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J Thorac Cardiovasc Surg 2002;123:1084-1091
© 2002 The American Association for Thoracic Surgery
Cardiopulmonary Support and Physiology (CSP) |
From the Division of Cardiac Anesthesia and Intensive Care,a Division of Cardiac Surgery,b Policlinico di Monza, Monza, and Epidemiology Unit, San Raffaele Hospital,c Milan, Italy.
Received for publication July 18, 2001. Revisions requested Sept 17, 2001; revisions received Sept 26, 2001. Accepted for publication Oct 3, 2001. Address for reprints: Valter Casati, MD, Division of Cardiac Anesthesia and Intensive Care, Policlinico di Monza, via Amati 111, 20052, Monza (Milan), Italy (E-mail: valter.casati{at}tin.it).
| Abstract |
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| Introduction |
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-aminocaproic acid and tranexamic acid, two synthetic antifibrinolytic drugs with demonstrated efficacy in reducing perioperative bleeding and allogeneic transfusions in cardiac surgery.
In our institution, as a consequence of previously published studies, we routinely administer tranexamic acid to patients undergoing cardiac operations.
5,6 The aim of this study was to evaluate the effects of tranexamic acid on perioperative bleeding and allogeneic transfusions also in patients submitted to elective thoracic aortic surgery.
| Methods |
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A standardized protocol for anesthesia was applied. Premedication was obtained with intramuscularly administered morphine (0.1 mg/kg) and scopolamine (0.5 mg). Induction and maintenance of anesthesia were performed with propofol, midazolam, and fentanyl, with nitrous oxide and isoflurane as needed. Muscle relaxation was obtained with pancuronium bromide.
Surgical protocol
Tables 1 and 2 summarize the aortic pathologic conditions and the interventions performed in the two groups of patients. All the patients were operated on through a full median sternotomy, with the exception of 2 patients with descending thoracic aortic aneurysm, 1 per group, who underwent the only replacement of the descending thoracic aorta through a left thoracotomy performed in the fourth intercostal space. Most patients had disease of the aortic root, and a combined operation on the aortic valve and ascending aorta was performed. A total of 6 patients (3 patients per group) required DHCA, 5 because of surgery involving the aortic arch and 1 because of surgery on a calcified ascending aorta. Before arterial cannulation (aorta or femoral artery), full heparinization was obtained (3 mg/kg), and additional heparin was administered to maintain a celite activated coagulation time 480 seconds or higher (Actalyke; Helena Laboratories, Beaumont, Tex). The circuit for extracorporeal circulation comprised a roller pump (SC Stockert; Stockert Instrumente GmbH, München, Germany), which guaranteed a nonpulsatile blood flow, and a hollow-fiber membrane oxygenator (Affinity; Dideco, Mirandola, Italy). Priming of the circuit consisted of 1700 mL of a balanced crystalloid and colloid solution (1300 mL Ringer lactate, 250 mL 18% mannitol, and 150 mL plasma expander). Myocardial protection during aortic crossclamping was achieved with cold blood cardioplegia. DHCA was achieved with standardized methods, and in these cases cerebral protection was performed through retrograde cerebral perfusion. At the end of CPB, heparin was antagonized with protamine sulfate (1:1 ratio); if needed, additional protamine was administered in 50-mg incremental doses to obtain an activated coagulation time value equal to or shorter than the baseline. A cell-saver circuit (Compact Advanced; Dideco) was used to recoup blood from the operative field and to process the blood remaining in the extracorporeal circuit after the cessation of CPB.
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Samples for evaluation of hemoglobin, hematocrit, platelet count, fibrinogen, prothrombin time, activated partial thromboplastin time, creatinine, creatine kinase, and creatine kinase MB isoenzyme were taken before the induction of anesthesia (time 1), on the patient's arrival in the intensive care unit (time 2), at 24 and 48 hours after the operation (times 3 and 4), and at discharge (time 5).
Criteria for allogeneic transfusion and surgical reexploration
A standardized intraoperative and postoperative protocol for transfusion of allogeneic products was applied. During CPB, packed red blood cells (PRBCs) were transfused if the hemoglobin value was less than 6.5 g/dL and the hematocrit value was less than 20%. After CPB and during the postoperative period, PRBCs were transfused if the hemoglobin value was less than 8 g/dL and the hematocrit value was less than 24%. Fresh-frozen plasma (FFP) was infused after protamine administration if prothrombin time value was 1.5 times the baseline and there was microvascular bleeding. Platelet concentrate (PLTC) was transfused in the presence of microvascular bleeding and a platelet count less than 50,000 cells/mm3. The total amount of allogeneic blood products transfused in each group was calculated as the sum of the single units: 1 bag of PRBCs was 300 mL, 1 bag of FFP was 500 mL, and one unit of PLTC was 50 mL.
Blood loss was recorded during the first 24 hours. We defined excessive bleeding as a total amount greater than 600 mL/24 h. Chest drains were removed when bleeding was less than 100 mL in the last 4 hours. Surgical reexploration was considered when bleeding in the first 2 hours was greater than 300 mL/h or if it was greater than 200 mL/h for 4 consecutive hours, with normal coagulation data.
Postoperative evaluation
As a possible consequence of antifibrinolytic therapy, the following thrombotic complications were recorded during the first 24 postoperative hours: myocardial infarction (new Q waves on electrocardiogram, creatine kinase MB isoenzyme to creatine kinase ratio greater than 10%, troponin I value greater than 0.1 ng/dL), acute renal insufficiency (creatinine value twice the baseline or need for dialysis), major neurologic dysfunction (transient ischemic attack or stroke), deep venous thrombosis, and pulmonary embolism.
Statistical analysis
The trial was designed to detect a difference between the groups of 200 mL in postoperative bleeding with an SD of 250 mL. This design was based on data emerging from a previous study.
5 To achieve significance, a minimum of 25 patients per group was required, with a one-tailed
error of .05 and a power of 80%. To test the normality of the distribution of the continuous variables, the Kolmogorov-Smirnov test was performed. The normally distributed data at each time were compared between the groups with a 2-tailed unpaired Student t test and expressed as mean ± SD. Nonnormally distributed variables were compared by Mann-Whitney U test and expressed as median and interquartile range (25th-75th percentiles). Categoric data were analyzed with the
2 test or the Fisher exact test as appropriate. Two-way analysis of variance with repeated measures on one factor was used to evaluate the main effect of group on the hematologic variables, the effect of the time, and the group-time interaction. Data were analyzed with the SPSS 6.0 statistical package (SPSS Inc, Chicago, Ill).
| Results |
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| Discussion |
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During cardiac operations performed with CPB, both the intrinsic pathway, through the contact of the blood with the foreign surfaces of the circuit for extracorporeal circulation, and the extrinsic pathway, through the activation of tissue factor, are intensively stimulated.
10,11 The wide surgical dissection areas determine activation of the extrinsic pathway through the release of tissue factor by endothelial cells. Hypothermia induces profound alteration of the coagulation system through speed reduction in enzymatic activity and alteration of platelet morphology, with decreased platelet aggregation following the reduction of thromboxane release and plasmin-related degradation of glycoprotein Ib receptors.
2,9 Circulatory arrest determines stagnation of the blood into the vascular bed, and through the production of tissue plasminogen activator by endothelial cells, thrombin is produced and the fibrinolytic system is induced. There is also the activation of protein C, which exerts a potent anticoagulant effect through the inhibition of factors Va and VIIIa and the inactivation of plasminogen activator inhibitor types I and III, thus promoting fibrinolysis.
8 All these factors contribute to the complex hemostatic alterations and the derived abnormal perioperative bleeding frequently seen in patients undergoing thoracic aortic surgery.
The principal consequence of excessive perioperative blood loss is an increased need for allogeneic transfusions, with the derived risks of immunologic reactions and viral infectious diseases such as hepatitis C and acquired immunodeficiency syndrome.
12 In addition, patients with excessive bleeding are exposed to a higher rate of surgical reexploration, with consequent increased risks of morbidity and mortality.
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A study by Svensson and colleagues
14 demonstrated that patients undergoing thoracic aorta operations who did not receive allogeneic blood transfusions had better outcomes. Methods of reducing allogeneic transfusions, such as preoperative autologous blood donation, intraoperative isovolemic hemodilution, intraoperative blood salvage and reinfusion, and the use of drugs with hemostatic properties, have therefore received great attention of late.
15 In particular, many previously published randomized, double-blind, prospective trials have evaluated the hemostatic effects of aprotinin in aortic surgery, particularly when performed with DHCA,
16-20 whereas no one has considered the synthetic antifibrinolytic drugs
-aminocaproic acid and tranexamic acid. Aprotinin is a product naturally derived from bovine lung with nonspecific antiprotease and antifibrinolytic properties, and it has a complex action on the coagulation system.
21 Even though significant reductions in perioperative bleeding and allogeneic transfusions have been reported with this drug, in various reports its use in aortic surgery with DHCA has been related to an increased risk of thrombotic complications, such as renal insufficiency, myocardial infarction, and death.
20,22-24 For these reasons the use of aprotinin continues to be debated.
Tranexamic acid and
-aminocaproic acid are two low-cost synthetic antifibrinolytic drugs that prevent the plasmin-mediated conversion of fibrinogen to fibrinogen split products through the inhibition of the lysine-binding sites on plasminogen and fibrinogen, thus blocking fibrinolysis.
25 They also exert a protective effect on platelets through the inhibition of plasminogen and plasmin at platelets, thus blocking the activation of platelets as a result of local plasmin concentration.
26 The use of
-aminocaproic acid in thoracic aortic surgery has been proposed by various authors.
14,15,27,28 In a retrospective study, Eaton and coworkers
27 compared aprotinin with
-aminocaproic acid in 49 patients undergoing aortic surgery involving DHCA. They concluded that the two drugs appeared equally efficacious in reducing perioperative bleeding and transfusion requirement. Svensson and colleagues
14,15 and Cohn and coworkers
28 proposed the administration of
-aminocaproic acid among potential strategies to reduce the bleeding associated with thoracic aortic surgery.
Until now no study has considered tranexamic acid as an antifibrinolytic drug in thoracic aorta surgery. In our institution, as a consequence of the results of previously published studies, tranexamic acid is routinely administered to all patients undergoing cardiac surgery with CPB,
5,6 and recently it has also been administered to patients undergoing beating-heart coronary operations without extracorporeal circulation.
29 We therefore elected to evaluate the hemostatic effects of tranexamic acid in patients undergoing thoracic aortic surgery. Our most important result was the significant reduction in perioperative bleeding, and consequently in the amount of allogeneic transfusions, among the patients treated with tranexamic acid. In particular we observed a reduction of about 30% in the number of patients who required at least one type of allogeneic blood product. The antihemorrhagic effects of the drug are clearly demonstrated by the reduction of bleeding, particularly during the first 4 postoperative hours when the drug is present in the blood in therapeutic concentrations.
25 In addition, the quantity of FFP transfused was clearly greater in the placebo group, although this difference did not reach statistical significance, probably because of the relatively small number of patients enrolled.
Another important aspect of the use of antifibrinolytic drugs is the theoretic possibility of an increased rate of thrombotic complications. In this relatively small series of patients we did not observe any difference between treated and untreated patients, and the occurrences of thrombotic complications in both groups were similar to those described in previous published studies.
30,31 One patient in the tranexamic acid group with a history of associated coronary disease died intraoperatively of cardiogenic shock; in this case an autopsy was not performed, so conclusions regarding a possible myocardial ischemia induced by a thrombotic complication related to tranexamic acid are not possible. Further studies on a greater number of patients with the primary outcomes of morbidity and mortality may lead to more precise answers.
One limitation of the study is the relatively small number of patients operated on with DHCA. Because of the profound alterations of coagulation seen with DHCA, this group could benefit greatly from therapy with tranexamic acid. This may be an interesting area for further studies. Another limitation is that this was a clinical study, with no specific laboratory evaluations of platelet function, coagulation, and fibrinolysis. Because of this, no conclusions regarding the functional aspect of tranexamic acid in this type of surgery are possible. Additional studies may compare tranexamic acid with the principal hemostatic drugs currently used in cardiac surgery, such as aprotinin and
-aminocaproic acid, to examine their different biochemical effects on coagulation and the fibrinolytic system.
| Conclusions |
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| References |
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-aminocaproic acid in primary cardiac surgery. Ann Thorac Surg. 1999;68:2252-7.
-aminocaproic acid for aortic surgery using deep hypothermic circulatory arrest. J Cardiothorac Vasc Anesth. 1998;12:548-52.[Medline]This article has been cited by other articles:
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