Role of microaggregate blood filtration in clinical medicine

Characterization of platelet concentrates using dynamic light scattering

BACKGROUND

Each year, millions of platelet transfusions save the lives of cancer patients and patients with bleeding complications. However, between 10 and 30% of all platelet transfusions are clinically ineffective as measured by corrected count increments, but no test is currently used to identify and avoid these transfusions. ThromboLUX(®) is the first platelet test intended to routinely characterize platelet concentrates prior to transfusion.

METHODS

ThromboLUX is a non-invasive, optical test utilizing dynamic light scattering to characterize a platelet sample by the relative quantity of platelets, microparticles, and other particles present in the sample. ThromboLUX also determines the response of platelets to temperature changes. From this information the ThromboLUX score is calculated. Increasing scores indicate increasing numbers of discoid platelets and fewer microparticles. ThromboLUX uses calibrated polystyrene beads as a quality control standard, and accurately measures the size of the beads at multiple temperatures.

RESULTS

Results from apheresis concentrates showed that ThromboLUX can determine the microparticle content in unmodified samples of platelet concentrates which correlates well with the enumeration by flow cytometry. ThromboLUX detection of microparticles and microaggregates was confirmed by microscopy.

CONCLUSION

ThromboLUX provides a comprehensive and novel analysis of platelet samples and has potential as a noninvasive routine test to characterize platelet products to identify and prevent ineffective transfusions.

White particulate matter: report of the ad hoc industry review group

BACKGROUND

In January 2003, blood center personnel in the American Red Cross, Southern Region in Atlanta, noticed whitish particulate material (WPM) that had not been observed previously in several units of red blood cells (RBCs). An expert panel was formed to evaluate studies of the material and make appropriate recommendations

STUDY DESIGN AND METHODS

The expert panel reviewed information provided by several investigations and organizations. This included: background information, and experiences relating to WPM; WPM composition; factors promoting WPM formation; risk of WPM (if any) to patients; and recommendations to prevent future occurrences.

RESULTS

WPM is derived from blood. No data suggest that external contamination or collection set components contribute to WPM development. A major constituent of WPM is platelets (PLTs). WPM is most commonly observed in RBCs that have been subjected to a hard spin without PLT separation. WPM is rarely, if ever, observed in RBCs that have been subjected to leukoreduction.

CONCLUSIONS

(1) WPM is not new, can be prevented, and can be removed. (2) WPM contains PLTs, white blood cells, fibrin, and cellular debris. (3) Changes in blood handling are not necessary. (4) WPM may be more frequent when higher g forces are used in component preparation. (5) Enhanced visual inspection of blood components need not be continued. (6) It appears that WPM may not form in RBC collected using automated devices. (7) WPM did not pose a risk to patients but should be avoided.

Filters in anaesthesia and intensive care

The use of various types of filters in anaesthesia and intensive care seems ubiquitous, yet authentication of the practice is scarce and controversies abound. This review examines evidence for the practice of using filters with blood and blood product transfusion (standard blood filter, microfilter, leucocyte depletion filter), infusion of fluids, breathing systems, epidural catheters, and at less common sites such as with Entonox inhalation in non-intubated patients, forced air convection warmers, and air-conditioning systems. For most filters, the literature failed to support routine usage, despite this seemingly being popular and innocuous. The controversies, as well as guidelines if available, for each type of filter, are discussed. The review aims to rationalize the place of various filters in the anaesthesia and intensive care environment.

Transfusion-associated graft versus host disease

OBJECTIVES

To review the epidemiology, pathophysiology, therapeutic and preventive strategies of transfusion associated graft versus host disease (TA-GVHD) and relate the findings to the critically ill child.

DESIGN

Review article of published medical literature related to TA-GVHD.

DATA SOURCES

Medline, bibliography search, published national and institutional guidelines.

STUDY SELECTION

Original publications including prospective studies, case reports, case series, laboratory studies, and animal work.

DATA EXTRACTION

Data were extracted manually after we reviewed selected articles and assessed their contribution to knowledge of TA-GVHD.

DATA SYNTHESIS

New and significant historic information from the selected publications relating to incidence, therapy, prevention, and complications of preventive therapy of TA-GVHD was incorporated.

CONCLUSIONS

Pediatric critical care practitioners should be aware of this preventable but fatal complication of cellular blood product transfusion. High-risk categories include congenital and acquired immunodeficiency, younger age, transfusion of blood donated by family members, and transfusion with fresh whole blood. Children at risk for the development of TA-GVHD include neonates, infants, and children with congenital heart disease, not restricted to children with "classic" DiGeorge syndrome. At present, risk identification and targeted prevention are the only methods to manage TA-GVHD. Aside from minimizing cellular blood product exposure, blood product irradiation is the only established and widely available method to prevent TA-GVHD. Transfusion guidelines need to reflect a balance between the incidence of TA-GVHD and the costs of instituting irradiation to selected groups or as routine transfusion policy.

Reducing donor exposure in preterm infants requiring multiple blood transfusions

Preterm infants frequently require multiple blood transfusions. Traditionally, 'fresh' (less than seven days old) blood has been used but this often results in transfusions from multiple donors. To reduce donor exposure the policy for top-up transfusions was changed. A unit of blood under five days old with additional satellite packs was ordered for each infant and used up to its expiry date, allowing up to eight transfusions from a single donation to be given. The mean (SD) number of transfusions per infant in 43 infants transfused according to previous policy and in 29 transfused according to the new policy was similar at 5.6 (4.0) and 5.3 (3.1), respectively. However, donor exposure fell following the change in policy from 4.9 (3.5) to only 2.0 (0.9). Only one infant was exposed to more than three donors compared with 24 infants in the control group. Plasma potassium concentrations were not significantly different following transfusion of blood stored for up to 33 days. This simple change in policy has reduced donor exposure in infants requiring multiple top-up transfusions.

Massive blood transfusion: the blood bank perspective

The pathophysiology and support of the massively transfused patient from the vantage of a blood banker is reviewed. Hypothermia, acidosis and shock must be reversed if blood component therapy is to be effective. Algorithms which employ ratios of various blood components have not proved themselves, nor are screening coagulation tests of value until they are remarkably abnormal. Thrombocytopenia, thrombocytopathy, and hypofibrinogenemia appear to be the parameters which predispose to continued bleeding and microvascular hemorrhage in these patients. A large part of the impaired hemostasis is due to a consumption coagulopathy rather than the anecdotal assumption that dilution of the hemostatic elements is to blame. Hypocalcemia, hypomagnesemia and hyperkalemia are rarely observed nor do they pose a problem for this group of individuals. The logistics of blood supply to the clinical areas are addressed by describing one system that has proved itself.

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.

Perioperative blood and blood component therapy

This overview examines blood, blood components, their indications and contra-indications, from an anaesthetist's viewpoint. The dangers of any blood transfusion, including infection transmission and immune suppression, as well as the risks of massive and rapid transfusions, are discussed. Autologous predonation, intraoperative haemodilution and salvage are described to help prevent some of the risks of homologous blood transfusion. Preoperatively an acceptable individualised haemoglobin concentration should be calculated for each patient and a history for potential bleeding problems taken. In most patients perioperative anaemia does not adversely influence patient morbidity and mortality. However, if blood is required, 4 ml.kg-1 body weight of packed red blood cells will raise the patient's haemoglobin concentration by 1 g.dl-1. The bleeding time as a test of platelet function does not predict perioperative blood loss. However, it remains a useful test in patients with a known bleeding problem or in operations where even small amounts of bleeding increase the surgical difficulty and patient morbidity. If bleeding is due to thrombocytopaenia it is usually slow enough to allow time to check platelet number and function before ordering and transfusing them. Fresh plasma is a much overused product which should mainly be used for coagulation factor replacement, in adequate volumes (4-8 packs in dilutional coagulopathy). The well-informed anaesthetist should be better able to use blood products which, while they may be life saving, are neither innocuous nor inexpensive.

Perioperative haemotherapy: II. Risks and complications of blood transfusion

Major life-threatening complications following blood transfusion are rare and human error remains an important aetiological factor in many. The infectious risk from blood transfusion is predominantly hepatitis, and non-A, non-B and hepatitis C (HCV) are the most common subtypes noted. The risk of post-transfusion hepatitis (PTH) appears to be decreasing and this is attributed to both deferral of high-risk donors and more aggressive screening of donated blood. Screening for HCV is expected to decrease this risk further. The risk of HIV transmission following blood transfusion is negligibly small. There are data to suggest that perioperative blood transfusion results in suppression of the recipient's immune system. Earlier recurrence of cancer and an increased incidence of postoperative infection have been associated with perioperative blood transfusion although the evidence is not persuasive. Microaggregate blood filters are not recommended for routine blood transfusion but do have a role in the prophylaxis of non-haemolytic febrile reactions caused by platelet and granulocyte debris in the donor blood. Patients should be advised when there is likely to be a requirement for perioperative blood transfusion and informed consent for transfusion should be obtained.

Platelet aggregates in small lung vessels and death during liver transplantation

10 children who died suddenly during liver transplantation were found at necropsy to have extensive obstruction of small lung vessels by platelet aggregates. In 7 of these patients pulmonary artery pressure changes before death were consistent with acute obstruction of the pulmonary vascular bed. Platelet aggregates were not strikingly increased in blood vessels in other tissues. No single obvious cause for these unusual histological findings could be identified, although the presence of intravascular catheters, perioperative blood and platelet concentrate transfusions, and cellular debris from the liver forced into the circulation during surgery might predispose to platelet aggregation.

In vitro evaluation of a new dual screen microaggregate filter

We compared a new second generation 40/150 mum dual screen microaggregate filter with a currently available 40 mum 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 mum 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 mum 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.

[Technical constraints in rapid vascular fluid replacement]

Rapid fluid infusion remains the cornerstone for therapy of hypovolaemic shock. The principal limitations of flow rate are governed by the four variables of Poiseuille's law: tube internal diameter and length, viscosity of the fluid passing through the tube, and the pressure gradient between the two ends of the tube. Conventional transfusion systems, with wide bore tubing (up to 5.0 mm internal diameter), large bore cannulas (8.5 French introducer catheters), high pressure (up to 300 mmHg) and diluted blood, can result in a maximum flow rate of about 1,000 ml.min-1 (for crystalloid solutions). Specific apparatus for rapid infusion can increase this to 1,500 ml.min-1 (Rapid Infusion System, Haemonetics). Dry-heat warming devices and microfiltration, to remove microaggregates and prevent non haemolytic febrile transfusion reactions, seem necessary when carrying out rapid transfusions. However, the use of microaggregate filters could be avoided by the routine production of leukocyte-poor red blood cell concentrates.

Decreasing blood donor exposure in neonates on extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation (ECMO) has been successful treatment (80% survival) in over 2,000 neonates with severe respiratory failure (80% predicted mortality without ECMO). Neonates on ECMO require frequent blood product replacement, which increases donor exposure (DE) and the risk of transfusion related complications. Successful, widespread usage of ECMO in neonatal respiratory failure is placing increased numbers of surviving infants at risk for acute and long-term transfusion related problems. We assessed DE rates in 21 consecutive neonatal ECMO survivors. In the first 12 patients packed red blood cell (PRBC) transfusions were administered as 10 mL/kg body weight for hematocrit less than 45%. PRBC exchange transfusions were used in patients with hematocrit less than 45% and hypervolemia. Fresh frozen plasma (FFP) and cryoprecipitate (CRYO) infusions were used empirically for evidence of hemorrhage. DE rates (donors per ECMO day, mean +/- SD) were: PRBC (2.8 +/- 0.6), FFP/CRYO (0.5 +/- 0.7), and platelet (2.0 +/- 1.0), with a total donor exposure rate of 5.3 +/- 2.0 donors per ECMO day. Mean duration of ECMO was 4.6 +/- 2.0 days and total DE per infant was 22.8 +/- 9.5 donors per ECMO run. In a protocol (n = 9) to minimize DE risks, exchange transfusions were eliminated and PRBC transfusion volumes were increased to 15 mL/kg. Empiric use of FFP and CRYO was discontinued. The blood bank divided standard units of PRBCs into four aliquots and dispensed each aliquot sequentially before dispensing blood from another unit.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical evaluation of commonly used blood administration sets

Five commonly available blood transfusion sets, the Fenwall Blood Recipient set, the Abbott HEMAR Y-type Blood Set, the Bentley Infusion Blood Set (PFF-100), the Medex Hi-Flo TraumaR Quad Set (MX 884) and the Pall Ultipor Transfusion Set with Filter are compared. Flow rates and lifespan are evaluated by measuring the time required for 150 mL aliquots of homogeneous units of human red blood cells to pass through the devices under 300 mmHg constant pressure. Microfiltration of blood is briefly reviewed.

Transfusion therapy in emergency medicine

Volume replacement is critical to the resuscitation of the hemorrhaging patient, but this usually can be accomplished quickly and safely with crystalloid and/or colloid solutions. Red cells should be used in addition to asanguinous fluids in the treatment of tissue hypoxia due to anemia. The need for whole blood as opposed to packed red blood cells is controversial. However, plasma should not be used as a volume expander, and its use to supplement coagulation factors during the massive transfusion of red cells should be guided by laboratory tests that document a coagulopathy. Similarly, platelet transfusions are indicated to correct documented thrombocytopenia or platelet dysfunction, and routine prophylaxis after fixed volumes of red cells results is unwarranted. Many anticipated complications of massive transfusions, including hemostatic abnormalities, acid-base imbalances, hyperkalemia, and hypocalcemia, are uncommon or of limited clinical significance. The risks of immune hemolysis and transfusion-transmitted diseases, on the other hand, are significant, and argue for judicious use of blood components. In emergencies in which blood is required immediately before compatibility testing can be completed, O-negative uncrossmatched blood can be requested. Careful blood specimen collection and patient identification prior to transfusion are critical. Practices that emphasize blood conservation, including the use of autologous salvaged blood, are always to the patient's advantage.

Anesthesia for trauma

Trauma is the leading cause of death for persons aged 1 to 38 years. Successful management is facilitated by prehospital endotracheal intubation, transport to regional trauma centers, rapid resuscitation by an on-site team of trained physicians, timely operative intervention, and provision of care by well-prepared anesthesiologists familiar with the potential complications typical of traumatized patients. No particular anesthetic agent or technique is ideal. Causes for intraoperative hypotension include hypovolemia, hemopneumothorax, pericardial tamponade, an intracranial mass, acidosis, and hypothermia. The anesthesiologist should play an active role in all phases of trauma management, including provision of postoperative intensive care and pain relief.

A survey of transfusion practices among anesthesiologists

A survey of transfusion practices was conducted among anesthesiologists practicing in the United States to determine if significant variation exists and to identify those areas toward which research and educational efforts should be directed. Thirty-seven percent (389) of 1,043 active members of the American Society of Anesthesiologists who received the survey responded. The indications for transfusion as well as the types of components administered were found to vary considerably. Among the areas which need to be addressed are arbitrary preoperative hemoglobin requirements, indications for fresh frozen plasma administration, preoperative blood ordering and autologous transfusion.

The mechanisms and management of noncardiogenic pulmonary edema following cardiopulmonary bypass

Cardiac surgeons have become more cognizant of the syndrome of noncardiogenic pulmonary edema after cardiopulmonary bypass. Although this syndrome is rare, its occurrence can be catastrophic. This article reviews the current understanding of several factors that have been implicated in the cause of this syndrome and discusses the various options for management of the problem once it has arisen.

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.

The present status of blood filtration

The history of the development of blood transfusion and blood filtration is outlined. Clinical and experimental evidence for the efficacy of microfiltration in both small and large volume transfusions is evaluated. Though microfilters do remove the micro-aggregates from stored blood, the results of clinical studies suggest that both the debris from septic processes in the body and the formation of micro-aggregates in the blood stream triggered by processes such as complement activation play a far more important role in the pathogenesis of adult respiratory distress syndrome. If this is so the enhancement of the reticulo-endothelial system by fibronectin therapy may be indicated. It also follows that the use of microfilters is probably an unnecessary expense and, where exsanguination is a risk, may be positively dangerous. Microfilters have been found useful in the preparation of granulocyte-free transfusions after centrifugation of the blood, but their routine use for transfusions, small or large, remains to be justified.

Intraoperative autologous transfusion

Intraoperative autologous transfusion is a technique that was first used almost 2 centuries ago but that has realized its potential only in the past 5 years. A growing national awareness of transfusion-related morbidity, of the need for alternative blood sources, and of improved methods for red blood cell recovery has led to an increased frequency of use of autologous transfusion. Most hospital programs use semicontinuous flow centrifugation or canister technology for the intraoperative salvage and reinfusion of shed blood. This technique is particularly valuable for cardiovascular surgical procedures but has been useful in many other types of surgical procedures as well. Deleterious effects formerly attributed to this technique have been eliminated by methodologic improvements. Concerns about use of autologous transfusion in patients who have an infection or a malignant lesion persist. Most hematologic aberrations are related to massive transfusions and should not be considered a contraindication to the general use of autologous blood.

Outdated blood and redundant buffy-coats as sources for the preparation of multiparameter controls for Coulter-type (resistive-particle) hemocytometry

Outdated, buffy-coat depleted, CPDA-1 blood and redundant buffy-coats were used as sources for the laboratory preparation of controls for Coulter-type (resistive-particle) hemocytometry. Deteriorated white blood cells and platelets and potentially interfering microaggregates with volumes not exceeding 400 fl are shown to be virtually completely removed by centrifugation and filtration. Addition of fixed red blood cells as white blood cell substitutes and of isolated, fixed platelets enable the preparation of multiparameter controls of short-to-medium-term stability. The availability of these simple, inexpensive controls can contribute significantly to optimal internal quality control in hemocytometry.