Non-invasive evaluation of macro- and microhemodynamic changes during induction of general anesthesia - A prospective observational single-blinded trial.

BACKGROUND: Hypotension and bradycardia are known side effects of general anesthesia, while little is known about further macro- and microhemodynamic changes during induction. Intriguing is furthermore, why some patients require no vasopressor medication to uphold mean arterial pressure, while others need vasopressor support. OBJECTIVE: Determination of macro- and microhemodynamic changes during induction of general anesthesia. METHODS: We enrolled 150 female adults scheduled for gynaecological surgery into this prospective observational, single-blinded trial. Besides routinely measuring heart rate (HR) and mean arterial blood pressure (MAP), the non-invasive technique of thoracic electrical bioimpedance was applied to measure cardiac output (CO), cardiac index (CI), stroke volume (SV), stroke volume variability (SVV) and index of myocardial contractility (ICON) before induction of anesthesia, 7 times during induction, and, finally, after surgery in the recovery room. Changes in microcirculation were assessed using sidestream dark field imaging to establish the perfused boundary region (PBR), a validated gauge of glycocalyx health. Comparisons were made with Friedman's or Wilcoxon test for paired data, and with Mann-Whitney-U test for unpaired data, with post-hoc corrections for multiple measurements by the Holm-Bonferroni method. RESULTS: 83 patients did not need vasopressor support, whereas 67 patients required therapy (norepinephrine, atropine or cafedrine/theodrenaline) to elevate MAP values to ≥70mmHg during induction, 54 of these receiving norepinephrine (NE) alone. Pre-interventional (basal) values of CO, CI, ICON, SV and SVV were all significantly lower in the group of patients later requiring NE (p < 0.04), whereas HR and MAP were identical for both groups. HR, MAP and CO decreased from baseline to 12 min after induction of general anesthesia in both the patients without and those with NE support. Heart rate decreased significantly by about 25% in both groups (-19 to -21 bpm). The median individual decrease of MAP amounted to -26.7% (19.7/33.3, p < 0.001) and -26.1% (11.6/33.2, p < 0.001), respectively, whereas for CO it was -40.7% (34.1/50.1, p < 0.001) and -43.5% (34.8/48.7). While these relative changes did not differ between the two groups, in absolute values there were significantly greater decreases in CO, CI, SV and ICON in the group requiring NE. Noteably, NE did not restore ICON or the other cardiac parameters to levels approaching those of the group without NE. PBR was measured in a total of 84 patients compiled from both groups, there being no intergroup differences. It increased 6.4% (p < 0.001) from pre-induction to the end of the operation, indicative of damage to microvascular glycocalyx. CONCLUSION: Non-invasive determination of CO provides additional hemodynamic information during anesthesia, showing that induction results in a significant decrease not only of MAP but also of CO and other cardiac factors at all timepoints compared to baseline values. The decrease of CO was greater than that of MAP and, in contrast to MAP, did not respond to NE. There was also no sign of a positive inotropic effect of NE in this situation. Support of MAP by NE must consequently result from an increase in peripheral arterial resistance, posing a risk for oxygen supply to tissue. In addition, general anesthesia and the operative stimulus lead to an impairment of the microcirculation.

Endothelial Glycocalyx.

The endothelial glycocalyx (EG) is the most luminal layer of the blood vessel, growing on and within the vascular wall. Shedding of the EG plays a central role in many critical illnesses. Degradation of the EG is associated with increased morbidity and mortality. Certain illnesses and iatrogenic interventions can cause degradation of the EG. It is not known whether restitution of the EG promotes the survival of the patient. First trials that focus on the reorganization and/or restitution of the EG seem promising. Nevertheless, the step "from bench to bedside" is still a big one.

Preinterventional hydrocortisone sustains the endothelial glycocalyx in cardiac surgery.

BACKGROUND: Patients undergoing cardiac surgery commonly develop systemic inflammation associated with tissue edema, which impairs outcome. One main pathomechanism leading to the edema is the deterioration of the endothelial glycocalyx, a key component of the vascular barrier. In animal models hydrocortisone has proved to be protective for the glycocalyx. OBJECTIVE: This trial evaluates the effect of hydrocortisone on glycocalyx integrity in patients undergoing cardiac surgery with cardiopulmonary bypass. METHODS: In a prospective, randomized interventional pilot trial, 30 patients received either hydrocortisone (100 mg over 10 min) or placebo (saline control) before surgery. Plasma concentrations of glycocalyx constituents (syndecan-1, heparan sulfate) and various clinical parameters (respiratory and renal function, inflammatory markers, use of vasopressors, length of stay at the intensive care unit) were measured. Primary endpoint was a significant difference of glycocalyx constituents in plasma. Comparisons were made with Friedman's and Wilcoxon tests (paired data), or the Kruskal-Wallis and Mann-Whitney U tests (unpaired data). Holm-Bonferroni method was used for post-hoc corrections. RESULTS: Heparan sulfate and syndecan-1 increased significantly during and after cardiac surgery with cardiopulmonary bypass in both groups. Whereas the maximum increase of heparan sulfate was 12.3-fold in the control vs. 3.8-fold in the pretreated group (p < 0.05), syndecan-1 values showed no significant difference between the groups (maximal increase 3-fold). The inflammatory markers C-reactive protein and interleukin-6 were also higher in the control than in the hydrocortisone group, but there was no difference in patient mortality (zero), or in any clinical parameters. CONCLUSIONS: Pretreatment with hydrocortisone ameliorated shedding of heparan sulfate, a major constituent of the endothelial glycocalyx, in patients undergoing cardiac surgery with cardiopulmonary bypass, but had no relevant influence on various clinical parameters or patient mortality. The relatively small number of patients in this pilot study probably precluded detection of positive outcome differences.

Chances and limitations of isolated mouse heart models for investigating the endothelial glycocalyx1.

BACKGROUND: The endothelial glycocalyx plays a decisive role in maintaining vascular homeostasis. Previous animal models have mainly focused on in-vitro experiments or the isolated beating guinea pig heart. To further evaluate underlying mechanisms of up- and down regulation, knock-out animals seem to be a promising option. OBJECTIVE: Aim of the present study was to evaluate if an isolated mouse-heart model is suitable for glycocalyx research. METHODS: Isolated beating mouse hearts (C57/Bl6J) underwent warm, no-flow ischemia and successive reperfusion. Coronary effluent was analyzed by ELISA and Western blot for the glycocalyx core protein: syndecan-1. Hearts were prepared for either immunofluorescence or electron microscopy and lysed for Western blot analysis. RESULTS: An endothelial glycocalyx covering the total capillary circumference and syndecan-1 were detected by electron and immunofluorescence microscopy. Ischemia/reperfusion seriously deteriorated both findings. Confoundingly, syndecan-1 was not detectable either in the coronary effluent or in the lysates of blood-free hearts by ELISA or Western blot technique. CONCLUSIONS: Blood vessels of mouse hearts contain an endothelial glycocalyx comparable to that of other animals also with respect to its core protein syndecan-1. But, for studies including quantification of intravascular soluble glycocalyx constituents, the amount of syndecan-1 in mouse hearts seems to be too low.

Vascular Endothelial Dysfunction during Cardiac Surgery: On-Pump versus Off-Pump Coronary Surgery.

BACKGROUND: Cardiac surgery often causes ischemia and development of a systemic inflammatory response syndrome, which impairs vascular barrier function, normally maintained by the endothelial cell line and the endothelial glycocalyx (EG). The EG normally covers and protects healthy endothelial cells throughout the vasculature. The aim of the present study was to assess the disruption of the cellular part of the microvascular barrier by determining parameters of endothelial cell activation known to influence and reflect cell-cell junctional integrity. Particular attention was placed on angiopoietins and their important effects on endothelial gap junctions. Furthermore, comparative measurements were undertaken in patients undergoing on- and off-pump cardiac surgery, the latter group presumably experiencing less ischemic stress. METHODS: 30 patients undergoing elective coronary artery bypass surgery were assigned to the conventional coronary artery bypass (CCAB) group (n = 15) or the off-pump coronary artery bypass grafting (OPCAB) group (n = 15). Blood samples were obtained for measuring angiopoietin-1 (Ang-1), angiopoietin-2 (Ang-2), vascular endothelial (VE)-cadherin, and endocan at various time points. RESULTS: There were significant increases in all measured parameters in both study groups versus the respective basal values. Maximal increases were as follows: Ang-1: CCAB +220%, OPCAB +166%, p < 0.05 each; Ang-2: CCAB +150%, OPCAB +20%, p < 0.05 each; VE-cadherin: CCAB +87%, OPCAB +66%, p < 0.05 each; endocan: CCAB +323%, OPCAB +72%, p < 0.05 each. CONCLUSION: The present study demonstrates the activation of endothelial cells, shedding of cell-cell contacts and a potential intrinsic counterregulation by Ang-1 and endocan in patients undergoing major cardiac surgery. Quantitatively greater deviations of parameters in the CCAB than in the OPCAB group suggest a relation between the occurrence of ischemia/reperfusion and the extent of endothelial activation.

Sevoflurane mitigates shedding of hyaluronan from the coronary endothelium, also during ischemia/reperfusion: an ex vivo animal study.

Glycosaminoglycan hyaluronan (HA), a major constituent of the endothelial glycocalyx, helps to maintain vascular integrity. Preconditioning the heart with volatile anesthetic agents protects against ischemia/reperfusion injury. We investigated a possible protective effect of sevoflurane on the glycocalyx, especially on HA. The effect of pre-ischemic treatment with sevoflurane (15 minutes at 2% vol/vol gas) on shedding of HA was evaluated in 28 isolated, beating guinea pig hearts, subjected to warm ischemia (20 minutes at 37°C) followed by reperfusion (40 minutes), half with and half without preconditioning by sevoflurane. HA concentration was measured in the coronary effluent. Over the last 20 minutes of reperfusion hydroxyethyl starch (1 g%) was continuously infused and the epicardial transudate collected over the last 5 minutes for measuring the colloid extravasation. Additional hearts were fixed by perfusion after the end of reperfusion for immunohistology and electron microscopy. Sevoflurane did not significantly affect post-ischemic oxidative stress, but strongly inhibited shedding of HA during the whole period, surprisingly even prior to ischemia. Immunohistology demonstrated that heparan sulfates and SDC1 of the glycocalyx were also preserved by sevoflurane. Electron microscopy revealed shedding of glycocalyx caused by ischemia and a mostly intact glycocalyx in hearts exposed to sevoflurane. Coronary vascular permeability of the colloid hydroxyethyl starch was significantly decreased by sevoflurane vs the control. We conclude that application of sevoflurane preserves the coronary endothelial glycocalyx, especially HA, sustaining the vascular barrier against ischemic damage. This may explain beneficial effects associated with clinical use of volatile anesthetics against ischemia/reperfusion injury.

Regulation of blood flow and volume exchange across the microcirculation.

Oxygen delivery to cells is the basic prerequisite of life. Within the human body, an ingenious oxygen delivery system, comprising steps of convection and diffusion from the upper airways via the lungs and the cardiovascular system to the microvascular area, bridges the gap between oxygen in the outside airspace and the interstitial space around the cells. However, the complexity of this evolutionary development makes us prone to pathophysiological problems. While those problems related to respiration and macrohemodynamics have already been successfully addressed by modern medicine, the pathophysiology of the microcirculation is still often a closed book in daily practice. Nevertheless, here as well, profound physiological understanding is the only key to rational therapeutic decisions. The prime guarantor of tissue oxygenation is tissue blood flow. Therefore, on the premise of intact macrohemodynamics, the microcirculation has three major responsibilities: 1) providing access for oxygenated blood to the tissues and appropriate return of volume; 2) maintaining global tissue flood flow, even in the face of changes in central blood pressure; and 3) linking local blood flow to local metabolic needs. It is an intriguing concept of nature to do this mainly by local regulatory mechanisms, impacting primarily on flow resistance, be this via endothelial or direct smooth muscle actions. The final goal of microvascular blood flow per unit of time is to ensure the needed exchange of substances between tissue and blood compartments. The two principle means of accomplishing this are diffusion and filtration. While simple diffusion is the quantitatively most important form of capillary exchange activity for the respiratory gases, water flux across the blood-brain barrier is facilitated via preformed specialized channels, the aquaporines. Beyond that, the vascular barrier is practically nowhere completely tight for water, with paracellular filtration giving rise to generally low but permanent fluid flux outwards into the interstitial space at the microvascular high pressure segment. At the more leaky venular aspect, both filtration and diffusion allow for bidirectional passage of water, nutrients, and waste products. We are just beginning to appreciate that a major factor for maintaining tissue fluid homeostasis appears to be the integrity of the endothelial glycocalyx.

Degradation of the endothelial glycocalyx in clinical settings: searching for the sheddases.

The endothelial glycocalyx has a profound influence at the vascular wall on the transmission of shear stress, on the maintenance of a selective permeability barrier and a low hydraulic conductivity, and on attenuating firm adhesion of blood leukocytes and platelets. Major constituents of the glycocalyx, including syndecans, heparan sulphates and hyaluronan, are shed from the endothelial surface under various acute and chronic clinical conditions, the best characterized being ischaemia and hypoxia, sepsis and inflammation, atherosclerosis, diabetes, renal disease and haemorrhagic viral infections. Damage has also been detected by in vivo microscopic techniques. Matrix metalloproteases may shed syndecans and heparanase, released from activated mast cells, cleaves heparan sulphates from core proteins. According to new data, not only hyaluronidase but also the serine proteases thrombin, elastase, proteinase 3 and plasminogen, as well as cathepsin B lead to loss of hyaluronan from the endothelial surface layer, suggesting a wide array of potentially destructive conditions. Appropriately, pharmacological agents such as inhibitors of inflammation, antithrombin and inhibitors of metalloproteases display potential to attenuate shedding of the glycocalyx in various experimental models. Also, plasma components, especially albumin, stabilize the glycocalyx and contribute to the endothelial surface layer. Though symptoms of the above listed diseases and conditions correlate with sequelae expected from disturbance of the endothelial glycocalyx (oedema, inflammation, leukocyte and platelet adhesion, low reflow), therapeutic studies to prove a causal connection have yet to be designed. With respect to studies on humans, some clinical evidence exists for benefits from application of sulodexide, a preparation delivering precursors of the glycocalyx constituent heparan sulphate. At present, the simplest option for protecting the glycocalyx seems to be to ensure an adequate level of albumin. However, also in this case, definite proof of causality needs to be delivered.

Acute degradation of the endothelial glycocalyx in infants undergoing cardiac surgical procedures.

BACKGROUND: There is no doubt today about the existence of the endothelial glycocalyx (EG) and its decisive role in maintaining vascular homeostasis in adult humans. Shedding of the EG has been demonstrated in adults with sepsis or trauma, in patients undergoing major operations, and after ischemia/reperfusion. The aim of the present study was to demonstrate whether shedding of the EG also occurs in infants undergoing heart operations. METHODS: Two major constituents of the EG (syndecan-1 and hyaluronan) were measured in the arterial serum of 42 infants during cardiac operations in a prospective observational study. The groups were defined according to the ischemic impact: cardiac operations with cardiopulmonary bypass under beating heart conditions (CPB group, regional ischemia of lungs, n = 10), operations with cardiopulmonary bypass and aortic clamping (CPB+AC group, regional ischemia of heart and lungs, n = 24), and cardiac operations with deep hypothermic circulatory arrest (CPB+AC+DHCA group, whole-body ischemia, n = 8). RESULTS: Syndecan-1 and hyaluronan were detected in all infants, providing an indication for the presence of a glycocalyx. During the operations, no significant difference in syndecan-1 concentration was observed in the CPB group, but levels increased significantly in both other groups (maximum increases: CPB+AC 3.0-fold, CPB+AC+DHCA 3.7-fold, p < 0.05). Hyaluronan increased significantly in the course of the operation in all groups (maximum increases: CPB 1.2-fold, CPB+AC 1.4-fold, CPB+AC+DHCA 1.7-fold, p < 0.05). CONCLUSIONS: The present data provides the first evidence for basal turnover of vascular EG in infants. Similarly to the process in adults, the shedding of this structure increases with ischemia/reperfusion, the extent being dependent on the degree of ischemic challenge.

Hypervolemia increases release of atrial natriuretic peptide and shedding of the endothelial glycocalyx.

INTRODUCTION: Acute normovolemic hemodilution (ANH) and volume loading (VL) are standard blood-sparing procedures. However, VL is associated with hypervolemia, which may cause tissue edema, cardiopulmonary complications and a prolonged hospital stay. The body reacts to hypervolemia with release of atrial natriuretic peptide (ANP) from the heart. ANP has been shown to deteriorate the endothelial glycocalyx, a vital part of the vascular permeability barrier. The aim of the present study was to evaluate and compare ANP release and damage to the glycocalyx during ANH and VL. METHODS: ANH or VL with 6% hydroxyethyl starch 130/0.4 was administered prior to elective surgery in patients of good cardiopulmonary health (n =9 in each group). We measured concentrations of ANP in plasma and of three main constituent parts of the glycocalyx (hyaluronan, heparan sulfate and syndecan 1) in serum before and after ANH or VL. Heparan sulfate and syndecan 1 levels in urine were also determined. RESULTS: In contrast to ANH, VL (20 ml/kg) induced a significant release of ANP (approximately +100%, P <0.05) and increased the serum concentration of two glycocalyx constituents, hyaluronan and syndecan 1 (both by about 80%, P <0.05). Elevation of syndecan 1 was also detected in the urine of patients undergoing VL, but no increase was found in patients undergoing ANH. Heparan sulfate levels were not influenced by either procedure. CONCLUSION: These data suggest that hypervolemia increases the release of ANP and causes enhanced shedding of the endothelial glycocalyx. This perturbation must be expected to impair the vascular barrier, implying that VL may not be as safe as generally assumed and that it should be critically evaluated.

Protection of glycocalyx decreases platelet adhesion after ischaemia/reperfusion: an animal study.

BACKGROUND: Strategies targeting the protection of the vascular barrier, in particular the endothelial glycocalyx, are subjects of current research. Antithrombin III and hydrocortisone have been shown to reduce shedding of the glycocalyx following ischaemia/reperfusion. Platelet adhesion to endothelial cells is one consequence of ischaemia/reperfusion. OBJECTIVE: Our goal was to evaluate the effect of pharmacological protection of the glycocalyx on platelet adhesion. DESIGN: An experimental interventional animal study. SETTING: The study was carried out in a basic science laboratory at the University of Munich. ANIMALS: Eighty male guinea pigs (250 to 300 g) were used for the experiment. MAIN OUTCOME MEASURES: The effect of preischaemic treatment with hydrocortisone 10 µg ml(-1) or antithrombin 1 IU ml on adherence of platelets was evaluated in isolated, beating guinea pig hearts (Langendorff model). Hearts were subjected to warm ischaemia (20 min at 37 °C) and consecutive reperfusion. Platelets were injected at the beginning of reperfusion via the aortic cannula and platelet concentration was measured in the effluent (after passing through the coronary vascular system). RESULTS: Ischaemia and reperfusion led to significant shedding of the endothelial glycocalyx. Coronary venous release of syndecan-1 increased nine-fold, and heparan sulphate showed a 20.3-fold increase after ischaemia/reperfusion (both P < 0.01). Pretreatment with hydrocortisone or antithrombin III reduced endothelial glycocalyx shedding significantly (P < 0.05). Adherence of platelets to the coronary vascular bed increased more than 2.5-fold when they were injected during reperfusion. About 40% of this increase was blocked by pretreatment of hearts with hydrocortisone or antithrombin. CONCLUSION: Pretreatment with hydrocortisone or antithrombin III can reduce platelet adhesion during reperfusion after warm ischaemia by protection of the endothelial glycocalyx.

The impact of crystalloidal and colloidal infusion preparations on coronary vascular integrity, interstitial oedema and cardiac performance in isolated hearts.

INTRODUCTION: Recent data suggested an interaction between plasma constituents and the endothelial glycocalyx to be relevant for vascular barrier function. This might be negatively influenced by infusion solutions, depending on ionic composition, pH and binding properties. The present study evaluated such an influence of current artificial preparations. METHODS: Isolated guinea pig hearts were prepared in a modified Langendorff mode and perfused with Krebs-Henseleit buffer augmented with 1g% human albumin. After equilibration the perfusion was switched to replacement of one half buffer by either isotonic saline (NaCl), ringer's acetate (Ri-Ac), 6% and 10% hydroxyethyl starch (6% and 10% HES, resp.), or 4% gelatine (Gel), the artificial colloids having been prepared in balanced solution. We analysed glycocalyx shedding, functional integrity of the vascular barrier and heart performance. RESULTS: While glycocalyx shedding was not observed, diluting albumin concentration towards 0.5g% by artificial solutions was associated with a marked functional breakdown of vascular barrier competence. This effect was biggest with isotonic saline and significantly attenuated with artificial colloids, the difference in the pressure dependent transvascular fluid filtration (basal vs. during infusion in groups NaCl, Ri-Ac, 6% HES, 10% HES and Gel, n = 6 each) being 0.31 ± 0.03 vs. 1.00 ± 0.04; 0.27 ± 0.03 vs. 0.81 ± 0.03; 0.29 ± 0.03 vs. 0.68 ± 0.02; 0.32 ± 0.03 vs. 0.59 ± 0.08 and 0.31 ± 0.04 vs. 0.61 ± 0.03 g/5min, respectively. Heart performance was directly related to pH value (7.38 ± 0.06, 7.33 ± 0.03, 7.14 ± 0.04, 7.08 ± 0.04, 7.25 ± 0.03), the change in the rate pressure product being 21,702 ± 1969 vs. 21,291 ± 2,552; 22,098 ± 2,115 vs. 14,114 ± 3,386; 20,897 ± 2,083 vs. 10,671 ± 1,948; 21,822 ± 2,470 vs. 10,047 ± 2,320 and 20,955 ± 2,296 vs. 15,951 ± 2,755 mmHg × bpm, respectively. CONCLUSIONS: It appears important to maintain the pH value within a physiological range to maintain optimal myocardial contractility. Using colloids prepared in calcium-containing, balanced solutions for volume replacement therapy may attenuate the breakdown of vascular barrier competence in the critically ill.

Physiological levels of A-, B- and C-type natriuretic peptide shed the endothelial glycocalyx and enhance vascular permeability.

Atrial natriuretic peptide (ANP) is a peptide hormone released from the cardiac atria during hypervolemia. Though named for its well-known renal effect, ANP has been demonstrated to acutely increase vascular permeability in vivo. Experimentally, this phenomenon was associated with a marked shedding of the endothelial glycocalyx, at least for supraphysiological intravascular concentrations. This study investigates the impact and mechanism of action of physiological doses of ANP and related peptides on the vascular barrier. In isolated guinea pig hearts, prepared and perfused in a modified Langendorff mode with and without the intravascular presence of the colloid hydroxyethyl starch (HES), we measured functional changes in vascular permeability and glycocalyx shedding related to intracoronary infusion of physiological concentrations of A-, B- and C-type natriuretic peptide (ANP, BNP and CNP). Significant coronary venous washout of glycocalyx constituents (syndecan-1 and heparan sulfate) was observed. As tested for ANP, this effect was positively related to the intracoronary concentration. Intravascular shedding of the glycocalyx was morphologically confirmed by electron microscopy. Also, functional vascular barrier competence decreased, as indicated by significant increases in transudate formation and HES extravasation. Ortho-phenanthroline, a non-specific inhibitor of matrix metalloproteases, was able to reduce ANP-induced glycocalyx shedding. These findings suggest participation of natriuretic peptides in pathophysiological processes like heart failure, inflammation or sepsis. Inhibition of metalloproteases might serve as a basis for future therapeutical options.

Ischemia-reperfusion-induced unmeasured anion generation and glycocalyx shedding: sevoflurane versus propofol anesthesia.

INTRODUCTION: Vascular leakage after ischemia-reperfusion (IR) is largely attributed to the destruction of the endothelial barrier and its associated negatively charged glycocalyx. In vitro, sevoflurane attenuates these changes. Therefore, we compared sevoflurane with propofol with regard to the protection of the glycocalyx and the release of negatively charged substances in vivo. METHODS: After surgical preparation under midazolam-fentanyl, nine pigs each received either propofol or sevoflurane. Ischemia of 90 min was induced by a balloon catheter in the thoracic aorta. After 120 min of reperfusion, the anesthetics were changed back to midazolam-fentanyl. Five animals, each without aortic occlusion, served as time controls. Blood electrolyte parameters were measured, from which the strong ion gap (SIG) was calculated. Serum heparan sulfate concentrations and immunohistology served as a marker of glycocalyx destruction. RESULTS: Immediately after reperfusion, SIG increased significantly only in the propofol group (+6.7 mEq/l versus baseline; p < .05), remaining stable in sevoflurane and both time-controlled groups. Initially, heparan sulfate concentration increased comparably in both experimental groups, but after 120 min, it became stable in sevoflurane-anesthetized animals, while increasing further in the propofol group (p < .05). CONCLUSIONS: Unmeasured anions, predictive of negative outcome in previous studies, did not increase significantly in sevoflurane-anesthetized animals. Additionally, there was less heparan sulfate shedding over time, signaling less destruction of the glycocalyx. Therefore, in this in-vivo situation, sevoflurane proves to be superior to propofol in protecting the endothelium from IR injury.

Mitochondrial thioredoxin reductase is essential for early postischemic myocardial protection.

BACKGROUND: Excessive formation of reactive oxygen species contributes to tissue injury and functional deterioration after myocardial ischemia/reperfusion. Especially, mitochondrial reactive oxygen species are capable of opening the mitochondrial permeability transition pore, a harmful event in cardiac ischemia/reperfusion. Thioredoxins are key players in the cardiac defense against oxidative stress. Mutations in the mitochondrial thioredoxin reductase (thioredoxin reductase-2, Txnrd2) gene have been recently identified to cause dilated cardiomyopathy in patients. Here, we investigated whether mitochondrial thioredoxin reductase is protective against myocardial ischemia/reperfusion injury. METHODS AND RESULTS: In mice, α-MHC-restricted Cre-mediated Txnrd2 deficiency, induced by tamoxifen (Txnrd2-/-ic), aggravated systolic dysfunction and cardiomyocyte cell death after ischemia (90 minutes) and reperfusion (24 hours). Txnrd2-/-ic was accompanied by a loss of mitochondrial integrity and function, which was resolved on pretreatment with the reactive oxygen species scavenger N-acetylcysteine and the mitochondrial permeability transition pore blocker cyclosporin A. Likewise, Txnrd2 deletion in embryonic endothelial precursor cells and embryonic stem cell-derived cardiomyocytes, as well as introduction of Txnrd2-shRNA into adult HL-1 cardiomyocytes, increased cell death on hypoxia and reoxygenation, unless N-acetylcysteine was coadministered. CONCLUSIONS: We report that Txnrd2 exerts a crucial function during postischemic reperfusion via thiol regeneration. The efficacy of cyclosporin A in cardiac Txnrd2 deficiency may indicate a role for Txnrd2 in reducing mitochondrial reactive oxygen species, thereby preventing opening of the mitochondrial permeability transition pore.

Sevoflurane reduces leukocyte and platelet adhesion after ischemia-reperfusion by protecting the endothelial glycocalyx.

BACKGROUND: Adhesion of polymorphonuclear neutrophils and platelets to the vessel wall contributes to generating ischemia-reperfusion injury. Endothelial adhesion molecules are harbored within the glycocalyx, which covers every healthy vascular endothelium but is deteriorated by ischemia-reperfusion. Pretreating the heart with volatile anesthetics reduces myocardial infarct size and protects against ischemia-reperfusion injury. The authors analyzed a possible protective effect of sevoflurane on the glycocalyx and implications for postischemic cell adhesion. METHODS: Isolated guinea pig hearts were perfused with crystalloid buffer and subjected to 20 min of global warm ischemia and 10 min of reperfusion. An intracoronary bolus of 3 x 10(6) polymorphonuclear neutrophilic leukocytes or 1 x 10(9) platelets of human origin was applied after reperfusion, either with or without pretreating with 0.5 or 1 minimal alveolar concentration sevoflurane. The number of sequestered cells was calculated from the difference between coronary input and output. Coronary effluent was collected throughout reperfusion to measure shedding of the glycocalyx. RESULTS: Ischemia-reperfusion induced a significant increase in median (interquartile range) adhesion versus control nonischemic hearts of both leukocytes (38.9 (36.3-42.9) vs. 14.5 (13.1-16.0)%) and platelets (25.0 (22.5-27.1) vs. 9.4 (8.4-10.7)%). Shedding was evidenced by eightfold increases in washout of syndecan-1 and heparan sulfate versus basal. Sevoflurane reduced cell adhesion to near basal at 1 minimal alveolar concentration (leukocytes: 21.2% (19.2-23.9%), platelets: 11.5% (10.4-12.0%). Shedding measurements and electron microscopy demonstrated that sevoflurane-treated hearts retained much of their 200 nm-thick glycocalyx. CONCLUSIONS: Sevoflurane reduces glycocalyx shedding in the postischemic coronary bed, maintaining the natural cover for endothelial adhesion molecules and, thus, reducing cell adhesion. This may explain beneficial outcomes linked to clinical use of volatile anesthetics after ischemia-reperfusion.

Release of atrial natriuretic peptide precedes shedding of the endothelial glycocalyx equally in patients undergoing on- and off-pump coronary artery bypass surgery.

The present study investigates why shedding of the endothelial glycocalyx occurs both in patients undergoing on- and off-pump coronary artery bypass surgery. Release of atrial natriuretic peptide (ANP) was of special interest, because ANP initiates shedding ex vivo. Three major constituents of the glycocalyx (syndecan-1, heparan sulfate and hyaluronan) were measured in arterial blood of patients undergoing coronary artery bypass surgery with (n = 15) and without (n = 15) cardiopulmonary bypass at various phases of the procedure. Additionally, the levels of the inflammatory cytokines interleukin (IL)-6, -8, and -10 and of ANP were evaluated. Elevations of all three components of the glycocalyx were detected in blood of patients undergoing on- (maximum increases: syndecan-1 15-fold, heparan sulfate ninefold, hyaluronan fivefold basal) and off-pump (maximum increases: syndecan-1 fourfold, heparan sulfate twofold, hyaluronan threefold basal) coronary artery surgery. Maximum ANP concentrations increased three- and fourfold basal in on- and off-pump coronary artery surgery, respectively (P < 0.05). There were significant increases in the three cytokine concentrations in both on- (maximum increases: IL-6 146-fold, IL-8 23-fold, IL-10 238-fold basal) and off-pump (maximum increases: IL-6 77-fold, IL-8 eightfold, IL-10 58-fold basal) coronary artery surgery. However, the elevations of ANP preceded those of the cytokines and coincided with or even preceded shedding of the human endothelial glycocalyx in both surgical procedures. These data suggest that release of ANP may lead to perturbation of the endothelial glycocalyx in both on- and off-pump coronary artery bypass surgery.

Perspectives in microvascular fluid handling: does the distribution of coagulation factors in human myocardium comply with plasma extravasation in venular coronary segments?

BACKGROUND: Heterogeneity of vascular permeability has been suggested for the coronary system. Whereas arteriolar and capillary segments are tight, plasma proteins pass readily into the interstitial space at venular sites. Fittingly, lymphatic fluid is able to coagulate. However, heart tissue contains high concentrations of tissue factor, presumably enabling bleeding to be stopped immediately in this vital organ. The distribution of pro- and anti-coagulatively active factors in human heart tissue has now been determined in relation to the types of microvessels. METHODS AND RESULTS: Samples of healthy explanted hearts and dilated cardiomyopathic hearts were immunohistochemically stained. Albumin was found throughout the interstitial space. Tissue factor was packed tightly around arterioles and capillaries, whereas the tissue surrounding venules and small veins was practically free of this starter of coagulation. Thrombomodulin was present at the luminal surface of all vessel segments and especially at venular endothelial cell junctions. Its product, the anticoagulant protein C, appeared only at discrete extravascular sites, mainly next to capillaries. These distribution patterns were basically identical in the healthy and diseased hearts, suggesting a general principle. CONCLUSIONS: Venular extravasation of plasma proteins probably would not bring prothrombin into intimate contact with tissue factor, avoiding interstitial coagulation in the absence of injury. Generation of activated protein C via thrombomodulin is favored in the vicinity of venular gaps, should thrombin occur inside coronary vessels. This regionalization of distribution supports the proposed physiological heterogeneity of the vascular barrier and complies with the passage of plasma proteins into the lymphatic system of the heart.

Endothelial glycocalyx and coronary vascular permeability: the fringe benefit.

Current concepts of vascular permeability are largely still based on the Starling principle of 1896. Starling's contribution to understanding vascular fluid homeostasis comes from realising that the transport of fluid to and from the interstitial space of peripheral tissues follows the balance between opposing oncotic and hydrostatic pressures. It is presumed that in peripheral tissues fluid is readily filtered from blood to tissues at the arterial/arteriolar side of the circulation and largely reabsorbed at the venular/venous aspect, excess fluid being removed from the tissue by the lymphatic system. This balance is determined particularly by the properties of the vascular barrier. Recent studies have shown that the endothelial glycocalyx, located with a thickness of at least 200 nm on the luminal side of healthy vasculature, plays a vital role in vascular permeability by constituting the vascular barrier together with the endothelial cells themselves. While water and electrolytes can freely pass through the glycocalyx, plasma proteins, especially albumin, interact strongly. Binding and intercalating plasma constituents with the structural elements of the glycocalyx creates the so-called endothelial surface layer. This is the actual interface between flowing blood and the endothelial cell membrane in vivo. The oncotic pressure difference pertinent to fluid homeostasis is not built up between the intravascular and the interstitial tissue spaces, but within a small protein-free zone beneath the glycocalyx surface layer. This explains why perturbation of the glycocalyx leads to a breakdown of both fluid and protein handling in the coronary vascular bed. Preventing damage to the glycocalyx seems to be a promising goal in cardioprotection in many clinical scenarios, including acute ischaemia, hypoxia and inflammation, and chronic vascular disease as in atherosclerosis, diabetes and hypertension.