Oxygen Carriers and Transfusion Medicine

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Abstract
The US blood supply is once again expanding (14 million units a year) and annual estimated whole blood and red blood cell (RBC) transfusion now exceeds 12 million units. The observed increase in total transfusions and units transfused per surgical procedure may result from more aggressive therapies, an aging population, and improved access to health care. While autologous blood collection has grown 20-fold in the past decade, autologous blood still accounts for < 8% of transfusions and is unlikely to replace much more of the allogeneic transfusion needs. Although safer than ever, allogeneic blood still transmits infectious disease (HIV: 1 in 225, 000 units, hepatitis: 1 in 3300 units, HTLV I/II:1 in 50, 000 units) and poses additional immunologic and non-immunologic risks. Allogeneic RBCs are probably underutilized because of safety concerns. While the cost of a unit of RBCs has been estimated at $150, costs are substantially higher in some areas and blood processing (filtration, gamma irradiation, washing) add additional expense. The narrowing margin between supply and demand, and repeated regional blood shortages argue for the value of safe, effective oxygen carriers. The last two decades have witnessed remarkable changes in the growth, use, and public perception of blood transfusion in the United States. National surveys indicate that blood collections and transfusions doubled between 1971 and 19 80 [1]. National Blood Policy, formulated in the early 1970's, outlined principles for an adequate, safe, available, and affordable blood supply; the national commitment to all volunteer blood donation, coupled with the use of sensitive screening tests for hepatitis B virus (HBV), promised to make these goals achievable. By 1980, blood collectors, medical practitioners, most policy makers, and the general public were largely satisfied with the apparent progress in securing a safe and available blood supply. By 1984 the situation had changed dramatically. Epidemiologic evidence had linked blood transfusion with a new and frightening fatal illness, the acquired immune deficiency syndrome (AIDS) [2]. Non-specific screening techniques that were introduced to improve blood safety by eliminating donors with high risk behavior had deferred large numbers of long-time donors. By 19 85, as many as 34 percent of blood donors in one survey believed that the blood donation process itself likely involved a risk of contracting AIDS [3]. While mass media concerns about blood safety increasingly centered on AIDS, the medical community became concerned simultaneously about the risk of hepatitis. The recognition of transfusion-transmitted hepatitis caused by virus (es) other than HBV led to the widespread and appropriate introduction of non-specific screening tests that eliminated 3 to 5% of American blood donors, most of these safe and healthy volunteers [4,5]. Transfusions of whole blood and red blood cells, which had peaked at 12.2 million units in 1986, declined to 11.6 million units in 1987 and collections of allogeneic blood reached a plateau at 13.3 million units [6]. By the end of the decade, public confidence in the volunteer blood supply had fallen to the extent that many otherwise reasonable and medically informed patients were accepting blood only from friends or relatives or refusing allogeneic transfusion altogether. Although it is treacherous to divine transfusion trends, several themes are now emerging. Blood transfusion is in fact increasing once more. The total US blood supply in 1989 was 14, 229, 000 units, an expansion of 1.2 percent over collections in 1987 [7]. A portion of this increase resulted from autologous donations. While estimates from a 1986 survey suggested that no more than 5 percent of eligible donors were predepositing autologous blood for elective surgery, predeposited autologous collections increased by 65 percent between 1987 and 1989 alone and represented 4.6 percent of the blood supply in 1989 [7,8]. Various less well controlled estimates place current autologous collections as high as 8 percent of donated units; however, autologous units are unlikely to far exceed 10 percent of total blood collections. Another source of growth in the American blood supply has been directed donations, blood solicited by patients from friends and relatives. Directed donations accounted for 2.5 percent of the blood supply in 1989. Directed donors must meet all the criteria required of volunteer community donors, however, like autologous blood collected from patient-donors, directed donor units have been found to test positive more frequently for markers of such infectious diseases as hepatitis [9]. The safety for general use of blood from patients and directed donors has been the subject of heated controversy [10]. Although both autologous and directed units, when appropriately collected and tested, may be “crossed over” into the general blood supply (46.7 percent of the autologous units and 55.4 percent of the directed units are not transfused), only 2 percent of autologous and 16.9 percent of directed units end up supplementing the national blood supply [7]. One source of blood for transfusion that is admittedly underestimated is intraoperative autologous blood (IAT), blood salvaged from the operative field and returned to the patient during the surgical procedure. No single reliable source collects and reports the amount of blood salvaged by IAT procedures. IAT is performed by regional blood centers, hospital transfusion services, anesthesia technicians, surgical support groups, and private for-profit companies. IAT is usually restricted to procedures such as cardiac, vascular, orthopedic and transplant surgery where large intraoperative blood loss is anticipated, and to emergency trauma surgery. However in these relatively limited situations, autologous salvage may replace large volumes of blood, 100 units or more in some procedures [11]. Massive IAT requires...