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Study Design -The dilution effect
- Madhusudhan Mali, Sian Jaggar (8 August 2006)
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Response to Muñoz et al's letter
- Miguel A Camarasa, Mateu Serra-Prat (7 June 2006)
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On the efficacy of antifibrinolytic agents in knee replacement surgery
- Manuel Muñoz, Jose A. Garcia-Erce, and Jorge Cuenca (28 April 2006)
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Madhusudhan Mali, Anaesthetics SPR Royal Brompton Hospital, Sian Jaggar
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Editor-We read with interest the paper by M. A. Camarasa et al on the Efficacy of aminocaproic, tranexamic acids in the control of bleeding during total knee replacement. Total Knee replacement surgeries form a significant proportion of orthopaedic practice and hence this study addressed a common and important problem. The paper highlights the significant contribution of hidden blood loss into the tissues, and bleeding secondary to the activation of the fibrinolytic system makes the use of antifibrinolytics a logical choice 1- 3. This study confirmed previous work4-5 that TXA and EACA are effective in decreasing blood loss and the need for transfusion, following TKR. However some issues in trial design detract from the claimed conclusions. 1. The study group and the control group were powered to obtain a difference of 300 mls which was considered significant blood loss. Unfortunately TXA and EACA are considered interchangeably in the study group,thus diluting the group and assuming no difference in activity between them. 2. The timing of the study drugs suggests differences in duration of antifibrinolytic activity namely, TXA (mean duration of action of 3 hrs) was given twice during the study, giving a 6 hour period of Antifibrinolytic activity. EACA (half life of less than 30 min) also given twice however the total duration of antifibrinolytic activity with EACA seems less than 4 hours. This supports the need to consider the drugs as different entities rather than a single one. Hence my concern about the use of two pharmacokinetically dissimilar drugs to cover the initial 5 hour period ,which was taken as a point of time for data collection. 3. The suggestion by the authors of the study was that these antifibrinolytics are safe to use with caution. However the study was not powered to identify the major feared complication of joint replacement i.e the occurrence of DVTs.This question should be addressed with a separate(clearly large ) study or a meta analysis. In summary, whilst this paper supports earlier work using TXA in Total Knee Replacements, I have felt convinced about changing practice in favour of using TXA ,However the data presented in this paper doesn’t seem powerful enough to back the recommendation. REFERENCES: 1. Murphy WG, Davies MJ, Eduardo A. The haemostatic response to surgery and trauma. Br J Anaesth 1993; 70: 205–13 2. Good L, Peterson E, Lisander B. Tranexamic acid decreases external blood loss but not hidden blood loss in total knee replacement. Br J Anaesth 2003; 90:596–9 3. Jansen AJ, Andreica S, Claeys M, D'Haese J, Camu F, Jochmans K. Use of tranexamic acid for an effective blood conservation strategy after total knee arthroplasty. Br J Anaesth 1999; 83:596–601 4. Cid J and Lozano M. Tranexamic acid reduces allogeneic red cell transfusions in patients undergoing total knee arthroplasty: results of a meta-analysis of randomized controlled trials. Transfusion 2005; 45:1302–7 5. Ho K and Ismail H. Use of intravenous tranexamic acid to reduce allogeneic blood transfusion in total hip and knee arthroplasty: a meta- analysis. Anaesth Intensive Care 2003; 31:529–37 Conflict of Interest:None declared |
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Miguel A Camarasa, Anaesthesiologist Hospital of Mataró, Mateu Serra-Prat
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Dear Editor, We thank Muñoz et al for the interest they showed in our article. We would like to make the following comments: The percentage of blood transfusions in our trial was 38.3% in the control group, 12.5% in the epsilon-aminocaproic group, and 2.8% in the tranexamic group, with a mean of 7.5% among those who received antifibrinolytic agents (AA) 1. These results were similar in effect to those obtained after postoperative reinfusion of shed blood (with and without washing) 2 3. Evaluating the efficacy of AA without the association of other strategies which reduce allogenic transfusions might be a more appropriate method but perhaps a less ethical one. The study assessed the efficacy of AA and therefore we could not deprive patients of techniques of proven efficacy 2 3. Moreover, the quantity of autologous reperfused blood was carefully measured both predonated and postoperative salvage, indicating the validity of the estimated real hemorrhage. As AA acts through a mechanism quite different from autotransfusion, similar reduction in bleeding can be expected in patients with preoperative autologous blood donation (PABD) to those with postoperative blood salvage. We agree with Muñoz et al in that the effects of AA in autologous and allogenic blood transfusion were not studied separately but that was not the main objective of the study. The number of transfusion units, by transfused patient, are in fact similar between the AA group and the control group. Significant differences were found in the percentage of transfused patients as indicated above. Likewise, we know that surgical infections are related to allogenic transfusions but although exposure to allogenic transfusions was lower in the PABD group (5.5%) than in the non-PABD group (18.5%) (P=.025) the low percentage of transfusions in AA (7.5%) did not seem to justify a PABD program in our conditions. Overall, 3 out of 4 units of extracted autotransfusion blood were discarded and, in the AA group, over 9 out of 10 bags were not used. We agree that the decrease in hemoglobin in the PABD group (1.8 g dL -1) between donation and preoperative admission is greater than expected by simple calculation, although the relation with extraction seems evident. However, we have not found references that confirm and explain the decrease we found in non-PABD patients (0.9 g dL –1) during the same period. We believe it could be related to a subsequent hemoconcentration caused by prior fasting. Preoperative analyses were performed in the morning, after 12 hours’ fasting, compared with no fasting before the admission analyses the night before the intervention. The benefit of preoperative iron administration seems unquestionable particularly in patients with a demonstrated deficiency. On the other hand, there are contradictory findings in trials assessing the efficacy of postoperative recovery from bleeding in total knee replacement, to reduce allogenic transfusions 3 5 6. We believe that strategies to reduce allogenic transfusions should begin with an appropriate diagnosis and treatment of preoperative anemia. In our practice we administer erythropoietin and iron to men with hemoglobin count less than 13 g dL-1 and women with less than 12 g dL-1, 21 days before operating. Of all the methods of reducing allogeneic transfusions, we believe that the analyzed AA are the easiest to implement (with specific peri-operative administration), the cheapest, and quite possibly the most efficacious 1. References. 1.Camarasa MA, Ollé G, Serra-Prat M, et al. Efficacy of aminocaproic, tranexamic acids in the control of bleeding during total knee replacement: a randomized clinical trial. Br J Anaesth 2006; 96: 576-582. 2.Thomas D, Wareham K, Cohen D, Hutching H. Autologous blood transfusion in total knee replacement surgery. Br J Anaesth 2001; 86: 669- 673. 3.Muñoz M, Ariza D, Garcerán MJ, Gómez A, Campos A. Benefits of postoperative shed blood reinfusion in patients undergoing unilateral total knee replacement. Arch Orthop Trauma Surg 2005; 125: 385-389. 4.Woolson ST, Wall WW. Autologous blood transfusion after total knee arthroplasty. A randomized, prospective study comparing predonated and postoperative salvage blood. J Arthroplasty 2003: 18: 243-249. 5.Rosencher N, Kerkkamp HE, Macheras G, et al. Orthopedic Surgery Transfusion Hemoglobin European Overview (OSTHEO) study: blood management in elective knee and hip arthroplasty in Europe. Transfusion 2003; 43: 459 -469. 6. Glynn A, McCarthy T, McCarroll M, Murray P. A prospective audit of blood usage post primary total knee arthroplasty. Acta Orthop Belg. 2006 Jan; 72(1):24-8. Conflict of Interest:None declared |
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Manuel Muñoz, Prof. GIEMSA, Scholl of Medicine, University of Málaga, Spain, Jose A. Garcia-Erce, and Jorge Cuenca
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Dear editor, We read this article with great interest and we appreciate the fact that antifibrinolytic agents (AA) produce a significant decrease in blood loss after total knee replacement, reflected in a reduction in the number of blood transfusion required (1). But there are a few points we would like to stress upon. Firstly, the overall allogeneic transfusion rate in patients receiving preoperative autologous blood donation (PABD) or postoperative blood salvage, with or without AA (11%) is not different to that reported previously for allogeneic blood in patients receiving washed (5%) or unwashed (11%) postoperative shed blood only (2,3). In addition, no significant differences in the prevalence of allogeneic blood transfusion was seen in a randomized trial comparing postoperative blood salvage with one PABD unit (0% vs. 5%, respectively) (4). Hence, the use of AA in combination with autologous blood transfusion techniques (PABD or postoperative blood salvage) does not seem appropriate to evaluate AA effects on allogeneic blood transfusion. In fact, Camarasa et al (1) report a reduction in total blood transfusion, but they do not evaluate the effects of AA on autologous and allogeneic blood transfusion separately. This seems to be important as allogeneic transfusion is associated with increased wound infection rate whereas PADB is not (5). Secondly, Camarasa et al (1) report a reduction in both transfusion rate and transfusion units for patient receiving AA (Table 2). However, the units of washed shed blood are taken into account for total blood loss calculation, but not for that of transfusion rate and index. Moreover, when calculated per transfused patient, there are not differences in transfusion index between control and AA groups (1.52 vs. 1.4 units, respectively, p=NS). On the other hand, they suggest that the autologous programme has an iatrogenic effect and it is not justified under the conditions of the present study (1). However, allogeneic transfusion rate was lower amongst patients with PABD (4/73, 5.5%) than amongst those without PABD (10/54, 18.5%) (RR: 0.30, 95%CI: 0.1-0.89, p<0.02). This continues to give PADB a role in blood conservation strategies if a more appropriate patient’s selection is made to avoid a high proportion of donated units being discarded. Thirdly, using a multivariate logistics regression analysis, Camarasa et al (1) confirm the well known fact that low preoperative haemoglobin levels favoured blood transfusion. However, the haemoglobin fall between preoperative assessment and admission in patients with PABD (1.8 g dl-1) is higher than that expected from the donation of 82 units (1.1 g dl-1), whereas the haemoglobin fall in patients without PABD (0.9 g dl-1) is totally unexplained. Moreover, no attempt was made to correct preoperative anaemia in these patients. In this regard, we reported low transfusion rates (4-6%) in patients undergoing knee replacement who received perioperative treatment with oral iron, starting 30-45 days before surgery (6), or with intravenous iron sucrose, plus one preoperative dose of recombinant human erythropoietin if preoperative haemoglobin level was lower than 13 g dl-1, starting the day before surgery (7). Hence, we believe that a standardized approach for the detection, evaluation, and management of anaemia in the preoperative surgical setting would enhance the blood saving effects of AA. References. 1.Camarasa MA, Ollé G, Serra-Prat M, et al. Efficacy of aminocaproic, tranexamic acis in the control of bleeding during total knee replacement: a randomized clinical trial. Br J Anaesth 2006; 96: 576-582. 2.Thomas D, Wareham K, Cohen D, Hutching H. Autologous blood transfusion in total knee replacement surgery. Br J Anaesth 2001; 86: 669- 673. 3.Muñoz M, Ariza D, Garcerán MJ, Gómez A, Campos A. Benefits of postoperative shed blood reinfusion in patients undergoing unilateral total knee replacement. Arch Orthop Trauma Surg 2005; 125: 385-389. 4.Woolson ST, Wall WW. Autologous blood transfusion after total knee arthroplasty. A randomized, prospective study comparing predonated and postoperative salvage blood. J Arthroplasty 2003: 18: 243-249. 5.Rosencher N, Kerkkamp HE, Macheras G, et al. Orthopedic Surgery Transfusion Hemoglobin European Overview (OSTHEO) study: blood management in elective knee and hip arthroplasty in Europe. Transfusion 2003; 43: 459 -469. 6.Cuenca J, Garcia-Erce JA, Martinez F, et al. Preoperative haematinics and transfusion protocol reduce the need for transfusion after total knee replacement. Int J Surg (in press). 7.Cuenca J, Garcia-Erce JA, Martinez F, et al. Perioperative intravenous iron, with or without erythropoietin, plus restrictive transfusion protocol reduce the need for allogeneic blood after knee replacement surgery. Transfusion (in press). Conflict of Interest:None declared |
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