Potentiation of platelet aggregation and adhesion by heparin both in vivo and in vitro

Porcine heparin increases postoperative bleeding in cardiopulmonary bypass patients

One hundred thirteen patients undergoing cardiopulmonary bypass were randomly assigned to receive either bovine or porcine heparin. Heparin was infused at 4.5 mg/kg during bypass and administered at the lesser of 70 units/kg or 5000 units/dose at 12-hour intervals postoperatively. Platelet counts decreased to 45% of preoperative levels during the first 3 days postoperatively (porcine, 44 +/- 13%, n = 50; bovine, 46 +/- 15%), but returned to preoperative levels by the seventh postoperative day. The average blood loss in the porcine heparin group significantly exceeded that of the bovine heparin group (porcine, 1350.7 +/- 727.8 ml; bovine, 1059.6 +/- 381.0 ml; p less than .01). Consequently, the platelet transfusion requirement was greater in the porcine heparin group (porcine, 1.7 +/- 3.9 units; bovine, 0.5 +/- 1.7 units; p less than .05); however, blood and blood component (with the exception of platelets) administration was not significantly different between the two groups. The four patients taking anticoagulants or antiinflammatory agents in the porcine group required a mean of 8.5 units of red blood cells (RBC) plus supplemental platelets. The seven such patients in the bovine group received a mean of 3.0 units of RBC and no platelets. Thus, the use of porcine heparin resulted in a generalized increase in postoperative bleeding with increased management problems in patients undergoing cardiopulmonary bypass.

The effect of Coumadin upon thrombus forming on foreign surfaces

Experience with the Stagnation Point Flow Experiment has revealed the earliest microscopic events surrounding thrombus inception and growth on foreign surfaces in a perfectly defined flow field. Using 40 and 80 X magnification, the effects of Coumadin upon these events was studied. These events include leukocyte adherence, fibrin deposition and platelet aggregation, deviation of flow streamlines around these aggregates, and subsequent downstream thrombus growth. Surface density of leukocytes was measured as a function of time and shear, and served as an index of the quantity of thrombus on the surface, which in turn, allowed direct comparisons of thrombus growth rate between experiments. Coumadin decreases the adhesive force between leukocytes or thrombi and the foreign surface. Emboli are more frequent with Coumadin, but are smaller. Thrombus inception is not altered. These results suggest that clinical benefit obtained from use of Coumadin derives from reduction in size of emboli.

Thrombus formation in the artificial kidney. Platelet and fibrin(ogen) content of experimental thrombi detected by radioisotope technique

In vitro studies in a "mini-Kiil" dialyser showed that, in spite of presumably adequate heparinization (2.5 IU/ml plasma), 51Cr-labelled platelets and 125I-labelled fibrin(ogen) deposited on membranes and blood lines, when freshly drawn human blood was dialyzed for 30 min. Platelet retention dominated, with a Cr/I ratio 3 times that of blood. Increasing the heparin concentration led to a reduction both of 51Cr- and 125I-activity, with a slight fall in the Cr/I ratio. Heparin was unable to prevent platelet retention in the dialyser, but the platelet aggregating effect of heparin was shown to be of minor importance compared to its anticoagulant activity and effect on thrombin induced platelet aggregation. Platelet retention by the blood lines exceeded that of the dialyser, in spite of a much smaller surface area. Differences in thrombogenicity between cuprophane and silicone rubber as well as different flow characteristics in the two situations were probably contributory. When heparinized tubing was used, the radioactivity retained was negligible, but membrane radioactivity was unaltered. A considerable reduction in blood radioactivity during dialysis, not accounted for by the deposits above, suggests the additional formation of more loosely attached platelet/fibrin(ogen) masses.

[Prophylaxis and therapy of shunt thrombosis in terminal renal insufficiency (author's transl)]

In terminal renal insufficiency thrombosis occurs almost exclusively in the arteriovenous shunt. The management of this acute, life threatening thrombosis is hardly contested. On the other hand, few results are available concerning effective thrombosis prophylaxis. In addition to the effectiveness, the pharmacokinetics of a substance and also possible bleeding complications must be taken into account. The parenteral administration of heparin and its short half life restrict it to use in thehospital. Oral anticoagulants, because they are difficult to dose, should be avoided when possible. Dextrans (Rheomacrodex) and acetylsalicylic acid (Colfarit) appear to be best suited for thrombosis prophylaxis in renal insufficiency. Dextran has the disadvantage of volume overload, and acetylsalicylic acid that of stomach intolerance. Sulfinpyrazone (Anturano) also appears to be effective, although its pharmacokinetic behaviour in renal insufficiency is still not known. Dipyridamole (Persantin), whose effectiveness for this purpose has not yet been demonstrate, should be administered even more cautiously.

Impaired anticoagulant effect of heparin in the artificial kidney. An experimental study

Dialysis of blood and plasma was performed in vitro, in a 'mini-Kill' dialyser as well as in dialysis bags. A marked shortening of the thrombin-clotting time was observed, indicating fall in heparin anticoagulant effect. The concentration of heparin, however, as measured by polybrene titration, was substantially less reduced. Fibrin formation, as evidenced by the ethanol gelation test, occurred more often in the dialysed than in the control plasma. In conclusion, the discrepancy between concentration and anticoagulant effect of heparin could be partly explained by influx from the dialysate of calcium, magnesium, and acetate ions. The fibrin-polymerizing effect of these ions was confirmed by a shortening of the clotting time with Reptilase, a proteolytic enzyme not influenced by thrombin inhibitors such as heparin. In addition, liberation of platelet factor 4 may be responsible for some reduction in antithrombin activity of heparin. No evidence of heparin being dialysed or adhering to the dialysis membrane was found.

Functional and ultrastructural status of platelets prepared by the Celltrifuge

Function and morphology of platelets collected by the Celltrifuge were investigated. In vitro platelet tests included aggregation by adenosine diplhosphate, collagen, and epinephrine, ability to support clot retraction, uptake and release of labeles serotonin, and morphology at the ultrastructural level. Each of these tests was also performed on platelets obtained from the same donor before the collection procedure was instituted. Data obtained from pre- and post-Celltrifuge platelet samples were compared and analyzed on individual donor basis as wass as on eight donors as a group. The hemostatic effectiveness of Celltrifuge-collected platelets was evaluated by their ability to raise platelet counts and to shorten the template bleeding time in four thrombocytopenic recipients. Our results indicate that platelets prepared by this continuous flow centrifugation equipment retained their functional and ultrastructural integrity, and significantly raised the platelet counts and shortened the bleeding time of all four patients.