Filtration of the microaggregates in stored blood

A Porous Media Model for Blood Flow within Reticulated Foam

A porous media model is developed for non-Newtonian blood flow through reticulated foam at Reynolds numbers ranging from 10-8 to 10. This empirical model effectively divides the pressure gradient versus flow speed curve into three regimes, in which either the non-Newtonian viscous forces, the Newtonian viscous forces, or the inertial fluid forces are most prevalent. When compared to simulation data of blood flow through two reticulated foam geometries, the model adequately captures the pressure gradient within all three regimes, especially that within the Newtonian regime where blood transitions from a power-law to a constant viscosity fluid.

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.

Evaluation of a strategy to limit blood donor exposure in high risk premature newborns based on clinical estimation of transfusion need

OBJECTIVES

Reservation of dedicated series of pedipacks, consisting of 3 to 4 units of 70 ml filtered red cell concentrate in additive solution SAGM from 1 donor, may reduce donor exposure. In this prospective efficacy study the benefits, release and expiration of pedipacks (PP) assigned to preterm infants requiring neonatal intensive care are analyzed.

METHODS

On the basis of clinical assessment of the need for multiple transfusions, 96 preterm neonates (gestational age < 32 wks and/or birth weight < 1500 g) were assigned to either the high risk group (HRG), who were to receive dedicated donor blood units, or the low risk group (LRG). Inclusion criteria for HRG were 1) estimated time of admission > 21 days and 2) expected need for multiple transfusions due to clinical cardiorespiratory instability, prolonged parental feeding or frequent blood sampling. To reduce wastage of donor blood, dedication of donor blood units was limited to 21 days.

RESULTS

50 series (192 PP) were assigned to 42 HRG infants. Two HRG infants received 3 series, 4 received 2 series and 36 received 1 series of PP. Mean transfusion rate was 3.1 PP in the HRG and 0.4 in the LRG. In the LRG 35 of 54 were not transfused, 19 received 1 to 2 PP. In both groups transfused newborns were exposed to 1.1 donors in average. In the HRG of 192 PP, 137 PP (71%) were used within 21 days, and another 30 (16%) before the expiration date < 35 days. Twenty five PP (13%) expired, mainly because of logistical problems in the introduction phase.

CONCLUSION

Assignment of dedicated PP on the basis of clinical parameters at entry considerably reduces donor exposure in HRG. Wastage of dedicated blood transfusions was reduced by limitation of the dedicated period (21 days). In terms of efficacy, reservation and use of PP can be optimized by standardized administrative measures.

Splenic platelet-sequestration following routine blood transfusion is reduced by filtered/washed blood products

The mean fall in the platelet count following 23 routine transfusions of 3-5 units packed cells for anaemia was 32.5%. This was significantly reduced to 12.5% in 15 similar transfusions through a 40 microns microaggregate filter (P less than 0.01) and to 4.6% following five transfusions through a polyester fibre filter (P less than 0.005). In 10 transfusions with frozen or polyester fibre filtered, washed red cells, the decrease in platelet count was 4.2% (P less than 0.001). A study of 111In-oxine labelled autologous platelets in nine patients indicated that the fall in platelet count was due to increased splenic sequestration. Since thrombocytopenia following routine transfusion is reduced by procedures which filter the packed cells, the decrease in platelets is probably caused by their adherence to infused microaggregate debris causing their premature removal from the circulation. Patients with preexisting thrombocytopenia who receive red cell transfusions for anaemia, should therefore receive blood products depleted of microaggregate debris in order to avoid exacerbation of thrombocytopenia and haemorrhagic complications.

Leukocyte-poor blood

The conventional techniques used to prepare leukocyte-poor red cell concentrates are described. These techniques conveniently group by their primary processing modalities which are centrifugation, freeze thawing, cell washing, and filtration. Each of these procedures has unique logistical requirements. The complexity, need of dedicated capital equipment, and stringent quality assurance requirements make the use of some of these techniques impractical for the hospital blood bank laboratory. The majority of patients benefit from the receipt of leukocyte-poor blood products prepared by an "in-line" microaggregate filtration technique. Those patients with symptoms which prove to be refractory to microaggregate-filtered blood products and those who require highly purified red cell concentrates to forestall sensitization to transplantation antigens should receive blood prepared either by the cryopreservation/deglycerolization technique or by cotton wool filtration.

Changes in plasma fibronectin levels after cardiac and pulmonary surgery: role of cardiopulmonary bypass

The changes in immunoassayable plasma fibronectin were studied during seven days after cardiac surgery with cardiopulmonary bypass (group A, 19 patients) or lung surgery without bypass (group B, 11 patients). In group A the fibronectin showed a series of rapid changes during the 24 perioperative hours. Simultaneous assessment of other plasma proteins (albumin, fibrinogen and immunoglobulin G) suggested that these changes mainly reflected hemodilution and hemoconcentration processes following the cardiopulmonary bypass, being influenced by the necessarily large transfusions of plasma. The fibronectin level decreased after day 1, with maximum depletion (averaging -32% of preoperative value) on day 3. Despite subsequent progressive rise, full restoration had not been reached by day 7. Group B did not show the initial rapid changes, but progressive fall in fibronectin level to a nadir on day 2 (-20% of preoperative) was followed by gradual return to outset value on days 4-5. The study demonstrated 1) that cardiac or lung surgery induces transient fibronectin depletion on days 2 to 3 postoperatively, and 2) that in surgery with cardiopulmonary bypass the decrease is significantly greater and more prolonged. It is proposed that this supplementary decrease is due to the large amounts of particulates of various origin entering the blood during the bypass.

A study of the efficiency of four blood microfilters

A new blood microfilter, Swank 6000-4, was compared with three established blood microfilters, Pall SQ40S, Fenwal 4C2423 and Intercept HR 18137-00 (1321). The flow rate decreased with increasing volume of filtered blood with all the microfilters (p less than 0.01). When the flow rates through each type of microfilter were compared there was no significant difference between them. Screen filtration pressure was restored to normal by the Swank, Fenwal and Intercept microfilters, but remained higher after filtration through the Pall microfilter (p less than 0.01). There was no evidence of red cell loss or damage with any of the microfilters after filtration.

Biological effects of di-(2-ethylhexyl) phthalate and other phthalic acid esters

Esters of o-phthalic acid are widely distributed in the ecosystem. The phthalate acid esters (PAE's) are used as plasticizers in the manufacture of polyvinylchlorides. They are also used as solvents in certain industrial processes and as vehicles for pesticides. The PAE's are used in enormous quantities for a variety of industrial uses in the formulation of plastics. While there are a number of important PAE's, di-ethylhexyl phthalate has perhaps been used the most extensively in the formulation of plastics used in medical devices and blood bag assemblies. The metabolism, biodistribution and excretion varies to some extent among the various PAE's. There are species differences with respect to the metabolism of the PAE's. The route of administration, and the level and length of exposure, are known to affect the toxicological profile of the various PAE's. There is little evidence of bioaccumulation of the various PAE's, and only at very large doses have there been reports of overt toxicity. Evidence for the carcinogenicity of certain PAE's apparently is related to prolonged exposure to high levels.

Fat embolism syndrome: incidence, significance and early features

During the period 1968 to 1978 a total of 447 patients were treated in the Royal Newcastle Hospital for acute respiratory failure after injury. In 321 patients respiratory failure occurred after thoracic and/or long bone injury. In only 17 of these could a diagnosis of fat embolism syndrome (FES) as a sole cause of respiratory failure be substantiated when strict diagnostic criteria were applied. In a further 15 patients FES may have coexisted with other causes of respiratory failure. The outstanding features of patients with FES were: (I) all were in the younger age groups; (II) all developed respiratory symptoms within 48 hours of admission to hospital; (III) most had multiple limb fractures; (IV) more than half had been transferred from other hospitals; and (V) three were pregnant and had sustained in comparison with the others, less severe long bone injuries.

Preparation of granulocyte-poor red blood cells by microaggregate filtration: a simplified method to minimize febrile transfusion reactions

A simple, effective method for removing granulocytes from stored blood is described. Microaggregate filtration removes approximately 95% of the granulocytes from blood which has been stored for 2 weeks, centrifuged and filtered. The mean number of remaining leukocytes is 8 +/- 3.7 x 10(8)/unit. The residual white cell population, which is composed almost entirely of lymphocytes, is substantially less than the average number of cells previously associated with febrile reactions. 45 patients were selected for the study. All had significant febrile transfusion reaction histories, and averaged one reaction for every 3.6 U of conventional red cell product transfused. Administration of 212 units of microaggregate filtered granulocyte poor red cells caused a 95% reduction in the incidence of fibrile reactions. The technique is inexpensive, easily incorporated into the routine of the clinical blood bank, and does not require "open-system' processing. These considerations make microaggregate filtration a logical first choice method for the preparation of granulocyte-poor red blood cells.

Effects of different filter positions and combinations in extracorporeal circulation

This study has demonstrated that best results are achieved when the arterial line filter and the coronary suction line filter and combined. The arterial line filter should not be used alone, as it does not replace the coronary suction line filter. Different flow patterns enable the coronary suction line filter to hold most of the very small particles, while those pass the arterial line filter easily. No significant differences could be demonstrated in the number of circulating cellular elements of the blood with one or more filters in place. However, during the second half of the extracorporeal circulation, up to 50% of the small particles disappear in the patient, although there is no difference between the number infused into the patient and the number found in the venous blood during the first 30 to 45 minutes of bypass.

Microfiltration of stored blood

Microaggregates begin to develop within a few hours of storage of blood in plastic or glass containers, but their numbers increase mainly towards the end of the first week. They include degenerated platelets, leucocytes, fibrin strands, denatured proteins and fragmented red cells, and range in size from 10 to 40 micrometer or more in diameter. The rate of formation is related to the platelet and leucocyte concentrations prior to storage and the anticoagulant used. While clinical and experimental evidence of deleterious pulmonary effects of these unwanted particles has been limited and contradictory, recent studies have demonstrated that significant increases in pulmonary arteriovenous shunting and alveolar-arterial oxygen differences occur in patients transfused more than 20% of their blood volume throught the standard 170 micrometer filters. These changes are not seen when the blood is passed through a 20 micrometer Dacron wool filter. Other methods of reducing the microaggregate content of transfused blood include the use of fresh blood (less than 2 days), glycerol-frozen fresh blood correctly thawed, or saline-washed packed red cells. Since none of these is feasible for routine use at present, removal by microfiltration prior to rransfusion is employed. Of the filters currently available, the 40 micrometer screen filters appear to offer important practical advantages over the alternative depth filters. Routine filtration of all stored blood transfused is advocated.

Intra- and postoperative autotransfusion in open heart surgery under simple hypothermia in children

A new autotransfusion unit was developed by the authors and the favorable results of 21 operations of open heart surgery under simple hypothermia were described. The patients were all children with simple congenital heart diseases. The amounts of autotransfused blood ranged from 2.8 to 15.5 ml/kg. Intraoperative autotransfusion proved to be an effective means of minimizing blood loss during surgery (range 3.2 to 12.8 ml/kg) and performing open heart surgery without donor blood transfusion. Postoperative autotransfusion (range 0 to 14.3 ml/kg) served as a supplementary means of avoiding homologous blood transfusion. Among the 21 autotransfused patients, there were no complications, while two patients developed hepatitis out of 19 patients who received homologous blood in the control group.

Autologous blood transfusion

Autologous blood transfusion is a procedure in which blood is removed from a donor and returned to his circulation at some later time. Autologous transfusion can be performed in three ways: (1) preoperative blood collection, storage, and retransfusion during surgery; (2) immediate preoperative phlebotomy with subsequent artificial hemodilution and later return of the phlebotomized blood; and (3) intraoperative blood salvage and retransfusion. All three methods of autologous transfusion offer a potentially superior method of blood transfusion which eliminates many of the problems and complications associated with the banking and administration of homologous donor blood.

Filter columns for preparation of leukocyte-poor blood for transfusion

Filter columns (Imugard filters) packed with cotton wool prepared from Gossypium barbadense cotton removed 95--100% of leukocytes from packed red cell suspensions. Recovery of red cells was about 95%. The efficacy was similar for ACD and heparinized blood. Blood was filtered below 10 degrees C within 30 min under pressures of less than 0.2 kg/cm2. The shape and functions of the red cells were not altered by filtration. No pyrogenic or toxic substances, and little particulate matter were eluted from the filters.

An evaluation of the Bentley PFF-100 transfusion filter

The effects of a new transfusion filter (Bentley PFF-100) 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 19.95 kPa (150 mm Hg) pressure were measured. Filtration did not significantly alter erythrocyte or leukocyte count, total or plasma haemoglobin, red cell fragility, plasma sodium, potassium, albumin, or globulin. Platelet counts were reduced by 31%. 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 Bentley PFF-100 filter combines the feature of moderately efficient microaggregate removal with rapid blood flow rate. Compared to its predecessor, the Bentley PF-127, this new filter design has improved flow characteristics without loss of efficiency of microaggregate removal.

Blood microfiltration. A review

The factors which contribute to the formation of microaggregates in stored blood for transfusion have been discussed and their significance assessed. The history of the development of blood microfiltration is described. The advantages and disadvantages of screen microfilters in comparison with depth filters are considered. Screen filters with a pore diameter of about 40 micron would appear to have definite advantages.

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.

Specialized blood filters and fresh whole blood

Platelet counts and platelet functions were determined in fresh whole blood before and after it passed through two types of specialized transfusion filters. Both filters were capable of trapping 20% to 40% of the functional platelets, necessary for hemostasis, especially if heparin was used as the anticoagulant. When fresh whole blood is needed to treat the bleeding patient who has already received massive blood transfusions, these specialized filters should probably not be used.

Events related to microembolism during extracorporeal perfusion in man: effectiveness of in-line filtration recorded by ultrasound

Microparticle generation during cardiopulmonary bypass was monitored continuously in 60 adult patients who underwent open-heart operations. Echo-ultrasound transducers of 5 mHz frequency were interposed in a bubble oxygenator arterial line proximal and distal to a commercially available micropore filter. Ordinary perfusion events correlated with an increase in embolic counts and were recorded graphically. Calculation of filter efficiency revealed that all filters decreased measurable embolic counts. Platelet and leukocyte determinations and plasma hemoglobin values were not altered beyond limits ordinarily encountered during perfusion without filters. No patient in any filter group experienced postoperative respiratory distress, diffuse pulmonary infiltrate, or low PaO2. The 20 mu woven nylon mesh filter and the Dacron-wool filter showed greater than 90% effectiveness in removing recorded particles. Insertion of a cardiotomy filter did not appreciably alter recorded embolic counts distal to the arterial line filter.

Microaggregate formation in stored human packed cells: comparison with formation in stored whole blood and a method for their removal

Experiments were performed to compare the formation of microaggregates in stored human whole blood (WB) with that in stored packed cells (PC) and also to compare the effectiveness of standard blood transfusion filters with dacron wool (Swank) micropore transfusion filters in removing such microaggregates. After 5, 10, 15 and 20 days of storage SFP and debris weights of PC's were considerably greater than those of matched WB samples. Passage of either WB or PC's through standard blood transfusion filters resulted in small decreases in SFP and debris weights. Passage of either WB or PC's through dacron wool (Swank) transfusion filters led to striking and highly significant decreases in both SFP and debris weights. When stored PC's were diluted to the same hematocrits as their corresponding WB samples, SFP remained considerably elevated above those of the WB samples. On the basis of this research, it is concluded that centrifugation of blood during component separation leads to a significant increase in microaggregate formation over and above that which progressively occurs during storage and that the risk of pulmonary microembolization during transfusion with stored PC's is greater than that during WB transfusion. For this reason, dacron wool (Swank) filters should always be used when PC's are being transfused.

The extracorporeal pump filter--saint or sinner?

An arterial line filter can become a grave source of platelet and fibrin destruction, with widespread deposition on the filter to form a membrane across the mesh, as proved by careful scanning electron microscopy. The same filter, when subjected to the low flows of the cardiotomy line, was well tolerated and served a very useful function. There was a 260% improvement in platelet counts and a 170% reduction in chest drainage when the arterial line filter was not used, perhaps through elimination of a degree of consumptive coagulopathy. Neurological changes did not occur in the absence of the arterial line filter, and operative mortality was 4.8% (5 of 103 patients).

The occurence and significance of microaggregates in stored blood

During storage whole blood progressively forms microaggregates by adhesion of platelets and leucocytes. This occurs from the second day of storage and the presence of such potential microemboli can be demonstrated by light microscopy of smears of blood samples. They cause an increase in the viscosity of the blood as measurable by the screen filtration pressure method. If infused into a patient they, by causing microvascular occlusion, result in multiple organ dysfunction, primarily of the lung. It is recommended that, if whole blood greater than 4 days in storage is to be infused, an in-line microfilter be used to remove the microaggregates from the transfusion. Alternatively, early separation, or the use of fresh blood is recommended.

A role of extracorporeal circuit in the post-perfusion thrombocytopenia: a scanning electronmicroscopic observation

Thrombocytopenia is one of the adverse effects of extracorporeal circulation (ECC) but the mechanism of which has not been fully understood. Blood-gas interface, mechanical agitation, rough surface of extracorporeal circuit and sequestration in the liver have been considered to be a cause of platelet loss. Extracorporeal circuit which provides large artificial surface for contact of blood has been blamed as the site of platelet destruction during oxygenation. However, the part of the oxygenator responsible for platelet loss has bot been located. This study was designed to identify the sites of extracorporeal circuit responsible for platelet loss during ECC with scanning electron microscopy (SEM) of the post-perfusion circuit. The accumulation of platelet aggregates was most pronounced at the defoaming net and blood filter where a sudden changes in velocity of blood flow take place. The aggregates were considered to be formed locally at these sites. However, there were no accumulation and/or adherence of platelet aggregates of significant degree at the other parts of the circuit, namely venous and arterial tubings, venous colum and arterial reservoir. Platelets seem to be removed from the circulation during each passage by defoaming net and blood filter. However the other parts of the circuit seem to be less blamed for the platelet loss. It was not possible to conclude whether the formation and trapping of platelet microaggregates at the defoaming net and blood filter or the destruction by oxygen bubbles is mainly responsible for the plateletloss during ECC.

Respiratory failure after liver transplantation

A rapidly growing haemangioendothelial sarcoma of the liver in a twenty-two year old woman was treated by liver transplantation. Disseminated intravascular coagulation resulted in massive blood loss during surgery, and contributed to the death of the patient from respiratory failure on the fourth post-operative day, despite continuous post-operative intermittent positive-pressure ventilation. Other factors leading to her respiratory failure are discussed. There was no evidence of dysfunction in the transplanted liver.

Oxygen consumption changes with stored blood infusions

Stored blood contains microaggregates, often implicated in the pathogenesis of post-traumatic pulmonary insufficiency. This study was an attempt to further elucidate the effect of autologous stored, filtered and non-filtered blood infusions and homologous stored and fresh blood infusions on pulmonary function and hemodynamics. Inconsistent changes in pulmonary hemodynamics and blood oxygenation were noted. The one significant finding was an increase in oxygen consumption, which occurred with unfiltered autologous or homologous blood but not with fresh or filtered blood. Since an increased oxygen consumption results in an oxygen demand which is difficult to meet in the face of multiple other injuries, it is conceivable that this observation implicates massive stored blood transfusion as a major contributing factor in the development of so-called irreversible shock.

Pulmonary microembolism associated with massive transfusion: II. The basic pathophysiology of its pulmonary effects

In animals pulmonary hypertension, a decrease in total body O2 consumption and metabolic acidosis occur after transfusion of blood with an elevated screen filtration pressure (SFP) through standard blood transfusion filters. The purpose of this study was to define in detail the pulmonary abnormalities that develop following transfusion of blood with an elevated SFP through standard blood transfusion filters. Exchange transfusions of approximately twice blood volume were administered through standard commercially available blood transfusion filters (measured pore size--200 microns) to 6 animals. SFP measurements verified the presence of large numbers of aggregates in the transfusions. Although filters reduced SFP of the stored blood somewhat, numerous microaggregates passed the filters, and post-filtration SFP remained high. After transfusion average O2 consumption decreased to 77% of normal and metabolic acidosis developed. Pulmonary arterial hypertension was associated with an increase in pulmonary shunting of blood and a decrease in pulmonary diffusing capacity. The presence of extensive numbers of microemboli in the pulmonary arteriolar and capillary bed was confirmed by microscopic examination of lung tissue.

Platelet aggregation: effects of cardiopulmonary bypass

This study was designed to determine whether reduction in platelet aggregate microembolization during the first 30 minutes of cardiopulmonary bypass is due to thrombocytopenia or to decreased ability of platelets to aggregate. The total volume of platelet aggregates induced in blood by adenosine diphosphate (ADP) was measured with a Coulter counter. The volume of platelets in blood was calculated by multiplying hemocytometry platelet counts by the mean platelet volume. Immediately before cardiopulmonary bypass, the total volume of aggregates induced in blood by ADP (2muM) was reduced when compared to normal donors because of (1) a slight fall in the volume of platelets, and (2) reduction in the percentage by volume of platelets which aggregated. After 30 minutes on bypass, the volume of both platelets and aggregates fell, but a greater percentage of platelets aggregated. This indicates that reduction of platelet aggregate formation during cardiopulmonary bypass is due to thrombocytopenia. It also suggests that anesthesia, surgical trauma and heparinization alter platelet reactivity more than cardiopulmonary bypass.

Evidence for pulmonary microembolization during hemodialysis

The generation of microaggregates during the extracorporeal circulation of heparinized blood through two types of hemodialyzers was demonstrated by increased screen filtration resistance. Arterial blood deoxygenation and widening of the alveolar-arterial oxygen difference occurred following either unfiltered or inadequately filtered dialysis. These changes were consistent with pulmonary microembolization. The blood gas abnormalities and the increased screen filtration resistance were reversed or improved when venous line microemboli filters were used.

Comparison of filtering efficiency of four new in-line blood transfusion filters

Efficient removal of debris from stored human blood prior to transfusion has become increasingly important. The debris, consisting largely of microaggregates of platelets and fibrin, is not effectively removed by passage through a standard transfusion filter. This study evaluated the performance of four of the currently available small pore in-line blood transfusion filters. Filters tested included the Bentley PF-127, the Pall Ultipor SQ-40, the Swank In-Line IL-200 and the Fenwal Microaggregate Blood Filter. A standard blood administration filter was also tested, the McGraw V-2950. The rate of blood flow through the filters was recorded using single and multiple units of blood. The screen filtration pressure and debris weight of the filtered blood were studied to compare effectiveness of filtration. The Swank filter was effective in debris removal and maintained good flow rates. The Bentley and Fenwall filters removed debris nearly as well, but had reduction of flow rates after smaller infusions. The Pall filter maintained high flow rates but did not remove debris as effectively, particularly with pressure infusion. The standard 170 mu pore blood transfusion filter does not remove microaggregates.