Dialysis Patients and Cardiovascular Problems: Can Technology Help Solve the Complex Equation?

Blood-incompatibility in haemodialysis: alleviating inflammation and effects of coagulation

Blood-incompatibility is an inevitability of all blood-contacting device applications and therapies, including haemodialysis (HD). Blood leaving the environment of blood vessels and the protection of the endothelium is confronted with several stimuli of the extracorporeal circuit (ECC), triggering the activation of blood cells and various biochemical pathways of plasma. Prevention of blood coagulation, a major obstacle that needed to be overcome to make HD possible, remains an issue to contend with. While anticoagulation (mainly with heparin) successfully prevents clotting within the ECC to allow removal of uraemic toxins across the dialysis membrane wall, it is far from ideal, triggering heparin-induced thrombocytopenia in some instances. Soluble fibrin can form even in the presence of heparin and depending on the constitution of the patient and activation of platelets, could result in physical clots within the ECC (e.g. bubble trap chamber) and, together with other plasma and coagulation proteins, result in increased adsorption of proteins on the membrane surface. The buildup of this secondary membrane layer impairs the transport properties of the membrane to reduce the clearance of uraemic toxins. Activation of complement system-dependent immune response pathways leads to leukopenia, formation of platelet–neutrophil complexes and expression of tissue factor contributing to thrombotic processes and a procoagulant state, respectively. Complement activation also promotes recruitment and activation of leukocytes resulting in oxidative burst and release of pro-inflammatory cytokines and chemokines, thereby worsening the elevated underlying inflammation and oxidative stress condition of chronic kidney disease patients. Restricting all forms of blood-incompatibility, including potential contamination of dialysis fluid with endotoxins leading to inflammation, during HD therapies is thus still a major target towards more blood-compatible and safer dialysis to improve patient outcomes. We describe the mechanisms of various activation pathways during the interaction between blood and components of the ECC and describe approaches to mitigate the effects of these adverse interactions. The opportunities to develop improved dialysis membranes as well as implementation strategies with less potential for undesired biological reactions are discussed.

The scientific principles and technological determinants of haemodialysis membranes

In most biological or industrial (including medical) separation processes, a membrane is a semipermeable barrier that allows or achieves selective transport between given compartments. In haemodialysis (HD), the semipermeable membrane is in a tubular geometry in the form of miniscule pipes (hollow fibres) and separation processes between compartments involve a complex array of scientific principles and factors that influence the quality of therapy a patient receives. Several conditions need to be met to accomplish the selective and desired removal of substances from blood in the inner cavity (lumen) of the hollow fibres and across the membrane wall into the larger open space surrounding each fibre. Current HD membranes have evolved and improved beyond measure from the experimental membranes available in the early developmental periods of dialysis. Today, the key functional determinants of dialysis membranes have been identified both in terms of their potential to remove uraemic retention solutes (termed ‘uraemic toxins’) as well subsidiary criteria they must additionally fulfill to avoid undesirable patient reactions or to ensure safety. The production of hundreds of millions of kilometres of hollow fibre membranes is truly a technological achievement to marvel, particularly in ensuring that the fibre dimensions of wall thickness and inner lumen diameter and controlled porosity—all so vital to core solute removal and detoxification functions of dialysis—are maintained for every centimetre length of the fragile fibres. Production of membranes will increase in parallel with the increase in the number of chronic kidney disease (CKD) patients expected to require HD therapies in the future. The provision of high-quality care entails detailed consideration of all aspects of dialysis membranes, as quality cannot in any way be compromised for the life-sustaining—like the natural membranes within all living organisms—function artificial dialysis membranes serve.

Multitargeted interventions to reduce dialysis-induced systemic stress

Hemodialysis (HD) is a life-sustaining therapy as well as an intermittent and repetitive stress condition for the patient. In ridding the blood of unwanted substances and excess fluid from the blood, the extracorporeal procedure simultaneously induces persistent physiological changes that adversely affect several organs. Dialysis patients experience this systemic stress condition usually thrice weekly and sometimes more frequently depending on the treatment schedule. Dialysis-induced systemic stress results from multifactorial components that include treatment schedule (i.e. modality, treatment time), hemodynamic management (i.e. ultrafiltration, weight loss), intensity of solute fluxes, osmotic and electrolytic shifts and interaction of blood with components of the extracorporeal circuit. Intradialytic morbidity (i.e. hypovolemia, intradialytic hypotension, hypoxia) is the clinical expression of this systemic stress that may act as a disease modifier, resulting in multiorgan injury and long-term morbidity. Thus, while lifesaving, HD exposes the patient to several systemic stressors, both hemodynamic and non-hemodynamic in origin. In addition, a combination of cardiocirculatory stress, greatly conditioned by the switch from hypervolemia to hypovolemia, hypoxemia and electrolyte changes may create pro-arrhythmogenic conditions. Moreover, contact of blood with components of the extracorporeal circuit directly activate circulating cells (i.e. macrophages-monocytes or platelets) and protein systems (i.e. coagulation, complement, contact phase kallikrein-kinin system), leading to induction of pro-inflammatory cytokines and resulting in chronic low-grade inflammation, further contributing to poor outcomes. The multifactorial, repetitive HD-induced stress that globally reduces tissue perfusion and oxygenation could have deleterious long-term consequences on the functionality of vital organs such as heart, brain, liver and kidney. In this article, we summarize the multisystemic pathophysiological consequences of the main circulatory stress factors. Strategies to mitigate their effects to provide more cardioprotective and personalized dialytic therapies are proposed to reduce the systemic burden of HD.

Fluid and hemodynamic management in hemodialysis patients: challenges and opportunities

Fluid volume and hemodynamic management in hemodialysis patients is an essential component of dialysis adequacy. Restoring salt and water homeostasis in hemodialysis patients has been a permanent quest by nephrologists summarized by the ‘dry weight’ probing approach. Although this clinical approach has been associated with benefits on cardiovascular outcome, it is now challenged by recent studies showing that intensity or aggressiveness to remove fluid during intermittent dialysis is associated with cardiovascular stress and potential organ damage. A more precise approach is required to improve cardiovascular outcome in this high-risk population. Fluid status assessment and monitoring rely on four components: clinical assessment, non-invasive instrumental tools (e.g., US, bioimpedance, blood volume monitoring), cardiac biomarkers (e.g. natriuretic peptides), and algorithm and sodium modeling to estimate mass transfer. Optimal management of fluid and sodium imbalance in dialysis patients consist in adjusting salt and fluid removal by dialysis (ultrafiltration, dialysate sodium) and by restricting salt intake and fluid gain between dialysis sessions. Modern technology using biosensors and feedback control tools embarked on dialysis machine, with sophisticated analytics will provide direct handling of sodium and water in a more precise and personalized way. It is envisaged in the near future that these tools will support physician decision making with high potential of improving cardiovascular outcome.

Volume Management by Renal Replacement Therapy in Acute Kidney Injury

Management of fluid balance is one of the basic but vital tasks in the care of critically ill patients. Hypovolemia results in a decrease in cardiac output and tissue perfusion and may lead to progressive multiple organ dysfunction, including the development of acute renal injury (AKI). However, in an effort to reverse pre-renal oliguria, it is not uncommon for patients with established oliguric acute renal failure, particularly when associated with sepsis, to receive excessive fluid resuscitation, leading to fluid overload. In patients with established oliguria, renal replacement therapy may be required to treat hypervolemia. Safe prescription of fluid loss during RRT requires intimate knowledge of the patient's underlying condition, understanding of the process of ultrafiltration and close monitoring of the patient's cardiovascular response to fluid removal. To preserve tissue perfusion in patients with AKI, it is important that RRT be prescribed in a way that optimizes fluid balance by removing fluid without compromising the effective circulating fluid volume. In patients who are clinically fluid overloaded, it is equally important that the amount of fluid removed be as exact as possible. Fluid balance errors can occur as a result of inappropriate prescription, operator error or machine error. Some CRRT machines have potential for significant fluid errors if alarms can be overridden. Threshold values for fluid balance error have been developed which can be used to predict the severity of harm. It is important that RRT education programs emphasize the risk associated with fluid balance errors and with overriding machine alarms.

Three-Dimensional Dialysate flow Analysis in a Hollow-Fiber Dialyzer by Perfusion Computed Tomography

Perfusion computed tomography (PCT) is a means to rapidly and easily evaluate cerebral perfusion in patients presenting with acute stroke symptoms, which provides insights into capillary-level hemodynamics. In this study, we used PCT to analyze the 3-dimensional dialysate flow in a low-flux hemodialyzer equipped with a standard fiber bundle. The dynamic CT studies were performed with 64-channel multi-detector row CT (MDCT) at a dialysate flow rate of 500 ml/min and a 1.0 ml/sec injection rate of contrast agent. Central volume principle was used to calculate hydrodynamic parameters by deconvolution of time-density curves (TDCs). Functional maps of dialysate flow (DF), dialysate volume (DV), and mean transit time (MTT) could quantitatively describe the dialysate flow maldistribution, variations in fiber packing, and perfusion pressure distribution in a hemodialyzer, respectively. PCT by means of analysis was able to overcome the limitations of conventional imaging techniques for analyzing dialysate flow distributions in hollow-fiber dialyzers. Not only local hydrodynamic phenomena at microscopic level but also macroscopic flow behavior of dialysate were visualized quantitatively. Therefore, we concluded that PCT is a quantitative analysis method to provide better insights into hydrodynamics of hollow-fiber dialyzers and is expected to contribute to optimization of artificial kidneys.

Renal transplant among type 1 and type 2 diabetes patients in Spain: A population-based study from 2002 to 2013

BACKGROUND

To describe trends in the rates and short-term outcomes of renal transplants (RTx) among patients with or without diabetes in Spain (2002-2013).

METHODS

We used national hospital discharge data to select all hospital admissions for RTx. We divided the study period into four three-year periods. Rates were calculated stratified by diabetes status: type 1 diabetes (T1DM), type 2 diabetes (T2DM) and no-diabetes. We analyzed Charlson comorbidity index (CCI), post-transplant infections, in-hospital complications of RTx, rejection, in-hospital mortality and length of hospital stay.

FINDINGS

We identified 25,542 RTx. Rates of RTx increased significantly in T2DM patients over time (from 9.3 cases/100,000 in 2002/2004 to 13.3 cases/100,000 in 2011/2013), with higher rates among people with T2DM for all time periods. T2DM patients were older and had higher CCI values than T1DM and non-diabetic patients (CCI≥1, 31.4%, 20.4% and 21.5%, respectively; P<0.05). Time trend analyses showed significant increases in infections, RTx-associated complications and rejection for all groups (all P values<0.05). Infection rates were greater in people with T2DM (20.8%) and T1DM (23.5%) than in non-diabetic people (18.7%; P<0.05). Time trend analyses (2002-2013) showed significant decreases in mortality during admission for RTx (OR 0.75, 95% CI 0.68-0.83). Diabetes was not associated with a higher in-hospital mortality (OR: 1.20, 95% CI 0.92-1.55).

INTERPRETATION

RTx rates were higher and increased over time at a higher rate among T2DM patients. Mortality decreased over time in all groups. Diabetes does not predict mortality during admission for RTx.

FUNDING

Instituto Salud Carlos III and URJC-Banco Santander.

[Heart failure in haemodialysis patients: evaluation and treatment]

Cardiovascular diseases are the leading cause of death in patients on haemodialysis. Cardiovascular mortality rate in these patients is approximately 9% per year, with the highest prevalence of left ventricular hypertrophy, ischemic heart disease and congestive heart failure being the most frequent cardiovascular complications. Risk factors for cardiac failure include hypertension, disturbed lipid metabolism, oxidative stress, microinflammation, hypoalbuminemia, anaemia, hyperhomocysteinemia, and increased concentration of asymmetric dimethylarginine, increased shunt blood flow and secondary hyperparathyroidism. Diagnostic strategy for early detection of patients with increased risk for the development of asymptomatic disturbances of systolic and diastolic left ventricular function should include echocardiografic examination, tests for determining coronary vascular disease, as well as tests of myocardial function (BNP, Nt-proBNP). Early detection of patients with a high risk of congestive heart failure enables timely implementation of adequate therapeutic strategy to provide high survival rate of HD patients.

Antibodies to platelet factor 4-heparin complex and outcome in hemodialysis patients with diabetes

BACKGROUND AND OBJECTIVES

Hemodialysis patients with type 2 diabetes exhibit an excessive cardiovascular risk and regularly receive heparin. We tested whether antibodies to the platelet factor 4-heparin complex (PF4-H-AB) contribute to outcome.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In 1255 hemodialysis patients with type 2 diabetes, the German Diabetes Dialysis Study evaluated the effect of atorvastatin (20 mg/d) versus placebo. In a post hoc analysis, the association among PF4-H-ABs, biochemistry, and prespecified, centrally adjudicated end points (combined cardiovascular end point [CVE], all-cause mortality, sudden death, myocardial infarction, stroke) was investigated.

RESULTS

During 4 years, 460 patients reached the CVE; 605 died, 159 of sudden death. Myocardial infarction and stroke occurred in 199 and 97 patients, respectively. Positive PF4-H-AB status was found in 231 (18.7%) of 1236 tested patients and was associated with lower albumin, higher C-reactive protein, and arrhythmia. In a multivariate model adjusted for demographics, comorbidities, and biochemistry, PF4-H-ABs were associated with sudden death. No significant association between PF4-H-ABs and all-cause mortality, myocardial infarction, stroke, or the CVE was observed. Detecting an interaction between acetylsalicylic acid and PF4-H-ABs regarding sudden death and mortality, we found that the association between PF4-H-ABs and outcomes was restricted to patients with acetylsalicylic acid use, most likely because of indication bias.

CONCLUSIONS

In hemodialysis patients who have type 2 diabetes and are treated with acetylsalicylic acid, PF4-H-ABs are associated with sudden and all-cause death. Further studies are needed to elucidate this association.

Lipoprotein (a) as an acute phase reactant in patients on chronic hemodialysis

Lipoprotein (a) [Lp(a)], is an independent risk factor for atherosclerotic cardiovascular disease in patients on chronic hemodialysis. A low concentration of high density lipoprotein cholesterol (HDL-C) and serum albumin are another potential risk factors. The purpose of this study was to explore in patients on chronic hemodialysis, whether Lp(a) elevated levels are influenced by activated acute phase response (APR) and the correlation of Lp(a) with HDL-C and serum albumin. In 69 hemodialysis patients with C-reactive protein (CRP) levels over than 10 mg/L and 101 hemodialysis patients with CRP levels in the normal range, Lp(a), HDL-C and serum albumin were determined in relation to CRP, as a sensitive marker of an APR. Results showed that serum concentration of CRP in 69 hemodialysis patients was significantly higher than in controls (44,62 mg/L versus 8,75 mg/L, p<0,01).Patients with elevated CRP had significantly higher serum levels of Lp(a) and lower serum levels of HDL-C and albumin, than patients with CRP in the normal range ( 35,39 mg/dl versus 28,6 mg/dl, p<0,01, 0,91 mmol/L versus 1,29 mmol/L, p<0,01 and 33,56 g/L versus 35,86 g/L, p<0,01). Lp(a) levels correlated positively with CRP and negatively with HDL-C and serum albumin, in patients with elevated CRP, but not in healthy controls. According to the results Lp(a) reacts as an acute phase protein, in patients with APR.

Improved survival of type 2 diabetic patients on renal replacement therapy in Finland

BACKGROUND

Survival of type 2 diabetes mellitus patients on maintenance dialysis therapy is poor mainly due to cardiovascular events. The aim was to examine whether survival of type 2 diabetes patients on renal replacement therapy (RRT) in Finland has improved during 1995-2005.

METHODS

Patients who entered RRT because of type 2 diabetes mellitus in 1995-99 (n = 314) and 2000-05 (n = 583) were identified within the Finnish Registry for Kidney Diseases. The two cohorts were followed up from start of RRT until death or end of follow-up on 31 December 2006. Survival probabilities and probabilities of receiving a kidney transplant were calculated using Kaplan-Meier curves. Multivariate modelling was performed using Cox regression.

RESULTS

Patients who entered RRT in 2000-05 had lower risk of dying than those who entered in 1995-99; hazard ratio (HR) was 0.76 (95% CI 0.65-0.89) and 0.74 (95% CI 0.63-0.87) with adjustment for age and gender. The decreased risk of death was most obvious in age groups 55-64 (HR 0.67, 95% CI 0.49-0.92) and 65-74 years (HR 0.69, 95% CI 0.56-0.87). Adjustment for albumin in addition to age and gender only slightly weakened the effect of study periods (HR 0.83, 95% CI 0.69-1.01). The patients in 2000-05 were more obese, had lower total and LDL cholesterol and higher HDL cholesterol and albumin concentration in serum than patients in 1995-99. Patients' probability to receive a kidney transplant was low in both groups.

CONCLUSIONS

Survival of type 2 diabetes patients on RRT improved during the time period 1995-2005 in Finland while the probability of receiving a kidney transplant remained low and unchanged.

Plasma dimethylarginine levels in chronic hemodialysis patients are independent of the type of dialyzer applied

BACKGROUND

Asymmetric dimethylarginine (ADMA) levels are increased in hemodialysis (HD) patients. Reports on the effect of various dialysis strategies on ADMA, symmetric dimethylarginine (SDMA) and L-arginine levels are inconclusive.

PATIENTS/METHODS

In this randomized crossover study, 15 patients were dialyzed for 4 weeks with 4 dialyzers, differing in biocompatibility and flux. Dimethylarginine and L-arginine levels were assessed at baseline, and after 4 weeks both before and after HD.

RESULTS

During HD, ADMA and SDMA levels decreased significantly with all dialyzers. Dimethylarginine and L-arginine levels remained stable after 4 weeks of HD with each membrane. After pooling all data, values were mainly explained by variation between time points and patients, not by the type of dialyzer.

CONCLUSION

Despite an intradialytic decrease in dimethylarginines, no changes occurred after 4 weeks of HD with either membrane. Furthermore, the variability of AMDA, SDMA and L-arginine levels was far more dependent on patient-related factors than on the type of dialyzer applied.

Effects of haemodialysis on circulating endothelial progenitor cell count

During haemodialysis (HD) the endothelium is the first organ to sense and to be impaired by mechanical and immunological stimuli. We hypothesized that a single HD session induces mobilization of endothelial progenitor cells (EPCs) and that cardiovascular risk factors may influence this process. We quantified EPCs at different maturational stages (CD34+, CD133+/VEGFR2+) in blood samples from 30 patients, during HD and on the interdialytic day, and in 10 healthy volunteers. Samples were drawn at the start of HD, 1, 2 and 3 h after, at the end of HD and at 24 h on the interdialytic day. Patients were divided into two groups based on a recent risk scoring system (SCORE project): low-risk (LR) and high-risk groups (HR). HD patients showed a significantly reduced basal number of EPCs with respect to healthy volunteers. In contrast, we observed increasing EPCs during HD whereas they diminished on the interdialytic day. The EPC number was directly correlated with HD time progression. The EPC number during HD was increased in the HR group with respect to the LR group. We had a direct correlation between risk score and number of EPCs. Cardiovascular risk factors influenced the mobilization of stem cells from the bone marrow. This feature could be the direct consequence of an augmented request of stem cells to respond to the most important endothelial impairment but could also show a defective capacity of EPCs to home in and repair the sites of vascular injury.