Heparin-grafted dialysis membrane allows minimal systemic anticoagulation in regular hemodialysis patients: a prospective proof-of-concept study

Adsorbed polymer conjugates to adaptively inhibit blood coagulation activation by medical membranes

Adaptive drug release can combat coagulation and inflammation activation at the blood-material interface with minimized side effects. For that purpose, poly(styrene-alt-maleic-anhydride) copolymers were conjugated to heparin via coagulation-responsive linker peptides and shown to tightly adsorb onto poly(ethersulfone) (PES)-surfaces from aqueous solutions as monolayers. Coagulation-responsive release of unfractionated as well as low molecular weight heparins from the respective coatings was demonstrated to be functionally beneficial in human plasma and whole blood incubation with faster release kinetics resulting in stronger anticoagulant effects. Coated poly(ethersulfone)/poly(vinylpyrrolidone) (PES/PVP) flat membranes proved the technology to offer an easy, effective and robust anticoagulant interfacial functionalization of hemodialysis membranes. In perspective, the modularity of the adaptive release system will be used for inhibiting multiple activation processes.

Laboratory Monitoring of Heparin Anticoagulation in Hemodialysis: Rationale and Strategies

Unfractionated heparin (UFH) and low-molecular-weight heparins (LMWHs) are commonly used to prevent clotting of the hemodialysis extracorporeal circuit and optimize hemodialysis adequacy. There is no consensus on the optimal dosing for UFH and LMWHs during hemodialysis. In clinical practice, semiquantitative clotting scoring of the dialyzer and venous chamber may help to guide UFH and LMWH dose adjustment. Laboratory monitoring has not been shown to improve clinical outcomes and is therefore not routinely indicated in most hemodialysis patients. It might, however, be considered in select patients, such as those with extremes of body weight or history of repeated clotting or bleeding. Methods for laboratory monitoring include the activated partial thromboplastin time, activated clotting time, and antifactor Xa assays for UFH and antifactor Xa assay for LMWHs. Target ranges for anticoagulation in hemodialysis have been suggested but not clearly defined. When utilizing these tests, issues such as availability, standardization, interfering factors, and interpretation must be considered. In this narrative review, we discuss the rationale and methods of monitoring anticoagulation in hemodialysis.

Standardization of Nomenclature for the Mechanisms and Materials Utilized for Extracorporeal Blood Purification

In order to develop a standardized nomenclature for the mechanisms and materials utilized during extracorporeal blood purification, a consensus expert conference was convened in November 2022. Standardized nomenclature serves as a common language for reporting research findings, new device development, and education. It is also critically important to support patient safety, allow comparisons between techniques, materials, and devices, and be essential for defining and naming innovative technologies and classifying devices for regulatory approval. The multidisciplinary conference developed detailed descriptions of the performance characteristics of devices (membranes, filters, and sorbents), solute and fluid transport mechanisms, flow parameters, and methods of treatment evaluation. In addition, nomenclature for adsorptive blood purification techniques was proposed. This report summarizes these activities and highlights the need for standardization of nomenclature in the future to harmonize research, education, and innovation in extracorporeal blood purification therapies.

How to Prolong Filter Life During Continuous Renal Replacement Therapy?

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2022. Other selected articles can be found online at https://www.biomedcentral.com/collections/annualupdate2022 . Further information about the Annual Update in Intensive Care and Emergency Medicine is available from https://link.springer.com/bookseries/8901 .

A mathematical estimation for quantified calcium supplementation during intermittent hemodialysis using regional citrate anticoagulation

BACKGROUND

Regional citrate anticoagulation has been recommended as an alternative of anticoagulation for patients at high risk of bleeding undergoing intermittent hemodialysis. Precise calcium supplementation is important for the safety of regional citrate anticoagulation. In this study we aimed to develop a possible method to optimize calcium supplementation for regional citrate anticoagulation in intermittent hemodialysis.

METHODS

The investigation consisted of a pilot study and a validation study. 18 patients undergoing intermittent hemodialysis anticoagulated by citrate and Six types of filters were included in the pilot study. The ionized calcium levels were monitored and maintained in the targeted range. Calcium-free dialysate was used in the study. After linear regression analysis of the clearance of non-protein bound calcium and calculating the ratio of the non-protein bound calcium concentration to total calcium concentration, we developed a mathematical model for estimation of extracorporeal circuit calcium removal. Another 8 maintenance hemodialysis patients (12 sessions) were enrolled in the validation study to validate the new version of the calcium supplementation approach.

RESULTS

In the pilot study, positive correlations were found between the clearance of non-protein bound calcium and the hematocrit-adjusted clearance of creatinine and phosphate given in the dialyzer leaflet (R² =0.31, p=0.0165). The ratio of the non-protein bound calcium concentration to total calcium concentration at the pre-filter point after infusion of citrate were constant about 0.75. In the validation study, we found that the systemic ionized calcium levels were stably maintained in the safe range and no filter clotting occurred during the hemodialysis when we used the new model of calcium supplementation.

CONCLUSIONS

We developed a possible method to quantify calcium supplementation for intermittent hemodialysis anticoagulated by citrate which may help to avoid negative calcium balance and reduce the incidence of complications.

Hemodiálisis extendida frente a convencional o hemodiafiltración en línea. Estudio comparativo de necesidad de heparina y coagulación del sistema

Introducción: La reciente aparición de membranas de corte medio ofrece una alternativa para la eliminación de moléculas medianas y nueva terapia dialítica, la hemodiálisis expandida. Estas membranas se caracterizan por un mayor tamaño de poro que podría afectar a la eliminación de la heparina utilizada durante las sesiones de hemodiálisis. Objetivo: Determinar si existen diferencias en la necesidad de heparina y el estado de coagulación del sistema y dializador según técnica dialítica empleada. Material y Método: Estudio cuasiexperimental en pacientes en hemodiálisis con dos periodos de estudio, en el primero, el paciente realizó hemodiálisis convencional o hemodiafiltración y en el segundo, hemodiálisis expandida con membranas de corte medio. Resultados: El dializador quedó parcialmente coagulado en el 10,3% de las sesiones de hemodiálisis expandida frente al 19,1% de las sesiones de hemodiálisis y el 11,4% de hemodiafiltración (p=0,011). Conclusiones: La hemodiálisis expandida ofrece mejor estado de coagulación final del sistema y dializador que otras membranas.

Advances in the Development of Biomaterials for Endotoxin Adsorption in Sepsis

Sepsis, a life-threatening and intractable disease without any specific treatment, is activated by endotoxin. Some attempts at removing endotoxin to treat sepsis from the blood circulation using different hemoperfusion cartridges have been proposed recently, but they have failed to reduce the mortality of severe septic patients. This review summarizes the latest advances in the development of endotoxin adsorbents. In particular, we highlight two critical parameters for endotoxin adsorbents when they are applied in blood purification: the dissociation constant and the maximum adsorption capacity. We also discuss potential challenges and research directions for the future development of endotoxin adsorbents.

Filter life and safety of heparin-grafted membrane for continuous renal replacement therapy - A randomized controlled trial

Polyethyleneimine-layered membrane with grafted heparin (oXiris) may improve filter life during continuous renal replacement therapy (CRRT) in addition to its immunoadsorptive capability, compared with that of conventional membrane. In this single center, prospective, open-label pilot study, we randomized critically ill patients with bleeding risk who underwent anticoagulation-free CRRT, to commence with oXiris or M150 filter with sequential crossover. We examined the filter life with each circuit and its effect on systemic coagulation parameters. We randomized 11 and nine patients to commence CRRT with oXiris and M150 respectively, with 19 oXiris and 20 M150 filter-circuits in all. Patient profiles in both arms were comparable for illness severity and comorbidities. Median filter lives for oXiris versus M150 circuits were 13 h versus 18 h (p = 0.10). Among 11 patients with paired crossover filters, filter lives for 14 oXiris-M150 circuit pairs were 13 h versus 16 h (p = 0.27), and corresponding transmembrane pressures increased to 111 mmHg versus 75 mmHg by 12 h (p = 0.02). Patients' coagulation parameters were comparable following both filter-circuits. CRRT with oXiris (vs. M150) was independently associated with shorter filter life, adjusted for prescribed dose, vascular access, and coagulopathy. Use of oXiris did not prolong filter life over conventional membrane with no evidence of systemic heparin exposure; significant membrane clogging is observed by 12 h with oXiris.

Recent advances in heparinization of polymeric membranes for enhanced continuous blood purification

Continuous blood purification technology such as hemodiafiltration has been used worldwide for saving patients suffering from severe diseases or organ function failure, especially in the intensive care unit and emergency setting. The filters as core devices are commonly made of polymer materials as hollow fiber membranes. However, the membrane is often inductively blocked by blood clot formation due to its interactions with blood components. Heparin is the anticoagulant often used in clinical practice for anti-coagulation. Recently, heparin is also employed to modify the hollow fiber membranes either chemically or physically to improve the filtration performance. This review summarizes recent advances in methodology for surface heparinization of such hollow fiber membranes, and their filtration performance improvement. The review also provides expert opinions for further research in this rapidly expanding field.

Micro-computed tomography for the quantification of blocked fibers in hemodialyzers

A novel technique based on micro-CT scanning is developed to quantify coagulation in fibers of hemodialyzers. This objectivation is needed to allow accurate assessment of thrombogenicity of dialyzers used during hemodialysis, for example when comparing different strategies to avoid coagulation and/or fiber blocking. The protocol allowed imaging at a resolution of 25 µm, making it possible to count the open, non-coagulated fibers in a non-invasive way. In 3 fresh, non-used FX600 hemodialyzers, patent fiber counts were extremely consistent (10748 ± 2). To illustrate the potential of this technique, different dialysis parameters currently used as surrogates for fiber blocking were evaluated during 20 hemodialysis sessions. After dialysis, the FX600 dialyzers were visually scored for clotting, dried and subsequently weighed and scanned. The number of patent fibers (10003 [8763,10330], range 534–10692) did not correlate with any of the recorded surrogate parameters. Micro-CT scanning is a feasible, objective, non-invasive, accurate and reproducible tool for quantification of the degree of fiber blocking in a hemodialyzer after use, making it a potential gold standard for use in studies on fiber blocking during renal replacement therapies.

An evaluation of four modes of low-dose anticoagulation during intermittent haemodialysis

Introduction

Intensive care participants that need dialysis frequently suffer from increased risk of bleeding. Standard intermittent haemodialysis (SHD) includes anticoagulation to avoid clotting of the dialysis system. The aim of this study was to clarify which of four different low-dose anticoagulant modes was preferable in reducing the exposure to i.v. unfractionated heparin (heparin) and maintaining patency of the dialysis circuit.

Methods

Twenty-three patients on SHD were included to perform haemodialysis with four modes of low-dose anticoagulation. For comparative analyses, patients served as their own control. Haemodialysis with a single bolus of tinzaparin at the start was compared to haemodialysis initiated without i.v. heparin but priming with (1) heparin in saline (H), (2) heparin and albumin in saline (HA), (3) heparin and albumin in combination with a citrate-containing dialysate (HAC), (4) saline and usinga heparin-coated filters (Evodial®). The priming fluid was discarded before dialysis started. Blood samples were collected at 0, 30 and 180 min during haemodialysis. Smaller bolus doses of heparin (500 Units/dose) were allowed during the modes to avoid interruption by clotting.

Findings

The mean activated partial thromboplastin (APTT) time as well as the doses of anticoagulation administered was highest with SHD and least with HAC and Evodial®. Mode H versus SHD had the highest rate of prematurely interrupted dialyses (33%, p = 0.008). The urea reduction rate was less with Evodial® vs. SHD (p < 0.01). One hypersensitivity reaction occurred with Evodial®. Changes in blood cell concentrations and triglycerides differed between the modes.

Discussion

If intermittent haemodialysis is necessary in patients at risk of bleeding, anticoagulation using HAC and Evodial® appeared most preferable with least administration of heparin, lowest APTT increase and lowest risk for prematurely clotted dialyzers in contrast to the least plausible H mode.

Electronic supplementary material

The online version of this article (10.1007/s00228-017-2389-x) contains supplementary material, which is available to authorized users.

β-Thromboglobulin may not reflect platelet activation during haemodialysis with the HeprAN membrane

BACKGROUND

When blood passes through the extracorporeal circuit during haemodialysis (HD) undesirable effects including platelet degranulation and coagulation activation take place. β-thromboglobulin (β-TG) is a sensitive marker of platelet activation. The aim of this study was to investigate platelet degranulation and coagulation activation during HD with the heparin-coated dialysis membrane HeprAN.

METHODS

Four HD sessions were evaluated in each of 12 chronic HD patients. None of the patients used oral warfarin, other anticoagulants or antiplatelet drugs. In the first session the HeprAN membrane or a conventional polyflux membrane was used in a randomized manner and thereafter alternately in a cross-over design, and 50% of the conventional dalteparin dose was given at start of HD. Prothrombin fragment 1 + 2 (PF1 + 2), β-TG and anti-factor Xa activity were measured repeatedly.

RESULTS

No dialysis sessions were terminated early due to clotting of the extracorporeal system. Activation of intravascular coagulation as assessed by change in PF1 + 2 during 4 hours of HD was the same with the two membranes. β-TG concentration decreased significantly during 4 hours of HD with the HeprAN membrane but remained stable with the polyflux membrane.

CONCLUSION

There were no differences in clotting scores or coagulation activation with the two membranes. The decrease in β-TG during HD with the HeprAN membrane suggests β-TG to be an inferior marker of platelet degranulation when using a heparin-coated dialysis membrane. A possible mechanism for the decline in β-TG concentration may be adherence of this heparin-binding protein to the heparin-coated dialysis membrane.

Comparison of the AN69ST Membrane versus Citrate-Enriched Dialysate on Clotting Events during Hemodialysis without Systemic Anticoagulation

BACKGROUND

The optimal management of anticoagulation in hemodialyzed patients with a high risk of bleeding is controversial.

METHODS

We compared premature termination of dialysis caused by clotting events between AN69ST membranes (G1) and 0.8 mmol/L citrate-enriched dialysate (G2). The number of sessions that had increased venous pressure (VP) and variations in urea-reduction ratio (URR) were analyzed.

RESULTS

Six hundred and two sessions were analyzed in 259 patients: 22.4% had sessions that ended prematurely (25% in G1 and 19.1% in G2, p = ns, OR 0.60 [0.34-1.08], p = 0.08). The increase in VP was lower in G2 (23 vs. 70, p < 0.001). URR was higher in G2 (0.56 vs. 0.60, p < 0.001).

CONCLUSION

Clotting events that led to the termination of dialysis were comparable in the 2 groups. However, UUR was better in G2, and the number of patients with increased VP in the sessions was lower in G2.

SHORT SUMMARY

Our study compared the effects of the AN69ST membrane and citrate-enriched dialysate on clotting events during the dialysis of 259 patients with a high risk of bleeding. URR was significantly better and fewer cases of increased VP occurred in the citrate group compared to the AN69 ST group. No significant difference was observed regarding the need to prematurely terminate a dialysis session.

Cardiovascular disease in haemodialysis: role of the intravascular innate immune system

Haemodialysis is a life-saving renal replacement modality for end-stage renal disease, but this therapy also represents a major challenge to the intravascular innate immune system, which is comprised of the complement, contact and coagulation systems. Chronic inflammation is strongly associated with cardiovascular disease (CVD) in patients on haemodialysis. Biomaterial-induced contact activation of proteins within the plasma cascade systems occurs during haemodialysis and initially leads to local generation of inflammatory mediators on the biomaterial surface. The inflammation is spread by soluble activation products and mediators that are generated during haemodialysis and transported in the extracorporeal circuit back into the patient together with activated leukocytes and platelets. The combined effect is activation of the endothelium of the cardiovascular system, which loses its anti-thrombotic and anti-inflammatory properties, leading to atherogenesis and arteriosclerosis. This concept suggests that maximum suppression of the intravascular innate immune system is needed to minimize the risk of CVD in patients on haemodialysis. A potential approach to achieve this goal is to treat patients with broad-specificity systemic drugs that target more than one of the intravascular cascade systems. Alternatively, 'stealth' biomaterials that cause minimal cascade system activation could be used in haemodialysis circuits.

Heparin albumin priming in a clinical setting for hemodialysis patients at risk for bleeding

INTRODUCTION

Intermittent hemodialysis (IHD) is sometimes necessary in patients with a bleeding risk, i.e., before/after surgery or brain hemorrhage. In such case IHD has to be modified to limit the conventional anticoagulation used to avoid clotting of the extracorporeal circuit (ECC). We evaluated if priming using a heparin and albumin (HA) mixture could minimize the exposure to heparin.

METHODS

Retrospective data from 1995 to 2013 were collected from 1408 acute dialysis treatment protocols that included 321 patients. Comparisons were made between IHD patients that had increased risk for bleeding and were treated by standard anticoagulation (Group-S), and patients at increased risk of bleeding (Group-HA). The ECC in Group-HA was primed with a solution of unfractioned heparin (UFH) (5000 Units/L) and albumin (1 g/L) in saline that was discarded after priming. There were 16 different dialyzers in the material.

FINDINGS

Comparing Group-S (n = 883) with Group-HA (n = 221), the mean age was 61.6 vs. 62.2 years (P = 0.8), dialysis time was 197 vs. 190 minutes (P = 0.002), and total dose of intravenous anticoagulant/IHD was at median 5000 Units vs. 1200 Units (P = 0.001). Twenty-four percent of patients were treated without any additional heparin. Clotting resulting in interrupted dialysis was similar in both groups (0.8% for Group-S vs. 1.0% for Group-HA, P = 0.8). No secondary bleeding was reported in either group.

DISCUSSION

HA priming minimized the risk of clotting and enabled acute IHD in vulnerable patients without increased bleeding, thus allowing completion of IHD to the same extent as for standard HD.

Anticoagulation in Chronic Hemodialysis: Progress Toward an Optimal Approach

Appropriate anticoagulation for hemodialysis (HD) requires a subtle balance between under- and over-heparinization to prevent extracorporeal circuit (ECC) clotting and bleeding, respectively. We discuss five key issues relating to anticoagulation therapy for chronic HD in adults following a review of relevant literature published since 2002: (i) options for standardization of anticoagulation in HD settings. The major nephrology societies have issued low evidence level recommendations on this subject. Interventional studies have generally investigated novel low-molecular weight heparins and provided data on safety of dosing regimens that cannot readily be extrapolated to clinical practice; (ii) identification of clinical and biological parameters to aid individualization of anticoagulation treatment. We find that use of clinical and biological monitoring of anticoagulation during HD sessions is currently not clearly defined in routine clinical practice; (iii) role of ECC elements (dialysis membrane and blood lines), dialysis modalities, and blood flow in clotting development; (iv) options to reduce or suppress systemic heparinization during HD sessions. Alternative strategies have been investigated, especially when the routine mode of anticoagulation was not suitable in patients at high risk of bleeding or was contraindicated; (v) optimization of anticoagulation therapy for the individual patient. We conclude by proposing a standardized approach to deliver anticoagulation treatment for HD based on an individualized prescription prepared according to the patient's profile and needs.

Inpatient hemodialysis without anticoagulation in adults

BACKGROUND

Anticoagulation use during hemodialysis (HD) is standard practice but issues related to an increased risk of hemorrhage associated with inpatients make this a concern.

METHODS

An anticoagulation-free protocol in which (i) the dialysis circuit is aggressively primed with normal saline (NS) in an attempt to flush it of all air, (ii) blood flow during the HD treatment is maximized to up to 400 mL/min, (iii) the dialysis circuit is flushed every 15 min with 100 mL of NS, and (iv) the use of bloodlines that lack a blood-air interface was developed and used for all adult inpatient HD treatments at Rush University Medical Center. The purpose of this study was to evaluate the rate of HD circuit clotting using this approach and to determine if factors such as access type, blood flow, arterial and venous bloodline pressures, the need for reversing the arterial and venous access lines for low blood flow or high venous or arterial bloodline pressures, or the amount of net ultrafiltration were associated with HD circuit clotting. Patients were excluded from analysis if they were on a heparin drip, clopidogrel, warfarin or direct thrombin inhibitors. We reviewed 400 HD treatments in 400 adult patients from 12/12 to 10/13.

RESULTS

The HD access in these patients consisted of catheters in 45%, native AV fistulas in 40% and grafts in 15% of the patients. The average blood flow in the treatments was 378 ± 46 mL/min. In 5% of the treatments, the arterial and venous bloodlines were reversed. Only 4 of the 400 (1%) of the treatments clotted the dialysis circuit. Factors associated with clotting were lower achieved blood flows (225 ± 50 mL/min versus 379 ± 44 mL/min), higher arterial bloodline pressures (-198 ± 24 mmHg versus -151 ± 45 mmHg) and reversal of arterial and venous access lines.

CONCLUSION

Our anticoagulation-free protocol allows inpatient HD to be performed in adults across all access types and with essentially no circuit clotting.

Results of the HepZero study comparing heparin-grafted membrane and standard care show that heparin-grafted dialyzer is safe and easy to use for heparin-free dialysis

Heparin is used to prevent clotting during hemodialysis, but heparin-free hemodialysis is sometimes needed to decrease the risk of bleeding. The HepZero study is a randomized, multicenter international controlled open-label trial comparing no-heparin hemodialysis strategies designed to assess non-inferiority of a heparin grafted dialyzer (NCT01318486). A total of 251 maintenance hemodialysis patients at increased risk of hemorrhage were randomly allocated for up to three heparin-free hemodialysis sessions using a heparin-grafted dialyzer or the center standard-of-care consisting of regular saline flushes or pre-dilution. The first heparin-free hemodialysis session was considered successful when there was neither complete occlusion of air traps or dialyzer, nor additional saline flushes, changes of dialyzer or bloodlines, or premature termination. The current standard-of-care resulted in high failure rates (50%). The success rate in the heparin-grafted membrane arm was significantly higher than in the control group (68.5% versus 50.4%), which was consistent for both standard-of-care modalities. The absolute difference between the heparin-grafted membrane and the controls was 18.2%, with a lower bound of the 90% confidence interval equal to plus 7.9%. The hypothesis of the non-inferiority at the minus 15% level was accepted, although superiority at the plus 15% level was not reached. Thus, use of a heparin-grafted membrane is a safe, helpful, and easy-to-use method for heparin-free hemodialysis in patients at increased risk of hemorrhage.

Rationale and design of the HepZero study: a prospective, multicenter, international, open, randomized, controlled clinical study with parallel groups comparing heparin-free dialysis with heparin-coated dialysis membrane (Evodial) versus standard care: study protocol for a randomized controlled trial

Background

Anticoagulation for chronic dialysis patients with contraindications to heparin administration is challenging. Current guidelines state that in patients with increased bleeding risks, strategies that can induce systemic anticoagulation should be avoided. Heparin-free dialysis using intermittent saline flushes is widely adopted as the method of choice for patients at risk of bleeding, although on-line blood predilution may also be used. A new dialyzer, Evodial (Gambro, Lund, Sweden), is grafted with unfractionated heparin during the manufacturing process and may allow safe and efficient heparin-free hemodialysis sessions. In the present trial, Evodial was compared to standard care with either saline flushes or blood predilution.

Methods

The HepZero study is the first international (seven countries), multicenter (10 centers), randomized, controlled, open-label, non-inferiority (and if applicable subsequently, superiority) trial with two parallel groups, comprising 252 end-stage renal disease patients treated by maintenance hemodialysis for at least 3 months and requiring heparin-free dialysis treatments. Patients will be treated during a maximum of three heparin-free dialysis treatments with either saline flushes or blood predilution (control group), or Evodial. The first heparin-free dialysis treatment will be considered successful when there is: no complete occlusion of air traps or dialyzer rendering dialysis impossible; no additional saline flushes to prevent clotting; no change of dialyzer or blood lines because of clotting; and no premature termination (early rinse-back) because of clotting.

The primary objectives of the study are to determine the effectiveness of the Evodial dialyzer, compared with standard care in terms of successful treatments during the first heparin-free dialysis. If the non-inferiority of Evodial is demonstrated then the superiority of Evodial over standard care will be tested. The HepZero study results may have major clinical implications for patient care.

Trial registration

ClinicalTrials.gov NCT01318486