Description
- Autologous transfusion describes returning the patient's own blood to them, whereas allogeneic transfusion describes transfusing someone else's blood to a patient. Autologous transfusion potentially avoids many of the adverse effects associated with allogeneic transfusion.
- Cell salvage, commonly referred to as "cell saver," involves suctioning, washing, and filtering blood from the surgical field, then returning it to the patient. This is the most common autologous transfusion technique.
- It is commonly (but not exclusively) used in cardiac, neurologic, hepatic, vascular, and orthopaedic surgery where expected blood loss is significant enough to merit the cost.
- History of cell salvage. First used in the 18th century when managing patients with postpartum hemorrhage. Blood-soaked swabs were washed in saline and then the mixture was reinfused; not surprisingly, this was associated with a high mortality. Throughout the 19th century, experimentation with cell salvage and autologous transfusion continued. In 1931, blood salvaged from hemothoraces was directly reinfused into patients. The first cell salvage autotransfusion device was developed in 1943 by straining suctioned blood through a cheese cloth, which forms the basis of modern cell salvage machines.
- The process of cell salvage can be separated into collection, washing, and reinfusion.
- Collection. A dedicated double-lumen suction device allows collection of red blood cells (RBCs) from the operative field. One lumen suctions blood from the operative field and the other lumen adds a predetermined volume of anticoagulant flush to the salvaged blood. Heparinized saline flush is commonly used; its composition depends on manufacturer guidelines, and typically consists of 30,000 U of heparin in 1,000 mL of 0.9% saline. Some centers substitute this with a citrate solution. The anticoagulated blood passes through a filter to remove debris and is then collected in a reservoir.
- Washing. Centrifugation separates the components of blood into RBCs and plasma. The washed RBCs are then filtered across a semipermeable membrane, which removes free hemoglobin, plasma, platelets, white blood cells, and heparin.
- Reinfusion. Salvaged RBCs are then suspended in normal saline at which point they can be reinfused via any peripheral or central venous catheter. The salvaged RBCs may be transfused immediately or within 6 hours (1). The solution has a hematocrit of 50–70%, depending on the cell saver machine. In practice, however, some heparin (up to 5%) is not removed, and a variable quantity of other substances such as leukotrienes and complement may also be mixed with the red cells. Plasma containing clotting factors and platelets are removed and wasted during the washing process.
Physiology/Pathophysiology
- The use of cell salvage in obstetrics and cases of malignancy or microbiological contamination remains controversial.
- Obstetrics. There exists a theoretical risk of precipitating amniotic fluid embolus (AFE) if amniotic fluid is not completely removed by the washing process. Recent evidence has shown that reinfusion of RBCs salvaged during elective Caesarean section is not associated with an increase in the incidence of AFE (2).
- Malignancy. Previously, was an absolute contraindication due to the theoretical risk of disseminating tumor cells. However, studies in patients with urological malignancy have showed that cell salvage and autologous transfusion were not associated with an increase in biochemical recurrence rates of prostate cancer and was effective at reducing allogeneic blood transfusion requirements (3). Therefore, certain cases may merit the use of cell salvage during surgery for malignancy, provided the risks and benefits are discussed with the surgeon and patient.
- Infection. In cases where there is potential contamination of salvaged blood with bowel contents or purulent material, the use of cell salvage is contraindicated by the manufacturers. However, there is some evidence that cell salvage in combination with a leucocyte depletion filter (LDF) may be safe. Therefore, infection or enteric content should no longer be considered an absolute contraindication. In cases where there is gross enteric content contamination, the surgeons should avoid suctioning the most contaminated areas, broad spectrum antibiotics should be administered, and the volume of saline wash should be increased. Risks and benefits of cell salvage use should be discussed with the surgeon and patient preoperatively.
- The aim of cell salvage is to reduce or eliminate the need for allogeneic blood transfusion. A recent meta-analysis found that cell salvage was efficacious in reducing the need for allogeneic blood transfusion in adult elective surgery by 39%, with an average saving of 0.7 units per patient (4). This could
- Reduce the risks of infectious and noninfectious complications of allogeneic blood transfusions.
- Increase the mean erythrocyte viability compared to autologous blood. Salvaged RBCs maintain their normal biconcave disk shape, whereas allogeneic blood assumes an echinocyte shape (after 14 days), which is thought to impair its ability to flow through the capillary beds.
- Increase 2,3-diphosphoglycerate (2,3-DPG) compared to autologous blood, which improves oxygen-carrying capacity and tissue oxygen delivery.
- Increase patient survival. Studies have shown that following an esophagectomy, there is increased survival, which may be due to the lack of immunomodulatory effects of salvaged blood compared to allogeneic blood.
- Have immunostimulatory effects that may reduce postoperative infections.
- Cell salvage should be considered in advance for cases where blood loss may exceed 1000 mL in adults and 10 mL/kg in pediatrics.
- If unsure about blood loss, consider setting up cell salvage as backup. This means prepare the reservoir, suction tubing, and heparinized saline flush (inexpensive and quick). If blood loss (after subtracting heparinized saline and any other wash fluids) occurs, the machine can then be set up to process the blood. If blood loss is minimal, this can then be discarded. Such a policy would generate considerable savings in terms of allogeneic blood, and potentially in healthcare costs.
- Cell salvage complications. The literature shows that complications associated with the use of cell salvage are rare. In cases where patients are autotransfused large volumes of processed RBCs, this may be accompanied by coagulopathy because of the loss of clotting factors and platelets (see above).
- In cases where the volume of blood washed is less than 30% of the patient's total blood volume, studies have shown that there is no increase in perioperative bleeding, and that no coagulopathy can be detected (5).
- The point at which coagulopathy associated with cell salvage becomes clinically relevant varies between patients, but it is not likely until >50% of the patient's blood volume has been washed (around 3,000 mL in the average sized adult).
- If the patient is actively bleeding, thromboelastography, prothrombin time, fibrinogen, and platelet counts should be performed.
- Blood product replacement with plasma, cryoprecipitate, and/or platelets should be performed.
- Allogeneic blood transfusions have been affiliated with the following risks:
- Tumor recurrence
- Postoperative infections
- Acute lung injury
- Perioperative myocardial infarction
- Postoperative low-output cardiac failure
- Increased morbidity and 5-year mortality
- Immunomodulation is dose dependent; transfusion of allogeneic blood is associated with decreased transplant rejection.
- Developing abnormal antibodies. Exposure to multiple units of allogeneic blood makes future cross-matching more difficult and time consuming.
Outline