15% of the circulating plasma volume.

CONCLUSIONS

A crystalloid fluid load expands a 0.4-0.5 L larger central fluid space than the circulating plasma volume. The excess volume is probably located in the glycocalyx layer.

Understanding volume kinetics

The distribution and elimination kinetics of the water volume in infusion fluids can be studied by volume kinetics. The approach is a modification of drug pharmacokinetics and uses repeated measurements of blood hemoglobin and urinary excretion as input variables in (usually) a two-compartment model with expandable walls. Study results show that crystalloid fluid has a distribution phase that gives these fluids a plasma volume expansion amounting to 50%-60% of the infused volume as long as the infusion lasts, while the fraction is reduced to 15%-20% within 30 minutes after the infusion ends. Small volumes of crystalloid barely distribute to the interstitium, whereas rapid infusions tend to cause edema. Fluid elimination is very slow during general anesthesia due to the vasodilatation-induced reduction of the arterial pressure, whereas elimination is less affected by hemorrhage. The half-life is twice as long for saline than for Ringer solutions. Elimination is slower in conscious males than conscious females, and high red blood cell and thrombocyte counts retard both distribution and re-distribution. Children have faster turnover than adults. Plasma volume expansions are similar for glucose solutions and Ringer's, but the expansion duration is shorter for glucose. Concentrated urine before and during infusion slows down the elimination of crystalloid fluid. Colloid fluids have no distribution phase, an intravascular persistence half-life of 2-3 hours, and-at least for hydroxyethyl starch-the ability to reduce the effect of subsequently infused crystalloids. Accelerated distribution due to degradation of the endothelial glycocalyx layer has not yet been demonstrated.

Volume kinetic analysis of fluid retention after induction of general anesthesia

Background

Induction of general anesthesia increases the hemodilution resulting from infusion of crystalloid fluid, which is believed to be due to slower distribution caused by arterial hypotension. When normal distribution returns is not known.

Methods

An intravenous infusion of 25 mL kg^− 1 of Ringer’s lactate was infused over 30 min to 25 volunteers just after induction of general anesthesia for open abdominal hysterectomy. A two-volume model was fitted to the repeated measurements of the blood hemoglobin concentration and the urinary excretion using mixed-effects modelling software. Individual-specific covariates were added in sequence.

Results

Distribution of infused fluid was interrupted during the first 20 min of the infusions. During this time 16.6 mL kg^− 1 of lactated Ringer’s had been infused, of which virtually all remained in the circulating blood. Thereafter, the fluid kinetics was similar to that previously been found in awake volunteers except for the elimination rate constant (k₁₀), which remained to be very low (0.86 × 10^− 3 min^− 1). Redistribution of infused fluid from the interstitium to the plasma occurred faster (higher k₂₁) when the arterial pressure was low. No covariance was found between the fixed parameters and preoperatively concentrated urine, the use of sevoflurane or propofol to maintain the anesthesia, or the plasma concentrations of two degradation products of the endothelial glycocalyx, syndecan-1 and heparan sulfate.

Conclusions

Induction of general anesthesia interrupted the distribution of lactated Ringer’s solution up to when 16.6 mL kg^− 1 of crystalloid fluid had been infused. Plasma volume expansion during this period of time was pronounced.

Trial registration

Controlled-trials.com (ISRCTN81005631) on May 17, 2016 (retrospectively registered).