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J Thorac Cardiovasc Surg 2000;119:575-580
© 2000 Mosby, Inc.
SURGERY FOR ACQUIRED CARDIOVASCULAR DISEASE |
From the Departments of Cardiac Surgery,a Anesthesiology,b and Institute of Hygiene and Public Health,c Catholic University, Rome, Italy.
Address for reprints: Michele De Bonis, MD, Via Graziano 18, 00165 Roma, Italy.
| Abstract |
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| Introduction |
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-aminocaproic acid,
-aminocaproic acid and is far less expensive than aprotinin.| Methods |
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Randomization was carried out with random-number tables by a research nurse attached to the Department of Cardiac Surgery but not to the operating theaters. Sealed envelopes were prepared and left in a box in the operating theater. On the day of surgery, the theater nurse selected the next card from the box, and this determined which solution was to be used. Neither the surgeons, anesthetists, scrub nurses, nor the perfusionists knew the composition of the solution administered. Forty consecutive patients were randomly assigned to group 1 (TA group) or group 2 (placebo group). Only two cardiac surgeons were responsible for the surgical hemostasis. The anesthetic management and conduct of CPB were standardized. All patients were premedicated with diazepam 0.1 to 0.15 mg/kg administered orally, morphine 0.1 to 0.15 mg/kg administered intramuscularly, and scopolamine 0.01 mg/kg administered intramuscularly. Anesthesia was induced with fentanyl 3 to 5 µg/kg and thiopental 3 mg/kg and maintained with boli of fentanyl 100 to 200 µg and midazolam 2.5 mg. Arterial hypertension was controlled by isoflurane administration. Muscle paralysis was obtained with pancuronium bromide 0.1 mg/kg. After endotracheal intubation, patients were connected to a Servo Ventilator D (Siemens, Solna, Sweden). Minute volume and fraction of inspired oxygen were adjusted to achieve arterial PCO 2 values between 30 and 45 mm Hg and arterial PO 2 values between 100 and 150 mm Hg. The extracorporeal circuit consisted of a hollow-fibber membrane oxygenator (Terumo Capiox E; Terumo Co, Tokyo, Japan). Polyvinyl chloride tubing was used throughout the circuit, except for the roller pump tubing, which was silicone rubber. Before CPB was established, each patient received 3 mg/kg bovine lung heparin; when the activated clotting time was shorter than 400 seconds, additional doses of heparin were administered. Heparin was reversed with protamine sulfate at a 1.3:1 ratio. Normothermia at 37°C and isothermic intermittent antegrade administration of blood potassium cardioplegic solution were used in all patients. Left internal thoracic artery grafts supplemented with saphenous vein grafts were routinely used. The left pleural space was opened intentionally during left internal thoracic artery harvesting. Before closure of the median sternotomy, mediastinal and thoracic drains were clamped, and 100 mL of saline solution (with or without 1000 mg of TA) at room temperature was poured into the pericardial cavity and over the mediastinal tissues. The clamps on the mediastinal and thoracic drains were released after closure of the median sternotomy.
After the patient was transferred to the intensive care unit, continuous low-grade suction (5 cm H2O) was applied, which was supplemented with periodic milking of the drains. Complete blood count, SMA-18 (Technicon Instruments Corp, Tarrytown, NY), prothrombin time, partial thromboplastin time, and platelet counts were measured before the operation and when the patients arrived at the intensive care unit. The drainage of mediastinal blood was measured hourly. The mediastinal and thoracic drains were removed when the total drainage was less than 240 mL over the previous 24 hours. Uniform transfusion criteria were adhered to in all patients. Blood and blood components were administered only when the hematocrit level fell to less than 0.24 or the hemoglobin level fell to 7.5 g/L in the postoperative period. Shed mediastinal blood was not transfused into any patient during this study. The number of grafts, duration of CPB, crossclamp time, incidence of reoperation for bleeding, and amount of total chest tube drainage were recorded for all patients. The plasma concentration of TA levels was assayed by electron-capture gas chromatography 2 hours after unclamping of the chest tubes to verify whether any systemic absorption of this antifibrinolytic agent occurred after its topical application into the pericardial cavity.
15,17
Means and SDs were reported provided that no significant deviations from normal distribution were observed graphically and with the Kolmogorov-Smirnov test. Differences between the two groups of patients concerning hematologic and coagulative parameters were analyzed by the 2-tailed, unpaired, Student t test. Data about blood loss during the first 24 postoperative hours were analyzed by 2-way analysis of variance (ANOVA) (TA vs placebo groups; time subdivided into 3-hour intervals) for repeated measures. The comparison of the blood loss during each 3-hour interval between the TA and placebo groups was carried out by linear contrast, as well as the comparison of the total amount of chest drainage after the first 24 postoperative hours. The difference in total postoperative bleeding was analyzed by using the 2-tailed, unpaired, Student t test because the chest tubes were removed after a variable interval of time. Statistical analyses were made by using Statistica for Windows software (Statsoft Inc, Tulsa, Okla).
| Results |
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| Discussion |
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In the effort to reduce postoperative bleeding, antifibrinolytic agents have also been applied topically into the pericardial cavity.
26,27 Tatar and colleagues
26 first reported in 1993 that the topical use of aprotinin reduces postoperative blood loss and the need for transfusion in coronary artery surgery. The fact that aprotinin could not be detected in the patients blood suggested that its effect was likely due to topical action. Similar results were described by the Oxford group.
27 Thus far, to the best of our knowledge, no prospective, randomized, double-blind study has been published concerning the topical use of TA in the pericardial cavity after myocardial revascularization. However, the hemostatic effect of topical TA in oral surgery,
14,15 bladder surgery,
12 and gynecologic hemorrhage
16 has been demonstrated. The present study showed that a single 1-g dose of TA applied into the pericardial cavity after primary CABG reduces blood loss by 36% during the first 3 hours and by 25% during the first 24 hours after operation in comparison with placebo. The reduction in blood loss occurs principally in the initial 3 postoperative hours. We believe that this may be due to the early hemostatic effect provided by topical TA. It has been suggested that a local fibrinolytic state persists after closure of the thoracic cavity and contributes to the postoperative blood loss.
28 The application of TA into the chest before closure of the median sternotomy could remove plasminogen from the fibrin surface of clots, thereby inhibiting plasmin-induced degradation of fibrin. Thus it might prevent the resolution of formed clots and lead to hemostasis by preserving their integrity. On the other hand, TA could not be detected in any of the blood samples collected from the l3 patients of the treatment group 2 hours after unclamping of the chest tubes. No studies are currently available regarding the absorption and fate of TA after topical application into the pericardial cavity. However, the pharmacokinetics of this drug after intravenous, oral, and intramuscular administration
17 allowed us to extrapolate that after 2 hours we would expect to detect TA in the plasma if any significant absorption had occurred. The therapeutic plasma level of TA is approximately 10 to 15 mg/mL. The electron-capture gas chromatography has been successfully used for the determination of levels of TA in plasma as low as 0.2 mg/mL.
17 In our opinion the fact that TA could not be detected in any of the blood samples collected strongly suggests that the drug remained restricted to the pericardial space and that its effect was due to topical action. We appreciate, however, that a proper pharmacokinetic study needs to be done to definitely clarify this issue. Our data demonstrate that the reduction in blood loss in the treatment group was statistically significant in the initial 3 hours after operation but not in the following 21 hours. It is likely that the 1% solution of TA used in this series was not sufficient to suppress local fibrinolysis for more than 3 to 4 hours. We believe that a larger dose of TA (eg, a 5% solution) could prolong the hemostatic effect of this drug. This hypothesis is in accordance with previously reported results of treatment in anticoagulant-treated patients undergoing oral surgery.
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We are aware that in the current study the total reduction in blood loss in the TA group compared with that found in the placebo group was less than 200 mL and therefore relatively small, although statistically significant. However, if we define excessive bleeding as total chest drainage of more than 700 to 800 mL, it should be stressed that most patients in this series bled little. Minimal bleeding overall might have helped hide the hemostatic efficacy of this pharmaceutical agent. Little postoperative bleeding was the result of both meticulous surgical hemostasis and the relatively low risk for bleeding of our population. All the patients were undergoing primary CABG with normothermic CPB, did not receive platelet-activating drugs within 14 days of operation, and did not have any kind of bleeding diathesis. Furthermore, only the left internal thoracic artery was routinely used as in situ arterial graft. A greater effect of topical TA in reducing blood loss could possibly occur in more prolonged and complex procedures with a higher risk of bleeding.
The failure of the current study to document a reduction in allogenic transfusions despite a statistically significant reduction in blood loss may be related to several factors: little overall postoperative bleeding, stringent transfusion criteria, and sample size insufficient to demonstrate a modest effect. When surgical blood loss is already minimal, the beneficial effect of the drug on consumption of blood products is likely to be small,
29 particularly if transfusion practice follows stringent guidelines. Indeed, the criteria we adopted required a hematocrit level of less than 24% to trigger a transfusion, thus providing an overall low incidence of transfusions. Because mean postoperative hematocrit levels exceeded 25% for each group, a group difference in transfusions would be unexpected. The practice of transfusion to a higher hematocrit level, such as a level of less than 30% rather than 24%, could more easily demonstrate an effect of topical TA on transfusion requirement.
The economic effect on the hospitals budget of the topical method described seems to be little. At our institution, 1000 mg of TA costs $2.50, whereas 1,000,000 kIU of aprotinin, as topically used by Tatar and colleagues,
27 has a price of $62.
-Aminocaproic acid has a cost of $0.70 per 1000 mg, but although there are no data about its topical use, its dosage is approximately 10 times higher than that of TA when administered intravenously. The low cost of TA is attractive, but to be fully justified, a reduction in blood loss has to be followed by a reduction in the need for transfusion requirements.
In conclusion, topical application of TA into the pericardial cavity after CPB in patients undergoing CABG operations significantly reduces postoperative bleeding in the first 3 hours after operation. This reduction in blood loss might be the consequence of the potential local antifibrinolytic effect of TA. When topical TA is used in a homogeneous population of patients with a low bleeding risk undergoing primary CABG, the decrease in blood loss is relatively small. Moreover, no effect is observed on the prevalence of transfusions, particularly if heightened attention is given to surgical hemostasis and stringent transfusion criteria are followed. We believe that a more pronounced effect on both postoperative bleeding and blood product requirement might be seen in procedures with a higher bleeding risk (eg, redo operations, complete arterial myocardial revascularization, hypothermic CPB, long CPB time, preoperative aspirin therapy, or coagulopathy). Further studies must be carried out to clarify this issue. Finally, it needs to be established whether a larger dose of topical TA could prolong the hemostatic action of this drug.
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