改良超滤与零平衡超滤结合应用于婴幼儿体外循环手术59例的体会

目的总结改良超滤与零平衡超滤在59例婴幼儿体外循环手术中结合应用的经验、方法及临床效果。方法 59例婴幼儿,其中男40例,女19例,年龄4月～3岁之间,体重5～14kg,体外循环手术中均采用在体外循环过程中根据灌注压、红细胞压积给予零平衡超滤,停机后给予改良超滤。结果 59例患儿均顺利停机,无1例死亡,未出现超滤并发症,转中血球压积18～30(22.5±2)%,停机改良超滤后血球压积上升至32～38(35.8±1.4)%,在CCU住院时间为2～6d,皆顺利出院。结论在婴幼儿体外循环中将零平衡超滤与改良超滤的结合应用,零平衡超滤利于炎性介质的滤出,改良超滤可在CPB结束后快速排出多余的水分,提高红细胞压积,改善心肺功能,适用于低体重血液稀释度大的婴幼儿及体外循环时间长者。     

Ambivalent roles of carboxypeptidase B in the lytic susceptibility of fibrin

Background

Removal of C-terminal lysine residues that are continuously exposed in lysing fibrin is an established anti-fibrinolytic mechanism dependent on the plasma carboxypeptidase TAFIa, which also removes arginines that are exposed at the time of fibrinogen clotting by thrombin.

Objective

To evaluate the impact of alterations in fibrin structure mediated by constitutive carboxypeptidase activity on the function of fibrin as a template for tissue plasminogen activator-(tPA) induced plasminogen activation and its susceptibility to digestion by plasmin.

Methods and results

We used the stable carboxypeptidase B (CPB), which shows the same substrate specificity as TAFIa. If 1.5 – 6 μM fibrinogen was clotted in the presence of 8 U/mL CPB, a denser fibrin network was formed with thinner fibers (the median fiber diameter decreased from 138 – 144 nm to 89 – 109 nm as established with scanning electron microscopy). If clotting was initiated in the presence of 5 – 10 μM arginine, a similar decrease in fiber diameter (82 -95 nm) was measured. The fine structure of arginine-treated fibrin enhanced plasminogen activation by tPA, but slowed down lysis monitored using fluorescent tPA and confocal laser microscopy. However, if lysis was initiated with plasmin in CPB-treated fibrin, the rate of dissolution increased to a degree corresponding to doubling of the plasmin concentration.

Conclusion

The present data evidence that CPB activity generates fine-mesh fibrin which is more difficult to lyse by tPA, but conversely, CPB and plasmin together can stimulate fibrinolysis, possibly by enhancing plasmin diffusion.     

Measurement of thrombin generation intra-operatively and its association with bleeding tendency after cardiac surgery

Introduction

Patients undergoing cardiac surgery with cardiopulmonary bypass (CPB) are susceptible to haemostatic disturbances. Monitoring the haemostatic capacity by conventional clotting tests is challenging.

Materials and Methods

Thrombin generation (TG) by Calibrated Automated Thrombography, clotting tests and tissue factor pathway inhibitor (TFPI) measurements were performed to describe the relationship between haemostatic changes and alterations in these tests. Blood samples were collected before, during and after CPB. Furthermore, it was investigated whether TG measured intraoperatively, is associated with increased risk of bleeding postoperatively.

Results

TG diminished significantly (p < 0.01) after heparinization in the presence and absence of platelets (37% and 50%) compared to baseline. After the start of CPB, TG elevated and persisted till the end of surgery but remained lower than preoperatively. Activated clotting time increased after heparinization and after the start of bypass compared to baseline (400% and 500%). Anti-FXa activity reduced on the start of CPB compared to the level after heparinization, to almost the baseline value following protamine reversal of heparin. The plasma levels of total and free TFPI elevated 9 and 14 fold during bypass and remained after protamine administration higher than preoperatively. Plasma D-dimer levels reduced (p < 0.01) when bypass started. However, a marked elevation was observed in the following time points. TG in platelet-rich plasma measured after heparinization and after the start of CPB associated (p < 0.05) with postoperative blood loss.

Conclusions

TG can be determined during CPB despite the high heparinization level, it reflects the haemostatic capacity better than clotting-based assays and might better predict bleeding when performed intraoperatively.