Particulate emboli retained by bypass blood filters

Platelets are essential for leukocyte recruitment in allergic inflammation

BACKGROUND

The role of platelets in inflammation is recognized but poorly characterized, and little is known of their interaction with leukocytes. However, platelet-leukocyte interactions have been demonstrated in cardiovascular disease, culminating in enhanced leukocyte recruitment.

OBJECTIVES

This study was undertaken to assess the possibility and potential role of similar phenomena occurring in asthmatic patients, a murine model of allergic inflammation, and in vitro adhesion studies.

METHODS

Asthmatic patients had blood taken at various time points to document the degree of leukocyte activation and the presence of platelet-leukocyte aggregates through FACS analysis before and after allergen exposure. Similar studies were carried out in mice exposed to allergen after previous sensitization, with some groups being selectively depleted of platelets through both an immunologic (antiplatelet antiserum) and nonimmunologic (busulfan) method. Additionally, lavage fluid and airway tissue were analyzed to assess the degree of pulmonary leukocyte recruitment. The importance of platelets on leukocyte adhesion to the endothelium was then assessed with in vitro incubation of radiolabeled leukocytes in the presence of activated platelets on cultured human vascular endothelial cells.

RESULTS

We have observed circulating platelet-leukocyte aggregates in the blood of allergic asthmatic patients during the allergen-induced late asthmatic response and in sensitized mice after allergen exposure. In platelet-depleted mice infiltration of leukocytes into airways after allergen challenge was significantly reduced and could be restored by means of infusion of platelets from allergic animals, indicating an essential role for platelets in leukocyte recruitment. CD11b expression on leukocytes involved in aggregates with platelets, although not on free leukocytes, was upregulated. Furthermore, the presence of autologous platelets augmented the adhesion of human polymorphonuclear leukocytes to cultured vascular endothelial cells, an effect that was found to be endothelial cell dependent and to involve platelet activation.

CONCLUSION

These results suggest that platelet participation in cell recruitment occurs at the level of the circulation and might involve the priming of leukocytes for subsequent adhesion and transmigration into tissues.

Thrombus formation and microaggregate removal during extracorporeal membrane oxygenation

Contemporary microporous membrane oxygenators have adequate gas transfer capacity and even prolonged oxygenation is relatively atraumatic to the blood elements. However, even with adequate heparinization, thrombus formation still takes place, albeit to a lesser degree than in direct blood-gas contact devices. In this work, scanning electron microscopy of the dissected devices in the extracorporeal circuit was performed on devices used during four aorto-coronary bypasses and two cardiac valve replacements. Membrane surfaces remained free of major deposits although thrombotic material could still be observed in parts of the oxygenators and the filters. Blood filtration from the cardiotomy reservoir may be more critical as it removes surgical debris and cells injured by suction which appear to enhance thrombus formation within the oxygenator. The return line arterial filter appears more useful as a bubble remover; its value appears much diminished as microemboli do not leave the device in large quantities.

Plasma administration to defibrinogenated dogs during extracorporeal circulation

Plasma, in an amount corresponding to 0.05 gm fibrinogen/Kg of body weight, was administered during one hour to defibrinogenated dogs subjected to extracorporeal circulation. Four blood filters included in the extracorporeal circuit were removed one by one at 30-minute intervals. The prefilter pressures rose gradually during the whole experiment. Scanning electron microscopy of the filter surface revealed equal amounts of deposits before, during and after the infusion of plasma. Only minimal amounts of fibrin were found on the filter surfaces by immunoelectrophoresis. Mean arterial pressure, arterial blood gases, fibrinogen concentration, platelet count and leukocyte count were followed before, during and after plasma infusion and showed no significant changes. Thus, it is possible to administer limited amounts of plasma to defibrinogenated dogs subjected to extracorporeal circulation.

Thrombus formation in a staged capillary membrane oxygenator associated with a microaggregate blood filter: a scanning electron microscope study

Blood contact at interfaces in extracorporeal devices is a source of traumas. Proteins are very rapidly adsorbed; then, depending on which proteins are left various degrees of platelet aggregation follow and thrombi develop. The scanning electron microscope reveals very instructive information on the morphology of the blood deposits which adhere to foreign surfaces. Oxygenators such as the Awad D, which is a staged one made of silicone rubber, become "thrombus invaded" after prolonged extracorporeal circulation in spite of adequate heparinization of the blood. In most cases, evaluation of membranes and devices is assessed with respect to transfer of blood gases. Careful examination of the morphology of deposits should be developed. This study shows the importance of blood flow rate, design, and materials.

Blood filter evaluation

Massive blood transfusion and extracorporeal circulation result in bombardment of the small pulmonary arterioles with micro-aggregates which are mainly composed of cellular degradation products, damaged platelets and leukocytes, fibrin strands, portions of cellular membrane and protein precipitates. Such amorphous material can cause patients to die of respiratory insufficiency without underlying chest trauma. Increasing amounts of stored blood are transfused to patients and extracorporeal circulation has become one of the most useful techniques for surgeons. Unfortunately, these procedures are often accompanied by disturbing post-operative consequences. This is because micro-aggregates invade the capillary network of several organs, especially lungs, kidneys, brain and retina. It is why blood filtration has recently gained added interest because of widespread efforts to minimise the number or emboli which are either transfused or reinfused to the patient through the blood return line.

Thrombus formation and microaggregate removal during prolonged extracorporeal circulation using a capillary membrane oxygenator. A scanning electron microscope study

Despite adequate heparinization, thrombus formation occurs at the blood/foreign material interface. Depending on the part of the device, the material and the blood flow, the amount and the components of thrombi vary greatly. This is not dangerous by itself but clots can be expelled downstream and damage the lungs, brain, kidney and retina. Interposition of a filter may prevent risks of embolization. The present paper reports the scanning electron microscope study carried out on the Awad oxygenator after use during prolonged extracorporeal circulation on 13 dogs. No filter has been inserted in the circuit for the first six experiments. A screen filter (4) or a polyurethane foam filter (3) was employed in the following ones.

Banked blood microfiltration. II. Dacron-wool microfilter

It is well established that debris tends to accumulate in banked blood, the amount of debris increasing with storage time. If such a blood is transfused to a patient, it will be filtered by the capillary network of the lungs and could cause various intensities of microemboli. These can be prevented by microfiltration--the Swank IL200 transfusion filter made of Dacron wool is perfectly suitable. It removes more than 70% of the debris 29-100 mum size from four blood units and its efficiency for particle removal is greatly increased by lactate priming.

Banked blood microfiltration. I. Microfilter composed of five polyurethane foam layers with graded pore size

Aggregates of amorphous material which develop with storage of banked blood may be a source of pulmonary microembolism in patients having massive transfusions. In order to remove such debris, blood microfilters have been developed and are in routine clinical use. This paper describes the evaluation of one such filter, the Bentley PF 127 model B, which is composed of five layers of polyurethane foam. The time of filtration as a function of the pressure applied, the number of particles removed, the observed changes in blood cells, and the results of scanning electron microscopy of the filter after filtration of human banked blood, are reported.