Platelet aggregation: effects of cardiopulmonary bypass

Thrombocytopenia in the Intensive Care Unit Setting

Thrombocytopenia is a commonly encountered labora tory abnormality in the intensive care unit setting. Al though moderate degrees of thrombocytopenia may be dismissed as clinically trivial, severe thrombocytopenia can have catastrophic consequences. This review di vides the potential pathogenesis of thrombocytopenia into three pathophysiological categories: (1) produc tive, (2) consumptive, and (3) distributional. The im portant etiologies and appropriate therapies for throm bocytopenia in each of these categories are discussed. We have attempted to emphasize the underlying patho genic mechanisms as well as highlight the diagnostic dilemmas likely to be faced by intensive care unit physi cians. Although this review stresses those thrombocyto penic disorders most likely to be encountered in the intensive care unit, chronic etiologies of thrombocy topenia are also discussed because preexistent throm bocytopenia will further complicate the care of any acutely ill intensive care unit patient.

1-Deamino-8-D-arginine vasopressin (DDAVP) increases platelet membrane expression of glycoprotein Ib in patients with disorders of platelet function and after cardiopulmonary bypass

1-deamino-8-D-Arginine vasopressin (DDAVP) shortens the bleeding time in some patients with platelet dysfunction and decreases blood loss in some cardiopulmonary bypass patients. We studied platelet membrane glycoproteins in patients with von Willebrand disease (vWD), disorders of platelet function, and in cardiopulmonary bypass patients after infusion of 0.3 microgram/kg of DDAVP. Platelets from 8 cardiopulmonary bypass patients, receiving DDAVP immediately after surgery, were compared to those of 14 patients not receiving DDAVP. We also studied 12 patients with vWD, and 8 patients with platelet dysfunction receiving DDAVP. Fixed platelets, stained with monoclonal fluorescein (FITC)-labeled antibodies directed against GPIb (CD42b antigen), GPIb/IX, GPIIb/IIIa (CD41a antigen), CD63 antigen (a platelet activation protein), and P-selectin (CD62 antigen) were studied by flow cytometry. Binding of CD42b monoclonal antibody (MoAb) and anti-GPIb/IX to platelets from both groups of bypass patients increased during the 18-20 hr after surgery, but the group receiving DDAVP showed the greater increase (P = 0.032). Platelets from patients receiving DDAVP for vWD or for platelet dysfunction, had increases in CD42b MoAb and anti-GPIb/IX binding (P < 0.01) that coincided with shortening of their bleeding time. No changes were seen in binding of other antibodies. When platelets from normal donors were incubated with DDAVP for 20 hr, there were increases in platelet surface CD42b MoAb binding, while immunogold-stained transmission electron micrographs of permeabilized platelets demonstrated decreases in cytoplasmic CD42b MoAb binding. DDAVP increases platelet membrane GPIb expression in a variety of patients and may account for improvement in hemostasis seen in some studies. Redistribution of GPIb from the cytoplasm to the membrane may account for this increased expression.

Ketanserin in the treatment of systemic hypertension during and following coronary artery bypass surgery

One of the most important problems during cardiac surgery is the prevention and treatment of hypertension, occurring in 40-60% of the patients following coronary artery bypass surgery (CABS). Hypertension should be avoided to prevent myocardial damage, neurologic complications, increased blood loss, and premature graft closure due to intimal damage. During and following cardiac surgery hypertension is routinely treated with vasodilating agents, which generally induce reflex tachycardia and increased intrapulmonary shunting. The results obtained with ketanserin, a specific S2-serotonergic receptor blocker with alpha 1-adrenergic receptor blocking properties, in the prevention and treatment of hypertension in patients undergoing cardiac surgery, are presented. Ketanserin effectively lowers blood pressure by decreasing systemic vascular resistance but does not completely prevent perioperative and postoperative hypertension when administered as a continuous infusion from the start of anesthesia. In contrast to sodium nitroprusside, ketanserin does not induce reflex tachycardia in the treatment of postoperative systemic hypertension following CABS. The compound improves diuresis and perfusion of the skin perioperatively. Ketanserin is devoid of rebound phenomena after its administration is stopped. It is postulated that the antihypertensive effect of ketanserin can be explained by its property of simultaneously blocking alpha 1-adrenergic and S2-serotonergic receptors.

A Comparison of Defective Platelet Count and Aggregation between the Valve Replacement and Cyanotic Congenital Heart Cases during Cardiopulmonary Bypass

Platelet count and ADP-induced platelet aggregation were studied in 10 single valve replacement (VR) patients and 10 cyanotic congenital heart disease (CCHD) patients undergoing cardiopulmonary bypass (CPB). The mean platelet count dropped to 78% in VR group and 73% in CCHD group at 30 minutes CPB as compared with the prebypass levels (being corrected for haemodilution). The mean prebypass platelet aggregation value was 65·5% ± 7·5% (Mean ± SEM) in VR group and 56·5% ± 5·2% in CCHD group; the values dropped to 54·2% ± 4·5% and 28·2% ± 4·8% respectively in VR and CCHD groups ( P < 0·01) at 30 minutes CPB. Both groups had a slight further drop at the end of the CPB, but only CCHD group had a further drop in platelet aggregation function after protamine administration. Mean plasma haemoglobin was much higher in the CCHD group than that in VR group at the termination of the bypass ( P < 0·05). Increased blood transfusion volumes were needed and greater blood losses noticed in the CCHD group. A significant negative correlation ( r = 0·5044. P < 0·05) was found between platelet function measured at the termination of CPB and postoperative bleeding. Cardiopulmonary bypass in patients with CCHD appears to be associated with greater platelet dysfunction and this results in more serious haemostatic defects after CPB. It is necessary to have further studies of the defective haemorrhagic status in these patients. More advanced perfusion techniques should be applied to preserve platelets during cardiopulmonary bypass.

Defective platelet aggregation in patients undergoing surgical repair of cyanotic congenital heart disease

Fifteen patients undergoing cardiopulmonary bypass for repair of cyanotic congenital defects were examined for evidence of platelet aggregation abnormalities by means of electronic particle sizing. Eight patients with polycythemia whose hematocrits were greater than or equal to 50% before bypass were compared with 7 patients without polycythemia whose hematocrits were less than 50%. Patients also were compared with 11 healthy volunteers. Before bypass, platelets in blood from the patients with polycythemia formed markedly smaller platelet aggregates (8.9 +/- 0.8 X 10(3) mu 3; mean +/- standard error of the mean) in response to adenosine diphosphate than those of the other group of patients (21.7 +/- 1.9 X 10(3) mu 3; p less than 0.001) or healthy volunteers (25.8 +/- 2.1 X 10(3) mu 3; p less than 0.001). Mean platelet aggregate sizes were not different between patients without polycythemia and normal volunteers (p greater than 0.05). In samples taken after bypass, patients with polycythemia again had smaller aggregates than the other group of patients (p less than 0.005). This platelet defect is quantitatively related to polycythemia, and may be a mechanical effect of the excess erythrocytes.

Transfusion of patients undergoing cardiopulmonary bypass

Although certain hematologic changes that occur as a consequence of cardiopulmonary bypass are unique, their influence on the transfusion requirements of open-heart surgical patients is not different from that on other bleeding patients. While knowledge of the peculiarities of open-heart surgery is important for the blood bank medical director, this clinical situation can be managed using the basic principles of component therapy as they apply to other clinical situations.