Increased Hepato-Splanchnic Vasoconstriction in Diabetics during Regular Hemodialysis

The gut microbiome tango in the progression of chronic kidney disease and potential therapeutic strategies

Chronic kidney disease (CKD) affects more than 10% population worldwide and becomes a huge burden to the world. Recent studies have revealed multifold interactions between CKD and gut microbiome and their pathophysiological implications. The gut microbiome disturbed by CKD results in the imbalanced composition and quantity of gut microbiota and subsequent changes in its metabolites and functions. Studies have shown that both the dysbiotic gut microbiota and its metabolites have negative impacts on the immune system and aggravate diseases in different ways. Herein, we give an overview of the currently known mechanisms of CKD progression and the alterations of the immune system. Particularly, we summarize the effects of uremic toxins on the immune system and review the roles of gut microbiota in promoting the development of different kidney diseases. Finally, we discuss the current sequencing technologies and novel therapies targeting the gut microbiome.

Changes of Hemodynamic Parameters after Intradialytic Glucose Injection

BACKGROUND

Intradialytic hypotension (IDH) is a frequent complication of hemodialysis (HD). Current methods of IDH prevention are insufficient.

METHODS

We analyzed the intradialytic time course of systolic (SBP), diastolic (DBP), mean arterial (MAP), pulse pressure (PP), and heart rate (HR) in a group of chronic kidney disease (CKD) patients. First, 30 min into HD, a 40% glucose solution was injected into the venous line of the extracorporeal circulation at a dose of 0.5 g/kg of dry weight. Pressures and HR were measured in frequent intervals. Relative volume overload was determined by bioimpedance spectroscopy.

RESULTS

Thirty-five participants were studied. SBP increased after 5, 10, and 20 min of glucose infusion. DBP increased after 2 and 3 h and also at the end of HD. PP increased after 5, 10, and 20 min of glucose infusion and fell after the 2nd and 3rd hour and also at the end of HD. MAP increased after 2 and 3 h of glucose injection and at the end of HD. Significant interactions of the time course of SBP, DBP, MAP, with HR at baseline and of the time course of PP with fluid overload were observed. Symptomatic hypotensive episodes were absent.

CONCLUSIONS

Glucose infusions during HD prevent symptomatic IDH and do not cause severe hypertensive episodes.

Fluid Overload and Precision Net Ultrafiltration in Critically Ill Patients

BACKGROUND

Fluid overload is present in two-thirds of critically ill patients with acute kidney injury and is associated with morbidity, mortality, and increased healthcare resource utilization. Kidney replacement therapy (KRT) is frequently used for net fluid removal (i.e., net ultrafiltration [UFNET]) in patients with severe oliguric acute kidney injury. However, ultrafiltration has considerable risks associated with it, and there is a need for newer technology to perform ultrafiltration safely and to improve outcomes.

SUMMARY

Caring for a critically ill patient with oliguric acute kidney injury and fluid overload is one of the most challenging problems. Although diuretics are the first-line treatment for management of fluid overload, diuretic resistance is common. Various clinical practice guidelines support fluid removal using ultrafiltration during KRT. Emerging evidence from observational studies in critically ill patients suggests that both slow and fast rates of net fluid removal during continuous kidney replacement therapy are associated with increased mortality compared with moderate UFNET rates. In addition, fast UFNET rates are associated with an increased risk of cardiac arrhythmias. Randomized trials are required to examine whether moderate UFNET rates are associated with a reduced risk of hemodynamic instability, organ injury, and improved outcomes in critically ill patients. There is a need for newer technology for fluid removal in patients who do not meet traditional criteria for initiation of KRT. Emerging newer and miniaturized ultrafiltration devices may address an unmet clinical need.

KEY MESSAGES

Among critically ill patients with acute kidney injury and fluid overload requiring continuous kidney replacement therapy, use of higher and slower UFNET rates compared with moderate UFNET rates might be associated with poor outcomes. Newer minimally invasive technologies may allow for safe and efficient UFNET in patients with acute kidney injury who do not meet criteria for initiation of KRT.

Impact of the nature of the capillary wall on plasma refilling during hemodialysis

OBJECTIVES

Our aim was to clarify the impact of the nature of the capillary wall, defined by the contribution of large (LP), small (SP), and ultrasmall (UP) pores, on plasma refilling in a hemodialysis session.

METHODS

This study included data from 78 patients. The relative blood volume change (ΔBV%) was monitored using a Crit-Line monitor. A bioimpedance device was used to measure extracellular and intracellular fluid volumes, and the excess fluid mass (M_ExF) was calculated. We simulated blood volume change (sΔBV%) based on a three-pore model. Hydraulic permeability of the capillary wall (LpS) and fractional contribution of LP to LpS (α_LP) were determined by fitting sΔBV to ΔBV. The total refilling volume (TV_ref) was calculated from the total ultrafiltration volume and total blood volume change. Values were standardized to a body surface area of 1.73 m² and are denoted by the subscript BSA.

RESULTS

LpS and α_LP were 3.09 (2.32, 4.68) mL/mmHg/min and 0.069 (0.023, 0.109), respectively. The standardized regression coefficient (β) of the ultrafiltration rate (UFR_BSA) and initial excess fluid mass (M_ExF,_BSA,0) by multiple linear regression analysis of TV_ref,BSA without (Model 1) and with (Model 2) α_LP were as follows: UFR_BSA, 0.714/<0.001 (β/p); M_ExF,_BSA,0, 0.247/<0.001 (Model 1); UFR_BSA, 0.799/<0.001; M_ExF,_BSA,0, 0.066/0.237; and α_LP, -0.327/<0.001 (Model 2).

CONCLUSIONS

The impact of volume overload (M_ExF,_BSA,0) on plasma refilling became insignificant with the addition of α_LP in the model, suggesting that the nature of the capillary wall described by inter-endothelial gaps (LP) may have a greater impact on plasma refilling than volume overload.

Association between hepatic oxygenation on near-infrared spectroscopy and clinical factors in patients undergoing hemodialysis

The hepato-splanchnic circulation directly influences oxygenation of the abdominal organs and plays an important role in compensating for the blood volume reduction that occurs in the central circulation during hemodialysis (HD) with ultrafiltration. However, the hepato-splanchnic circulation and oxygenation cannot be easily evaluated in the clinical setting of HD therapy. We included 185 HD patients and 15 healthy volunteers as the control group in this study. Before HD, hepatic regional oxygen saturation (rSO2), a marker of hepatic oxygenation reflecting the hepato-splanchnic circulation and oxygenation, was monitored using an INVOS 5100c oxygen saturation monitor. Hepatic rSO2 was significantly lower in patients undergoing HD than in healthy controls (56.4 ± 14.9% vs. 76.2 ± 9.6%, p < 0.001). Multivariable regression analysis showed that hepatic rSO2 was independently associated with body mass index (BMI; standardized coefficient: 0.294), hemoglobin (Hb) level (standardized coefficient: 0.294), a history of cardiovascular disease (standardized coefficient: -0.157), mean blood pressure (BP; standardized coefficient: 0.154), and serum albumin concentration (standardized coefficient: 0.150) in Model 1 via a simple linear regression analysis. In Model 2 using the colloid osmotic pressure (COP) in place of serum albumin concentration, the COP (standardized coefficient: 0.134) was also identified as affecting hepatic rSO2. Basal hepatic oxygenation before HD might be affected by BMI, Hb levels, a history of cardiovascular disease, mean BP, serum albumin concentration, and the COP. Further prospective studies are needed to clarify whether changes in these parameters, including during HD, affect the hepato-splanchnic circulation and oxygenation in HD patients.

Meal timing and frequency implications in the development and prognosis of chronic kidney disease

Patients with chronic kidney disease (CKD) have a higher risk of death than the general population, the main cause being cardiovascular disease (CVD). Nutrition plays a key role in the prevention and treatment of CVD and kidney diseases. Currently, new evidence reinforces the importance of specific foods and general dietary patterns rather than isolated nutrients for cardiovascular risk. In addition, dietary patterns and healthy eating habits seem extremely relevant in decreasing risk factors. Epidemiologic and clinical intervention studies have suggested that late-night dinner and skipping breakfast are associated with an increased risk of obesity, insulin resistance, and CVD. In CKD, despite important changes in nutritional counseling in recent decades, less attention has been paid to meal timing and frequency. Therefore, the purpose of this review is to discuss the evidence of meal timing and frequency in CKD development and prognosis, presented under three main topics: risk of developing CKD, importance of dietary habits, and implications of fasting.

Monitoring relative blood volume changes during hemodialysis: Impact of the priming procedure

The monitoring of relative blood volume (RBV) changes during hemodialysis is increasingly used to evaluate the effect of dialyzer ultrafiltration on intravascular volume to guide the removal of excess fluid in a manner that maintains hemodynamic stability of the patient. RBV monitoring is typically based on an optical or acoustic sensor placed in the arterial blood line that measures a marker of hemoconcentration, such as hematocrit, hemoglobin, or total blood protein. However, the accuracy of RBV monitors and the impact of their clinical use remain the subject of ongoing debate. Here, we show that, depending on the procedure of filling the extracorporeal circuit with the patient's blood at the beginning of the dialysis session, the indications of an RBV monitor may be misleading as to the actual changes of the intravascular volume. When the blood is first pumped into the dialyzer, the priming fluid (saline) that fills the circuit may be either infused into the patient or disposed of to a drain bag. In the latter case, the intravascular volume is suddenly reduced, which is not accounted for by RBV monitors that track only the subsequent reductions in blood volume due to dialyzer ultrafiltration. We analyzed this general aspect of RBV monitoring using model-based simulations and showed quantitatively how RBV changes calculated using hematocrit differ depending on the priming procedure.

Ultrafiltration in critically ill patients treated with kidney replacement therapy

Management of fluid overload is one of the most challenging problems in the care of critically ill patients with oliguric acute kidney injury. Various clinical practice guidelines support fluid removal using ultrafiltration during kidney replacement therapy. However, ultrafiltration is associated with considerable risks. Emerging evidence from observational studies suggests that both slow and fast rates of net fluid removal (that is, net ultrafiltration (UFNET)) during continuous kidney replacement therapy are associated with increased mortality compared with moderate UFNET rates. In addition, fast UFNET rates are associated with an increased risk of cardiac arrhythmias. Experimental studies in patients with kidney failure who were treated with intermittent haemodialysis suggest that fast UFNET rates are also associated with ischaemic injury to the heart, brain, kidney and gut. The UFNET rate should be prescribed based on patient body weight in millilitres per kilogramme per hour with close monitoring of patient haemodynamics and fluid balance. Dialysate cooling and sodium modelling may prevent haemodynamic instability and facilitate large volumes of fluid removal in patients with kidney failure who are treated with intermittent haemodialysis, but the effects of this strategy on organ injury are less well studied in critically ill patients treated with continuous kidney replacement therapy. Randomized trials are required to examine whether moderate UFNET rates are associated with a reduced risk of haemodynamic instability, organ injury and improved outcomes in critically ill patients.

The Effects of Hemodialysis and Peritoneal Dialysis on the Gut Microbiota of End-Stage Renal Disease Patients, and the Relationship Between Gut Microbiota and Patient Prognoses

Gut microbiota alterations occur in end-stage renal disease (ESRD) patients with or without dialysis. However, it remains unclear whether changes in gut microbiota of dialysis ESRD patients result from dialysis or ESRD, or both. Similarly, there is a dearth of information on the relationship between gut microbiota and ESRD prognoses. We collected fecal samples and tracked clinical outcomes from 73 ESRD patients, including 33 pre-dialysis ESRD patients, 19 peritoneal dialysis (PD) patients, and 21 hemodialysis (HD) patients. 16S rRNA sequencing and bioinformatics tools were used to analyze the gut microbiota of ESRD patients and healthy controls. Gut microbiota diversity was different before and after dialysis. Bacteroidetes were significantly deceased in HD patients. Twelve bacterial genera exhibited statistically significant differences, due to dialysis (all P < 0.05, FDR corrected). HD reversed abnormal changes in Oscillospira and SMB53 in pre-dialysis patients. Functional predictions of microbial communities showed that PD and HD altered signal transduction and metabolic pathways in ESRD patients. Furthermore, Bacteroides and Phascolarctobacterium were associated with cardiovascular mortality. Dorea, Clostridium, and SMB53 were related to peritonitis in PD patients. This study not only demonstrated differences in gut microbiota between pre-dialysis and dialysis ESRD patients, but also firstly proposed gut bacteria may exert an impact on patient prognosis.

Exploring the Link Between Hepatic Perfusion and Endotoxemia in Hemodialysis

Introduction

The liver receives gut-derived endotoxin via the portal vein, clearing it before it enters systemic circulation. Hemodialysis negatively impacts the perfusion and function of multiple organs systems. Dialysate cooling reduces hemodialysis-induced circulatory stress and protects organs from ischemic injury. This study examined how hemodialysis disrupts liver hemodynamics and function, its effect on endotoxemia, and the potential protective effect of dialysate cooling.

Methods

Fifteen patients were randomized to receive either standard (36.5°C dialysate temperature) or cooled (35.0°C) hemodialysis first in a two-visit crossover trial. We applied computed tomography (CT) liver perfusion imaging to patients before, 3 hours into and after each hemodialysis session. We measured hepatic perfusion and perfusion heterogeneity. Hepatic function was measured by indocyanine green (ICG) clearance. Endotoxin levels in blood throughout dialysis were also measured.

Results

During hemodialysis, overall liver perfusion did not significantly change, but portal vein perfusion trended towards increasing (P = 0.14) and perfusion heterogeneity significantly increased (P = 0.038). In addition, ICG clearance decreased significantly during hemodialysis (P = 0.016), and endotoxin levels trended towards increasing during hemodialysis (P = 0.15) and increased significantly after hemodialysis (P = 0.037). Applying dialysate cooling trended towards abrogating these changes but did not reach statistical significance compared to standard hemodialysis.

Conclusion

Hemodialysis redistributes liver perfusion, attenuates hepatic function, and results in endotoxemia. Higher endotoxin levels in end-stage renal disease (ESRD) patients may result from the combination of decreased hepatic clearance function and increasing fraction of liver perfusion coming from toxin-laden portal vein during hemodialysis. The protective potential of dialysate cooling should be explored further in future research studies.

Changes in tissue oxygenation in response to sudden intradialytic hypotension

A 76-year-old woman on hemodialysis (HD) for diabetic nephropathy was admitted to our hospital with occasional intradialytic hypotension (IDH). We continuously monitored the regional oxygen saturation (rSO₂) in the brain, liver, and lower limb muscle during HD. The time course of changes in rSO₂ ratios in each region was evaluated throughout HD. The rSO₂ ratio was defined as the ratio of rSO₂ value at t (min) during HD to the rSO₂ value before HD. During the early phase of HD, blood pressure (BP) gradually decreased and both hepatic and lower limb muscle rSO₂ ratios decreased with changes in BP, whereas the cerebral rSO₂ ratio was relatively maintained. At around 90 min after HD initiation, the BP decreased to 71/46 mmHg (mean BP, 54 mmHg) and the previously maintained cerebral rSO₂ ratio also suddenly decreased. Soon after the onset of IDH, ultrafiltration was stopped, normal saline was infused, and intravenous noradrenaline infusion was started. After the BP recovered, cerebral and hepatic rSO₂ ratios improved, but the lower limb muscle rSO₂ ratio remained low. After restarting ultrafiltration, improvement in the lower limb muscle rSO₂ ratio was delayed, although cerebral and hepatic oxygenation were maintained. This observation aids in our understanding of the effect of IDH on regional tissue oxygenation.

Hepato-splanchnic circulatory stress: An important effect of hemodialysis

The gastro-intestinal tract is being increasingly recognized as the site of key pathophysiological processes in the hemodialysis patient. Intestinal dysbiosis, increased intraluminal toxin production, and increased intestinal permeability are commonly observed processes which contribute to the pathogenesis of cardiovascular disease and thus elevated mortality. The acute circulatory effects of dialysis itself may contribute significantly to the development of gastrointestinal dysfunction as a result of both local and distant effects. Additionally, the liver, a relatively unknown entity in this process, has a substantial role as a functional barrier between the portal and systemic circulation and in the metabolism of pathogenic gut-derived uremic toxins. Here we summarize the evidence for acute gastro-intestinal and hepatic effects of hemodialysis and identify gaps in knowledge to date which require further study.

Intradialytic hypotension and splanchnic shifting: Integrating an overlooked mechanism with the detection of ischemia-related signals during hemodialysis

In the most simple analysis, a patient's hematocrit during hemodialysis will rise when the rate of ultrafiltration exceeds the rate at which the fluid is mobilized from extravascular spaces; the greater the rise in hematocrit, the lower blood volume is and the more likely intradialytic hypotension (IDH) is to occur. A secondary mechanism of IDH may be due to sudden shift of blood volume away from the heart under conditions of borderline cardiac filling. A substantial portion of blood volume resides in the splanchnic venous system. During the early part of dialysis, a centripetal shift of red cells from this anatomical region to the central circulation has been documented to occur. The magnitude of this shift is unpredictable, and it may depend on the level of splanchnic vasoconstriction predialysis. The amount of splanchnic shift may also be reduced in patients with autonomic dysfunction. Once this central shift in blood volume has occurred, it can be reversed during further ultrafiltration due to ischemia-induced release of vasodilatory molecules that cause dilation of upstream splanchnic arterioles; this causes increased transmission of arterial pressure to the splanchnic veins, acutely increasing their capacity. The increased splanchnic venous capacity may cause a sudden shift of blood away from the central circulation to fill these veins under conditions where cardiac filling has already been reduced. The result can be severe IDH due to insufficient cardiac filling and cardiac output. One fruitful preventive approach might be to continuously monitor the blood or dialysate for the sudden appearance of such ischemia-related molecules or other signals which may herald not only dialysis hypotension but tissue stunning, warning that the fluid removal rate should be immediately reduced.

Effect of ultrafiltration during hemodialysis on hepatic and total-body water: an observational study

BACKGROUND

The hepatic circulation is involved in adaptive systemic responses to circulatory stress. However, it is vulnerable to both chronic hypervolemia and cardiac dysfunction. The influence of hemodialysis (HD) and ultrafiltration (UF) upon liver water content has been understudied. We conducted a detailed pilot study to characterize the effects of HD upon liver water content and stiffness, referenced to peripheral fluid mobilization and total body water.

METHODS

We studied 14 established HD patients without liver disease. Magnetic resonance imaging (MRI) together with ultrasound-based elastography and bioimpedance assessment were employed to measure hepatic water content and stiffness, body composition, and water content in the calf pre- and post-HD.

RESULTS

Mean UF volume was 8.13 ± 4.4 mL/kg/hr. Fluid removal was accompanied with effective mobilization of peripheral water (measured with MRI within the thigh) from 0.85 ± 0.21 g/mL to 0.83 ± 0.18 g/mL, and reduction in total body water (38.9 ± 9.4 L to 37.4 ± 8.6 L). However, directly-measured liver water content did not decrease (0.57 ± 0.1 mL/g to 0.79 ± 0.3 m L/g). Liver water content and IVC diameter were inversely proportional (r = - 0.57, p = 0.03), a relationship which persisted after dialysis.

CONCLUSIONS

In contrast to the reduced total body water content, liver water content did not decrease post-HD, consistent with a diversion of blood to the hepatic circulation, in those with signs of greater circulatory stress. This novel observation suggests that there is a unique hepatic response to HD with UF and that the liver may play a more important role in intradialytic hypotension and fluid shifts than currently appreciated.

Hemodialysis Ultrafiltration Rate Targets Should Be Scaled to Body Surface Area Rather than to Body Weight

The association between higher ultrafiltration rates and poor outcomes in hemodialysis patients has received increased attention, to the point that various regulatory entities are considering adding ultrafiltration rate as a quality measure to be monitored and controlled. Most of the discussion to date has focused on ultrafiltration rate scaled to body weight, or more correctly, body mass (ml/hour per kg). One outcome study suggests that ultrafiltration rate might best be not scaled at all to body size, as modestly higher ultrafiltration rate in very small-size patients may be associated with some survival benefit, probably via increased dietary intake. Outcomes studies also suggest that the risk of exceeding a weight-scaled ultrafiltration target may be magnified in very large patients, and that body weight-scaled ultrafiltration targets in such patients should be set a lower level. Here, we present an analysis, based on physiological hemodynamic arguments, that it would be better to scale ultrafiltration rate to body surface area rather than to body mass. Whatever ultrafiltration rate is scaled to, attempts to restrict ultrafiltration rate by limiting interdialytic weight gain in small, possibly malnourished patients, should be done cautiously, to prevent an inadvertent lowering of intake of calories and dietary protein.

Structural and functional differences in gut microbiome composition in patients undergoing haemodialysis or peritoneal dialysis

Complications of end-stage renal disease (ESRD) are critically related to inflammation. The gut microbiome is a key driver of inflammation. Since dialysis modalities may differently influence the gut microbiome, we aimed to compare the effects of haemodialysis (HD) and peritoneal dialysis (PD) on patients' gut microbiome composition and function. We therefore studied faecal microbiome composition and function as well as inflammation and gut permeability in 30 patients with ESRD (15 HD, 15 PD) and compared to 21 healthy controls. We found an increase in potentially pathogenic species and a decrease in beneficial species in patients on HD and to a lesser extend in patients on PD when compared to controls. These changes in taxonomic composition also resulted in differences in predicted metagenome functions of the faecal microbiome. In HD but not in PD, changes in microbiome composition were associated with an increase in c-reactive protein (CRP) but not with intestinal inflammation or gut permeability. In conclusion microbiome composition in ESRD differs from healthy controls but also between modes of dialysis. These differences are associated with systemic inflammation and cannot completely be explained by dialysis vintage. The mode of renal replacement therapy seems to be an important driver of dysbiosis in ESRD.

Mode of renal replacement therapy determines endotoxemia and neutrophil dysfunction in chronic kidney disease

Bacterial infection and sepsis are common complications of chronic kidney disease (CKD). A vicious cycle of increased gut permeability, endotoxemia, inadequate activation of the innate immune system and resulting innate immune dysfunction is hypothesized. We assessed endotoxemia, neutrophil function and its relation to oxidative stress, inflammation and gut permeability in patients with CKD grade 3–5 without renal replacement therapy (CKD group, n = 57), patients with CKD stage 5 undergoing haemodialysis (HD, n = 32) or peritoneal dialysis (PD, n = 28) and patients after kidney transplantation (KT, n = 67) in a cross-sectional observational study. In HD patients, endotoxin serum levels were elevated and neutrophil phagocytic capacity was decreased compared to all other groups. Patients on HD had a significantly higher mortality, due to infections during follow up, compared to PD (p = 0.022). Oxidative stress, neutrophil energy charge, systemic inflammation and gut permeability could not completely explain these differences. Our findings suggest that dialysis modality and not renal function per se determine the development of neutrophil dysfunction and endotoxemia in CKD-patients. HD patients are particularly prone to neutrophil dysfunction and endotoxemia whereas neutrophil function seems to improve after KT. Multi-target approaches are therefore warranted to improve neutrophil function and potentially reduce the rate of infections with patients undergoing haemodialysis.

1,3-ß-d-Glucan testing is highly specific in patients undergoing dialysis treatment

BACKGROUND

The aim of this combined in-vitro and in-vivo study was to investigate whether state of the art dialysis modalities produce false positive serum 1,3-ß-d-Glucan (BDG) levels.

METHODS

Dialysis fluid for simulated dialysis treatments was spiked with BDG from different sources. Samples were taken from the dialysate and dialyzer blood compartments at various time points. In addition, serum samples were obtained in three groups of patients without invasive fungal disease: a.) twelve patients on chronic hemodialysis (HD)/hemodiafiltration (HDF); b.) ten patients on continuous ambulatory peritoneal dialysis (CAPD); and c.) ten patients with stable chronic kidney disease (CKD) but without dialysis.

RESULTS

Median BDG levels in BDG spiked dialysate were 3250.9, 2050.4, and 390.1 pg/ml respectively. All corresponding samples from the blood compartments were BDG negative. In HD/HDF patients no increase of serum BDG levels could be observed over the duration of treatment. 71/72 BDG tests in this group remained negative. BDG tests were also negative in 9/10 CAPD patients, both in in- and outflow dialysates as well as in all ten patients with CKD.

CONCLUSION

We conclude that state of the art renal replacement therapies using up-to-date treatments are not a cause of falsely elevated serum BDG levels.