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Ann Thorac Surg 1997;63:68-73
© 1997 The Society of Thoracic Surgeons
Cardiothoracic Department, Killingbeck Hospital, Leeds, United Kingdom
Accepted for publication July 19, 1996.
| Abstract |
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Methods. In a prospective, randomized study, 38 patients undergoing elective coronary artery bypass grafting were investigated. Nineteen patients received low-dose aprotinin (2 x 106 KIU [280 mg] in the pump), and a control group of 19 did not. Complement activation, cytokine production, leukocyte elastase release, D-dimer level, full blood count, postoperative blood loss, and transfusion requirements were analyzed before, during, and after CPB.
Results. Interleukin-1ß was not detected in either group, whereas traces of tumor necrosis factor-
were infrequently observed. Plasma elastase, interleukin-6, interleukin-8, and neutrophil count increased (p < 0.001) during and after CPB compared with the baseline levels, reaching a peak at 2 hours after protamine administration in both groups before returning toward baseline at 24 hours. Proinflammatory cytokine markers did not differ significantly (p > 0.1) between the groups throughout the study period. The C5b-9 level increased (p < 0.001) in both groups perioperatively, reaching its peak 15 minutes after protamine. Twenty-fourhour postoperative blood loss was significantly (p < 0.001) reduced in the aprotinin group in association with markedly reduced D-dimer levels (p < 0.001). Patients in the aprotinin group also received significantly less banked blood postoperatively than the control group (p < 0.01).
Conclusions. Low-dose aprotinin fails to modify proinflammatory cytokine release, yet confers hemostatic improvement through reduced fibrinolysis in patients undergoing routine coronary artery bypass grafting.
| Introduction |
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Cardiopulmonary bypass (CPB) induces hemorrhagic complications and initiates a biochemical and cellular "whole-body inflammatory response," which may be associated with substantial morbidity and mortality [13]. A common mechanism is thought to be responsible, involving the inflammatory mediators of the complement system and cytokines [24]. Cytokines are potent intercellular signaling molecules known to participate in the regulation of cellular growth, function, and differentiation [24]. Interleukin-6 (IL-6) and interleukin-8 (IL-8) levels have been shown to be elevated during and after CPB and are associated with cardiac and pulmonary dysfunction after bypass [5, 6]. Various interventions have been used to reduce the intensity of the systemic inflammatory response secondary to CPB, eg, administration of corticosteroids [7], use of nonsteroidal antiinflammatory drugs [8], use of a leukocyte depletion filter [9], and use of heparin-coated circuits [1012].
Aprotinin is a low-molecular-weight peptide inhibitor of trypsin, kallikrein, and plasmin that is commonly used in cardiac operations for its ability to reduce postoperative blood loss in high-risk patients or procedures [1316]. Recent studies have shown that aprotinin in "high" doses can attenuate the whole-body inflammatory response by inhibiting kallikrein production completely, and complement and neutrophil activation partially [17, 18]. We conducted the present study to assess the influence of "low-dose" aprotinin (2 x 106 KIU [280 mg], favored by some as a potentially safer and cost-effective [19] alternative to a high-dose regimen) on hemostasis and proinflammatory cytokine levels in patients undergoing routine coronary artery bypass grafting.
| Patients and Methods |
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The techniques of anesthesia and CPB were standardized. After premedication, anesthesia was induced with fentanyl (30 µg/kg, intravenously); muscle relaxation was achieved with pancuronium bromide (0.1 to 0.2 mg/kg, intravenously). Mechanical ventilation was initiated (tidal volume 10 to 15 mL/kg, rate 12 to 15 breaths/min), and anesthesia was supported by inhalation of 1% isoflurane. Operative monitoring was identical in all patients. The extracorporeal circuit comprised a Stockert roller pump (Shiley Inc, Irvine, CA), a Shiley S100 membrane oxygenator, and polyvinylchloride tubes. In the aprotinin group, after a test dose, 2 x 106 KIU (280 mg) of aprotinin (Trasylol; Bayer AG, Leverkusen, Germany) was added to the priming solution of the extracorporeal circuit. The control group received an equivalent prime volume without aprotinin. Patients were given heparin just before the institution of CPB with 300 IU/kg, with additional dosing as necessary to maintain the activated clotting time greater than 480 seconds. Nonpulsatile extracorporeal circulation was initiated at flows of 2.4 to 2.6 Lm-2min-1. Moderate systemic hypothermia (28° to 30°C, nasopharyngeal) was uniformly used. Cardiac arrest was achieved by infusion of 1 L of cold blood cardioplegic solution and topical slush. All distal anastomoses were performed during a single period of cross-clamping, and the proximal anastomoses to the aorta were completed during the rewarming period. Extracorporeal circulation was terminated at a nasopharyngeal temperature of 37°C. Heparin was neutralized after the end of CPB with protamine sulfate (1 mg/100 IU heparin).
Laboratory Measurements
Venous blood samples (20 mL) were drawn into sodium citrate (0.32% w/v, 1:9 parts blood) immediately after the induction of anesthesia; 5 minutes after the onset and 5 minutes before the end of CPB; and 20 minutes, 2 hours, and 24 hours after protamine sulfate administration. Blood was centrifuged (10 minutes, 3,000 rpm, 4°C) to obtain plasma. Plasma specimens were frozen and stored at -80°C before batch analysis. Enzyme-linked immunosorbent assay techniques were used to measure each of the cytokines (tumor necrosis factor-
[TNF-
], IL-1ß, IL-6, and IL-8) (R&D Systems, Minneapolis, MN), D-dimer (Diagnostica Stago Asnieres sur Seine, France), and terminal complement complex C5b-9 (Quidel, San Diego, CA). Plasma neutrophil elastase concentrations were determined using an autoanalyzer technique (E. Merck Diagnostica, Darmstadt, Germany). The limit of sensitivity of each assay was: TNF-
= 5 pg/mL, IL-1ß = 0.3 pg/mL, IL-6 = 3 pg/mL, IL-8 = 20 pg/mL, C5b-9 = 16 ng/mL, and elastase = 20 ng/mL.
Full blood counts were measured at each sampling point, and no adjustment was made for hemodilution. Blood loss and blood transfusion were recorded until 24 hours after the operation. Packed red blood cells were infused when the hematocrit was less than 30%. Cardiac output was measured by the thermodilution technique through a Swan-Ganz catheter (Baxter Edward) from the mean of three readings. Cardiac index was calculated and reported in milliliters per kilogram. Systemic and pulmonary vascular resistances were calculated by conventional formulas and were not indexed.
Statistical Analysis
The Mann-Whitney U test was used to assess the significance of differences between groups, and the Wilcoxon test was used for nonparametric repeated measures. Pearson's correlation coefficient was used to assess associations (Statistica software). In all cases, less than 0.05 was considered significant.
| Results |
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and Interleukin-1ß
and IL-1ß did not change significantly with CPB in either group. Interleukin-1ß was not detectable at all in either group, whereas traces of TNF-
were detected in only 5 patients in the control group and 7 patients in the aprotinin group.
D-Dimer
Plasma D-dimer levels (Fig 2
) were similar in both groups at induction, then increased and continued to increase during and at the end of CPB (p < 0.01), reaching a peak at 20 minutes after protamine administration in both groups: 2,360 ng/mL (range, 377 to 3,316 ng/mL) in the control group versus 805 ng/mL (range, 322 to 2,092 ng/mL) in the aprotinin group (p < 0.0001). At 24 hours, the level of D-dimer returned to baseline in the aprotinin group but remained significantly elevated (p < 0.01) in the control group. The D-dimer level in the control group correlated significantly with postoperative blood loss: r = 0.50, p < 0.04 (Fig 3
).
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Full Blood Counts
Initial neutrophil numbers did not differ significantly between the groups. After initial bypass hemodilution, there was a progressive rise in the neutrophil count that began during rewarming, reaching a similar peak level 2 hours after protamine (median, 11.0 x 109/L [range, 5.2 to 13.8 x 109/L] versus 11.7 x 109/L [range, 6.3 to 19 x 109/L] in the control and aprotinin groups, respectively; p = not significant). Levels returned to baseline after 24 hours. Platelet numbers fell in both groups after the institution of bypass and remained low during the operation. Thereafter, the count rose in both groups. There was no significant difference between the groups.
| Comment |
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The present study confirms the proinflammatory response to CPB, with increases in IL-6, IL-8, C5b-9, plasma leukocyte elastase, and absolute neutrophil counts occurring in both groups. The anaphylatoxins C3a and C5a as well as the terminal complement complex C5b-9 have been shown to be elevated during CPB [2, 3, 10], and this rise precedes that of IL-6 [3]. This is consistent with our findings. Studies have shown that terminal complement complex (C5b-9) is a more useful index than C3 and C5 activation for accurate assessment of the inflammatory response to CPB [3, 10]. The complement products have been implicated in the increase in neutrophil activation and degranulation and endothelial adhesion. However, in contrast to other authors [13], we found no difference at any measured point between the aprotinin and the control groups in terms of C5b-9 or plasma leukocyte elastase.
Although complement activation with the release of elastase has been shown to increase the production of IL-1ß and TNF-
[3], reports to date on the plasma IL-1ß and TNF-
response to CPB have been conflicting. In this study, no significant increase in IL-1ß or TNF-
was demonstrated in either group. This agrees with some [3, 4], but not all previous reports [12, 20], and this disparity in the data may be attributable to the use of high-sensitivity assay kits by some groups.
Interleukin-6 is a major promoter of the acute-phase response and is synthesized by a variety of cell types, including endothelium and leukocytes [2, 12]. The acute-phase response refers to the large and diverse systemic and metabolic changes that occur in response to events such as trauma and infection. This response is characterized by fever, leukocytosis, thrombocytosis, and production of many hormones. It is now evident that the acute-phase response may, in part, be responsible for some of the adverse complications of CPB. We did not find any difference between the groups in terms of IL-6 release, which is consistent with the findings of Seghaye and colleagues [21] in a pediatric cohort, in which low-dose aprotinin therapy proved unremarkable in terms of cytokine release.
Interleukin-8 is a potent chemotactic factor that activates neutrophils and induces degranulation, loss of endothelial basement membrane integrity, and ultimately transendothelial neutrophil migration [4, 22]. The positive correlation of IL-8 with plasma elastase release in our study is consistent with that in another study [4], suggesting that elastase is released from damaged neutrophils activated by IL-8. Observations by Finn and associates [4] in pediatric patients undergoing CPB and by Endo and co-workers [23] in septic patients with adult respiratory distress syndrome also indicated that IL-8 was closely involved in the production and release of elastase.
Although Wachtfogel and colleagues [18] in vitro and Van Oeveren and associates [13] in vivo have demonstrated an inhibitory effect of aprotinin on neutrophil activation and plasma elastase release and proposed related therapeutic benefits in cardiac operations, we did not observe these effects. Furthermore, no differences were revealed between the aprotinin and control groups with regard to proinflammatory cytokine profiles. This could be due to a dose-dependent phenomenon, as high-dose aprotinin (approximately 4 to 6 x 106 KIU [560 to 840 mg]) was used, in contrast to low-dose aprotinin (2 x 106 KIU [280 mg]) in the present study. Paradoxically, Blauhut and colleagues [24] made observations consistent with our own regarding elastase release, despite using high-dose aprotinin. Ethically, high-dose aprotinin use cannot be justified in routine coronary artery bypass grafting because of concerns relating to its impact on graft occlusion and other possible clinical sequelae [19, 25].
Low-dose aprotinin used in the pump is technically simple to administer and confers substantial blood-saving benefit equivalent to that observed with the high-dose protocol, yet at approximately half the cost. The implication of this study for our unit has been to adopt this low-dose regimen in all patients at high risk of postoperative bleeding, in the belief that this measure is likely to be both cost-effective and associated with fewer morbid sequelae than high-dose aprotinin.
In summary, low-dose aprotinin fails to blunt the proinflammatory cytokine response to CPB; its major clinically relevant action appears to be at the fibrinolytic level. Further studies are indicated in high-risk cohorts to determine whether high-dose aprotinin use modifies the proinflammatory response and cytokine release.
| Footnotes |
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| References |
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