Therapies for Blood Disorders
The surgical removal of the spleen (splenectomy) is sometimes necessary after trauma to the abdomen. Because the spleen is very vascular, severe hemorrhage can result if the spleen is ruptured. Under such circumstances, splenectomy becomes an emergency procedure.
Splenectomy is also a possible treatment for other hemato-logic disorders. For example, an enlarged spleen may be the site of excessive destruction of blood cells. If the destruction is life-threatening, surgery may be lifesaving. This is the case in autoimmune hemolytic anemia or ITP when these disorders do not respond to more conservative measures, such as cortico-steroid therapy. Some patients with severe anemia due to in-herited RBC defects (eg, thalassemia) may also benefit from splenectomy.
In general, the mortality rate after splenectomy is low. Lap-aroscopic splenectomy can be used in selected patients, with a resultant decrease in the postoperative morbidity rate. Compli-cations that may result from surgery are atelectasis, pneumonia, abdominal distention, and abscess formation. Although young children are at the highest risk after splenectomy, all age groups are vulnerable to overwhelming lethal infections and should re-ceive pneumovax before undergoing this surgical procedure if possible.
Patients are instructed to seek prompt medical attention if even relatively minor symptoms of infection occur. Often, patients with high platelet counts have even higher counts after splenectomy— more than 1 million/mm3—which can predispose them to serious thrombotic or hemorrhagic problems. This increase is, however, transient.
Apheresis is a Greek word meaning separation. In therapeutic apheresis (or pheresis), blood is taken from the patient and passed through a centrifuge, where a specific component is separated from the blood and removed (Table 33-9). The remaining blood is then returned to the patient. The entire system is closed, so the risk of bacterial contamination is extremely low. When platelets or WBCs are removed, the decrease in these cells within the circulation is temporary. However, the temporary decrease provides a window of time until suppressive medica-tions (eg, chemotherapy) can have therapeutic effects. Some-times plasma is removed rather than blood cells—typically so that specific, abnormal proteins within the plasma will be tran-siently lowered until a long-term therapy can be initiated.
Apheresis is also used to obtain larger amounts of platelets from a donor than can be provided from a single unit of whole blood. A unit of platelets obtained in this way is equivalent to six to eight units of platelets obtained from six to eight separate donors via standard blood donation methods. Platelet donors can have their platelets apheresed as often as every 14 days. WBCs can be obtained similarly, typically after the donor has received growth factors (G-CSF, GM-CSF) to stimulate the formation of additional WBCs and thereby increase the WBC count. The use of these growth factors also stimulates the re-lease of stem cells within the circulation. Apheresis is used to harvest these stem cells (typically over a period of several days) for use in PBSCT.
Therapeutic phlebotomy is the removal of a certain amount of blood under controlled conditions. Patients with elevated hematocrits (eg, those with polycythemia vera) or excessive iron absorption (eg, hemochromatosis) can usually be managed by pe-riodically removing 1 unit (about 500 mL) of whole blood. Even-tually this process can produce iron deficiency, leaving the patientunable to produce as many RBCs. The actual procedure for ther-apeutic phlebotomy is similar to that for blood donation (see later discussion).
A single unit of whole blood contains 450 mL of blood and 50 mL of an anticoagulant. A unit of whole blood can be processed and dispensed for administration. However, it is more appropriate, economical, and practical to separate that unit of whole blood into its primary components: RBCs, platelets, and plasma (WBCs are rarely used; see later discussion). Because the plasma is re-moved, a unit of RBCs (packed RBCs, PRBCs) is very concen-trated (hematocrit, approximately 70%). Each component must be processed and stored differently to maximize the longevity of the viable cells and factors within it; each individual blood com-ponent has a different storage life. PRBCs are stored at 4°C. With special preservatives, they can be stored safely for up to 42 days before they must be discarded. In contrast, platelets must be stored at room temperature because they cannot withstand cold temperatures, and they last for only 5 days before they must be discarded. To prevent clumping, platelets are gently agitated while stored. Plasma is immediately frozen to maintain the ac-tivity of the clotting factors within; it lasts for 1 year if it remains frozen. Plasma can be further pooled and processed into blood derivatives, such as albumin, immune globulin, factor VIII, and factor IX. Table 33-10 describes each blood component and how it is commonly used.
Factor VIII concentrate (antihemophilic factor) is a lyophilized, freeze-dried concentrate of pooled fractionated human plasma. It is used in treating hemophilia A. Factor IX concentrate (pro-thrombin complex) is similarly prepared and contains factors II, VII, IX, and X. It is used primarily for treatment of factor IX de-ficiency (hemophilia B). Factor IX concentrate is also useful in treating congenital factor VII and factor X deficiencies.
Plasma albumin is a large protein molecule that usually stays within vessels and is a major contributor to plasma oncotic pressure. This protein is used to expand the blood volume of patients in hypovolemic shock and, rarely, to increase the concentration of circulating albumin in patients with hypo-albuminemia.
Immune globulin is a concentrated solution of the antibody IgG; it contains very little IgA or IgM. It is prepared from large pools of plasma. The intravenous form (IVIG) is used in various clinical situations to replace inadequate amounts of IgG in patients who are at risk for recurrent bacterial infection (eg, those with CLL, those receiving BMT or PBSCT). IVIG, in contrast to all other fractions of human blood, cells, or plasma, are able to survive being subjected to heating at 60°C (140°F) for 10 hours to free them of viral contaminants.
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