1Morriston Hospital, Swansea NHS Trust, Swansea SA6 6NL, UK. 2University of Glamorgan, Pontypridd CF37 1DL, UK*Corresponding author
Accepted for publication: December 5, 2000
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Abstract |
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Br J Anaesth 2001; 86: 66973
Keywords: transfusion, allogeneic; transfusion, autotransfusion; blood, salvage; surgery, knee replacement
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Introduction |
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There is some inconclusive evidence,1 suggesting that patients may suffer fewer peri-operative infections if they avoid allogeneic blood transfusion at the time of surgery. Using autotransfusion may be one way of maintaining peri-operative haemoglobin concentrations, reducing the need for allogeneic blood transfusion.25 If peri-operative transfusion practices were aimed at a minimum haemoglobin concentration, rather than trying to maintain a pre-operative value, this would further decrease peri-operative transfusions.
Because of the paucity of evidence in the literature from randomized, controlled studies we decided to undertake a randomized controlled trial to confirm our findings from a small pilot study,6 which suggested that a marked reduction in allogeneic blood transfusion could be achieved safely by using post-operative red cell salvage (PRCS) and a haemoglobin transfusion trigger.
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Patients and methods |
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The collected blood was washed and re-suspended in saline before re-infusion using a centrifugal cell washing machine (Cell Saver 5 Haemonetics). The patients in the cell salvage group were also transfused if their haemoglobin fell below the preset trigger after autotransfusion. We chose a transfusion trigger to standardize the transfusion incidence in both groups. Although the American Society of Anaesthesiology recommended a trigger of 7 g dl1, we felt this was perhaps too aggressive and it would be difficult to apply. Many anaesthetists would be reluctant to withhold blood at this level of anaemia knowing the correlation with an optimum oxygen delivery and haemoglobin of 10 g dl1. Haemoglobin concentrations were measured on days 1, 2, 3, 4, and 7 in all patients. The TKR was conducted as routine. Data were collected by research nurses for post-operative length of stay, peri-operative and post-hospital discharge infection rates, adverse events, wound healing rates and quality of life (EuroQol EQ-5D).7
One of the investigators scrutinized all adverse events in a blinded fashion to determine which were possibly related to transfusion effects, for example, wound infection, embolic events, myocardial ischaemic events, and cardiopulmonary complications.
Data were loaded onto an SPSS version 7.5 computer programme (SPSS Inc., Chicago, USA) and all statistical analysis was performed using this program. The level of statistical significance for all tests was set up at a P-value of <0.05. For bivariate analysis, a two-tailed test of significance was used. Patient characteristics were examined using Fischers Exact Test or the Independent Sample t-test. In respect to adverse events, the comparison was examined using chi-squared test.
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Results |
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Twelve patients in the autologous arm of the study received an allogeneic transfusion. Two were inappropriate, as both patients had a haemoglobin concentration greater than 9 g dl1 and were asymptomatic, and could be classed as a procedure deviation. The remaining 10 patients had haemoglobin concentrations between 7.6 and 8.9 g dl1. Of the 10 patients whose transfusion was warranted, four of these were from the 18 patients in whom cell salvage failed and a further three patients had only a small amount of blood salvaged (<150 ml).
In the control group, 33 patients received allogeneic blood. The majority (76%) received two units, 6% three units, 6% four units, and 12% one unit.
There was no significant difference in length of stay, wound healing, serious adverse events or mortality, or health related quality of life (EuroQol) 6 months after surgery (Fig. 1). There was a significantly lower (7%) incidence of allogeneic blood transfusion in the cell salvage group, compared with 28% in the controls (P<0.001). There was no difference in post-operative mean haemoglobin concentration between the two groups (Fig. 2).
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Discussion |
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The present study shows that further significant reductions can be achieved by the use of PRCS, decreasing overall use of allogeneic transfusion to below 7% in the autologous group. Despite publication of other studies showing a similar trend,26 8 our study is one of the largest randomized controlled trials yet performed. Criticism has also been levelled at the lack of outcome measures applied to many studies assessing the practice of PRCS. In our study, no patients failed to leave hospital from either group. It was reassuring that the end of study mortality (in some cases indicating a 2-yr follow up and/or a minimum of 6 months post-hospital discharge) was similar in both groups, when deaths from all causes were considered. This mortality rate compared very favourably with a large orthopaedic audit reported from the Mayo clinic.9
The data did not support a difference in immediate post-operative infection or earlier hospital discharge, as had been suggested by earlier publications. The well-recognized effect of immunomodulation because of allogeneic blood transfusion was not apparent. This may add weight to the argument that universal leucodepletion offers only minor benefit. The length of stay was consistent with data from other Welsh hospitals (personal communication, Department of Public Health). Assessment using EuroQol Health State score did not show a difference between groups (Fig. 1), in contrast to the proposal that patients receiving autologous blood have improved health and well being when compared with those receiving allogeneic blood. It was noted that the EuroQol scores improved in both groups when pre-operative and 12 weeks post-operative scores were compared.
The only area where we found a statistical difference between groups was in the post-hospital infective complications with allogeneic recipients having increased infection. This effect became even more significant if those who received rescue transfusion were included in the allogeneic group. These findings are supported by the reduced readmissions and visits to general practitioners by patients who had been randomized to receive an autologous transfusion.
We have shown that reducing allogeneic transfusion can be achieved safely by using a combination of PRCS and limiting the transfusion when the patient has haemoglobin greater than 9 g/dl1. This may be considered as a conservative haemoglobin trigger and appropriate for even those patients with significant cardiac disease.1015 Of course the group of patients undergoing this type of joint replacement are more elderly than the general population and thus more likely to suffer from heart disease. We believe therefore that such blood conservation techniques are clinically indicated in the light of present evidence. There is a need to seek safe alternatives to allogeneic blood, both to decrease the risk of future unknown blood-borne transmitted disease and to increase the availability of allogeneic blood supplies where there are no available alternatives.
Our cost analysis showed that autologous transfusion was overall more expensive, despite having lower re-admission and post-operative general practitioner costs. At the time of the study the unit cost of allogeneic blood was £50.83. In addition, staff time of £49.34 was estimated on a cell-salvage operator being present throughout the post-operative collection period. In practice, this is not necessary. Processing of the drained blood had a mean time of 20 min. These two factors would now make a cost comparison more favourable.
Moreover, although autologous transfusion was not shown to be cost-effective, it should be noted that this analysis was short term and ignores the value attached to reduced risk of transmission of virus related illness. A recent US study16 has estimated median willingness to pay for autologous blood to reduce this risk at $900 per patient, which is considerably more than the excess cost per patient in the experimental arm of the present study. It seems that the reluctance to adopt such techniques in routine practice is because of a number of factors. This includes cost, organization and, perhaps, motivation. The recent increase in cost of production of all red cell products, because of improved testing for Hep C and the leucodepletion of all blood products to decrease the risk of nvCJD transmission, may make post-operative red cell salvage more attractive.
We would hope that if cost is the most important driver, then significant reduction in red cell use, without increased morbidity or mortality, might aid motivation and organization of such transfusion alternatives.
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Acknowledgements |
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References |
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