A mathematical model of aluminum depth filtration with ceramic foam filters: Part I. Validation for short-term filtration

This work presents a mathematical model to compute the efficiency of depth filtration of molten aluminum using ceramic foam filters. In the model, the porous structure of foam filters was represented by a unit cell that takes into account the convergent-divergent nature of the flow field. The steady, two-dimensional, and fully developed flow field within the unit cell was obtained from the numerical solution of the continuity and Navier-Stokes equations. The assessment of the proper assumptions for the model was carried out by comparing the computed velocity field with that experimentally determined for a physical model of the unit cell with scale 10:1 and containing an aqueous solution of CaCl₂. The measurements were done using the particle image velocimetry (PIV) technique. The efficiency and the coefficient of initial filtration for foam filters were obtained from the determination of the particle limiting trajectory, resulting from a force balance on a spherical inclusion. This balance included the buoyancy and the viscous drag forces. The last force took into consideration the wall effect on the particle motion. The values of the computed initial filtration coefficient show an excellent agreement with the corresponding measured ones reported for laboratory and plant tests for short-term filtration. This comparison involves several combinations of particle sizes and downward fluid superficial velocities. This model is further extended to study long-term filtration in the second part of the article.     

A mathematical model of aluminum depth filtration with ceramic foam filters: Part II. Application to long-term filtration

The mathematical model to compute the efficiency of depth filtration of molten aluminum, previously presented in Part I, was further developed and applied to study long-term filtration. In this case, the incoming suspension entering the unit cell was not assumed homogeneous, and the times and positions of particle at the inlet were obtained stochastically from a random number generator. The particles that were transported by the fluid flow to the wall and collided against this surface remained attached to the wall and accumulated within the domain. The accumulation of particles decreased the effective area for fluid to flow through the pore, causing distortion of the overall velocity field in the domain. The flow field was obtained from the numerical solution of the continuity and Navier-Stokes equations for transient flow, the particle trajectories were calculated using the Langrangian motion equation including the buoyancy, and the viscous drag force corrected for the wall effect. The model predicted a preferred particle accumulation around the windows to form a cake of particles and the effect that inclusion accumulation has on the flow field, pressure drop, and filtration coefficient. This work studied the influence of particle concentration and fluid velocity on the evolution of the filtration coefficient and pressure drop. It was found that these quantities were practically constant for TiB₂ particles suspended in aluminum at a concentration of 1 ppm and filtered during 60 minutes through the unit cell of a 30 ppi foam filter. However, at a particle concentration of 10 ppm, the model predicted that the filtration coefficient and pressure drop changed appreciably for the same period of filtration. The results, obtained from first principles, provide a rationale to explain fluctuations of the filtration coefficient and pressure drop, reported in the literature, without introducing any empirical or probability factor in the respective equations.     

Anti-Rd (Radin) following the transfusion of a Radin positive unit of blood

Anti-Rd (Radin) was first described in association with five cases of hemolytic disease of the newborn. The authors report an anti-Rd that was demonstrated following the transfusion of a Radin positive unit of blood. The antibody appears to be of the IgG immunoglobulin class and increased in titer following the transfusion.     

Creutzfeldt-Jakob disease (CJD) after blood product transfusion from a donor with CJD

We report a second case of an association between an albumin transfusion and Creutzfeldt-Jakob disease. On balance, we believe our case represents a chance and not a causal relation.     

Costs of blood transfusion: a process-flow analysis

PURPOSE: To determine the cost of transfusing 2 units (U) of packed RBCs at a comprehensive cancer center. METHODS: We performed a process-flow analysis to identify all costs of transfusing 2 U of allogeneic packed RBCs on an outpatient basis to patients with either (1) solid tumor who did not undergo bone marrow transplantation (BMT), (2) solid tumor who underwent BMT, (3) hematologic malignancy who did not undergo BMT, (4) hematologic malignancy who underwent allogeneic BMT, or (5) hematologic malignancy who underwent autologous BMT. We conducted structured interviews to determine the personnel time used and physical resources necessary at all steps of the transfusion process. RESULTS: The mean cost of a 2-U transfusion of allogeneic packed RBCs was $548, $565, $569, $569, and $566 for patients with non-BMT solid tumor, BMT solid tumor, non-BMT hematologic malignancy, allogeneic BMT hematologic malignancy, and autologous BMT hematologic malignancy, respectively. Sensitivity analysis showed that total transfusion costs were sensitive to variations in the amount of clinician compensation and overhead costs, but were relatively insensitive to reasonable variations in the direct costs of blood tests and the blood itself, or the probability or extent of transfusion reaction. CONCLUSION: The costs of the transfusion of packed RBCs are greater than previously analyzed, particularly in the cancer care setting.     

Haemorrhagic syndrome after massive transfusion of blood for traumatic liver rupture: disseminated intravascular coagulation? (Author''s transl)

The rate of control of thyrotoxicosis during the first 2 weeks of treatment was documented in 63 patients. Twenty-three patients received carbimazole 40 mg plus lithium carbonate 750 mg daily and a comparable group of 20 patients were given carbimazole 40 mg plus potassium iodide 120 mg daily. In the lithium treated patients the mean percentage fall of serum T4 after 2 weeks treatment was 49% and the fall in serum T3 57%. The results were similar in the iodide treated patients; the mean falls in serum T4 and T3 being 47% and 64%, respectively. Serum lithium values varied between 0.1-1.25 mEq./l; lithium side effects were minor. In a companion study 20 patients were treated with carbimazole alone. The responses in this group were less impressive; the mean falls in serum T4 and T3 at 2 weeks being 18% and 36%, respectively. It is concluded that lithium is a safe adjunct to conventional antithyroid drug therapy in the initial treatment of acute thyrotoxicosis.     

Prevention of pulmonary micro-embolism during blood transfusion by means of fine mesh filters (author's transl)

Disturbances of the pulmonary micro-circulation may be due to embolic obstruction by particles in stored blood. Mechanical blocking of the lung circulation plays an important pathogenetic role in the development of progressive respiratory failure. Extraneous micro-particles can be partly eliminated from stored blood by filtration. Although a detailed clinical study of the value of microfiltration of stored bloods is still missing, the prophylactic use of fine mesh filters is advisable for all transfusions of whole blood or corpuscle concentrates regardless of the quantity to be transfused.     

Transmission of human T cell lymphotropic virus (HTLV) type II by transfusion of HTLV-I-screened blood products

Blood donors have been screened for antibodies to human T cell lymphotropic virus (HTLV) type I since December 1988. Screening for HTLV-II has been simultaneously done because of cross-reactivity between antibodies to the two viruses. Currently, < 1 in 10,000 US blood donors is positive for HTLV-I or -II. Lookback studies led to the identification of 6 HTLV-II-infected patients. Three received transfusions before introduction of HTLV-I screening tests, while the other 3 received blood components that tested negative for HTLV-I. The HTLV-II subtypes of each of 4 donor/recipient pairs, as determined by DNA amplification using polymerase chain reaction, were identical, supporting the view that transfusions were the source of infection. In conclusion, currently licensed blood donor screening tests for HTLV-I lack sensitivity for HTLV-II, and transfusion of blood from HTLV-II-infected donors that test negative on HTLV-I screening tests may result in infection.     

Untoward effects of blood transfusion: common problems and simple safeguards

Potential transfusion reactions include hemolysis, disease transmission (particularly hepatitis), allergic and febrile reactions, and symptoms of circulatory overload. Limiting the number of transfusions given to patients for whom the procedure will achieve some clearly defined clinical goal is one way of reducing the number of adverse reactions. When transfusion is to be carried out, great care should be taken in correctly identifying both patient and blood to avoid ABO mix-ups, and thorough pretransfusion laboratory testing should be done. During and after transfusion the patient should be closely observed for complications.     

Shed mediastinal blood transfusion after cardiac operations: a cost-effectiveness analysis

BACKGROUND: Cardiac surgical patients consume a significant fraction of the annual volume of allogeneic blood transfused. Scavenged autologous blood may serve as a cost-effective means of conserving donated blood and avoiding transfusion-related complications. METHODS: This study examines 834 patients after cardiac operations at the University of Alabama Hospital. Data were collected on patients receiving unwashed, filtered, autologous transfusions from shed mediastinal drainage and those receiving allogeneic transfusions. The data were incorporated into clinical decision models; confidence intervals for parameters were estimated by bootstrapping sample statistics. Costs were estimated for transfusing both allogeneic and autologous blood. RESULTS: The study found a 54% reduction in transfusion risk or a mean reduction of 1.41 allogeneic units per case (95% confidence interval, 1.04 to 1.79 units). The process saved between $49 and $62 per case. CONCLUSIONS: The use of autologous blood has the potential to significantly reduce the costs and risks associated with transfusing allogeneic blood after cardiac operations.     

Haemophilia A and the blood transfusion service: a Scottish study

The demand for blood products containing factor VIII for treating patients with haemophilia A in south-east Scotland was reviewed. From 1961 to 1975 the demand for fresh frozen plasma (FFP), cryoprecipitate (CP), and antihaemophilic factor (AHF) increased by seven and a half times, while total donations increased by only a third. Patients with severe haemophilia A treated at the regional haemophilia centre used about 85% of the factor VIII issued in 1971-4, most of which was used on demand. A patient with severe haemophilia A on unlimited ondemand home treatment would need about 500 units of factor VII/kg body weight/year, and a regional haemophilia centre, treating moderate and mild cases as well as severe ones, would use 15000 units/patient/year. Altogether about 50 million units of factor VIII will be needed each year in the UK. Although cryoprecipitate is much harder to store and administer than AHF, its yield from plasma may be far greater and its cost far smaller. Unless the blood transfusion services receive increased amounts of money and reappraise their functions and operation, it seems likely that they will have to rely increasingly on commercial (and costly) sources for the major plasma fractions.     

Hepatitis C update: implications of the blood transfusion "lookback"

Over the next several years, physicians will be called upon to notify past blood transfusion recipients of blood that may have been contaminated with hepatitis C virus (HCV). This article reviews the screening, care, and follow-up of persons at risk for hepatitis C virus infection from all sources.     

Leukodepletion blood filters: filter design and mechanisms of leukocyte removal

Modern leukocyte removal filters have been developed after years of refinement in design. Current filters are composite filters in which synthetic microfiber material is prepared as a nonwoven web. The filter material may be surface modified to alter surface tension or charge to improve performance. The housing design promotes effective contact of blood with the filter material and decreases shear forces. The exact mechanisms by which these filters remove leukocytes from blood components are uncertain, but likely represent a combination of both physical and biological processes whose contributions to leukocyte removal are interdependent. Small-pore microfiber webs result in barrier phenomena that permit retention of individual cells and increase the total adsorptive area of the filter. Modifications in surface charge can increase or decrease cell attraction to the fibers. Optimum interfacial surface tensions between blood cells, plasma, and filter fibers not only permit effective blood flow through small fiber pores, but also facilitate cell contact with the material. Barrier retention is a common mechanism for all modern leukocyte-removal filters and applies to all leukocyte subtypes. Because barrier retention does not depend on cell viability, it is operative for cells of any age and will retain any nondeformable cell, including whole nuclei from lymphocytes or monocytes. Barrier retention is supplemented by retention by adhesion. RBCs, lymphocytes, monocytes, granulocytes, and platelets differ in their relative adhesiveness to filter fibers. Different adhesive mechanisms are used in filters designed for RBCs compared with filters designed for platelets. Although lymphocytes, monocytes, and granulocytes can adhere directly to filter fibers, the biological mechanisms underlying cell adhesion may differ for these cell types. These differences may depend on expression of cell adhesion molecules. In the case of filtration of fresh RBCs, platelet-leukocyte interaction seems to supplement other mechanisms of leukocyte retention. The interactions of cells with biomaterials is an area of important research for implantable medical devices, artificial organs, and orthopedic, vascular, and dental prosthetics. Research in these areas is likely to contribute to improved biomaterials for blood filters. Improved techniques for the preparation of hybrid polymers and new techniques for surface modification of existing polymers will increase the technical opportunities for the development of synthetic surfaces ideally designed for leukocyte removal. It is therefore likely that the performance of leukocyte-removal filters will continue to improve. The development of cost-effective leukocyte removal filters specifically designed for use during component preparation would permit leukocyte depletion of all cellular blood components.     

Potential alternatives to erythrocyte transfusion in hemoglobinopathies: hydroxyurea (HU), erythropoietin (EPO), butyrate derivatives, blood substitutes

OBJECTIVE: To evaluate the invaginated sleeve technique for continent cystostomy in humans. PATIENTS AND METHODS: Over the past 5 years six patients have undergone this operative procedure. An essential principle utilized in the technique is the property of partial thickness bladder grafts to stretch longitudinally, so that each tubularized pedicle graft could be directed transmurally and extended extravesically to reach the skin of the lower abdominal wall. As a consequence a urothelial-lined tract, both extravesically and through the bladder wall, was provided for intermittent self-catheterization. RESULTS: Apart from one woman, whose cystostomy tract was disrupted by inappropriate catheterization in the immediate post-operative period to attempt to stop leakage through exposed fenestrations in the suprapubic stent, this procedure provided robust, continent catheterizing routes for all patients for periods of 63, 52, 12, 7 and 1.5 months respectively. Two patients developed discrete stenoses at their mucocutaneous junctions at 3 and 5 months which were corrected easily. CONCLUSION: This simple, minimally morbid technique, which avoids the use of non-urinary tract epithelial structures and maintains bladder capacity, is strongly recommended for patients who need to practise clean intermittent self-catheterization and for whom the urethral route is impracticable.