Removal Of Microaggregates Research Articles

A brief history of blood filtration: clot screens, microaggregate removal, and leukocyte reduction

A historical perspective of the evolution of blood filtration is presented. Topics addressed include recognition of aggregates in blood as mediators of morbidity, targeted for removal with gross clot screens, and evolution through the implementation of universal leukocyte reduction. Future directions for the development of blood filters are also described.

In Vitro evaluation of a new dual screen microaggregate filter

We compared a new second generation 40 150 μm dual screen microaggregate filter with a currently available 40 μm screen microaggregate filter. The evaluation included comparison of filter flow rate, capacity, degree of microaggregate removal, degree of leukocyte removal, and extent of filtration-induced hemolysis. We also studied the effect of both devices on filtration of stored platelet concentrates. The 40 150 μm dual screen microaggregate filter showed results comparable to that of the control screen filter following filtration of various types of units of red blood cells as well as units of stored platelet concentrates. Importantly, mean flow rates with the new 40 150 μm filter of 45 g/min after gravity filtration of 1600 mL of blood, make the filter suitable for use in trauma or other massive transfusion settings. We conclude that this new second generation microaggregate filter is suitable for use in clinical transfusion practice.

Observations on the removal of microaggregates from stored blood by centrifugation and filtration through a standard 170 micron transfusion filter.

The effect of centrifugation (5 minutes, 6900 X g) on the amount and particle size of blood microaggregates was studied in order to assess whether centrifugation and filtration by a standard (170 micron) transfusion set filter could be used for aggregate removal instead of microfiltration. Aggregates were quantitated using a method based on nylon screens with graded pore sizes. At the beginning of storage, centrifugation increased the particle size of aggregates only slightly. In 7-day-old blood, aggregates capable of passing a 160 micron screen amounted to 308 +/- 107 (SD) mg of debris protein per liter of blood before and 55 +/- 26 (SD) mg of protein (n = 10) after centrifugation. In 14-day-old blood centrifugation increased the size of aggregates even more effectively: 311 +/- 81 (SD) before and 29 +/- 14 (SD) mg of protein following centrifugation. Microaggregates can thus be removed effectively by the centrifugation and filtration method from blood stored for more than 1 week. A standard transfusion set filter can be used instead of a micropore filter.

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.

Evaluation of the Swank IL-201 transfusion filter.

The effects of a new transfusion filter (Swank IL-20U) on stored, whole blood have been examined. Six filters were preloaded by passage of two units of outdated, type-specific bank blood, and the effects of filtration on a third unit of 21-day-old blood flowing under 150 mm Hg pressure were measured. Filtration did not significantly alter erythrocyte or leukocyte count, total or plasma hemoglobin, red-cell fragility, and plasma sodium, potassium, albumin, or globulin. Platelet counts were reduced by 33%. Removal of microaggregates, assessed by Coulter counting, screen filtration pressure, total screen protein, wet and dry weight of material retained, and scanning electron microscopy, was shown to be effective over the entire range of particle size. In comparison with other transfusion filters previously examined in this laboratory, the Swank IL-201 filter combines the features of efficient microaggregate removal with moderate blood-flow rate. Compared to its predecessor, the Swank IL-200, this new filter design has improved flow characteristics without loss of microaggregate removal efficiency. In view of the similarity of performance demonstrated for several of the available filters, it seems likely that relative cost will constitute an important determinant of filter selection.

Effects of Fenwal 4C2423 transfusion microfilter on microaggregates and other constituents of stored blood.

The effects of a new micropore transfusion filter (Fenwal 4C2423) on stored whole blood have been examined. Five filters were preloaded by passage of two units of outdated type specific bank blood, and the effects of filtration on a third unit, consisting of 21-day-old blood, flowing under 150 mmHg pressure, were measured. Filtration did not significantly alter red blood cell count, total hemoglobin, red blood cell fragility, plasma sodium, potassium, albumin, or globulin. Some platelets and white blood cells were removed and a small amount of hemolygis of erythrocytes (less than 0.1%) was observed. Removal of microaggregates, assessed by Coulter counting, screen filtration pressure, total screen porteins, wet and dry weights of material retained, and scanning electron microscopy, was shown to be excellent over the entire range of particle size. Comparison of the Bentley PFS-127, Fenwal 4C2417, Johnson & Johnson Intersept, Pall Ultipore, and Swank IL200 filters led to the conclusion that the Fenwal 4C2423 was both a significant improvement over the previous Fenwal design and comparable to the most efficient of these filters for both the removal of microaggregates during massive blood transfusion and for the blood flow rates obtained.

Polyurethane foam (Bentley) micropore blood transfusion filter: filtration characteristics.

Stored human blood of varying age was passed through polyurethane foam (Bentley) micropore blood transfusion filters. Passage through these filters resulted in decreased screen filtration pressure (SFP) of the blood and increased filter weights. Numerous microaggregates were removed and SFP returned to normal after filtration. Occlusion of the filter occurred after passage of only 2 units of whole blood. On the basis of this research, we conclude that polyurethane foam (Bentley) micropore blood transfusion filters are effective in removal of microaggregates from stored human blood. Because the filtering capacity is not great, it is recommended that when these filters are used during transfusion a new filter be used for each unit of blood administered.

The source and removal of microaggregates in aged human blood and human blood components

Microaggregates are formed during the storage of human blood and are composed largely of platelets and leukocytes. These microparticles reside in the buffy coat fraction of blood. The formation of microaggregates can be successfully prevented by removal of the buffy coat or by treatment of blood with drugs which inhibit platelet function prior to storage. Once formed, the volumes of microaggregates in aged blood can be significantly reduced by washing, centrifugation or treatment with urokinase or streptokinase. Glycerol frozen red blood cells and blood components--packed red blood cells and plasma--are free of microaggregates, and they can be infused without fear of embolic consequence.

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.

The source and removal of microaggregates in aged human blood and human blood components

The source and removal of microaggregates in aged human blood and human blood components

Disposable filters for microaggregate removal from extracorporeal circulation

A comparative study of three commercially available blood filters for use in extracorporeal circuits was made in dogs. All filters were efficient in removing infused microclots from the circulation, but all caused mild thrombocytopenia and two produced minimal hemolysis. In dogs infused with microclots, only those animals without blood filters in the infusing circuit showed evidence of pulmonary microembolism at autopsy. It was concluded that while the filters have minimal disadvantages, their potential in reducing microembolism in extracorporeal circuits far outweighs these disadvantages.

Filtration characteristics of dacron wool (Swank) blood transfusion filters.

Stored human blood of varying age was passed through standard commercial blood transfusion filters (pore size, 170 mu) and Swank Dacron wool blood transfusion filters (pore size, 20mu). Passage through the Dacron filter resulted in a marked decrease in SFP and an increase in filter weight indicating removal of microaggregates which have been implicated as a cause of pulmonary insufficiency. The commercial filter tested did not appear to be effective in removing these harmful aggregates. On the basis of this research it is concluded that the Swank Dacron wool blood transfusion filter will prevent pulmonary microemboli during transfusion. Because aggregate removal appeared to be quantitative, it is recommended that no more than four units of blood be passed through each Dacron wool filter.

Tetrameric Structure and Conformation of Heat-Microaggregated Human Serum Albumin

131I-labeled heat-microaggregated human serum albumin is a colloid used in a method that measures liver blood flow through a determination of the rate of removal of microaggregates from the circulation. The heat-microaggregated material, either labeled or unlabeled, has a molecular weight (mol. wt.) of 273,000 daltons and a sedimentation coefficient of 8.6 S. Since the precursor, human serum albumin, has a molecular weight of 67,000 daltons and a sedimentation coefficient of 4.6 S, the microaggregate is a tetramer. The tetramer may be converted to subunits with a molecular weight of 72,000-76,000 daltons and a sedimentation coefficient of 4.7 S by the addition of buffered urea, guanidinium chloride, or formamide or by decreasing the pH to 2.2. Immunological studies indicate that this subunit has a different conformation from that of native human serum albumin. Hydrodynamic calculations indicate that the colloid has a particle size between 50 × 50 × 200 Å and 50 × 100 × 100 Å.