Effects of aspirin and desmopressin on platelet reactivity in patients undergoing cardiac surgery with extracorporeal circulation

The effect of desmopressin on platelet function in patients with continued antiplatelet therapy undergoing cardiac surgery is discussed controversially. We assessed platelet reactivity in 86 patients undergoing elective coronary artery bypass grafting (CABG) under extracorporeal circulation. Twenty-nine of these patients were without preoperative antiplatelet therapy (group A), while 57 were treated with acetylsalicylic acid (ASA) 100 mg qd up to the day of surgery. Out of this cohort, 24 patients received no desmopressin perioperatively (group B), whereas 33 patients were treated with desmopressin 0.4 microg/kg after administration of protamine due to increased bleeding tendency (group C). Multiple electrode platelet aggregometry with arachidonic acid as agonist showed a marked decrease of platelet reactivity in patients without antiplatelet therapy immediately after extracorporeal circulation compared to preoperative control (375 ± 227 vs. 749 ± 330 AU*min, p<0.001). Platelet reactivity recovered to preoperative controls in group A at 24 hours after protamine administration (662 ± 295 AU*min). Platelet reactivity in patients on ASA was not decreased further after extracorporeal circulation (group B: 197 ± 126 vs. 251 ± 203 AU*min, p=0.14; group C: 212 ± 100 vs. 245 ± 248 AU*min, p=0.43) and improved significantly within 24 hours. A statistically significant effect of desmopressin, however, could not be determined (group B: 392 ± 223 AU*min; group C: 439 ± 324 AU*min at 24 hours after protamine, p=0.63 for between-subjects contrast). Our data suggest that desmopressin does not affect platelet reactivity in patients on ASA undergoing CABG and is, therefore, not useful in this clinical setting.     

Critical temperature ranges of hypothermia-induced platelet activation: possible implications for cooling patients in cardiac surgery

Cooling of the patient is routinely applied in cardiac surgery to protect organs against ischemia. Hypothermia induces activation of platelets, but the effects of temperatures such as used during cardiac surgery are not well described. To investigate this in an in-vitro study heparinized whole blood was incubated at different temperatures (37 degrees C, 34.5 degrees C, 32 degrees C, 29.5 degrees C, 27 degrees C, 24.5 degrees C, 22 degrees C, 19.5 degrees C and 17 degrees C). The effect of these temperatures on aggregation, P-selectin expression, GP IIb/IIIa activation and platelet microparticle (PMP) formation of unstimulated and ADP-stimulated platelets of 36 subjects was evaluated in flow cytometry. A four-parametric logistic model was fitted to depict the temperature effect on platelet parameters. Lower temperatures increased aggregates, P-selectin expression, and GP IIb/IIIa activation. The number of PMPs decreases with hypothermia. Additional experiments revealed a slight influence of heparin on platelet P-selectin expression but excluded an effect of this anticoagulant on the other evaluated parameters. Threshold temperatures, which mark 5% changes of platelet parameters compared to values at 37 degrees C, were calculated. On ADP-stimulated platelets the thresholds for P-selectin expression and GP IIb/IIa activation are 34.0 degrees C and 36.4 degrees C, respectively, and lie in the temperature range routinely applied in cardiac surgery. Hypothermia-induced platelet activation may develop in most patients undergoing cardiac surgery, possibly resulting in thromboembolic events, coagulation defects, and proinflammatory leukocyte bridging by P-selectin bearing platelets and PMPs. These findings suggest that pharmacological protection of platelets against hypothermia-induced damage may be beneficial during cardiac surgery.     

Reductions in platelet contractile force correlate with duration of cardiopulmonary bypass and blood loss in patients undergoing cardiac surgery

Blood loss secondary to platelet dysfunction is known to be increased when the duration of cardiopulmonary bypass (CPB) is prolonged. The ability to correlate alterations in platelet function with the duration of bypass and early postoperative blood loss, however, has remained elusive. Platelet contractile force, a novel measure of platelet-mediated clot retraction, is known to be reduced following cardiac surgery and blockade of platelet adhesion receptors. The aim of this study was to determine if alterations in platelet contractile force (measured using whole blood) correlated with the duration of CPB and early postoperative blood loss. Thirty patients were entered into a study designed to measure platelet function before, during, and after CPB. Platelet aggregometry and surface expression of CD42b and CD61 were also measured (using whole blood) in a subset of subjects (n=10) to further characterize the intrinsic structural and functional defects induced by CPB. Reductions in platelet contractile force had a significant correlation with duration of CPB (r=0.564; P=0.002) and early blood loss (r=0.545; P=0.003). Although decreases in platelet contractile force and aggregation both correlated with CPB time in the smaller subset of patients tested, only platelet contractile force correlated with decreases in CD42b, CD61 and blood loss. The results of this study suggest that prolongation of CPB is related to increasing degrees of platelet dysfunction and that reductions in platelet contractile force are related to decreases in platelet adhesion receptors and early postoperative blood loss.     

Effects of tranexamic acid, CIS-AMCHA, and 6-aminohexanoic acid on the activation rate of plasminogen by urokinase in the presence of clot

When human plasma was mixed with 50 units of urokinase and clotted with thrombin in the presence of S-2251, the hydrolysis of S-2251 in the clot was higher than that in the plasma. The presence of 10 μM of tranexamic acid resulted in decrease in the activation rate of plasminogen in the clot but not in the plasma. Further increase in its concentration resulted in marked increase in plasminogen activation in both clot and plasma. The addition of 6-aminohexanoic acid or cis-AMCHA showed changes in the rate of plasminogen activation similar to that shown in the presence of tranexamic acid. Fifty μM of tranexamic acid totally inhibited urokinase induced clot lysis, while 1 mM of cis-AMCHA and 6-aminohexanoic acid totally inhibited clot lysis. The presence of 1 mM of these ω-aminoacids remarkably increased the activation of plasminogen by urokinase, but no clot lysis was observed.     

Heparin-protamine complexes and C-reactive protein induce activation of the classical complement pathway: studies in patients undergoing cardiac surgery and in vitro

The administration of protamine to patients undergoing cardiopulmonary bypass (CPB) to neutralize heparin and to reduce the risk of bleeding, induces activation of the classical complement pathway mainly by heparin-protamine complexes. We investigated whether C-reactive protein (CRP) contributes to protamine-induced complement activation. In 24 patients during myocardial revascularization, we measured complement, CRP, and complement-CRP complexes, reflecting CRP-mediated complement activation in vivo. We also incubated plasma from healthy volunteers and patients with heparin and protamine in vitro to study CRP-mediated complement activation. During CPB, CRP levels remained unchanged while C3 activation products increased. C4 activation occurred after protamine administration. CRP-complement complexes increased at the end of CPB and upon protamine administration. Incubation of plasma with heparin and protamine in vitro generated complement-CRP complexes, which was blocked by phosphorylcholine and stimulated by exogenous CRP. C4d-CRP complex formation after protamine administration correlated clinically with the incidence of postoperative arrhythmia. Protamine administration during cardiac surgery induces complement activation which in part is CRP-dependent, and correlates with postoperative arrhythmia.     

Effects of SK-potentiator and fibrinogen on SK-plasminogen complex in the presence of tranexamic acid

The addition of tranexamic acid to the mixture of plasminogen and streptokinase (called SK-activator activity) resulted in decreased extent of hydrolysis of TAMe (tosyl arginine methyl ester). The addition of SK-potentiator to the mixture of SK (streptokinase), plasminogen and tranexamic acid prevented the decrease in SK-activator activity caused by tranexamic acid, thus SK-potentiator counteracting with the effects of tranexamic acid. Fibrinogen potentiated SK-activator activity, but did not prevent the decrease of the activity caused by tranexamic acid. Fibrinogen added to SK and plasminogen prior to tranexamic acid prevented the decrease in SK-activator activity. From these data it is suggested that SK-potentiator and fibrinogen bind with lysine binding sites of plasminogen part of SK-activator, and SK-potentiator binds with SK-plasminogen (or -plasmin) complex faster than fibrinogen.     

Conversion of Glu-plasminogen to plasmin by urokinase in the presence of tranexamic acid

When Glu-plasminogen (Glu-plg) was incubated with urokinase (UK) in the presence of various concentrations of tranexamic acid and S-2251, the hydrolysis of S-2251 increased in the presence of 1 mM of tranexamic acid, but decreased in the presence of more than 10 mM of tranexamic acid. Use of SDS-polyacrylamide gel electrophoresis indicated: 1) Glu-plg was converted to plasmin better in the presence of 1 mM of tranexamic acid, but in the presence of more than 10 mM of tranexamic acid it was less converted. 2) Plg I (of higher molecular weight) was more easily converted than plg II by UK, but binding of tranexamic acid with lysine binding sites of plasminogen caused almost equal rate of activation of plg I and II.     

The effect of long-term, low-dose tranexamic acid treatment on platelet dysfunction and haemoglobin levels in haemodialysis patients

Some previous studies suggest that activation of the fibrinolytic system may induce platelet dysfunction in haemodialysis patients. Accordingly, inhibition of fibrinolysis may improve platelet dysfunction, and speculatively increase haemoglobin levels. We tested this hypothesis. The study group comprised 22 patients (14 male, 8 female, median age 62), who had been on maintenance haemodialysis for more than one year. Patients were treated for three months with low-dose tranexamic acid (TXA), a potent anti-fibrinolytic agent. The dosages of erythropoietin and the haemodialysis procedure were not changed significantly during the study. We primarily followed platelet function (by in vitro closure time test) and haemoglobin values. Patients were divided into those with substantially prolonged (N = 9) and those with slightly delayed or normal (N = 13) in vitro closure time. Treatment with TXA resulted in a significant improvement of platelet function and increased levels of haemoglobin in the first group, and no changes in either platelet function or haemoglobin values in the second group. TXA in the dosage used was biologically active, since a significant decrease in plasminogen and D-dimer were found in both groups. No significant changes in other fibrinolytic parameters or von Willebrand factor were found. No complications in terms of arterial or venous thrombosis were observed. Our pilot study suggests that long-term, low-dose TXA treatment of haemodialysis patients with substantially prolonged in vitro closure time results in a significant improvement of platelet dysfunction and a significant increase in haemoglobin values. These new, promising results merit further investigation in larger studies.     

Effect of tranexamic acid on intraoperative blood loss and transfusion requirements in patients undergoing excision of intracranial meningioma

Surgical excision of meningioma is often complicated by significant blood loss requiring blood transfusion with its attendant risks. Although tranexamic acid is used to reduce perioperative blood loss, its blood conservation effect is uncertain in neurosurgery. Sixty adults undergoing elective craniotomy for meningioma excision were randomized to receive either tranexamic acid or placebo, initiated prior to skin incision. Patients in the tranexamic acid group received intravenous bolus of 20 mg/kg over 20 min followed by an infusion of 1 mg/kg/h till the conclusion of surgery. Intraoperative blood loss, transfusion requirements and estimation of surgical hemostasis using a 5-grade scale were noted. Postoperatively, the extent of tumor excision on CT scan and complications were observed. Demographics, tumor characteristics, amount of fluid infusion, and duration of surgery and anesthesia were comparable between the two groups. The amount of blood loss was significantly less in tranexamic acid group compared to placebo (830 ml vs 1124 ml; p = 0.03). The transfusion requirement was less in tranexamic acid group (p > 0.05). The patients in tranexamic acid group fared better on a 5-grade surgical hemostasis scale with more patients showing good hemostasis (p = 0.007). There were no significant differences between the groups with regards to extent of tumor removal, perioperative complications, hospital stay or neurologic outcome. To conclude, administration of tranexamic acid significantly reduced blood loss in patients undergoing excision of meningioma. Fewer patients in the tranexamic acid group received blood transfusions. Surgical field hemostasis was better achieved in patients who received tranexamic acid.     

血小板激活及血小板参数变化在脑梗死发病机制中的作用

目的研究血小板激活以及血小板参数变化在脑梗死发病机制中的作用。方法采用流式细胞术测定急性脑梗死患者168例和健康对照者40名外周血P选择素(CD62p)、溶酶体蛋白(CD63)的阳性表达率,同时测定血小板计数(PLT)、血小板平均体积(MPV)和血小板最大聚集率(MAR)。并进行比较及相关因素分析。结果(1)脑梗死患者CD62p、CD63及MPV、MAR明显高于健康对照组,并且上述指标急性期均高于恢复期(均P<0·01);(2)全前循环梗死(TACI)亚型的脑梗死患者CD62p、CD63及MPV、MAR显著高于部分前循环梗死(PACI)、后循环梗死(POCI)及腔隙性梗死(LACI)亚型,在PACI及POCI亚型中上述各测定值较LACI亚型显著增高,差异均具有显著性(均P<0·01);而在PACI及POCI亚型之间差异并无显著性(P>0·05);(3)PLT在脑梗死患者急性期、恢复期与健康对照组之间以及牛津郡社区卒中项目(OCSP)各亚型之间差异无显著性(均P>0·05)。(4)CD62p、CD63呈显著正相关(r=0·826,P<0·01),且与MPV及MAR亦呈明显正相关(r=0·703、0·698,均P<0·01);但与PLT之间无相关性(均P>0·05)。结论脑梗死患者血小板的大量激活及其体积和最大聚集率的升高参与了脑梗死的病理过程,监测MPV和MAR较PLT更能反映脑梗死的病情程度,为应用抗血小板聚集药物提供依据。     

Degradation of Glu- and Lys-plasminogen by elastase in the presence or absence of tranexamic acid

Glu-plasminogen (Glu-plg) was degraded by elastase in the presence or absence of tranexamic acid. Glu-plg was degraded faster in the presence of tranexamic acid. Increase in the concentration of tranexamic acid resulted in increase in the appearance of degradation products, reaching a plateau level at 1 mM of tranexamic acid. Fifty percent increase in the concentration of one of degradation products was obtained at 0.22 mM of tranexamic acid, which is similar to a dissociation constant (Kd) of low affinity lysine binding sites (LBS) with tranexamic acid. As to the degradation rate of two isozymes of Glu-plg (Glu-plg I and II), Glu-plg II containing one carbohydrate chain was degraded faster than Glu-plg I containing two carbohydrate chains. Comparison of the degradation rates of Glu-plg and Lys-plg indicated that Lys-plg was degraded faster.     

Effects of fibrinogen and platelet supplementation on clot formation and platelet aggregation in blood samples from cardiac surgery patients

Introduction

Bleeding after cardiac surgery may be caused by surgical factors, impaired haemostasis, or a combination of both. Transfusion of blood products is used to improve haemostasis, but little is known about what combination is optimal. We hypothesized that addition of both fibrinogen and platelets to blood samples from cardiac surgery patients would improve clot formation and platelet aggregation to a greater extent than if the components were added separately.

Materials and Methods

Increasing doses of fibrinogen concentrate (+ 0.5, 1.0, and 1.5 g · l^- 1) and/or platelet concentrate (+ 46, 92, and 138 × 10⁹ platelets l^- 1) were added to postoperative blood samples from 15 cardiac surgery patients. Clot formation was assessed with rotational thromboelastometry and platelet aggregation was assessed with multiple-electrode aggregometry before and after addition of the blood products. The effects of the different additives were compared.

Results and Conclusions

Ex vivo supplementation with fibrinogen or platelet concentrate resulted in significantly shortened clotting time and improved clot strength in a dose-dependent manner. Combination of fibrinogen and platelets further improved the clotting time and strength. Platelet supplementation enhanced platelet aggregation in a dose-dependent manner while fibrinogen had no or reducing effect. Combining fibrinogen and platelets improved platelet aggregation less than the use of platelets alone. In conclusion, combined platelet and fibrinogen supplementation of blood samples from cardiac surgery patients had an additive effect on clot formation compared to the individual components, but it resulted in less platelet aggregation than with platelet supplementation alone. These results may have implications for clinical transfusion protocols.     

Effects of pretreatment with clopidogrel on platelet and coagulation activation in patients undergoing elective coronary stenting

BACKGROUND: Current data suggest that pretreatment with clopidogrel (in addition to aspirin) prior to elective percutaneous coronary intervention (PCI) might be associated with a reduced incidence of subsequent adverse ischemic events. The aim of this placebo-controlled study was to find out whether an extended pretreatment period with clopidogrel before an elective PCI might confer a superior inhibition of the platelet activation and aggregation than clopidogrel given not until PCI. METHODS: Twenty patients with stable angina being already on aspirin were randomly assigned to receive the loading dose of 300 mg clopidogrel, either 24 h before or immediately after stent implantation. At several time points before and after PCI, the activation of both the platelet and the coagulation system was determined by measuring beta-thromboglobulin (beta-TG) and prothrombin fragment f1.2 (f1.2), respectively, in venous blood and in blood emerging from a microvascular injury (shed blood). RESULTS: Pretreatment with clopidogrel before PCI exhibited a slight reduction of beta-TG (from 178 to 139 ng/ml, p=0.085) and of f1.2 (from 0.81 to 0.75 nmol/l, p=0.045) in venous blood. Heparin administration (at the beginning of PCI) resulted in a 65% inhibition of ss-TG (from 10,590 to 2833 ng/ml) and 90% inhibition of f1.2 formation (from 38.7 to 4.2 nmol/l) in shed blood of patients with clopidogrel pretreatment. The extent of inhibition was, however, comparable to that observed in patients without clopidogrel pretreatment (beta-TG: from 8025 to 2812 ng/ml, 76% inhibition, p=0.47; f1.2: from 34.9 to 3.8 nmol/l, 86% inhibition, p=0.80). After PTT normalisation (6 h after PCI), levels of beta-TG and f1.2 both in venous blood and in shed blood did not differ between the two treatment regimens up to 48 h after PCI. CONCLUSION: Pretreatment with clopidogrel did not result in a pronounced inhibition of the platelet and coagulation system activation in patients on aspirin undergoing elective coronary stent implantation.     

Neuropsychological change and S-100 protein release in 130 unselected patients undergoing cardiac surgery.

BACKGROUND AND PURPOSE: S-100 protein promises to be a valuable surrogate end point for cerebral injury. This is of particular interest within the context of cardiac surgery. We sought to explore the relationship between change in neurospychological performance attributable to cardiopulmonary bypass and the release of brain-specific S-100 protein. METHODS: In an observational comparative study in a University Hospital Cardiac Surgical Unit, S-100 protein release during and 5 hours after the onset of cardiopulmonary bypass was compared with change (from preoperative to 6 to 8 weeks postoperative) in neuropsychological tests in 130 patients undergoing the full range of cardiac surgical procedures. RESULTS: Neuropsychological performance usually improved, being significantly so in 10 of 25 parameters. S-100 area under the curve (AUC) protein release correlated with age (r=0.24, P<0.008) and bypass time (r=0.17, P<0.02). S-100 Cmax correlated with bypass times (r=0.29, P<0.0001). Bypass times correlated with memory performance (Rey R5; r=-0.21, P<0.03). Less S-100 protein release was associated with better neuropsychological performance, as indexed by significant correlations with the Rey Auditory Verbal Learning memory test, descending Critical Flicker Fusion thresholds, and the Hospital Anxiety and Depression rating scales, typically around r=0.2. Multiple regression models showed that neuropsychological tests accounted for 23% of the variance associated with S-100 AUC release, after partialing out the effects of age and bypass time. CONCLUSIONS: The correlation between S-100 protein release and neuropsychological function supports the belief that it is a measure of brain injury, which may be useful in future studies of mechanisms and prevention.     

乌司他丁对心肺转流心内直视术患者认知功能的影响

目的 研究乌司他丁对体外循环(CPB)下心内直视手术患者认知功能的影响.方法 择期CPB下二尖瓣置换术患者24例,随机分为乌司他丁组(U组)和对照组(C组),每组12例.U组给予100万U乌司他丁于体外循环预充液中,C组用生理盐水代替.术前及术后24h行神经功能(MMSE)评分,并于术前(T1)、CPB开始后30min(T2)、CPB结束后1h (T3)、术后6h(T4)及24h(T5)测定血清S-100β蛋白浓度.结果 术前与术后24h MMSE评分差值U组低于C组(P<0.05).C组T2～5血清S-100β浓度高于T1,U组T3～4高于T1,U组T3～5血清S-100β浓度升高幅度低于C组(P<0.05或P<0.01).结论 乌司他丁在一定程度上减轻CPB后认知功能损伤,有一定的脑保护作用.     

The utility of the intracarotid Amytal procedure in determining hemispheric speech lateralization in pediatric epilepsy patients undergoing surgery

The usefulness of the intracarotid Amytal (amobarbital) procedure (also called the Wada procedure) in identifying hemispheric language dominance in pediatric patients has not been independently confirmed with intraoperative language mapping techniques. Currently, data are extrapolated from adult studies. To better establish the usefulness of the intracarotid Amytal procedure in identifying hemispheric language dominance in pediatric patients, we reviewed the records of 77 consecutive pediatric patients who underwent sodium amobarbital testing. Among these 77 subjects, 34 underwent intraoperative language mapping, the results of which all completely confirmed the Amytal results. It was also shown that among these pediatric epileptic patients who underwent Amytal testing, there existed not only a strong correlation between left-handedness and atypical speech lateralization (right, bilateral hemisphere), but also between right-sided hemiparesis (i.e., early left-hemisphere injury) and atypical speech.