[Use of antiplatelet agents in patients with chronic kidney disease: what is the evidence?]

Patients with chronic kidney disease are particularly prone to cardiovascular disorders because of a tendency to thrombosis, but also have an enhanced hemorrhagic risk. The use of antiplatelet agents in this subset of patients is not yet well defined and caution should be given on which AAP is prescribed to them.

Importance of platelet aggregation in patients with end-stage renal disease

The exact etiology of the conflicting hemostatic disorder in the advanced stage of chronic renal disease, i.e. prothrombotic versus bleeding tendency, is not completely understood. Abnormal platelet function in patients with renal failure is not caused by high concentrations of urea, although the presence of fibrinogen fragments may prevent binding of normal fibrinogen and formation of platelet aggregates. Hemostatic abnormalities in end-stage kidney disease may be affected, to some extent, by the choice of renal replacement therapy. Patients on hemodialysis have an increased risk of thrombotic events, primarily due to the release of thromboxane A2 and adenosine diphosphate into the circulation, as well as platelet degranulation. Some activation of platelets occurs due to the exposure of blood to the roller pump segment, but microbubbles may also play a role. Renal transplantation is the treatment of choice for patients with end-stage renal disease. Immunosuppressive therapy is associated with an increased risk of thromboembolic complications. Additional research is required to identify the potential benefits of different immunosuppressive therapies in relation to platelet aggregation, keeping in mind the long- term need for immunosuppression in renal transplant patients.

A propensity score case-control comparison of aprotinin and tranexamic acid in high-transfusion-risk cardiac surgery

BACKGROUND

Cardiac surgery with cardiopulmonary bypass may result in excessive fibrinolysis and platelet (PLT) dysfunction, resulting in impaired hemostasis and excessive blood loss. Prophylactic use of the antifibrinolytic drugs aprotinin and tranexamic acid is thought to prevent these hemostatic defects. Their relative clinical utility and safety in high-transfusion-risk cardiac surgery, however, is not known.

STUDY DESIGN AND METHODS

Using propensity scores, 449 patients who received aprotinin for high-transfusion-risk cardiac surgery were matched to 449 patients who received tranexamic acid from a pool of 10,870 consecutive patients who underwent cardiac surgery at a single center, 586 of whom received aprotinin and the remainder of whom received tranexamic acid.

RESULTS

The two matched groups were well balanced in terms of measured perioperative variables. Blood product transfusion rates were similar in the aprotinin and tranexamic acid groups: red blood cells, 79 percent versus 76 percent (p = 0.3); PLTs, 56 percent versus 50 percent (p = 0.06); and plasma, 66 percent versus 61 percent (p = 0.1). Adverse events rates were comparable in the two groups, except for renal dysfunction (defined as a greater than 50% increase in creatinine concentration during the first postoperative week to >100 micromol/L in women and >110 micromol/L in men or a new requirement for dialysis support), which occurred in 24 percent (107/449) of aprotinin patients and 17 percent (75/449) of tranexamic acid patients (p = 0.01).

CONCLUSIONS

Aprotinin and tranexamic acid have similar hemostatic effectiveness in high-transfusion-risk cardiac surgery. Within the confines of propensity score matching, our results suggest that aprotinin may be associated with renal dysfunction.

Drug-induced thrombotic microangiopathy: incidence, prevention and management

The term thrombotic microangiopathy (TMA) describes syndromes characterised by microangiopathic haemolytic anaemia, thrombocytopenia and variable signs of organ damage due to platelet thrombi in the microcirculation. In children, infections with Shigella dysenteriae type 1 or particular strains of Escherichia coli are the most common cause of TMA; in adults, a variety of underlying causes have been identified, such as bacterial and viral infections, bone marrow and organ transplantation, pregnancy, immune disorders and certain drugs. Although drug-induced TMA is a rare condition, it causes significant morbidity and mortality. Antineoplastic therapy may induce TMA. Most of the cases reported are associated with mitomycin. TMA has also been associated with cyclosporin, tacrolimus, muromonab-CD3 (OKT3) and other drugs such as interferon, anti-aggregating agents (ticlopidine, clopidogrel) and quinine. The early diagnosis of drug-induced TMA may be vital. Strict monitoring of renal function, urine and blood abnormalities, and arterial pressure has to be performed in patients undergoing therapy with potentially toxic drugs. The drug must be discontinued immediately in the case of suspected TMA. Treatment modalities sometimes effective in other forms of TMA have been used empirically. Although plasma exchange therapy seems to be of value, the effectiveness of this approach has yet to be proved in multicentre, randomised clinical studies.

Hemostatic defects in massive transfusion: rapid diagnosis and management

Severe hemostatic defects that occur during massive transfusion are related to the volume of blood transfused, preexisting hemostatic abnormalities, concomitant pathologic changes, and therapeutic maneuvers. The relative role of each factor in the bleeding can be rapidly determined by using routine clinical laboratory tests. This determination requires an understanding of the properties of selected clotting factors, what coagulation screening tests measure, how these tests behave as the levels of factors change, and test profiles characteristic of different defects. Screening tests include platelet count, prothrombin time, partial thromboplastin time, thrombin time, and fibrinogen level. These tests are generally available on an emergent basis and can be completed within 25 minutes. The pattern associated with hemodilution is universal in massive transfusion. Patterns characteristic of the other pathologic processes that may be encountered are simply superimposed on the characteristics of hemodilution. Successful management of the contributing causes of bleeding depends on the administration of the appropriate blood components in the dose necessary to ensure that the levels of platelets and clotting factors are returned to and maintained at hemostatic levels.

Low-dose protamine based on heparin-protamine titration method reduces platelet dysfunction after cardiopulmonary bypass

OBJECTIVE

The heparin-protamine titration method that uses the Hepcon hemostasis management system (Medtronic HemoTec Inc, Englewood, Colo) reduced blood loss in cardiac surgery in previous reports, but the mechanism is not fully understood. This study tests the hypothesis that reduced protamine administration preserves platelet function in human cardiac surgery.

METHODS

Platelet count, alpha-granule secretion, and aggregation to thrombin before and after cardiopulmonary bypass in human beings were evaluated. In the control group (n = 14), a fixed dose of protamine (3 mg/kg) was administered. In the titration group (n = 20), protamine doses were based on the heparin concentration measured by the Hepcon system.

RESULTS

Heparin concentrations before protamine administration were higher in the titration group (P =.0012), but protamine doses of patients in the titration group were markedly lower than those of the control group (P <.0001). During protamine infusion at a rate of 0.3 mg. kg(-1). min(-1), the percentage of granule membrane protein-140-positive platelets significantly increased in the control group compared with the titration group (18.8% +/- 8.6% vs 13.0% +/- 5.3%, P =.0188). After protamine administration, aggregation of washed platelets to thrombin recovered almost to the preoperative level in the titration group; however, it remained lower in the control group (20% +/- 20% vs 55% +/- 18%, P =.0009).

CONCLUSION

Low-dose administration of protamine, based on a heparin-protamine titration method, restores not only the blood coagulation but also the platelet responses to thrombin and attenuates platelet alpha-granule secretion during heparin neutralization. Overdose of protamine activates platelets and may predispose patients to excessive bleeding after cardiac surgery.

Low molecular weight heparin stimulates megakaryocytopoiesis in bone-marrow transplantation patients

The use of low molecular weight heparin (LMWH) as prophylaxis for veno-occlusive disease of the liver has been studied in patients undergoing bone marrow transplantation (BMT). The present study analyzes the effect of LMWH on the time course of platelet recovery after BMT. Significantly accelerated platelet recovery in conjunction with lessened requirements of platelet transfusions was observed in the LMWH-treated patients.

Toxic health effects including reversible macrothrombocytosis in workers exposed to asphalt fumes

We investigated an outbreak of irritative and neurotoxic symptoms associated with exposure to asphalt fumes in a commercial lighting factory; 27 symptomatic female workers were clinically assessed including hematologic testing. When compared with a laboratory reference group (n = 107), the workers' mean platelet volume (MPV) was significantly higher and mean platelet count was lower (p = 0.013 and p = 0.048, respectively). Five months later, the factory's ventilation system was substantially modified. Follow-up assessments 6 months postmodification on 15 of the original workers documented a significant decline in acute symptoms and a lowering of the subjects' mean MPV towards normal (p = 0.0007 by paired t-test). The findings suggest that reversible macrothrombocytosis (enlarged platelets) can occur among symptomatic workers exposed to asphalt fumes.

Patient-controlled analgesia (PCA) using fentanyl in a parturient with a platelet function abnormality

A term parturient with documented platelet dysfunction presented to the case room for induction of labour. Since this bleeding abnormality contraindicated the use of lumbar epidural analgesia (LEA), we elected to use an iv fentanyl patient-controlled analgesia (PCA) technique for pain relief during labour. The patient received a 50 micrograms fentanyl loading dose after which 20 micrograms boluses of fentanyl were self-administered every three minutes as required. The patient received a total of 400 micrograms of fentanyl over the 3 1/2 hr of active labour. Mother and neonate tolerated the fentanyl without sequelae. If facilities to monitor the neonate and mother are present, this method of analgesia is useful in those patients where LEA is contraindicated.

Preservation of platelet function during trimethaphan infusion

The effect of trimethaphan (Arfonad) infusion on platelet function was prospectively evaluated in 38 (n = 38) patients (28 patients receiving trimethaphan, ten control patients) undergoing elective cardiac surgery. Any patient with a positive history for the ingestion of medication known to interfere with platelet function was excluded from the study. Following induction of anesthesia with fentanyl (and prior to cardiopulmonary bypass) 28 patients (n = 28) received trimethaphan as clinically indicated to maintain a mean blood pressure of 80 mmHg. The infusion rate and total dose of trimethaphan delivered was recorded for each patient. The evaluation of platelet function was performed via adenosine diphosphate (ADP) and epinephrine-induced platelet aggregation tests. The administration of trimethaphan failed to result in any detrimental effect on platelet function as assessed via these aggregation studies. Template bleeding times were also performed on all study patients. Bleeding time measurements performed in patients following trimethaphan administration were unchanged from baseline values. Platelet aggregation studies and bleeding time performed in control group following the administration of fentanyl (30 micrograms/kg) plus enflurane (inspired concentration 0.5-1%) did not reveal any deviation from baseline values. These results are in contrast to a previous study that demonstrated a negative effect upon platelet function following sodium nitroprusside administration (at clinically acceptable doses). These data demonstrate that trimethaphan provides control of arterial pressure with preservation of platelet function.

[The effect of vitamins A, E, C, P and PP on blood coagulation in experimental thromboplastinemia]

In experiments on white rats it was established that combination of vitamins A, E, P and C, without producing a significant change in normal hemocoagulation, induces weakening of hypocoagulemia developing during coagulation activation induced by surgery or exogenic thromboplastinemia in experiment. In exogenic thromboplastinemia the development of hypocoagulemia is effectively prevented by combination of vitamins A, E, C and P, when they are administered in doses similar to therapeutic, during 12 days, before interference provoking activation of blood coagulation. A conclusion has been made on the expediency of the study of possibility of using the above combination of vitamins for nonspecific prophylaxis of thrombohemorrhagic complications in surgery.

Prophylaxis of thromboembolic disease and platelet-related changes following total hip replacement: a comparative study of aspirin and heparin-dihydroergotamine

A prospective study involving 120 consecutive patients undergoing total hip replacement was performed to compare the effectiveness of aspirin (high and low dose) or a combination of heparin plus dihydroergotamine (heparin-DHE) in preventing isotopic and phlebographic deep vein thrombosis (DVT), and to evaluate their effect on postoperative platelet changes. Phlebographic DVT was demonstrated in 9 cases (30%) in control group, in 1 (3.3%) in aspirin (high-dose) group (p less than 0.01), in 1 (3.3%) in aspirin (low-dose) group (p less than 0.01) and in 5 (16.6%) in heparin-DHE group (p = NS). Aspirin was able to reduce the postoperative increase in circulating platelet aggregates, platelet factor 4 and beta-thromboglobulin observed in control group. This study shows that aspirin is effective in the prevention of DVT for patients undergoing total hip replacement. Small aspirin dose (250 mg/day) represents an effective form of prophylaxis in these patients.

Applicability and significance of salicylate screening in sera of voluntary blood donors: evaluation of two analytical methods

Salicylate concentrations in 3819 sera of apparently healthy voluntary blood donors were determined in view of the significance of this drug in the induction of allergic reactions and its possible interference in platelet function. Two hundred and ninety-five sera were found by a modified colorimetric determination to contain salicylates. The colorimetric determination was compared with a high performance liquid chromatography (HPLC) analysis of salicylate-containing sera. Drug concentrations detected were mostly in the range of 20-100 mg/l. Such concentrations have been reported to evoke allergic reactions and to affect the haemostatic action of platelets.

Prevention by glucocorticoids of various blood parameter changes following surgical intervention and endotoxin administration in the rat

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