Ton Lisman

Coagulation disorders and hemostasis in liver disease: Pathophysiology and critical assessment of current management

Normal coagulation has classically been conceptualized as a Y‐shaped pathway, with distinct “intrinsic” and “extrinsic” components initiated by factor XII or factor VIIa/tissue factor, respectively, and converging in a “common” pathway at the level of the FXa/FVa (prothrombinase) complex. Until recently, the lack of an established alternative concept of hemostasis has meant that most physicians view the “cascade” as a model of physiology. This view has been reinforced by the fact that screening coagulation tests (APTT, prothrombin time – INR) are often used as though they are generally predictive of clinical bleeding. The shortcomings of this older model of normal coagulation are nowhere more apparent than in its clinical application to the complex coagulation disorders of acute and chronic liver disease. In this condition, the clotting cascade is heavily influenced by numerous currents and counter‐currents resulting in a mixture of pro‐ and anticoagulant forces that are themselves further subject to change with altered physiological stress such as super‐imposed infection or renal failure. This report represents a summary of a recent multidisciplinary symposium held in Charlottesville, VA. We present an overview of the coagulation system in liver disease with emphasis on the limitations of the current clinical paradigm and the need for a critical re‐evaluation of the current tenets governing clinical practice. With the realization that there is often limited or conflicting data, we have attempted to represent diverse opinion and experience from the perspectives of both hepatology and hematology beginning with a brief update on the physiology of normal coagulation. (HEPATOLOGY 2006;44:1039–1046.)

Elevated levels of von Willebrand Factor in cirrhosis support platelet adhesion despite reduced functional capacity.

Cirrhosis of the liver is frequently accompanied by complex alterations in the hemostatic system, resulting in a bleeding tendency. Although many hemostatic changes in liver disease promote bleeding, compensatory mechanisms also are found, including high levels of the platelet adhesive protein von Willebrand Factor (VWF). However, conflicting reports on the functional properties of VWF in cirrhosis have appeared in literature. We have measured a panel of VWF parameters in plasma from patients with cirrhosis of varying severity and causes. Furthermore, we assessed the contribution of VWF to platelet adhesion, by measuring the ability of plasma from patients with cirrhosis to support adhesion of normal or patient platelets under flow conditions. VWF antigen levels were strongly increased in patients with cirrhosis. In contrast, the relative collagen binding activity, as well as the relative ristocetin cofactor activity, was significantly lower in patients as compared with controls, indicating loss of function. Accordingly, patients had a reduced fraction of high‐molecular‐weight VWF multimers. Both strongly elevated and reduced activity and antigen levels of the VWF cleaving protease ADAMTS13 were found in individual patients. Adhesion of either normal or patient platelets to a collagen surface was substantially increased when these platelets were resuspended in plasma of patients with cirrhosis, as compared with control plasma. In conclusion, highly elevated levels of VWF in patients with cirrhosis contribute to the induction of primary hemostasis despite reduced functional properties of the molecule. This phenomenon might compensate for defects in platelet number and function in patients with cirrhosis. (HEPATOLOGY 2006;44:53–61.)

Rebalanced hemostasis in patients with liver disease: evidence and clinical consequences

Patients with liver disease frequently acquire a complex disorder of hemostasis secondary to their disease. Routine laboratory tests such as the prothrombin time and the platelet count are frequently abnormal and point to a hypocoagulable state. With more sophisticated laboratory tests it has been shown that patients with liver disease may be in hemostatic balance as a result of concomitant changes in both pro- and antihemostatic pathways. Clinically, this rebalanced hemostatic system is reflected by the large proportion of patients with liver disease who can undergo major surgery without any requirement for blood product transfusion. However, the hemostatic balance in the patient with liver disease is relatively unstable as evidenced by the occurrence of both bleeding and thrombotic complications in a significant proportion of patients. Although it is still common practice to prophylactically correct hemostatic abnormalities in patients with liver disease before invasive procedures by administration of blood products guided by the prothrombin time and platelet count, we believe that this policy is not evidence-based. In this article, we will provide arguments against the traditional concept that patients with liver failure have a hemostasis-related bleeding tendency. Consequences of these new insights for hemostatic management will be discussed.

Hemostasis and thrombosis in patients with liver disease: The ups and downs

Patients with chronic or acute liver failure frequently show profound abnormalities in their hemostatic system. Whereas routine laboratory tests of hemostasis suggest these hemostatic alterations result in a bleeding diathesis, accumulating evidence from both clinical and laboratory studies suggest that the situation is more complex. The average patient with liver failure may be in hemostatic balance despite prolonged routine coagulation tests, since both pro- and antihemostatic factors are affected, the latter of which are not well reflected in routine coagulation testing. However, this balance may easily tip towards a hypo- or hypercoagulable situation. Indeed, patients with liver disease may encounter both hemostasis-related bleeding episodes as well as thrombotic events. During the 3rd International Symposium on Coagulopathy and Liver disease, held in Groningen, The Netherlands (18-19 September 2009), a multidisciplinary panel of experts critically reviewed the current data concerning pathophysiology and clinical consequences of hemostatic disorders in patients with liver disease. Highlights of this symposium are summarized in this review.

Venous thrombosis risk associated with plasma hypofibrinolysis is explained by elevated plasma levels of TAFI and PAI-1

Elevated plasma clot lysis time (CLT) increases risk of venous and arterial thrombosis. It is unclear which fibrinolytic factors contribute to thrombosis risk. In 743 healthy control subjects we investigated determinants of CLT. By comparison with 770 thrombosis patients, we assessed plasma levels of fibrinolytic proteins as risk factors for a first thrombosis. Plasminogen activator inhibitor-1 (PAI-1) levels were the main determinants of CLT, followed by plasminogen, thrombin-activatable fibrinolysis inhibitor (TAFI), prothrombin, and alpha2-antiplasmin. Fibrinogen, factor VII, X, and XI contributed minimally. These proteins explained 77% of variation in CLT. Levels of the fibrinolytic factors were associated with thrombosis risk (odds ratios, highest quartile vs lowest, adjusted for age, sex, and body mass index: 1.6 for plasminogen, 1.2 for alpha2-antiplasmin, 1.6 for TAFI, 1.6 for PAI-1, and 1.8 for tissue plasminogen activator [t-PA]). Adjusting for acute-phase proteins attenuated the risk associated with elevated plasminogen levels. The risk associated with increased t-PA nearly disappeared after adjusting for acute-phase proteins and endothelial activation. TAFI and PAI-1 remained associated with thrombosis after extensive adjustment. In conclusion, CLT reflects levels of all fibrinolytic factors except t-PA. Plasminogen, TAFI, PAI-1, and t-PA are associated with venous thrombosis. However, plasminogen and t-PA levels may reflect underlying risk factors.

Collagens are functional, high affinity ligands for the inhibitory immune receptor LAIR-1

Collagens are the most abundant proteins in the human body, important in maintenance of tissue structure and hemostasis. Here we report that collagens are high affinity ligands for the broadly expressed inhibitory leukocyte-associated immunoglobulin-like receptor-1 (LAIR-1). The interaction is dependent on the conserved Gly-Pro-Hyp collagen repeats. Antibody cross-linking of LAIR-1 is known to inhibit immune cell function in vitro. We now show that collagens are functional ligands for LAIR-1 and directly inhibit immune cell activation in vitro. Thus far, all documented ligands for immune inhibitory receptors are membrane molecules, implying a regulatory role in cell–cell interaction. Our data reveal a novel mechanism of peripheral immune regulation by inhibitory immune receptors binding to extracellular matrix collagens.

Ex vivo Normothermic Machine Perfusion and Viability Testing of Discarded Human Donor Livers

In contrast to traditional static cold preservation of donor livers, normothermic machine perfusion may reduce preservation injury, improve graft viability and potentially allows ex vivo assessment of graft viability before transplantation. We have studied the feasibility of normothermic machine perfusion in four discarded human donor livers. Normothermic machine perfusion consisted of pressure and temperature controlled pulsatile perfusion of the hepatic artery and continuous portal perfusion for 6 h. Two hollow fiber membrane oxygenators provided oxygenation of the perfusion fluid. Biochemical markers in the perfusion fluid reflected minimal hepatic injury and improving function. Lactate levels decreased to normal values, reflecting active metabolism by the liver (mean lactate 10.0 ± 2.3 mmol/L at 30 min to 2.3 ± 1.2 mmol/L at 6 h). Bile production was observed throughout the 6 h perfusion period (mean rate 8.16 ± 0.65 g/h after the first hour). Histological examination before and after 6 h of perfusion showed well‐preserved liver morphology without signs of additional hepatocellular ischemia, biliary injury or sinusoidal damage. In conclusion, this study shows that normothermic machine perfusion of human donor livers is technically feasible. It allows assessment of graft viability before transplantation, which opens new avenues for organ selection, therapeutic interventions and preconditioning.

Normal to increased thrombin generation in patients undergoing liver transplantation despite prolonged conventional coagulation tests

BACKGROUND & AIMS Patients with liver disease often show substantial changes in their hemostatic system, which may aggravate further during liver transplantation. Recently, thrombin generation in patients with stable disease was shown to be indistinguishable from controls provided thrombomodulin, the natural activator of the anticoagulant protein C system, was added to the plasma. These results indicated that the hemostatic balance is preserved in patients with liver disease, despite conventional coagulation tests suggest otherwise. METHODS Here we examined thrombin generation profiles in serial plasma samples taken from ten consecutive patients undergoing liver transplantation. RESULTS At all time points, the endogenous thrombin potential (ETP) was slightly lower compared to healthy volunteers, despite substantially prolonged PT and APTT values. However, when thrombin generation was tested in the presence of thrombomodulin, the ETP was equal to or even higher than that in healthy subjects. In fact, thrombin generation was hardly affected by thrombomodulin, while thrombin generation in healthy subjects decreased profoundly upon the addition of thrombomodulin. In patients undergoing liver transplantation, efficient thrombin generation in the presence of thrombomodulin may be explained by decreased levels of protein C, S, and antithrombin, and by elevated levels of FVIII. CONCLUSIONS Thrombin generation in patients undergoing liver transplantation is equal or even superior to thrombin generation in healthy volunteers when tested in the presence of exogenous thrombomodulin. These results support the recently advocated restrictive use of plasma during liver transplantation and warrants further study of the prophylactic use of anticoagulants to reduce thromboembolic complications after transplantation.

Platelet Transfusion During Liver Transplantation Is Associated with Increased Postoperative Mortality Due to Acute Lung Injury

BACKGROUND: Platelet transfusions have been identified as an independent risk factor for survival after orthotopic liver transplantation (OLT). In this study, we analyzed the specific causes of mortality and graft loss in relation to platelet transfusions during OLT. METHODS: In a series of 449 consecutive adult patients undergoing a first OLT, the causes of patient death and graft failure were studied in patients who did or did not receive perioperative platelet transfusions. RESULTS: Patient and graft survival were significantly reduced in patients who received platelet transfusions, compared with those who did not (74% vs 92%, and 69% vs 85%, respectively at 1 yr; P < 0.001). Lower survival rates in patients who received platelets were attributed to a significantly higher rate of early mortality because of acute lung injury (4.4% vs 0.4%; P = 0.004). There were no significant differences in other causes of mortality between the two groups. The main cause of graft loss in patients receiving platelets was patient death with a functioning graft. CONCLUSIONS: These findings suggest that platelet transfusions are an important risk factor for mortality after OLT. The current study extends previous observations by identifying acute lung injury as the main determinant of increased mortality. The higher rate of graft loss in patients receiving platelets is related to the higher overall mortality rate and does not result from specific adverse effects of transfused platelets on the grafted liver.

Hemostatic Alterations in Liver Disease: A Review on Pathophysiology, Clinical Consequences, and Treatment

In most patients with acute or chronic liver failure, extensive changes in all pathways contributing to hemostasis are found. These hemostatic alterations concern both pro- and antihemostatic pathways, and therefore the net result of the hemostatic dysbalance is unclear. Although it is generally believed that patients with liver disease have a hemostasis-related bleeding tendency, this concept is challenged in recent literature. Although the bleeding problems in patients with liver disease are obvious, the clinically most relevant bleeding episodes, i.e., bleeding from ruptured varices or ulcers, are due to vascular abnormalities and portal hypertension, and not to an abnormal hemostatic system. Moreover, patients with liver disease sometimes experience thrombosis of the portal vein or hepatic artery, which is in part attributed to hypercoagulation. In addition, a substantial part of the patients with liver disease undergoing liver transplantation can nowadays undergo this major surgical procedure, which involves significant hemostatic challenges, without transfusion of blood products. Therefore, the recent debate on the presence of a major hemostatic defect in patients with liver disease seems justified. This paper will review the hemostatic changes that occur in acute and chronic liver failure, and will review hemostasis testing and reversal of coagulopathy in these patients.