Anticoagulation in hemodialysis: A narrative review

Systemic anticoagulation in maintenance hemodialysis (HD) has historically been considered necessary to maintain the extracorporeal circuit (ECC) and preserve dialysis efficiency. Unfractionated heparin (UFH) is the most commonly used anticoagulant due to low cost and staff familiarity. Despite widespread use, there is little standardization of heparin dosing protocols in the United States. Although the complication rates with UFH are low for the general population, certain contraindications have led to exploration in alternative anticoagulants in patients with end-stage kidney disease (ESKD). Here we review the current evidence regarding heparin dosing protocols, complications associated with heparin use, and discuss alternatives to UFH including anticoagulant-free routine HD.

Reticulated platelets in uremic patients: effect of hemodialysis and continuous ambulatory peritoneal dialysis

Platelet RNA content can be detected by flow cytometry using thiazole orange staining to identify platelets recently released into the circulation. We studied platelet RNA content and platelet function in uremic patients under different treatment regimens. Four groups were studied: (I) 15 end-stage renal disease (ESRD) patients (10M/5F) on maintenance hemodialysis (HD); (II) 11 ESRD patients (6M/5F) on continuous ambulatory peritoneal dialysis (CAPD); (III) 8 patients with chronic renal failure managed conservatively (5M/3F); and (IV) 34 controls (20M/14F). A double color labeling technique using a phycoerythrin-tagged antibody against glycoprotein Ib (CD42b) and RNA labeling by thiazole orange was performed and read by flow cytometry. Aggregation studies were made in platelet-rich plasma using ADP, epinephrine, collagen, arachidonic acid, and ristocetin. In group I, samples were also obtained after HD. Platelet counts did not differ among the groups. Aggregation studies showed a lower response to ADP and ristocetin in the HD patients, but not in the CAPD or in the chronic renal failure patients. The percentage of platelets with high RNA content in group I was significantly lower than in controls (3.72 +/- 1.72% vs. 9.05 +/- 3.53%, P < 0.01), but was also lower than in the remaining groups (I vs. II P < 0.01, and I vs. III P < 0.01). No differences were seen in platelet RNA content among groups II (8.67 +/- 2.73%), III (9.14 +/- 3.04%) and IV. In group I, the percentage of reticulated platelets decreased further after HD (2.14 +/- 1.09%, P < 0.01). Aggregation studies showed a significantly lower response to ADP and ristocetin in group I (P < 0.05), but not in groups II or III in comparison with controls. Aggregation response to ADP and ristocetin decreased after HD (P < 0.05). In conclusion, HD may decrease the percentage of RNA-rich platelets through elimination of the younger and more active platelets and worsen the thrombopathy present in uremic patients.

Defective platelet aggregation in uremia is transiently worsened by hemodialysis

Bleeding is a prominent feature of uremia and remains a significant cause of morbidity in hemodialysis (HD)-dependent patients. To measure the impact of the HD procedure, we performed a prospective cross-over study in eight patients placed consecutively for 2-week periods each on low-flux biocompatible polymethylmethacrylate, low-flux complement-activating cuprophane, and high-flux biocompatible polysulfone membranes. The primary measure of platelet function studied was shear-induced platelet aggregation (SIPA), which has been shown to be a physiologically relevant marker of platelet function and involves the interaction of von Willebrand factor (vWf) with platelet membrane glycoproteins (GP) Ib and IIb-IIIa. Flow-cytometric analysis of the surface expression of platelet membrane GP Ib and GP IIb-IIIa was performed using fluorescein isothiocyanate (FITC)-conjugated monoclonal antibodies CD42b and CD41a, respectively. Multivariate analysis did not demonstrate a statistically significant effect of the type of dialysis membrane on platelet aggregation, calcium flux, or thromboxane B2 production. There was a marked decrease of SIPA in HD patients (pre-HD, mean +/- SEM, 19% +/- 3%) compared with normal controls (43% +/- 3%, P < 0.001), with a further decrease after the HD procedure (post-HD, 12% +/- 2%, P = 0.015 compared with pre-HD). This intradialytic decrease in SIPA correlated with a decrease in GP Ib (pre-HD, 385 +/- 21 mean fluorescence intensity [MFI]; post-HD, 285 +/- 21 MFI, P = 0.0001). GP IIb-IIIa was also significantly decreased post-HD (pre-HD, 1,022 +/- 70 MFI; post-HD, 881 +/- 64 MFI, P = 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

A review of continuous renal replacement therapy

Patients in the Intensive Care Unit commonly develop acute renal failure (ARF). The kidneys are rarely the only organs failing in these patients. Frequently ARF is part of multiple organ dysfunction syndrome. The choice of dialytic therapy should consider, not only the efficacy of the therapy, but also the undesirable effects such therapy may have on the other failing organs. Intermittent Haemodialysis and Peritoneal Dialysis were the conventional forms of dialysis available. Both are associated with complications which may make them unsuitable for use in the haemodynamically unstable, hypercatabolic patients, seen in the Intensive Care setting. Continuous Renal Replacement Therapy (CRRT) has been introduced in many Intensive Care Units to provide a more stable, flexible form of dialysis. The purpose of this article is to give an overview of the various forms of CRRT and to discuss the advantages of this form of therapy.

Development of a new dynamic method for quantitative evaluation of in vitro hemocompatibility of biomedical materials

In this study a new dynamic method is introduced allowing the estimation of blood cell adhesion on flat test surfaces by measuring the cell loss in the bulk phase of surface contacting test blood under defined rheological conditions. This was achieved by constructing a novel test chamber permitting the contact of small amounts of blood with a large geometrical test surface. The construction consists of a spiral-shaped flow channel of 0.3 cm width, 0.02 cm height and 78 cm length covered with the biomaterials to be tested from both sides. Laminarity of blood flow in the conduit was confirmed theoretically by the calculation of an equivalent to the Reynolds number for curved systems the so-called Dean number. Furthermore, flow laminarity was proved experimentally finding that the flow rate of blood with different hematocrit values was proportional to the hydrostatic pressure applied. The applicability of the novel 'spiral method' for the estimation of hemocompatibility was demonstrated by evaluation of platelet adhesion onto different polymers in comparison to siliconized and fibrinogen coated glass as reference surfaces. Additionally, it was possible under distinct conditions to determine the adhesion of leucocytes and the detachment of platelet aggregates. Therefore, it was concluded that the spiral method can be used for the assessment of the hemocompatibility of flat biomedical polymers. As main advantages of the new method can be considered the high time efficiency and accuracy without labelling or optical detection of adherent cells.

Alterations in hemostatic parameters during hemodialysis with dialyzers of different membrane composition and flow design. Platelet activation and factor VIII-related von Willebrand factor during hemodialysis

The effect of dialyzer membrane and design on hemostatic parameters during hemodialysis were evaluated in a prospective controlled study. This study demonstrated that hemodialysis is associated with significant platelet activation and loss, which are influenced by both dialyzer configuration and membrane composition. In addition, use of the cuprophan membrane is associated with greater perturbations of the vascular endothelium, as reflected in changes in factor VIII-related von Willebrand factor and 6-keto-prostaglandin F1 alpha concentrations not seen with the polyacrylonitrile membrane. Of the dialyzers studied, the polyacrylonitrile membrane in a hollow-fiber configuration appears to minimize platelet loss and activation, and to minimize increases in factor VIII-related von Willebrand factor and 6-keto-prostaglandin F1 alpha.

Bile acids of patients with renal failure receiving chronic hemodialysis

Bile acids in serum, urine and dialysate of 8 patients with renal failure in chronic hemodialysis were analyzed by gas chromatography and gas chromatography-mass spectrometry. The following results were obtained: 1. Lithocholic acid, 3 beta-hydroxy-5-cholen-24-oic acid, deoxycholic acid, chenodeoxycholic acid, ursodeoxycholic acid, and cholic acid were identified in hemodialysate as well as in serum and urine. 2. The serum bile acid concentration of the patients was 2.78 +/- 0.57 micrograms/mL before hemodialysis and 1.34 +/- 0.48 micrograms/mL after a 5-h period hemodialysis with cuprophane membrane. The proportions of secondary bile acids in predialysis and postdialysis serum of patients were significantly higher than those of healthy subjects. 3. Two out of 8 patients excreted urine. But the amounts of bile acids in urine of the patients were very small compared to those of healthy subjects. 4. The amount of bile acids removed from blood by hemodialysis was 0.70 +/- 0.25 mg. In dialysate, cholic acid constituted a larger proportion of the total bile acids, and lithocholic acid a smaller proportion, when compared to those in urine of patients and healthy subjects.

Platelets and antithrombin III in uraemia: the acute effect of haemodialysis

In 14 haemodialysis patients, platelet count, secondary platelet aggregation rate, immunological antithrombin III and antithrombin III activity were lower and plasma beta-thromboglobulin higher than in 14 age- and sex-matched controls. In contrast, primary platelet aggregation, the degree of secondary aggregation and circulating platelet aggregates did not differ. Haemodialysis was associated with signs of platelet damage reflected by increase in plasma beta-thromboglobulin, extraction of platelets in the dialyser and decline in platelet count. Platelets in the dialyser effluent line were less aggregable than platelets in arterial blood. Circulating platelet aggregates and immunological antithrombin III were unchanged during dialysis whereas antithrombin III activity showed a minor rise. In conclusion, uraemics show a decreased rate of secondary platelet aggregation, and haemodialysis confers further platelet injury due to blood/surface interactions during extracorporeal circulation. The defective platelet function and low antithrombin III activity may help to explain the paradoxical occurrence of both haemorrhagic and thrombotic complications in uraemia.

The effect of dialyser membrane material on intradialytic changes in platelet count, platelet aggregation, circulating platelet aggregates and antithrombin III

Blood surface interaction during hemodialysis leads to impairment of platelet function and decrease in platelet number, which besides heparinization, may cause or exacerbate bleeding in risk patients. Furthermore, antithrombin III has been shown to increase during dialysis, probably due to vascular endothelial injury caused by infusion of activated platelets into the patient. 23 patients were examined during two successive dialyses, using membranes based on regenerated cellulose (RC) and cellulose acetate (CA). In 12 of the patients, platelet aggregation induced by ADP, circulating platelet aggregates and immunological AT III and AT III activity were determined. Irrespective of the membrane used, hemodialysis was associated with deterioration of platelet function, reflected by a decrease in platelet aggregation with return to predialysis values at the end of dialysis. However, the decline in platelet count and the increase in circulating platelet aggregates were membrane dependent, with RC causing greater changes than CA. No changes in threshold concentration of ADP inducing secondary platelet aggregation or in either immunological AT III or AT III activity were seen during dialysis.

Prevention of platelet deposition and thrombus formation on hemodialysis membranes: a double-blind randomized trial of aspirin and dipyridamole

A double-blind crossover study comparing low-dose aspirin (ASA) and dipyridamole (DPM) (100 mg ASA + 75 mg DPM, t.d.s.), high-dose ASA and DPM (300 mg ASA + 75 mg DPM, t.d.s.), and placebo on platelet deposition and thrombus formation on hemodialysis membranes was undertaken in 17 long-term dialysis patients. The high-dose combination significantly reduced the fall in platelet count during dialysis and also significantly increased postdialysis heparin concentrations. Scanning electron microscopy of the Cuprophan membranes showed a reduction in platelet deposition and fibrin formation during both treatment schedules, but this was most marked with the high-dose combination. The results of this study indicate that there is a graded response to combined ASA-DPM treatment and that this can significantly reduce platelet consumption and contact activation of fibrin during hemodialysis with Cuprophan membranes.