Defective platelet aggregation in response to platelet-activating factor in uremia associated with low platelet thromboxane A2 generation

The Crosstalk between Nephropathy and Coagulation Disorder: Pathogenesis, Treatment, and Dilemmas

ABSTRACT

The interaction between the kidney and the coagulation system greatly affects each other because of the abundant vessel distribution and blood perfusion in the kidney. Clinically, the risks of complicated thrombosis and bleeding have become important concerns in the treatment of nephropathies, especially nephrotic syndrome, CKD, ESKD, and patients with nephropathy undergoing RRTs. Adverse effects of anticoagulant or procoagulant therapies in patients with nephropathy, especially anticoagulation-related nephropathy, heparin-induced thrombocytopenia, and bleeding, seriously worsen the prognosis of patients, which have become challenges for clinicians. Over the decades, the interaction between the kidney and the coagulation system has been widely studied. However, the effects of the kidney on the coagulation system have not been systematically investigated. Although some coagulation-related proteins and signaling pathways have been shown to improve coagulation abnormalities while avoiding additional kidney damage in certain kidney diseases, their potential as anticoagulation targets in nephropathy requires further investigation. Here, we review the progression of research on the crosstalk between the coagulation system and kidney diseases and systematically analyze the significance and shortcomings of previous studies to provide new sight into future research. In addition, we highlight the status of clinical treatment for coagulation disorder and nephropathy caused by each other, indicating guidance for the formulation of therapeutic strategies or drug development.

Approach to the Assessment of Platelet Function: Comparison between Optical-based Platelet-rich Plasma and Impedance-based Whole Blood Platelet Aggregation Methods

Platelet aggregation studies play an important role in the assessment of hereditary and acquired platelet function defects. The first aggregation test introduced into laboratory practice used platelet-rich plasma (PRP) where aggregation was detected by an optical method. The assessment of platelet function using whole blood (WB) aggregation by an impedance method followed up nearly 20 years later. The WB impedance aggregation assay appears to be superior to the optical method because it 1) evaluates platelets in a physiologic milieu in the presence of red and white blood cells, which are known to modulate platelet function; 2) is faster; 3) has higher sensitivity; and 4) does not require centrifugation, thus avoiding injury to platelets and loss of giant thrombocytes. These two assays were compared. Clearly, the WB impedance aggregation methodology has many advantages over the optical PRP assay for the assessment of the hyperactive platelet syndrome and the effects of anti-platelet drugs.

Spontaneous splenic rupture due to uremic coagulopathy and mortal sepsis after splenectomy

Nontraumatic spontaneous splenic rupture (NSSR) has been encountered much more rarely compared with the traumatic splenic rupture. Although NSSR generally emerges in dialysis patients on account of such causes as the use of heparin during hemodialysis, uremic coagulopathy, infections, and secondary amyloidosis. Herein, we aimed to present a case of spontaneous splenic rupture which had developed soon after the inclusion of the case suffering from end-stage renal disease in routine hemodialysis program in the absence of any trauma or other prespecified risk factors for splenic rupture. A 55-year-old male patient was admitted to our hospital to have the ureteral double J stent removed. The operation was completed without any complication. Complaining an abdominal pain more prominent in the left upper abdominal quadrant in the first postoperative day, the patient underwent a through physical examination which disclosed abdominal distension, widespread tenderness, and rebound and defense positivity. The abdominal tomography depicted 122 × 114 × 95 mm lesion compatible with a hematoma. On the basis of these findings, an emergency exploratory operation was decided to be performed. Following clearance of the retroperitoneal hematoma, splenectomy was implemented. Experiencing progressive deterioration in his clinical status despite antibiotherapy, the patient unfortunately died of sepsis with multiorgan failure on the 25^th postoperative day. In conclusion, NSSR is such an entity that may be missed out, can pursue variable clinical courses, and requires emergency therapy upon definitive diagnosis. The possibility of spontaneous bleedings should be kept in mind in any case with the history of hyperuricemia even in the absence of overt trauma, no matter if they are included in routine hemodialysis or not.

Treatment of bleeding in dialysis patients

Bleeding is a common and potentially serious complication of acute and chronic renal failure. The pathogenesis of bleeding in uremia is multifactorial; however, the major role is played by abnormalities in platelet-platelet and platelet-vessel wall interaction. Platelet dysfunction is partially due to uremic toxins present in circulating blood. Despite decreased platelet function, abnormalities of blood coagulation and fibrinolysis predispose the uremic patients to a hypercoagulable state carrying the risk of cardiovascular and thrombotic complications. Dialysis improves platelet abnormalities and reduces, but does not eliminate, the risk of hemorrhage. Hemodialysis can even contribute to the bleeding through the continuous platelet activation induced by the interaction between blood and artificial surfaces and the use of anticoagulants. Correction of anemia improves hemostasis in uremic patients. Therapeutic management of bleeding in patients with uremia is discussed.

Platelet dysfunction and end-stage renal disease

Patients with end-stage renal disease (ESRD) develop hemostatic disorders mainly in the form of bleeding diatheses. Hemorrhage can occur at cutaneous, mucosal, or serosal sites. Retroperitoneal or intracranial hemorrhages also occur. Platelet dysfunction is the main factor responsible for hemorrhagic tendencies in advanced kidney disease. Anemia, dialysis, the accumulation of medications due to poor clearance, and anticoagulation used during dialysis have some role in causing impaired hemostasis in ESRD patients. Platelet dysfunction occurs both as a result of intrinsic platelet abnormalities and impaired platelet-vessel wall interaction. The normal platelet response to vessel wall injury with platelet activation, recruitment, adhesion, and aggregation is defective in advanced renal failure. Dialysis may partially correct these defects, but cannot totally eliminate them. The hemodialysis process itself may in fact contribute to bleeding. Hemodialysis is also associated with thrombosis as a result of chronic platelet activation due to contact with artificial surfaces during dialysis. Desmopressin acetate and conjugated estrogen are treatment modalities that can be used for uremic bleeding. Achieving a hematocrit of 30% improves bleeding time in ESRD patients.

[Thrombocytopathy and blood complications in uremia]

Bleeding diathesis and thrombotic tendencies are characteristic findings in patients with end-stage renal disease. The pathogenesis of uremic bleeding tendency is related to multiple dysfunctions of the platelets. The platelet numbers may be reduced slightly, while platelet turnover is increased. The reduced adhesion of platelets to the vascular subendothelial wall is due to reduction of GPIb and altered conformational changes of GPIIb/IIIa receptors. Alterations of platelet adhesion and aggregation are caused by uremic toxins, increased platelet production of NO, PGI(2), calcium and cAMP as well as renal anemia. Correction of uremic bleeding is caused by treatment of renal anemia with recombinant human erythropoietin or darbepoetin alpha, adequate dialysis, desmopressin, cryoprecipitate, tranexamic acid, or conjugated estrogens. Thrombotic complications in uremia are caused by increased platelet aggregation and hypercoagulability. Erythrocyte-platelet-aggregates, leukocyte-platelet-aggregates and platelet microparticles are found in higher percentage in uremic patients as compared to healthy individuals. The increased expression of platelet phosphatidylserine initiates phagocytosis and coagulation. Therapy with antiplatelet drugs does not reduce vascular access thrombosis but increases bleeding complications in endstage renal disease patients. Heparin-induced thrombocytopenia (HIT type II) may develop in 0-12 % of hemodialysis patients. HIT antibody positive uremic patients mostly develop only mild thrombocytopenia and only very few thrombotic complications. Substitution of heparin by hirudin, danaparoid or regional citrate anticoagulation should be decided based on each single case.

Challenging patients in an ambulatory setting

An increasing number of surgical procedures are now performed on an ambulatory basis. This article reviews these conditions and defines the appropriate preoperative evaluation and perioperative management. Our goal is to define those patients who would benefit in having care in an inpatient setting or those who require more intensive medical evaluation or preparation prior to outpatient surgery.

Pharmacokinetics and pharmacodynamics of low-molecular-weight heparins and glycoprotein IIb/IIIa receptor antagonists in renal failure

Data regarding the use of low-molecular-weight heparins (LMWHs) and glycoprotein (GP) IIb/IIIa receptor antagonists in patients with renal failure are limited. Renal failure has the potential to increase the risk of adverse drug events associated with LMWHs and GP IIb/IIIa receptor antagonists. This is due to changes in the pharmacokinetic and pharmacodynamic profiles of these agents in patients with renal failure. Until more data are available, clinicians should consider alternative therapies in this patient population.

Prevalence of preterminal pulmonary thromboembolism among patients on maintenance hemodialysis treatment before and after introduction of recombinant erythropoietin

The prevalence of pulmonary thromboembolism at autopsy was assessed in a retrospective study of a cohort of 185 patients undergoing maintenance hemodialysis treatment who died in the last decade. The overall frequency of thromboembolism was 12.43% in the dialysis population, which statistically was significantly less than in a control group of 8,051 nondialysis patients (21.77%; P = 0.0023). Moreover, pulmonary thromboembolism was less frequently fatal or contributing to death in the dialysis group than in the control group (P = 0.039). The prevalence of pulmonary thromboembolism in the dialysis group remained statistically unchanged over the 10-year period and was independent of a steady increase in the percentage of patients receiving recombinant erythropoietin therapy and the average hematocrit values. The occurrence of preterminal pulmonary thromboembolism was associated with a shorter period since onset of hemodialysis treatment and with infection as cause of death (P = 0. 031; P = 0.029, respectively). No statistically significant influence of the type of basic renal disease, type of dialysis anticoagulation, or dialysis access could be found. Our data suggest that, at least in the preterminal stage, the introduction of recombinant erythropoietin within the last decade had no substantial influence on the prevalence of pulmonary thromboembolism.

Uremic bleeding: pathogenesis and therapy

BACKGROUND

We reviewed current understanding of the pathophysiology of the uremic bleeding diathesis and discuss accepted therapeutic interventions that minimize the risk of bleeding in the uremic patient.

METHODS

Computerized literature searches and references from previous publications, including articles describing original research and reviews pertaining to the pathophysiology of and clinical approach to uremic bleeding.

RESULTS

The most common hemorrhagic manifestations in uremia are prolonged bleeding from puncture sites; nasal, gastrointestinal and genitourinary bleeding; and subdural hematomas. The most useful clinical laboratory test to assess both bleeding risk and response to therapy is bleeding time. It correlates better with clinical bleeding complications than indices of azotemia (eg, blood urea nitrogen [BUN], creatinine) or in vitro platelet aggregation tests. A low hematocrit is also correlated with increased bleeding risk. Anemia plays an important role in the bleeding diathesis of uremia and its correction with red cell transfusions or human recombinant erythropoietin is critical. Anticoagulation during hemodialysis may transiently exacerbate the bleeding diathesis. Hemodialysis and peritoneal dialysis improve the hemostatic defect and renal transplantation totally corrects it. Cryoprecipitate has been largely replaced by desmopressin acetate, which acts promptly (in less than 1 hour) but has a short duration of action (hours) and exhibits tachyphylaxis. Conjugated estrogens are slower in the onset of action (about 6 hours) but their effect lasts for about 2 weeks.

CONCLUSIONS

The pathophysiology of the bleeding diathesis of uremia is complex and incompletely understood but useful clinical tests and therapies have evolved empirically. Broadly available dialysis and the advent of erythropoietin are likely to reduce the magnitude of this problem.