Leukocyte Reduction of Intraoperatively Salvaged Blood

Intra-operatively salvaged blood often undergoes considerable processing before reinfusion begins. Concentrating the cells in a centrifugation-based cell salvage device followed by saline washing provides a packed cell preparation contaminated with anything entering the device that is as heavy or heavier than a red cell including microaggregates and debris. Despite adequate pre-filtration with a screen filter in a cardiotomy reservoir, large pieces of debris can be found in the processed blood. Recognition of this observation is reflected in the AABB guidelines for blood transfusion which state that "Blood recovered by intra-operative salvage cannot be transfused to other patients and must be filtered".²

For an example of how large pieces of debris can be recovered from intra-operatively salvaged concentrated and washed packed blood cells following blood transfusion, see Figure 1.

Figure 1. Photomicrograph (40X) of large piece of debris recovered (screen openings are 40 micron) from only 25ml of intra-operatively salvaged blood that was first filtered through a cardiotomy sock filter, prior to having packed cells concentrated with a centrifugation-based cell salvaged device and saline washed.

The nature of the debris has been further characterized in Figure 2, in which leukocytes are clearly visible and entangled in a fibrous material.³ The presence of leukocyte rich debris from intra-operatively salvaged blood corroborates the work of Bull and coworkers, who report on the remnants of leukocytes and platelet aggregates, found within the bowl of a cell salvage device. Bull et al⁴ suggest disseminated intravascular inflammation may be related to the reinfusion of these components of salvaged blood.

Figure 2. Photomicrograph of section of debris shown in Figure 1 stained with hemotoxylin and eosin examined at 400X using light microscopy.

This observation neither appears to be related to the brand of cell salvage equipment nor to individual operator practices. Similar observations of debris recovered from intra-operatively salvaged blood were made at other institutions as Figure 3 illustrates. Clearly, the AABB recommended guidelines for filtration of salvaged blood has merit.

Figure 3. Photomicrograph (40X) of large piece of debris recovered (on pre-filtration media in a Pall LeukoGuard® RS leukoreducing filter for salvaged blood) from 25ml of washed intra-operatively salvaged blood. (Smallest scale division approximately 40 microns.)5

The fatty marrow of the sternum often sheds into the surgical field and is aspirated in the process of cell salvage. Although the fat embolism syndrome leading to pulmonary dysfunction is appreciated in osteo-trauma and orthopedic surgery⁶ its relevance in open heart surgery is not well understood. However, there is evidence to suggest that fat globules may be responsible for compromised lung function in cardiac patients.

What is far less appreciated is the amount of fat present in salvaged blood, particularly a washed intra-operatively salvaged blood product. Using the method of Valeri and coworkers, measurement of fat globules present in intra-operatively salvaged blood following washing were collected from two institutions each using different brands of cell washing machines. The data show detectable levels of fat globules (mostly in the size range less than 10 microns) in contrast with undetectable levels of fat globules in non-surgical patients (see Figure 4). Although fat globules in the circulation have been associated with morbidity and mortality in osteo-trauma, effect of reinfusion in cardiac patients has not been studied.

Measurable Fat Globule Concentrations are Present in Intraoperatively Salvaged Washed Blood

Figure 4. Fat particles present in salvaged blood.9

Far more is known about the deleterious effects the patient’s own activated neutrophils can impart in the setting of open heart surgery.¹⁰ However, the contribution of reinfusing autologous activated leukocytes has only recently become appreciated.¹

The exposure of blood to foreign surfaces activates complement and, in turn, leukocytes.¹¹ It should not be surprising that aspirating blood from the surgical field, part of the salvage process, results in complement activation.¹² Although washing eliminates the complement from a salvaged blood product, the effect of leukocyte stimulation, once initiated, likely persists.

Support for this view is provided by Perttila¹³ and coworkers who reported that leukocytes are present in high concentrations in washed salvaged blood (ranging from 4 to 12 thousand cells per microliter). Leukocytes were disproportionately higher in levels of neutrophils than circulating blood and the neutrophils reinfused in some patients showed a 30% upregulation (as determined by chemiluminescence) compared to the pre-reinfusion circulating blood samples of the same patients.¹³ Corroborating these data are the observations shown in Figure 5.

Figure 5. Leukocyte burden in intra-operatively salvaged blood is near or above circulating levels in cardiac patients.

More recently, the likelihood that reinfusing leukoreduced salvaged blood might improve lung function was strengthened by the observation that arterial blood gas measurements taken post-operatively from patients in whom residual CPB circuit blood was leukoreduced (by 96%) showed higher P_aO₂ values compared to non-filtered reinfusion controls as shown in Figure 6.

Effect Of Returning Residual Circuit Blood On P_aO₂

Figure 6. Leukoreduction of salvaged blood improves pulmonary function.1 (ICU = Intensive Care Unit; post ext = post extubation)

1. Gu YJ, de Vries AJ, Boonstra PW, van Oeveren W: Leukocyte depletion results in improved lung function and reduced inflammatory response after cardiac surgery. Jour Thorac Cardiovasc Surg 1996; 112: 494-500.
2. AABB Transfusion Therapy, A Physician's Handbook, 4th Edition. American Association of Blood Banks, 1993.
3. Photographs presented as Figures 1 and 2 courtesy of Dr. Thomas Brucker, Department of Pathology. St. Luke's Medical Center, Milwaukee, WI.
4. Bull BS, Bull MH: Hypothesis: Disseminated intravascular inflammation as the inflammatory counterpart to disseminated intravascular coagulation. Proc Nat'l Acad Sci (USA) 1990; 91:8190-8194.
5. Photomicrograph obtained with the generous cooperation of Commander Paul S. Potter, MD, Director of Autotransfusion, Department of Anesthesiology, US Navy Medical Center, San Diego, CA.
6. Capan L, Miller SM, Pattel KP: Fat Embolism. Anesthesiology Clinics of North America 1993; 11:25-54.
7. Adolph MD, Fabian HF, el-Khairi SM, Thornton JC, Oliver AM: The pulmonary artery catheter: a diagnostic adjunct for fat embolism syndrome. J Orthrop Trauma 1994; 8: 173-176.
8. Blevins FT, Shaw B, Valeri RC, Kasser J, Hall J: Reinfusion of shed blood after orthopaedic procedures in children and adolescents. Jour Bone Joint Surg 1993; 75-A: 363-371 modified from Greenspan P, Mayer EP, Fowler SD: Nile red: a selective fluorescent stain for intracellular lipid droplets. Jour Cell Biol 1985; 100:965-973.
9. Data on file with Pall Corporation; available upon request.
10. Ortolano GA: Potential for reduction in morbidity and cost with total leukocyte control for cardiac surgery. Perfusion 1995; 10:283-290.
11. Kirklin JK: Prospects for understanding and eliminating the deleterious effects of cardiopulmonary bypass. Ann Thorac Surg 1991; 51: 529-531.
12. Sieunarine K, Wetherall J, Lawrence-Brown MM, Goodman MA, Prendergast FJ, Hellings M: Levels of complement factor C3 and its activated product, C3a, in operatively salvaged blood. Aust NZ Jour Surg 1991; 61: 302-395; Bengtsson A, Lisander B: Anaphylatoxin and terminal complement complexes in red cell salvage. Acta Anaethesiol Scand 1990; 34: 339-341.
13. Perttila J, Leino L, Poyhonen M, Salo M: Leukocyte content in blood processed by autotransfusion devices during open heart surgery. Acta Anaesthesiol Scandinavica 1995; 39:445-448.  

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