Yj Gu

Heparin-coated circuits reduce the inflammatory response to cardiopulmonary bypass

Cardiopulmonary bypass generates a systemic inflammatory response including the activation of the complement cascade and leukocytes contributing to postoperative morbidity. To evaluate whether the use of heparin-coated extracorporeal circuits could reduce these activation processes, we performed a study on 30 patients undergoing coronary artery bypass grafting who were randomly perfused with a heparin-coated circuit (Duraflo II, n = 15) or with a similar noncoated circuit (control, n = 15). Standardized systemic heparinization was applied for every patient before cardiopulmonary bypass. The use of heparin-coated circuits resulted in a reduction of systemic leukocyte activation during cardiopulmonary bypass reflected by reduced elastase release (p < 0.05) and tumor necrosis factor generation (p < 0.05) manifest after release of the aortic cross-clamp. In addition, blood samples taken from both the right and left atria after reperfusion revealed that the elastase release from the pulmonary microcirculation was absent in the Duraflo II group in contrast to the control group (p < 0.05). The pattern of complement activation, likely initiating this inflammatory reaction, was modified by heparin coating in two different aspects. There was a significant reduction of C3a generation after protamine administration in patients perfused with heparin-coated circuits, and there was a decrease of complement hemolytic capacity in pooled human serum incubated with heparin-coated tubing. These observations suggest that heparin coating might bind some of the complement components from the classic pathway, thereby reducing the inflammatory response to cardiopulmonary bypass.

ENDOTOXIN RELEASE AND TUMOR-NECROSIS-FACTOR FORMATION DURING CARDIOPULMONARY BYPASS

Endotoxin, when released into the systemic circulation during cardiopulmonary bypass (CPB), might induce activation of plasmatic systems and blood cells during CPB, in addition to a material-dependent blood activation during CPB. However, the role of endotoxin in the development of this so-called whole-body inflammatory reaction in CPB is still unclear. We investigated the release of endotoxin into the systemic circulation in relation with the activation of the complement system and in particular the formation of tumor necrosis factor in 10 patients undergoing CPB. Immediately after the start of CPB the endotoxin concentrations increased significantly (p less than 0.01), accompanied by increases in C3a concentration (p less than 0.05). After release of the aortic cross-clamp, there was a second increase in endotoxin followed by a continuous increase in tumor necrosis factor, reaching a peak concentration 1 hour after the end of CPB (p less than 0.01). These observations demonstrate a release of endotoxin into the systemic circulation associated with tumor necrosis factor formation, which contributes to the whole-body inflammatory reaction associated with CPB.

Leukocyte depletion results in improved lung function and reduced inflammatory response after cardiac surgery

Leukocyte depletion during cardiopulmonary bypass has been demonstrated in animal experiments to improve pulmonary function. Conflicting results have been reported, however, with clinical depletion by arterial line filter of leukocytes at the beginning of cardiopulmonary bypass. In this study, we examined whether leukocyte depletion from the residual heart-lung machine blood at the end of cardiopulmonary bypass would improve lung function and reduce the postoperative inflammatory response. Thirty patients undergoing elective heart operations were randomly allocated to a leukocyte-depletion group or a control group. In the leukocyte-depletion group (n = 20), all residual blood (1.2 to 2.1 L) was filtered by leukocyte-removal filters and reinfused after cardiopulmonary bypass, whereas in the control group an identical amount of residual blood after cardiopulmonary bypass was reinfused without filtration (n = 10). Leukocyte depletion removed more than 97% of leukocytes from the retransfused blood (p < 0.01) and significantly reduced circulating leukocytes (p < 0.05) and granulocytes (p < 0.05) compared with the control group. Levels of the inflammatory mediator thromboxane B2 determined at the end of operation (p < 0.05) were significantly lower in the depletion group than in the control group, whereas no statistical differences in interleukin-6 levels were found between the two groups. After operation, pulmonary gas exchange function (arterial oxygen tension at a fraction of inspired oxygen of 0.4) was significantly higher in the leukocyte-depletion group 1 hour after arrival to the intensive care unit (p < 0.05) and after extubation (p < 0.05). There were no statistical differences between the two groups with respect to postoperative circulating platelet levels and blood loss, and no infections were observed during the whole period of hospitalization. These results suggest that leukocyte depletion of the residual heart-lung machine blood improves postoperative lung gas exchange function and is safe for patients who are expected to have a severe inflammatory response after heart operations.

Leukocyte activation with increased expression of CR3 receptors during cardiopulmonary bypass

The effects of cardiopulmonary bypass (CPB) on the expression of leukocyte adhesive receptors, ie, complement receptor type 3 (CR3), were studied in 16 patients. The CR3 expression on leukocytes was determined by time-resolved fluoroimmunoassay on a standardized number of cells isolated from blood samples taken during various times during CPB. The results demonstrated that CR3 expression on leukocytes increased immediately after the start of CPB (p less than 0.05), concomitant with an early sharp increase of plasma concentrations of C3a (p less than 0.01). After release of the aortic cross-clamp, a second peak of leukocyte CR3 expression was induced (p less than 0.05), paralleled by a significant increase of leukotriene B4 (p less than 0.05) and elastase (p less than 0.05) levels in the late period of CPB. In vitro studies with leukocytes isolated from healthy donors (n = 5) showed a dose-dependent increase of CR3 expression stimulated by zymosan-activated plasma, indicating that the rapid CR3 expression on leukocytes is likely mediated by complement activation. However, the mechanisms for the second peak of leukocyte CR3 expression during CPB remain to be further elucidated. In conclusion, CR3 expression on leukocytes increased immediately after the start of CPB and was followed by a second peak of expression in the late phase of CPB. Pharmacological blockage of these adhesive receptors might reduce the leukocyte-mediated deleterious effects of CPB.

Heparin-coating of extracorporea circuits reduces thrombin formation in patients undergoing cardiopulmonary bypass

This clinical study was performed to evaluate the inhibiting effects of heparin- coated extracorporeal circuits on thrombin formation during cardiopulmonary bypass (CPB). Thirty patients undergoing coronary artery bypass grafting were randomly divided into two groups with (Duraflo II, n=15) orwithout (control, n=15) the use of heparin-coated circuits. Standard systemic heparinization was performed in all the patients before CPB. The results showed that thrombin formation during the first phase of CPB was inhibited by heparin-coating identified by the significantly lower concentrations of thrombin-antithrombin III (TAT) complex formed in plasma in the Duraflo II group than in the control group (p <0.05). Heparin concentrations were higher in the Duraflo II group than in the control group at the end of CPB (p <0.05). However, after release of the aortic crossclamp in the second phase of CPB, thrombin became strongly activated in both the Duraflo II and the control groups indicated by a sharp increase of TAT complex as well as fibrinopeptide A. Thus, Duraflo II heparin-coating reduces thrombin formation in the early phase of CPB, however, this beneficial effect was counteracted after aortic crossclamp release by material-independent stimuli. Therefore, adequate systemic heparinization is still required despite improved haemocompatibility of the circuits offered by heparin-coating.

In Vitro Effect of Hemodilution on Activated Clotting Time and High-Dose Thrombin Time During Cardiopulmonary Bypass

BACKGROUND Extreme dilution of clotting factors, as may occur during pediatric or neonatal cardiopulmonary bypass, often leads to inadequate monitoring of anticoagulation with activated clotting time (ACT). In this study we postulate that the high-dose thrombin time (HiTT) is less influenced by extreme dilution of clotting factors because it stimulates clotting through the common pathway. METHODS Heparinized prebypass blood was obtained from 30 adult cardiac surgical patients and was diluted in a laboratory setting with saline solution to mimic the clinical clear prime solution (group I; n = 10), with saline solution containing similar heparin as in the prebypass blood (group II; n = 10), and with fresh frozen plasma to substitute clotting factors in the diluted blood (group III; n = 10). Blood was diluted to four different degrees: a control without dilution, 25%, 50%, and 75% dilution. The ACT and HiTT were measured and compared. RESULTS In group I, significant prolongation of ACT was observed in blood diluted to 75% as compared with the nondiluted blood (p < 0.01). In contrast, HiTT was not prolonged at any degree of dilution but reduced proportionally to dilution up to 75%, reflecting the concomitant reduction of heparin. In group II, ACT increased at 25% dilution (p < 0.01) whereas HiTT increased at 50% dilution (p < 0.01). In group III, no prolongation of ACT or HiTT was found in any degree of dilution. Furthermore, adding fibrinogen to the diluted blood (n = 4) did not cause ACT to recover at 75% dilution, suggesting that dilution of other factors in the early clotting cascade rather than fibrinogen alone increases ACT. CONCLUSIONS These results imply that when blood is extremely diluted during cardiopulmonary bypass with a clear prime without substituted clotting factors, HiTT is a better test than ACT for anticoagulation monitoring.

Clotting and fibrinolytic disturbance during lung transplantation: Effect of low-dose aprotinin

UNLABELLED Patients undergoing lung transplantation are often confronted with a bleeding problem that may be due in part to the use of cardiopulmonary bypass and its activation of blood clotting and fibrinolysis. OBJECTIVE We performed a prospective study to determine whether and to what extent the clotting and fibrinolytic systems are being activated and whether low-dose aprotinin is effective in inhibiting blood activation during lung transplantation. METHODS Thirty lung transplantations performed on 29 patients were divided into a group with cardiopulmonary bypass alone (n = 12), a group with cardiopulmonary bypass and 2 x 10(6) KIU aprotinin administered at the beginning of bypass in the pump prime (n = 12), and a group without cardiopulmonary bypass (n = 6). Serial blood samples were taken from the recipient before anesthesia, seven times during the operation, and 4 and 24 hours thereafter. RESULTS Results show that in the group having cardiopulmonary bypass alone, the concentration of the clotting marker thrombin/antithrombin III complex increased significantly during the early phase of the operation (p < 0.01) and remained high until the end of the operation. Levels of tissue-type plasminogen activator, a trigger of fibrinolysis released by injured endothelium, also increased sharply in the early phase of the operation in the cardiopulmonary bypass group (p < 0.01), followed by a significant increase in fibrin degradation products (p < 0.01). In the aprotinin group, a significant reduction of thrombin/antithrombin III complex (p < 0.05), tissue-type plasminogen activator (p < 0.05), and fibrin degradation products (p < 0.05) was observed in the early phase of the operation compared with levels in the bypass group, but these markers increased late during bypass associated with a significant drop (p < 0.05) of plasma aprotinin level monitored by plasmin inhibiting capacity. In the nonbypass group, concentrations of thrombin/antithrombin III complex and tissue-type plasminogen activator also rose significantly (p < 0.05) in the early phase of the operation, but the levels were significantly lower than those of the bypass group (p < 0.05). Blood loss during the operation was 2521 +/- 550 ml in the bypass group, 1991 +/- 408 ml in the aprotinin/bypass group, and 875 +/- 248 ml in the nonbypass group. CONCLUSION These results suggest that clotting and fibrinolysis are activated during lung transplantation, especially in patients undergoing cardiopulmonary bypass. Aprotinin in a low dose significantly reduced activation of clotting and fibrinolysis in the early phase of the operation but not during the late phase of lung transplantation.

Leucocyte depletion during cardiac surgery: a comparison of different filtration strategies

The results of leucocyte filtration during cardiac surgery are conflicting. This may be due to timing and duration of the filtration procedure, and to flow and pressure conditions in the filter. Therefore, we prospectively compared three major leucocyte filtration strategies in cardiac surgical patients. Forty patients were randomly divided into four groups. Group I: leucofiltration of arterial blood throughout cardiopulmonary bypass (CPB) (associated with high-flow and pressure gradients), Group II: leucofiltration of a part of the venous return blood in the re-warming phase during CPB (associated with intermediate flow, but high pressure), Group III: leucofiltration of residual heart-lung machine blood during transfusion into the patient after CPB (associated with low flow and low pressure), Group IV: control group without leucofiltration. We measured circulating leucocyte counts, plasma elastase levels and arterial blood oxygenation. Filters were postoperatively examined using scanning electronmicroscopy (SEM). Leucocyte counts increased over time and oxygenation decreased in all groups, without significant differences between the groups. SEM demonstrated extensive protein deposits and damaged leucocytes in the deeper layers of the filters from Group I. This was not observed in the filters from Group III. The postoperative plasma elastase levels increased in Groups II and IV and decreased in Groups I and III. In conclusion, we could not demonstrate a clinical difference among the three leucocyte depletion strategies. However, our laboratory results suggest that leucocyte filtration at low flow and pressure conditions is associated with less leucocyte damage and less release of elastase.

Clinical performance of a high-efficiency rapid flow leucocyte removal filter for leucocyte depletion of heparinized cardiopulmonary bypass perfusate.

The method of leucocyte depletion has been recently introduced to the field of cardiopulmonary bypass to reduce leucocyte-mediated organ dysfunction. In this study, we evaluated the efficacy and biocompatibility of the Pall RC400 filters for leucocyte depletion of heparinized cardiopulmonary bypass (CPB) perfusate taken from the heart-lung machine during routine cardiac surgery. For each filter, 700 ml blood were used as filtrate. Filtration was divided into the following groups to study the effect of loading pressure on the efficacy of the filters: under gravity pressure as a control (n = 8), under 100 mmHg (n = 8), 200 mmHg (n = 8), and 300 mmHg loading pressure (n = 8) driven by a roller pump. In addition, heparinized predonation blood taken at the beginning of CPB (n = 8) was filtered under gravity in comparison with the perfusate taken at the end of CPB. The results showed that the average leucocyte removal rate by an RC400 filter for 700 ml of blood was 96.8%. There was no significant difference of leucocyte removal rate between filtration under gravity and under loading pressure up to 300 mmHg. This allows clinical filtration at a speed up to 500 ml/min. The platelet removal rate was significantly higher in blood taken at the beginning of CPB than in blood taken at the end of CPB. Complement split product, C5a, increased only slightly during filtration indicating that this filter, made from polyester, has a good blood compatible characteristic. We conclude that the Pall RC400 leucocyte removal filter is suitable and safe to be used for leucocyte filtration of heparinized CPB perfusate during cardiac surgery.

Activation of plasma components by leukocyte removal filters.

The technique of leukocyte filtration has been introduced into cardiac surgery to reduce leukocyte mediated reperfusion injury. When autologous whole blood (WB) is used as filtrate, it is more likely to be activated by the filter material than are banked red blood cell concentrates (RCC), because of its richness in plasma components. This study was designed to compare the activation of plasma components during leukocyte filtration from WB (n = 10) taken from the heart-lung machine, with RCC (n = 10) obtained from the blood bank. Leukocyte filters made from either cellulose acetate or polyester were used. Blood samples were taken simultaneously from the inlet and outlet of the filter after filtration of either 700 ml of WB or 350 ml of RCC. Results indicated that the complement cascade was activated, as reflected by the increase of C3a and C5a during filtration of WB by filters made from cellulose acetate. In contrast, there was no significant increase of C3a and C5a during filtration of RCC. The clotting system, indicated by fibrinopeptide A, and the fibrinolytic system, indicated by fibrinogen degradation products, were not activated during leukocyte filtration. These data suggest that it is the WB taken from the heart-lung machine rather than the RCC from the blood bank that is being activated during leukocyte filtration. Thus, careful selection of filter material is important for leukocyte filtration of autologous whole blood during cardiac surgery.