Delayed thrombin generation with hirudin anticoagulation during prolonged cardiopulmonary bypass

Patients with heparin-induced thrombocytopenia requiring urgent cardiac surgery present a unique challenge that must be addressed by the use of nonheparin alternatives for anticoagulation during cardiopulmonary bypass. Although isolated cases have been presented involving the use of antithrombin III independent thrombin inhibitor hirudin in this situation, its ability to completely inhibit thrombin activity has not been demonstrated. In this report we describe the efficacy of this drug in inhibiting thrombin during a case requiring prolonged cardiopulmonary bypass.     

Aprotinin inhibits thrombin formation and monocyte tissue factor in simulated cardiopulmonary bypass.

BACKGROUND: Aprotinin reduces perioperative bleeding after open heart surgery, primarily by inhibiting fibrinolysis. In addition, the drug has both procoagulant and anticoagulant effects that involve complex reactions of coagulation proteins and cells that are incompletely understood. This study tests the hypothesis that aprotinin has an anticoagulant effect on the extrinsic coagulation pathway. METHODS: Human heparinized blood was recirculated through a membrane oxygenator with and without high concentrations of aprotinin (18.4 microM). Serial plasma samples were obtained at intervals up to 240 minutes. RESULTS: Aprotinin significantly reduced the progressive increase in prothrombin fragments (F1.2) and thrombin-antithrombin complex beginning immediately. Aprotinin also significantly reduced monocyte expression of tissue factor and Mac-1. Aprotinin did not significantly reduce factor VII or factor VIIa. CONCLUSIONS: During simulated cardiopulmonary bypass, aprotinin immediately inhibits kallikrein and thrombin formation via the intrinsic coagulation pathway. Later, aprotinin inhibits monocyte expression of tissue factor and the extrinsic coagulation pathway. The ability of aprotinin to inhibit monocyte tissue factor provides a means to reduce thrombin formation in blood aspirated from the wound during open heart surgery.     

Matrix metalloproteinase-9, tissue inhibitor of metalloproteinase-1 and tumour necrosis factor alpha release during cardiopulmonary bypass

An inflammatory response occurs during cardiac surgery involving cardiopulmonary bypass. Matrix metalloproteinase-9 is an enzyme involved in cytokine processing and leucocyte extravasation. It is secreted as a pro-enzyme in response to several inflammatory mediators and is inhibited by endogenous tissue inhibitor of metalloproteinase-1. The interaction between matrix metalloproteinase-9 and its inhibitor during cardiopulmonary bypass is not known. We measured tumour necrosis factor alpha, and matrix metalloproteinase-9 and its inhibitor using enzyme immunoassay at three time points in 20 patients undergoing elective coronary artery bypass grafting with cardiopulmonary bypass. Tumour necrosis factor and matrix metalloproteinase concentrations increased in all patients during bypass (both p < 0.0001), whereas the inhibitor in contrast, decreased (p < 0.0001). We conclude that matrix metalloproteinase-9 is released as part of the inflammatory response during cardiac surgery. Levels of the endogenous inhibitor of metalloproteinase, however, show a different pattern of release, suggesting independent regulation.     

Tissue factor pathway inhibitor antigen and activity in 96 patients receiving heparin for cardiopulmonary bypass

OBJECTIVE: To identify patients with poor tissue factor pathway inhibitor (TFPI) response to heparin and observe any association with increased risk of excessive coagulation activation, morbidity, or mortality. DESIGN: Prospective, observational cohort study. SETTING: University hospital. PARTICIPANTS: Patients (n = 96) undergoing cardiopulmonary bypass for various types of surgery. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: TFPI antigen and activity were determined in patients before and after heparin administration, before cardiopulmonary bypass for cardiac surgery. The clinical progress of each patient was recorded. Median levels of TFPI activity were 0.98 U/mL (interquartile range, 0.83 to 1.14 U/mL) preheparin and 2.34 U/mL (2.18 to 2.54 U/mL) postheparin (p < 0.0001), representing a median 2.3-(2.1- to 2.8-) fold increase. Median TFPI antigen levels were 92.4 ng/mL (73.0 to 119.5 ng/mL) preheparin and 422.9 ng/mL (398.7 to 501.6 ng/mL) postheparin (p < 0.0001), representing a median 4.6-fold (3.6- to 6.2-fold) increase. Two patients had low (<300 ng/mL) postheparin levels of TFPI antigen that were not associated with low functional TFPI or adverse clinical outcome. Fourteen patients showed a low ratio of increased functional TFPI postheparin; all had a ratio of TFPI antigen increase of at least 3-fold. CONCLUSION: The TFPI response to heparin is heterogenous. Two nonresponders were identified, with low postheparin levels of TFPI antigen, who did not suffer adverse clinical outcomes.     

Complement activation during cardiopulmonary bypass: mechanism and prevention

The mechanism of complement activation during cardiopulmonary bypass was studied for the prevention. In ten patients undergoing open-heart procedures, the serum levels of complement fractions (C3, C4, and C3 activator) were measured by a single radial immune diffusion method. In four of ten patients, the plasma levels of C3a, C4a, and C5a fractions were studied by the radioimmunoassay 2 antibodies method. The serum levels of C3, C4, and C3 activator decreased after cardiopulmonary bypass. The plasma levels of C3a, C4a, and C5a increased after bypass. The lower level of C3 activator shows that C3 activator was not excessively produced during cardiopulmonary bypass. Therefore it can be thought that much C4b2a from classical pathway as well as C3a over-production localizing extra-corporeal circuits and little inhibitors on alternative pathway resulted in increased complement activation. The prevention should be done from these etiologies.     

High dose thrombin time versus the activated clotting time during cardiopulmonary bypass

In this study we compared the High Dose Thrombin Time (HiTT) with the Activated Clotting Time (ACT) during cardiopulmonary bypass (CPB) in non-aprotinin treated patients. On the advice of the HiTT test manufacturer each institution should perform comparative ACT/HiTT assays in the cardiac surgery population. In previous tests our target ACT value of 480 seconds corresponds with a mean HiTT value of 190 seconds. Our results showed that after heparinization (300-400 IU/kg body weight) 8 out of 20 patients did not reach the target ACT of 480 seconds, while the HiTT results in those 8 patients were higher than our target time of 190 seconds. Four heparin pretreated patients who received 400 IU/kg heparin, had relatively low ACT values (467 +/- 14 sec.) and high HiTT values (324 +/- 47 sec.). Before and during CPB there was a poor correlation between the HiTT and ACT (r = 0.38). The results of this study show that for the individual patient the target HiTT of 190 seconds is no guarantee for reaching an adequate ACT of 480 seconds. Although the HiTT may be a very useful assay for monitoring heparin effects during CPB, the determination of the target time can be a point of discussion. In contrast of the advice of the manufacturer we therefore suggest that comparative ACT/HiTT assay should be done in every individual patient to determine a safe target HiTT time, instead of the whole group of patients.     

Airborne contamination during cardiopulmonary bypass: the role of cardiotomy suction

Airborne contamination of the wound area and the cardiopulmonary bypass circuit during sham open-heart operations on dogs was studied. The air of the operating room (OR) was contaminated with two typeable bacterial strains. It was found that the number of wounds, blood specimens, oxygenators, and cardiotomy reservoirs contaminated with Staphylococcus aureus was related to the number of S. aureus present in the air of the OR, but that contamination with Serratia marcescens was related to the type of suction used. This form of contamination was considerably higher when air was aspirated together with blood into the suction line (p less than 0.05). The oxygenator and cardiotomy reservoir were contaminated mainly by aspirating wound fluid from the airborne-contaminated wound area. The low number of sample sites positive for S. marcescens may be due to a better preserved host defense mechanism if only wound fluid is sucked. A rather high incidence of postoperative infections occurred even in dogs operated on in an OR with a low level of airborne contamination.     

Mucosal tissue oxygenation of the porcine jejunum during normothermic cardiopulmonary bypass

Cardiopulmonary bypass (CPB) has been associated with intestinal tissue hypoxia, but direct measurements of mucosal oxygenation have not been performed. In anaesthetized pigs, jejunal mucosal oxygen tension and microvascular haemoglobin oxygen saturation were measured by a Clark- type electrode and tissue reflectance spectrophotometry. In pigs, normothermic CPB with systemic oxygen transport equivalent to baseline values was performed. In control animals, mucosal oxygen tension and mucosal haemoglobin oxygen saturation were mean 5.01 (SD 1.08) kPa and 38.0 (2.3)%, respectively. CPB was associated with a decrease in mucosal oxygen tension to 2.26 (1.21) kPa, decrease in mucosal microvascular haemoglobin oxygen saturation to 26.0 (3.9)% and appearance of oscillations in mucosal microvascular haemoglobin oxygen saturation. With CPB, arterial lactate concentrations increased from 1.77 (1.37) to 3.52 (1.58) mmol litre-1, but transvisceral lactate and splanchnic venous-arterial carbon dioxide tension gradients remained unchanged. Our results support the concept that CPB is associated with diminished oxygenation of intestinal mucosa that is probably caused by regional redistribution.      

Inactivation of the MEK/ERK pathway in the myocardium during cardiopulmonary bypass

OBJECTIVES: A general pro-inflammatory response after cardiopulmonary bypass (CPB) may involve changes in signal transduction and in part be responsible for arrhythmias and myocardial dysfunction after cardiac surgery. The MEK/ERK (mitogen-activated protein kinase kinase/extracellular regulated kinase) pathway is common to many stimuli and may play a pivotal role in morbidity associated with CPB. We investigated the changes in MEK/ERK pathway and related enzymes after CPB in pigs. METHODS: We examined ventricular and atrial tissue from pigs before 90 minutes of normothermic CPB and after 90 minutes of post-CPB perfusion. The activities and protein levels of kinases MEK1/2, ERK1/2, a cellular tyrosine kinase (c-Src), protein kinase B (Akt), and the protein levels of mitogen-activated protein kinase phosphatase (MKP-1) were studied by immunoblotting ventricular and atrial myocardium lysates and labeling sections with antibodies that recognize the activated forms of the kinases and the phosphatase. Control pigs were subjected to sternotomy and heparinization but not CPB. RESULTS: We found a consistent inactivation of MEK/ERK pathway in both ventricular and atrial myocardium with an increase in MKP-1, a negative regulator of ERK1/2. The activities and protein levels of c-Src and Akt were not significantly modified before or after CPB, suggesting a certain degree of specificity for the MEK/ERK pathway. Such changes were not observed in controls. The decrease of ERK1/2 and MEK1/2 phosphorylation 90 minutes after termination of CPB (as well as the increase of nuclear MKP-1 protein levels) was also apparent by confocal microscopy. CONCLUSIONS: These results collectively reveal a prevalence of inhibitory mechanisms in the MEK/ERK signal transduction machinery in myocardium subjected to CPB.     

心肺转流不同氧分压对红细胞衰变加速因子的影响

目的 探讨心肺转流(CPB)中不同动脉氧分压(PaO2)对红细胞衰变加速因子(DAF或CD55)的影响.方法 40例心脏病患者随机均分为四组:紫绀型先天性心脏病高氧分压组(A组)及正常氧分压组(B组),非紫绀型心脏病高氧分压组(C组)及正常氧分压组(D组).CPB中,A、C组PaO2控制在300～500 mm Hg,B、D组PaO2控制在100～250 mm Hg.于CPB前(T1)、CPB15 min(T2)、主动脉开放15 min(T3)、术后24 h(T4)采集动脉血,用小鼠抗人CD55 FITC荧光单克隆抗体直接标记,流式细胞仪检测红细胞CD55活性及数量.结果 A组T2、T3时的红细胞CD55活性明显高于T1时(P<0.05).但红细胞CD55数量差异无统计学意义.B、C、D三组各时点红细胞CD55活性及数量差异无统计学意义.结论 CPB中高氧分压可使紫绀型心脏病患者的红细胞CD55活性明显增强,缺氧红细胞可能存在再氧合损伤;控制氧分压对红细胞免疫功能有一定的保护作用.     

An evaluation of the effects of a standard heparin dose on thrombin inhibition during cardiopulmonary bypass in neonates

We compared the adequacy of heparinization in neonates and older children undergoing cardiopulmonary bypass (CPB) by measuring heparin activity, thrombin formation, and thrombin activity. Ten neonates and 10 older children were administered 400 U/kg of heparin before CPB. Heparin anti-Xa activity, prothrombin fragment 1.2 (F1.2), and fibrinopeptide A (FPA) were measured at baseline, after 30 min on CPB, immediately post-CPB, and 3 and 24 h post-CPB. Heparin anti-Xa activity was significantly decreased during and immediately post-CPB in the neonatal group. F1.2 and FPA levels in neonates were significantly higher at baseline, decreased with the commencement of CPB, and increased to levels higher than those in older children after CPB. Our data show that with standard heparin doses, neonates exhibit less heparin anti-Xa activity during CPB. Higher baseline levels of F1.2 and FPA present in neonates indicate preoperative activation of their coagulation systems as compared with older children. Although F1.2 and FPA levels initially decrease with the commencement of CPB, probably representing hemodilution, the subsequent increase in these markers indicates significantly more thrombin formation and activity during and after CPB. These results raise the concern that 400 U/kg of heparin may not adequately suppress thrombin formation and activity in neonates undergoing CPB.     

体外循环期间纤溶系统的变化规律及其机制的探讨

目的　探讨体外循环 (CPB)心脏直视手术期间纤溶系统的动态变化规律 ,探讨纤溶系统激活的机制。方法　 2 0例心脏直视手术患者 ,分别于麻醉诱导后切皮前、体外循环开始后 8、3 0min、鱼精蛋白中和肝素后 10min、术后 2h采集血标本 ,检测组织型纤溶酶原激活物 (t PA)、纤溶酶原激活物抑制剂 (PAI)、纤溶酶活性 (PLm)、D 二聚体 (D dimer)的动态变化。结果　术中t PA活性与术前相比显著升高 ,术后 2h恢复正常。PAI活性术中术后与术前相比差异无显著性。体外循环期间t PA/PAI比值显著升高 ,术后 2h恢复正常。手术期间D 二聚体含量显著升高 ,术后 2h仍维持较高水平。PLm活性在体外循环期间及中和后显著升高。结论　体外循环期间纤溶系统被明显激活 ,其主要机制是t PA分泌增加 ,t PA、PAI间的平衡失调和纤溶酶原的激活。     

Tissue factor as the main activator of the coagulation system during cardiopulmonary bypass

OBJECTIVE: This study investigates the influence of foreign material and blood aspirated from nonvascular structures on activation of coagulation, hemolysis, and blood loss. METHODS: The series comprises 3 randomized groups (groups C, S, and S+P) of 10 patients undergoing routine coronary artery bypass grafting with cardiopulmonary bypass. In group C, the control group, all aspirated blood was returned into the circulation. In group S suction blood was discarded, whereas group S+P was identical to group S, with surfaces coated with phosphorylcholine. Plasma concentrations of beta-thromboglobulin, thrombin generation, haptoglobin, and free hemoglobin, as well as blood loss, were measured. RESULTS: A steady increase in free plasma hemoglobin, as well as an increased generation of thrombin, was noticed in group C. Moreover, a close correlation (r = 0.916) between the generation of thrombin and its inhibition (thrombin-antithrombin complexes) was observed. Platelets were clearly activated in group C and, to a lesser extent, in group S. In contrast, platelet activation in group S+P was negligible, resulting in a 30% decrease in blood loss (P =.05). CONCLUSIONS: Aspirated blood contaminated by tissue contact is the most important activator of the coagulation system and the principal cause of hemolysis during cardiopulmonary bypass. Contact with a foreign surface is not a main variable in the procoagulant effect of bypass. Mimicking the outer cell membrane structure resulted in decreased platelet activation and decreased blood loss.     

影响体外循环前后儿童心肌地高辛含量的多因素分析

目的　探讨体外循环前后的各种因素对儿童心肌地高辛含量的影响。方法　儿童先天性心脏病室间隔缺损肺高压病人，口服维持剂量地高辛１ 周以上，体外循环前后各取右心耳５０ ｍｇ 测量心肌地高辛含量，将可能影响心肌地高辛含量的各种因素进行多因素的逐步回归分析，其结果结合临床综合考虑，从而探讨影响心肌地高辛含量的诸因素。结果　术前心肌地高辛含量与病人术前肾功能（ＢＵＮ） 、血清总蛋白及术前血球压积、血红蛋白有关；体外循环结束时的心肌地高辛含量与术中的停跳液及预充液量、术前地高辛按体表面积计算的用药剂量、手术结束时的总蛋白、血液ｐＨ 值以及血清钠镁离子浓度有关。结论　影响小儿体外循环前后心肌地高辛含量的因素各有不同；术前主要与肾功能、血球压积及总蛋白有关，而停机时则与术前的用药时间、用药剂量有关外，还与术中影响心肌与地高辛结合的酸碱平衡及钠镁离子浓度及与是否造成心肌脱水因素的机器预充及停跳液量相关，在临床的用药过程中应综合考虑。     

基质金属蛋白酶-9抑制剂巴马司他对心肺转流急性肺损伤的保护作用

目的 研究外源性基质金属蛋白酶-9(MMP-9)抑制剂巴马司他在心肺转流急性肺损伤中的保护作用.方法 30只健康杂种幼犬随机分为对照组、低剂量组和高剂量组.低剂量组术前 连续3 d每天腹腔注射巴马司他10 mg/ks,高剂量组术前连续3 d每天腹腔注射巴马司他30 mg/kg.分别计算术前和术后肺泡-动脉氧分压差(A-aDO_2)和呼吸指数(RI).从手术前开始计时,分别于0、60、120和270 min时采集静脉血样,酶联免疫吸附法测血浆MMP-9浓度,RT-PCR法测定血MMP-9 mRNA表达变化.比色法测定支气管肺泡灌洗液(BALF)髓过氧化物酶活性,明胶酶谱法测定BALF MMP-9活性.计算肺湿/干质量比.光镜和电镜下观察肺组织形态学改变.结果 270 min时高剂 量组血浆MMP-9浓度(17.36±1.18)μg/L,低于对照组的(30.47±2.22)μg/L(P<0.05).高剂量组 术后A-aDO_2和RI较对照组明显改善(P<0.05),高剂量组肺湿/干质量比(2.8±0.5)较对照组(4.7 ±0.6)明显减低(P<0.05),且肺组织的病理改变显著减轻;但三组间血MMP-9 mRNA表达无明显差异(P>0.05).结论 巴马司他通过降低MMP-9的浓度及活性,减轻细胞基底膜的降解,减轻肺 泡白细胞浸润和肺水肿,起到肺保护的作用.     

Effect of perfusion flow rate on tissue oxygenation in newborn piglets during cardiopulmonary bypass

BACKGROUND: Our knowledge of the best perfusion flow rate to use during cardiopulmonary bypass (CPB) in order to maintain tissue oxygenation remains incomplete. The present study examined the effects of perfusion flow rate and patent ductus arteriosus (PDA) during normothermic CPB on oxygenation in several organ tissues of newborn piglets. METHODS: The experiments were performed on 12 newborn piglets: 6 with PDA ligation (PDA-L), and 6 without PDA ligation (PDA-NL). CPB was performed through the chest at 37 degrees C. During CPB, the flow rate was changed at 15-minute intervals, ranging from 100 to 250 ml/kg/min. Tissue oxygenation was measured by quenching of phosphorescence. RESULTS: For the PDA-L group, oxygen in the brain did not change significantly with changes in flow rate. In contrast, for the PDA-NL group, oxygen was dependent upon the flow rate. Statistically significant decreases in cortical oxygen were observed with flow rates below 175 ml/kg/min. Within the myocardium, liver, and intestine, there were no significant differences in the oxygen levels between the PDA-L and PDA-NL groups. In these tissues, the oxygen decreased significantly as the flow rate decreased below 150 ml/kg/min, 125 ml/kg/min, and 175 ml/kg/min, respectively. Oxygen pressure in skeletal muscle was not dependent on either PDA ligation or flow rate. CONCLUSIONS: In newborn piglets undergoing CPB, the presence of a PDA results in reduced tissue oxygenation to the brain but not to other organs. In general, perfusion flow rates of 175 ml/kg/min or greater are required in order to maintain normal oxygenation of all organs except muscle.