Page 1931 - Hematology_ Basic Principles and Practice ( PDFDrive )

Chapter 111 Principles of Red Blood Cell Transfusion 1711

many of these procedures are now performed using laparoscopy or in fact, manufacturers contraindicate the use of cell salvage in cases
other techniques to limit blood loss, the demand for predeposit where there is potential contamination of salvaged blood with enteric
autologous transfusion support has fallen in recent years. contents. However, in recent years this viewpoint has been reconsid-
Autologous blood has been safely collected from women during ered as studies have found that autotransfusion of microbiologically
pregnancy for use during childbirth. Nevertheless, the transfusion contaminated salvaged blood have demonstrated no adverse outcomes
rate at delivery is quite low (<2.5% in many institutions) and most or increase in postoperative infectious complications. Tumor cells have
autologous donations are unused. Long-term (frozen) storage of been found in blood salvaged during cancer operations, and thus
autologous RBCs in the absence of a planned transfusion episode is many practitioners consider cancer another contraindication. Others
largely ineffective and expensive. believe that filtration would remove salvaged tumor cells.
Approximately one-half the blood lost during surgery can be sal-
vaged. The rest is usually irretrievably absorbed in drapes and sponges
Intraoperative Blood Salvage or damaged during collection. The use of salvaged autologous blood
has been associated with a 50% reduction in allogeneic blood use in
Cell salvage occurs in three phases: collection, washing, and reinfu- orthopedic procedures such as spinal surgery and hip replacement, and
sion. RBCs are collected from the operative field using a dedicated is also effective in vascular surgical procedures such as aortic recon-
double lumen suction device. One lumen suctions blood from the struction. Autologous salvage has been a useful adjunct in the treatment
operative field and the other lumen adds heparinized saline to the of some Jehovah’s Witnesses whose literal acceptance of the Bible
salvaged blood. The anticoagulated blood then passes through a filter includes abstention from routine allogeneic blood transfusions.
and is collected in a reservoir. If less than 1 L of blood is collected, Both the canister systems and RBC processors used to collect
further processing is foregone and the collected blood is discarded. intraoperative autologous blood can also be used to collect postopera-
In most circumstances the contents in the bag can be washed to tive blood drainage, such as that from the mediastinum after open
remove free Hb, surgical irrigation solutions, and other debris. Instru- heart surgery, from the knee or hip after orthopedic procedures, or
ments are available that include both a reservoir for collecting salvaged from the peritoneal cavity after hepatic injury. Because blood salvaged
blood and a centrifugal washer. Large aliquots (>500 mL) can be fully from a serosal cavity has little residual fibrinogen and platelets, clot-
washed in as little as 3 minutes. As a result of this speed, autologous ting is not a problem, and the addition of anticoagulants is usually
blood salvage has become practical in situations in which blood loss unnecessary. Shed mediastinal blood after open-heart surgery contains
may be extremely rapid, such as trauma or liver transplantation. high levels of cardiac muscle enzymes, especially creatine kinase, as
The hematocrit level of unwashed blood is typically low because well as lactate dehydrogenase from hemolyzed RBCs. Therefore,
of dilution from irrigating surgical fluids and some degree of mechani- reinfusion of shed blood results in elevated levels of both enzymes
cal hemolysis. Free Hb levels are sometimes greater than 1000 mg in that can confound the diagnosis of myocardial infarction (MI) in the
unwashed blood, and hemoglobinemia and hemoglobinuria may postoperative period. Reinfusion of shed mediastinal blood has been
occur after the transfusion, although renal sequelae are surprisingly shown to reduce the need for allogeneic transfusions.
low. Despite this evidence of red cell injury, the survival rate of
51 Cr-labeled salvaged cells is normal in most patients studied.
There are many potential complications associated with cell Hemodilution
salvage, such as nonimmune hemolysis, air embolus, febrile nonhe-
molytic transfusion reactions, mistransfusion, coagulopathy, and The collection of autologous blood during surgery for later reinfusion
contamination with drugs. Transfusion of salvaged blood has resulted at the end of the procedure was first suggested in open-heart opera-
in coagulation abnormalities, including hypofibrinogenemia, pro- tions, in which it was hoped that a supply of platelets undamaged by
longed prothrombin time and partial thromboplastin time, elevated exposure to the membrane oxygenator might reduce the incidence of
fibrin degradation products, and thrombocytopenia. These coagula- coagulopathies. Hemodilution itself reduces RBC loss: a patient with
tion abnormalities most likely reflect the characteristics of the salvaged a hematocrit level of 45% and 2 L blood loss during surgery loses
blood itself, which, after exposure to serosal surfaces, becomes defi- roughly 900 mL of RBCs, but one with a hematocrit level of 20%
cient in coagulation factors and platelets and, in the case of unwashed from hemodilution loses only 400 mL of RBCs. Hemodilution is less
blood, has high levels of fibrin degradation products (Table 111.5). expensive to accomplish than preoperative autologous blood dona-
Fat, fibrin, bone fragments, and microaggregates often contami- tion and may be the only option available when surgery is performed
nate salvaged autologous blood. However, infusion of unwashed in other than elective settings. Proponents claim that the induced
blood has not been proved harmful in either animals or humans, anemia may even be beneficial to the patient, in that oxygen delivery
possibly because routine blood filters remove most particulate mate- at a hematocrit level of 30% is enhanced by an increased cardiac
rial. Other contaminants, such as heparin, topical antibiotics, hemo- output resulting from the decreased blood viscosity. Other advantages
static agents, and biologic substances such as tissue enzymes, can be of hemodilution over predeposit autologous transfusion are the provi-
at least partially removed by washing. Complete removal of bacteria sion of fresh red cells along with plasma and platelets that may be
is also not possible, even when the salvaged blood is washed with important in maintaining hemostasis.
antibiotics. Thus, collection of blood from a contaminated site (e.g., Reductions in allogeneic blood needs have been reported after
with intestinal contents) is usually considered to be contraindicated; marked intraoperative hemodilution (after the hematocrit is lowered

TABLE Autologous Blood Salvage Systems : Characteristics of Collected Blood
a
111.5
Coagulation Fibrin Degradation
System Hardware Software Hematocrit Free Hemoglobin Platelet Count Factors Products
3
Collection without Rigid plastic container Plastic bag Low (25%) Very high Low (100,000/mm ) Low (35–75%) High (300 mg%)
washing (200 mg%)
3
Collection followed Integral or separate Disposable plastic High (60%) Low (<50 mg%) Very low (10,000/mm ) Absent (0%) Absent (0%)
by washing blood cell processor bowl and tubing
a Typical results of laboratory tests are shown. Transfusion of large volumes of salvaged blood results in similar alterations in these tests in the recipient.
Data from Noon GP: Intraoperative autotransfusion. Surgery 84:719, 1978; and Silva R, Moore EE, Bar-Or D, et al: The risk: benefit ratio of autotransfusion-comparison
to banked blood in a canine model. J Trauma 24:557, 1984.