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© 2001 International Anesthesia Research Society
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Abstract |
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Implications: Bowl-based autotransfusion devices reduce the amount of fat found in shed blood, but cannot completely eliminate fat particles. When fat is seen on the surface of the processed blood, this blood should be filtered with a leukocyte removal filter before retransfusion.
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Introduction |
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TopAbstractIntroductionMethodResultsDiscussionReferences |
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Layers of fat are repeatedly found on salvaged autologous blood, especially in patients undergoing major orthopedic surgery (1–7). Retransfusion of fat probably increases the risk of a fat embolism syndrome, which is mostly associated with acute lung injury (8,9), but may also result in postoperative neurological deficit (10–13). Thus, retransfusion of fat should be minimized, or, even better, it should be avoided. Currently, two methods are available to eliminate fat from salvaged blood, autotransfusion devices that wash and hemoconcentrate autologous red blood cells, and filtration of salvaged blood.
Conventional autotransfusion, such as the Haemonetics Cell Saver (Haemonetics GmbH; Munich, Germany) devices are capable of reducing but not completely removing the amount of fat in autologous blood. Even the use of warm or more washing solution cannot solve the problem (4,5). We demonstrated that a new autotransfusion device based on cell separator technology (CATS; Fresenius AG, Bad Homburg, Germany) is capable of complete elimination of fat (14). However, this technology is currently not available to most hospitals.
We hypothesized that with conventional autotransfusion devices, the fat will be primarily found either under the spacer of the Latham bowl and close to the in-/outlet port while the centrifuge is rotating or on the surface of the blood within the Latham bowl after the centrifuge has stopped. Consequently, the fat should either be found in the first or in the last portion of processed autologous blood. Therefore, in Experiment A, we looked at the quantity of fat found in these portions. If fat was to be found primarily in one of these portions, then a simple modification of the automatic mode of the autotransfusion device may guarantee its waste, thus preventing fat from being pumped into the retransfusion bag. With such a small modification, even conventional autotransfusion devices could guarantee a fat-free autologous blood product.
Filtration of shed blood is another option to reduce the amount of fat. Conventional filters, however, are not capable of effectively removing fat (6). Recently, a new filter became commercially available that is especially designed to eliminate fat from autologous blood (LipiGuard; Pall Corporation, Portsmouth, England). In Experiment B, we looked at the efficacy of this filter for fat removal and compared it to an ordinary blood filter (Microfilter Sangopur 40 µm; B. Braun Medical Division, Melsungen, Germany) and to a leukocyte removal filter (Purecell RC 400; Pall Corporation, Portsmouth, England).
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Method |
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TopAbstractIntroductionMethodResultsDiscussionReferences |
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In this nonblinded in vitroinvestigation, we used outdated units of homologous packed red blood cells.
Experiment A
Packed red blood cells (250 mL) were diluted with 250 mL of saline to mimic a clinically relevant hematocrit. Normal saline was used for dilution because it does not interfere with any of the analyzed variables. Two hundred mL of soybean oil (Melyp GmbH, Herford, Germany) was added. Soybean oil was used because gas chromatography revealed that its spectrum of fatty acids is similar to the spectrum of fatty acids found in bone marrow of patients and found as fat layers on intraoperatively salvaged autologous blood (14). This solution was washed and hemoconcentrated by the Haemonetics Cell Saver in its automatic mode. After completion of this process, the blood was pumped from the Latham bowl into the retransfusion bag. However, the first and the last portion (i.e., 30 mL each) were collected separately. The amount of fat in each portion could easily be determined two hours later when the fat had accumulated on the surface as a result of its lower density. This experiment was repeated six times, using a new autotransfusion set and new tubing each time.
Experiment B
Packed red blood cells (250 mL) were diluted with 250 mL of saline. As in experiment A, normal saline was used for dilution because it does not interfere with any of the analyzed variables. Further, shed blood processed by any autotransfusion device is washed and reconstituted with normal saline. Therefore, this in vitrosetup mimics the clinical situation. Thirty mL of soybean oil was added. This mixture was filtered by one of the following filters: LipiGuard, Microfilter Sangopur 40 µm or Purecell RC 400. This experiment was performed 10 times for each filter.
All data are presented as mean ± the SEM. A probability of <5% was defined as significant. Significance was tested by the use of a factorial analysis of variance with post hoc Scheffé F-test (Statview II; Version 1.04, Abacus Concepts Inc., Berkeley, CA).
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Results |
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TopAbstractIntroductionMethodResultsDiscussionReferences |
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Experiment A
Processing the mixture with the Haemonetics Cell Saver reduced the amount of fat by 87% (from 200 ± 0 mL to 26 ± 2.5 mL). Although the concentration of fat was the largest in the last portion of processed blood, fat could be found in all portions of processed blood ( Table 1).
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Experiment B
All filters were capable of removing fat to a certain extent. Although the Purecell RC 400 removed 99% of the fat load, the two other filters removed only 2/3 of the fat load ( Table 2).
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Discussion |
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As a result of modern surgical techniques, fat embolism is decreasing. However, fat embolism is still of significant clinical importance (9). Although the fat embolism itself is nontoxic, plasma esterases release free fatty acids with a short time delay. These fatty acids are toxic and may cause capillary leakage as well as the release of proinflammatory cytokines, leading to acute lung injury (9,15), and in some cases even leading to death (16). Although fat embolism syndrome is mostly seen in orthopedic surgery, fat emboli are also found in cardiac surgery (17).
Conventional autotransfusion devices are capable of partially removing fat. Therefore, layers of fat are repeatedly seen on processed autologous blood, mainly in patients undergoing major orthopedic surgery. Figure 1 shows such a layer of fat found in one of our orthopedic cases. Certainly, such fat layers are to be found in only a few patients, but bearing in mind the potential development of a fat embolism syndrome, which in some patients may be lethal, the retransfusion of fat should definitely be avoided or at least minimized.
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In our experiment, fat was reduced by 87%. This is in line with our previous findings (14). The remaining fat was found in all portions of the processed blood. The concentration of fat found in the processed blood was the largest in the last portion of processed blood. When the centrifuge stops for emptying, there seems to be a tendency for fat to accumulate on the surface of the blood within the Latham bowl. However, substantial amounts of fat could also be found in all other portions, indicating mixing of the processed red blood cells and the separated fat in the stopping process. Unfortunately, this implies that neither wasting the first nor the last portion of processed blood would guarantee an autologous fat free blood unit. Consequently, it does not make sense to modify the automatic mode in conventional autotransfusion devices in a way that automatically discards the first or last portion of the processed blood, especially because this process decreases the blood volume to be retransfused.
Filtration was tried in former studies as a method to reduce the amount of fat in autologous blood just before retransfusion. Although the tested filters removed some of the fat, none of them was capable of complete fat elimination (6). According to the manufacturer, blood filtered by the LipiGuard will contain only 16% of the initial fat load. In our experiment, the remaining fat load equaled 38.2%. This difference may be explained by the fact that the manufacturer used a different technique to estimate the amount of fat removed by this filter. Astonishingly, the Purecell RC 400 produced by the same manufacturer removed 99% of the fat load. Although the LipiGuard was especially designed to remove fat from autologous blood, it was less effective than the leukocyte removal filter. Even more surprisingly, the LipiGuard was only as effective in fat removal as the ordinary blood filter with a pore size of 40 µm (Sangopur). This lack of filtration may be related to the differences in filter surface; although the binding capacities of the microaggregate filters are already exceeded with the fat load, this is not the case for the leukocyte removal filter.
In summary, conventional bowl-type autotransfusion devices are unable to completely remove fat from autologous blood. Although the fat is not equally distributed within the processed autologous blood and approximately 35% can be found in the last 30 mL of washed blood, the efficacy of conventional autotransfusion devices for fat removal cannot be sufficiently improved by simple modification of the blood processing procedure.
Although the LipiGuard was especially designed for fat removal from autologous blood, this filter is only as effective as a normal microaggregate blood filter (pore size 40 µm). However, the leukocyte removal filter (Purecell RC 400) removed 99% of the fat load.
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References |
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[Abstract/Free Full Text] - Ahmad K. Cerebral dysfunction after cardiopulmonary bypass linked to length of surgery. Lancet 2000; 355: 903.
- Booke M, Fobker M, Fingerhut D, et al. Fat elimination during intraoperative autotransfusion: an in vitro investigation. Anesth Analg 1997; 85: 959–62.[Abstract]
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[Abstract/Free Full Text]
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A J de Vries, Y J Gu, and W van Oeveren The rationale for fat filtration during cardiac surgery Perfusion, March 1, 2002; 17(2_suppl): 29 - 33. [Abstract] [PDF]
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