| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Concern about risks of allogeneic transfusion has led to an interest in methods for decreasing perioperative transfusion. To determine whether cell salvage reduces patient exposure to allogeneic blood, we performed meta-analyses of randomized trials, evaluating the effectiveness and safety of cell salvage in cardiac or orthopedic elective surgery. The primary outcome was the proportion of patients who received at least one perioperative allogeneic red cell transfusion. Twenty-seven studies were included in the meta-analyses. Cell salvage devices that do not wash salvaged blood were marginally effective in cardiac surgery patients when used postoperatively (relative risk [RR] = 0.85, 95% confidence interval [CI] = 0.790.92). Devices that wash or do not wash salvaged blood considerably decreased the proportion of orthopedic surgery patients who received allogeneic transfusion (RR = 0.39, 95% CI = 0.300.51 and RR = 0.35, 95% CI 0.260.46, respectively). No studies of cell savers that wash salvaged blood during cardiac surgery were included. Cell salvage did not appear to increase the frequency of adverse events. We conclude that cell salvage in orthopedic surgery decreases the risk of patients exposure to allogeneic blood transfusion perioperatively. Postoperative cell salvage in cardiac surgery, with devices that do not wash the salvaged blood, is only marginally effective. Implications: This meta-analysis of all published randomized trials provides the best current estimate of the effectiveness of cell salvage and is useful in guiding clinical practice. We conclude that cell salvage in orthopedic surgery decreases the proportion of patients requiring allogeneic blood transfusion perioperatively, but postoperative cell salvage is only marginally effective in cardiac surgery.
Concern about the side effects of allogeneic blood transfusion has led to the development of many methods intended to minimize perioperative transfusion. Like preoperative autologous donation (PAD) (1,2), isovolemic hemodilution (3), and the use of drugs such as aprotinin (4), tranexamic acid (5), and erythropoietin (6), the use of cell salvage may reduce perioperative transfusion of allogeneic blood. Cell salvage involves reinfusion of blood collected from the operative field, either directly or after centrifugal washing to remove noncellular matter. The first human autotransfusion of shed blood was described in 1860 in a patient who underwent an amputation of the thigh as a result of an infection of the knee joint and extensive suppuration (7). Previous devices were often associated with severe complications, such as air embolism, but this is now rare (8). Cell salvage can be performed intra- or postoperatively, or both. Numerous articles have been written about the use of cell salvage, but the majority are nonrandomized studies that are likely to overestimate the benefit of treatment (9,10). In this first meta-analysis of available randomized trials, we evaluated the efficacy of cell salvage in decreasing exposure to allogeneic red cell transfusion in adults undergoing cardiac or orthopedic elective surgery.
An unrestricted Medline search was performed for dates ranging from January 1966 to December 1997 to identify all articles with the text words "autotransfusion," "cell salvage," "device," or the Medical Subject Headings "autologous blood transfusion" or "randomized controlled trials." Structured searches of Current Contents (1997) and Science Citations Index (19771997) were also performed. All titles and abstracts were examined for studies evaluating the efficacy of cell salvage for minimizing perioperative blood use. References of retrieved articles and of a published bibliography of perioperative autotransfusion (11) were also reviewed for other potentially useful trials. To be included in the meta-analysis, randomized, controlled trials had to meet four criteria: 1) patients allocated to undergo cell salvage were compared with patients who did not, 2) patients underwent cardiac or orthopedic elective surgery (only two articles dealt with vascular surgery and were not considered), 3) the proportion of patients transfused with allogeneic blood was reported, and 4) in cardiac surgery, both groups had to be treated identically on bypass. Studies were included regardless of whether they were full publications, abstracts, or letters to the editor, and were published in English or non-English journals. Duplicate publications, studies enrolling children, and trials in which patients were randomized postoperatively were excluded. Data from the studies were independently abstracted on study data forms by two investigators (AL, AK). Disagreements were resolved by consensus. No attempt was made to conceal the identity of the author or the medium of publication. The primary outcome measure was the proportion of patients receiving at least one unit of allogeneic packed red blood cells. Other data abstracted were the type of salvaged blood retransfused (washed or unwashed), the time of cell salvage use (intraoperative, postoperative, or both), the type of surgery (cardiac or orthopedic), whether PAD was used, whether the use of a transfusion protocol (including both allogeneic and shed blood) was reported, the amount of blood collected by cell salvage, the amount of salvaged blood retransfused, the mean units of packed red cells transfused per patient, and the postoperative hematocrit. If blood transfusion was only reported in milliliters, this value was divided by 300 mL to determine the mean number of units transfused. We evaluated the methodological quality of the trials using the scale of Jadad et al. (12), which assesses randomization (yes and appropriate, yes and inappropriate, not randomized), double-blinding (yes and appropriate, yes and inappropriate, not double-blinded), and full disclosure of withdrawals or drop-outs, yielding a score from zero (worst score) to five (best score). Two series of analyses were performed. The first series of analyses included all studies that compared cell salvage with an appropriate control group. Some of these studies evaluated cell salvage alone, whereas others evaluated the addition of cell salvage to another intervention (e.g., cell salvage and acute normovolemic hemodilution versus acute normovolemic hemodilution alone). The second series of analyses included only studies that evaluated cell salvage alone.
For both series of analyses, three meta-analyses were conducted according to the type of surgery and the type of device: cardiac surgery with devices that do not wash the salvaged blood, orthopedic surgery with devices that wash the salvaged blood, and orthopedic surgery with devices that do not wash the salvaged blood. No trials in cardiac surgery with devices that wash the salvaged blood met our eligibility criteria. The effect of cell salvage on the proportion of patients who received allogeneic blood was summarized with an overall estimate of the relative risk (RR) by using the Mantel and Haenszels (13) fixed-effects model with the Meta-Analyst software (Metaworks, Boston, MA) (14). RRs are presented with their 95% confidence intervals (CI). An RR of 1.0 suggests that there was no difference between cell salvage and control; an RR <1.0 suggests that fewer patients in the cell salvage group received at least one allogeneic transfusion, and an RR >1.0 suggests that more patients in the cell salvage group received at least one allogeneic transfusion. Study heterogeneity (a measure of the variability between trials) was tested using the
Of 902 references identified, 755 were excluded based on their title or abstract. Of the 145 full references reviewed, 118 were excluded: 30 were irrelevant because they were either nonclinical studies or cell salvage was used to process blood in the bypass circuit; 57 were not randomized; 12 did not have an appropriate control or treatment arm (1627); and 19 did not provide data on the number of patients exposed to allogeneic red cells in the two groups2 (2845). Thus, 27 references, representing 28 randomized, controlled trials were included in the meta-analysis (4672). Three of the included trials did not use a true method of randomization (i.e., pseudo-randomization) (47,55,64). All of the 28 trials included in this study scored between zero and three on the Jadad scale. Because it is difficult to "blind" the operative team to the presence or absence of cell salvage, the Jadad score would rarely be expected to be greater than 3. Twelve trials used cell salvage in cardiac surgery, and 16 used cell salvage in orthopedic surgery (Tables 1 and 2). One trial studied two different cell salvage devices and is referred to as Rollo 1 and Rollo 2 (64). The sample sizes varied from 24 to 232, with a total of 2061 patients (1023 control, 1038 cell salvage) included in the meta-analysis.
There were 12 randomized controlled trials that evaluated devices used to collect and reinfuse unwashed shed blood after bypass in the presence of other strategies used for blood conservation (Figure 1). In these trials, cell salvage decreased exposure to allogeneic blood (RR = 0.85, 95% CI = 0.790.92). In the meta-analyses confined to trials evaluating cell salvage alone (Figure 2), cell salvage devices also decreased the likelihood of exposure to allogeneic blood (RR = 0.84, 95% CI = 0.770.93).
In the meta-analyses, which included all trials in orthopedic surgery (Figure 1), both cell salvage devices that wash salvaged blood (RR = 0.39, 95% CI = 0.300.51) and those that do not wash salvaged blood (RR = 0.35, 95% CI = 0.260.46) had a statistically significant effect on the proportion of patients receiving transfusion. Although there was statistically significant heterogeneity in the analysis of both devices that wash (P < 0.05) and do not wash salvaged blood (P < 0.01), we were unable to identify any clinical or methodological reason for this. The results were similar in the meta-analyses of trials evaluating cell salvage alone (Figure 2). The RR was similar among subgroups, and no subgroup in whom cell salvage was particularly effective or ineffective was identified (Table 3). There was a slight tendency for a higher effectiveness of cell salvage devices that wash salvaged blood in orthopedic patients who had not predonated autologous blood (Table 3). There were other slight differences among subgroups, for example, in studies with Jadad score greater than and less than 2 in orthopedic patients. However, the heterogeneity in these subgroups remained high. Furthermore, in contrast to devices that wash salvaged blood, most studies dealing withunwashed salvaged blood reported a limited amount of shed blood, but this limit varied dramatically from one study to another and could not be adequately summarized. Finally, no asymmetry in any of the funnel plots was detected (data not shown).
Only 15 trials enrolling 1030 patients specifically reported mortality. The cell salvage procedure had no statistically significant effect on perioperative mortality (RR = 1.41, 95% CI = 0.583.45) (48,49,5153,5557,60,63,65,67,68,71,72). Only four trials enrolling 305 patients reported myocardial infarction (RR = 1.17, 95% CI = 0.423.23) (46,66,67,71), whereas deep venous thrombosis was recorded in 11 trials assessing 615 patients (RR = 1.35, 95% CI = 0.603.05) (50,53,55,57,5961,63,65,67,68). Nine trials enrolling 555 patients provided data on the incidence of postoperative infection (RR = 0.52, 95% CI = 0.181.48) (53,55,57,60,61,63,6567). Other rare complications were wound hematoma (RR = 0.67, 95% CI = 0.311.46) (53,55,57,59,60,6365,67,68), wound infection (RR = 1.19, 95% CI = 0.453.11) (51,53,55,57,59,60,6365,67,68,71), pulmonary complications not attributed by authors to the cell salvage procedure (RR = 1.12, 95% CI = 0.572.22) (47,51,53,55,57,60,63,65,67), and posttransfusion reactions: increase in blood pressure (three patients), fever (three patients), chills (two patients), and rigors (one patient) (RR = 1.72, 95% CI = 0.575.17) (47,5355,57,60,63,65,67).
The results of this meta-analysis showed that, in orthopedic surgery, both devices that wash and do not wash salvaged blood decrease the proportion of patients who receive a perioperative allogeneic transfusion. The postoperative use of devices that do not wash salvaged blood in cardiac surgery was only marginally effective. No studies of cell savers that wash blood in cardiac surgery met the inclusion criteria of our study. Cell salvage did not appear to increase adverse events, although side effects were inconsistently reported, and the number of patients studied was relatively small. There are many possible explanations for the discrepancy in the efficacy of cell salvage in cardiac and orthopedic surgery. In cardiac surgery, patients are exposed to massive heparinization and subsequent protamine administration, which are both associated with significant derangements in platelet function and fibrinolysis (73,74). Further, virtually all the blood components may be irreversibly changed caused by the blood-biomaterial interaction from the bypass circuit. This is not the case in orthopedic surgery. Thus, the blood retransfused in cardiac and orthopedic surgery is different, although the exact biochemical cause of the difference in efficacy is not clear. As a result, these technologies in these two types of surgery should be considered separately to understand more clearly the benefits of each. For similar reasons, we removed trials that used washed blood remaining in the extracorporeal circulation. This plasma should not be different from that which was circulated only moments before discontinuation of bypass, thus rendering washing not clinically relevant. Further, the trials in which this strategy was tested were generally of poor quality and often did not include appropriate comparison groups. Randomized trials directly comparing devices that wash the salvaged blood with those that do not, would provide the best evidence of the relative efficacy of the two techniques. However, we did not perform separate meta-analyses of such studies, because it seemed logical to determine whether the technologies were individually effective before comparing them. Also, there were few articles directly comparing the two types of devices. In orthopedic patients, only one study compared patients who received either unwashed drainage or washed drainage but did not provide the number of patients exposed to allogeneic blood (29). In cardiac patients, three studies compared the two types of devices but were excluded (17,19,22). One study did not provide the number of patients exposed to allogeneic blood (19), and, in another, cell salvage was associated with normovolemic hemodilution in all patients (22). Thus, these three studies could not be combined. Nevertheless, our results suggest that, in orthopedic surgery, the two types of devices appeared to decrease the frequency of exposure to allogeneic blood to a similar degree, when compared with a control. This finding is important, because devices that wash salvaged blood can be more cumbersome to use and more expensive than those that do not. Although unwashed blood contains factors that can cause an increase in perioperative bleeding, this did not translate into an obvious difference in effectiveness between the two types of devices. However, all of the trials evaluating devices that do not wash blood used the devices postoperatively in orthopedic patients. The method of unwashed cell salvage is not advocated for intraoperative use, because serious side effects have been described (11). The results of this meta-analysis must be interpreted with some caution. The sample size of most studies included in the analyses was small. The largest trial enrolled 232 patients, and the largest meta-analysis included only 899 patients. Other studies have shown that the results of meta-analysis including small numbers of patients can be misleading, compared with subsequent large trials (75,76). Also, the heterogeneity that was found in some of the analyses makes the interpretation of the results difficult. There was no obvious cause for the heterogeneity, but it is possible that it reflects the influence of unknown covariates upon the efficacy of cell salvage. Unfortunately, data from 19 published randomized, controlled trials could not be included, because the number of patients who received allogeneic red cell transfusions was not described. This supports the need for uniform and comprehensive methods when reporting the results of blood conservation studies (77). Furthermore, because it is difficult to blind the intervention, the transfusion behavior of the practitioners could have been driven by knowledge of group assignment, especially when transfusion guidelines were not set. The decrease in the proportion of patients who receive allogeneic transfusion can be related to either the intrinsic efficacy of cell salvage or a transfusion behavior of the practitioner, especially when transfusion guidelines have not been set. Because most studies with published transfusion protocols did not indicate how rigorously those protocols were followed, it is possible that there was a difference in the indications for transfusions in the two groups, which might have favored the cell salvage group. Strengths of this meta-analysis include clear inclusion and exclusion criteria, a thorough literature search, and extensive subgroup analyses. Furthermore, all identified non-English studies (Russian, Japanese, Czech, German, Italian, Danish, and Norwegian) were included because the exclusion of papers for linguistic reasons has been found to affect the results of meta-analyses (78,79). Cell salvage has both advantages and disadvantages when compared with other alternatives used to minimize exposure to allogeneic blood. Cell salvage does not carry the risk of side effects from medications, such as anaphylaxis associated with aprotinin, or the risk of transfusing the wrong unit of blood associated with PAD (8). Also, patients can avoid the inconvenience and time associated with predonation. Disadvantages of cell salvage include contraindications to the reinfusion of salvaged blood (bacterial contamination, malignancy, and sickle hemoglobin), complications of the procedure itself, such as air embolism, nephrotoxicity, and coagulation disorders (8). Moreover, the cost-utility ratio of cell salvage, approximately $120,000 per quality adjusted life year (80), is considerably higher than ratios conventionally considered attractive (81,82). An important unanswered issue about cell salvage, used exclusively or combined with other blood conservation alternatives (83), is how it compares with these other methods of minimizing exposure to perioperative allogeneic transfusion. In recently completed meta-analyses, the efficacy of PAD, aprotinin, tranexamic acid, and erythropoietin was found to be effective with odds ratios varying from 0.17 to 0.50 (8486). Thus, to determine which blood conservation technology is most appropriate, large head-to-head comparisons of cell salvage with other modalities are needed.
We thank Miss Gabrielle Martin, Drs. Roger Ngombet and Jana Zvarova for reading and translating some of the articles, and Mrs. Evelyne Mouillet and Mrs. Maïté Courbin for assistance with the literature searches.
1The International Study of Perioperative Transfusion (ISPOT) Investigators are Coordinating Center and Canadian Investigators are Phil Wells, MD; George Wells, PhD; Fraser Rubens, MD; Annette OConnor, PhD; Laura McAuley, BSc; Andreas Laupacis, MD (Chair); Paul Hébert, MD; Ian Graham, PhD; Dean Fergusson, MHA (Coordinator); Greg Bryson, MD at the Clinical Epidemiology Unit, Loeb Medical Research Institute, Ottawa Civic Hospital, University of Ottawa, Ottawa, Ontario. Other investigators are Chris Hillyer, MD, Jeff Etchason, MD, Angela Blair, MPH, Emory University, Decatur, GA; Brian McClelland, MD, Patricia Phillips, SES Scotland Transfusion Service, Edinburgh, Scotland; Jordi Gol-Freixa, MD, Antonio Gracia, MSc, Agencia de Evaluacion de Tecnologias Sanitarias, Madrid, Spain; Ankie Koopman-van Gemert, MD, PhD, Hospital Gooi Noord, Blaricum, The Netherlands; Akinori Hisashige, MD, PhD, University of Tokushima, Tokushima, Japan; Nachum Egoz, MD, MPH, Luis Gaitini, MD, Edna Katz, MD, Mustafa Somri, MD, Bnai Zion Medical Center, Haifa, Israel; Luc Noël, MD, Etablissement de Transfusion Sanguine, Versailles, France; L. Rachid Salmi, MD, PhD, Charlotte Huët, MD, Université Victor Segalen Bordeaux II, Bordeaux, France; Helga Sigmund, MSc, Danish Institute of Health Technology Assessment, Copenhagen, Denmark; Katherine McGrath, MD, Department of Health, Government of Australia; Kim Henderson, MSc, David Henry, MD, Carla Treloar, MSc, University of Newcastle, Newcastle, Australia.
2von Bormann B, Schafer H, Otto H, et al. Einsparung von fremdblut in der herzchirurgie durch verwendung des cell-savers [abstract]. Anaesthesist 1984;33:482.
This article has been cited by other articles:
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|