Role of the donor liver in the origin of platelet disorders and hyperfibrinolysis in liver transplantation

Disseminated Intravascular Coagulation as a Risk Factor for Clinical Outcome After Liver Transplantation in Pediatric Patients With Kasai Portoenterostomy Failure

BACKGROUND

Disseminated intravascular coagulation (DIC) is a serious complication in critically ill pediatric patients. This study aimed to evaluate the association between pretransplant DIC and perioperative clinical outcomes of liver transplantation (LT) in pediatric patients with Kasai portoenterostomy (KPE) failure.

METHODS

We enrolled pediatric patients who received LT after KPE failure between January 2005 and April 2021. We retrospectively reviewed the electronic medical records of included patients and evaluated the presence of DIC using the International Society on Thrombosis and Hemostasis (ISTH) criteria and association with perioperative clinical outcome.

RESULTS

The study included 106 patients. Their median age and body weight at the time of pediatric intensive care unit (PICU) admission were 28.7 months and 9.25 kg, respectively. Of these patients, 23 had undergone pretransplant DIC (22%). Patients with pretransplant DIC required significantly more blood transfusions during operation. They had significantly higher serum lactate levels, pediatric end-stage liver disease scores, pediatric risk for mortality III (PRISM III) scores, longer durations of mechanical ventilator support, and longer PICU stays (all P < .05).

CONCLUSIONS

The presence of pretransplant DIC in pediatric patients requiring LT after KPE failure was associated with poor clinical outcomes, which required more intensive and meticulous supportive management in the perioperative period of LT. DIC would be a promising prognostic factor in these patients.

Viscoelastic tests in liver disease: where do we stand now?

Hemostasis is a complex physiological process based on the balance between pro-coagulant and anticoagulant systems to avoid pathological bleeding or thrombosis. The changes in standard coagulation tests in liver disease were assumed to reflect an acquired bleeding disorder, and cirrhotic patients were considered naturally anticoagulated. In the light of the new evidence, the theory of rebalanced hemostasis replaced the old concept. According to this model, the hemostatic alteration leads to a unique balance between pro-coagulant, anticoagulant, and fibrinolytic systems. But the balance is fragile and may prone to bleeding or thrombosis depending on various risk factors. The standard coagulation tests [INR (international normalized ratio), platelet count and fibrinogen] only explore parts of the hemostasis, not offering an entire image of the process. Rotational thromboelastometry (ROTEM) and thromboelastography (TEG) are both point of care viscoelastic tests (VET) that provide real-time and dynamic information about the entire hemostasis process, including clot initiation (thrombin generation), clot kinetics, clot strength, and clot stability (lysis). Despite prolonged PT/INR (international normalized ratio of prothrombin time) and low platelet counts, VET is within the normal range in many patients with both acute and chronic liver disease. However, bleeding remains the dominant clinical issue in patients with liver diseases, especially when invasive interventions are required. VET has been shown to asses more appropriately the risk of bleeding than conventional laboratory tests, leading to decrial use of blood products transfusion. Inappropriate clotting is common but often subtle and may be challenging to predict even with the help of VET. Although VET has shown its benefit, more studies are needed to establish cut-off values for TEG and ROTEM in these populations and standardization of transfusion guidelines before invasive interventions in cirrhotic patients/orthotopic liver transplantation.

Normothermic Ex Vivo Liver Perfusion Prevents Intrahepatic Platelet Sequestration After Liver Transplantation

BACKGROUND

The detrimental role of platelets in sinusoidal endothelial cell (SEC) injury during liver transplantation (LT) has been previously addressed after static cold storage (SCS), however, it is currently unknown after normothermic ex vivo liver perfusion (NEVLP).

METHODS

Pig LT was performed with livers from heart-beating donors or donation after circulatory death (DCD) donors subjected to SCS or NEVLP (n = 5/group).

RESULTS

All pigs except for 1 (DCD-SCS-group) survived 4 days. The heart-beating donor- and DCD-NEVLP-groups showed significantly lower aspartate transaminase-levels compared with the SCS-groups 3 hours post-LT (P = 0.006), on postoperative day (POD) 2 (P = 0.005), POD3 (P = 0.007), and on POD4 (P = 0.012). Post-LT total platelet count recovered faster in the NEVLP than in the SCS-groups at 12 hours (P = 0.023) and 24 hours (P = 0.0038). Intrahepatic sequestration of platelets was significantly higher in the SCS-groups 3 hours postreperfusion and correlated with severity of SEC injury. In both SCS-groups, levels of tumor growth factor-β were higher 3 hours post-LT, on POD1 and on POD3. Moreover, platelet factor 4 levels and platelet-derived extracellular vesicles were increased in the SCS-groups. Hyaluronic acid levels were significantly higher in the SCS-groups, indicating a higher grade of endothelial cell dysfunction. Platelet inhibition achieved by pretreatment with clopidogrel (n = 3) partly reversed the detrimental effects on SEC injury and therefore provided further evidence of the important role of platelets in ischemia/reperfusion injury and SEC injury.

CONCLUSIONS

Normothermic perfusion of liver grafts before transplantation effectively reduced platelet aggregation and SEC injury, which translated into an improved posttransplant organ function.

Sirolimus-Induced Delayed Severe Thrombocytopenia After Liver Transplantation: A Case Report

OBJECTIVE

Thrombocytopenia is a common condition in patients undergoing liver transplantation (LT). Thrombocytopenia is prevalent in early postoperative phase, and it gradually improves after several weeks. Delayed severe thrombocytopenia occurring after the initial recovery of platelets is rare. We report a case of a patient with delayed severe thrombocytopenia 59 weeks after LT.

CASE PRESENTATION

Our patient was a 61-year-old man who presented to our institution 59 weeks after undergoing LT. He presented for removal of a bile duct stent that was inserted 3 months prior. Tacrolimus replaced sirolimus for immunosuppression during the seventh week after transplantation due to sirolimus-induced nephrotoxicity. On admission, the patient's vital signs were normal and his physical examination was unremarkable. Laboratory parameters demonstrated that the platelet (PLT) level was significantly decreased to 18 × 10⁹/L. PLTs reached a nadir of 3 × 10⁹/L even after utilization of interleukin-11, thrombopoietin, and low-dose prednisone. Although rare, sirolimus toxicity was suspected. Therefore, sirolimus was gradually replaced by cyclosporin A in combination with low-dose prednisone. Subsequently, a normal PLT level was gradually recovered. This study was approved by the ethical committee of the First Hospital of Jilin University and was performed in accordance with the ethical standards of the Helsinki Congress and Istanbul Declaration.

CONCLUSIONS

Recurrent delayed severe thrombocytopenia is rare after LT. Sirolimus toxicity might be a reason for its occurrence if other possible factors are excluded. After diagnosis, sirolimus therapy should be discontinued and patients should be treated with an alternative immunosuppressive regimen.

Platelet and liver regeneration after liver surgery

The success of liver surgery, including resection and transplantation, is largely dependent on the ability of the liver to regenerate. Despite substantial improvement in surgical techniques and perioperative care, one of the main concerns is post-hepatectomy liver failure and early allograft dysfunction, both of which are associated with impaired liver regeneration. Recent studies have demonstrated the positive role of platelets in promoting liver regeneration and protecting hepatocytes; however, the underlying mechanisms responsible for these effects are not fully understood. In this review, we updated the accumulated evidence of the role of platelets in promoting liver regeneration, with a focus on liver resection and liver transplantation. The goal of these studies was to support the clinical implementation of platelet agents, such as thrombopoietin receptor agonists, to augment liver regeneration after liver surgery. This "platelet therapy" may become a treatment choice for post-hepatectomy liver failure and early allograft dysfunction.

The Coagulation Profile of End-Stage Liver Disease and Considerations for Intraoperative Management

The coagulopathy of end-stage liver disease results from a complex derangement in both anticoagulant and procoagulant processes. With even minor insults, cirrhotic patients experience either inappropriate bleeding or clotting, or even both simultaneously. The various phases of liver transplantation along with fluid and blood product administration may contribute to additional disturbances in coagulation. Thus, anesthetic management of patients undergoing liver transplantation to improve hemostasis and avoid inappropriate thrombosis in the perioperative environment can be challenging. To add to this challenge, traditional laboratory tests of coagulation are difficult to interpret in patients with end-stage liver disease. Viscoelastic coagulation tests such as thromboelastography (Haemonetics Corporation, Braintree, MA) and rotational thromboelastometry (TEM International, Munich, Germany) have helped to reduce transfusion of allogeneic blood products, especially fresh frozen plasma, but have also lead to the increased use of fibrinogen-containing products. In general, advancements in surgical techniques and anesthetic management have led to significant reduction in blood transfusion requirements during liver transplantation. Targeted transfusion protocols and pharmacologic prevention of fibrinolysis may further aid in the management of the complex coagulopathy of end-stage liver disease.

Relation between dynamic changes of platelet counts and 30-day mortality in severely burned patients

Thrombocytopenia is a common event in severely burned patients and associated with adverse outcome. The underlying relationship between the dynamic changes of platelet counts and mortality has not been well defined. We performed a 6-year retrospective chart of adult patients with a burn index of 50 or greater admitted to two burn centers and collected data on patient demographics, laboratory results, and patient outcomes. The mean daily increase in the platelet count (∆PC/∆t) from day 3 to day 10 was calculated, and 30-day mortality was determined. For the study, 141 survivors and 65 nonsurvivors were enrolled. The sequential changes in PCs presented a biphasic pattern after admission, with a slump to the nadir during the first 3 days and a subsequent recovery. With respect to 30-day mortality, compared with the AUC of APACHE-Ⅱ score (0.841), no significant difference was noted between ΔPC/ΔT and APACHE-Ⅱ score (p = 0.0648). The ΔPC/ΔT associated with the best discrimination between survivors and nonsurvivors was 20.57 × 10⁹/L due to the cutoff with optimal Youden index (0.453). By multiple logistic regression, ΔPC/ΔT ＜ 20.57 × 10⁹/L was one of the prognostic predictors of 30-day mortality. Furthermore, Kaplan-Meier estimates of hospital survival according to the size of ΔPC/ΔT revealed that a blunted increase with ΔPC/ΔT ＜ 20.57 × 10⁹/L was associated with increased 30-day mortality. A blunted daily increase in PCs, especially ΔPC/ΔT < 20.57 × 10⁹/L, is associated with increased 30-day mortality, which provides prognostic information for mortality risk assessment in severely burned patients.

Thrombocytopenia in chronic liver disease

Thrombocytopenia is a common haematological disorder in patients with chronic liver disease. It is multifactorial and severity of liver disease is the most influential factor. As a result of the increased risk of bleeding, thrombocytopenia may impact upon medical procedures, such as surgery or liver biopsy. The pathophysiology of thrombocytopenia in chronic liver disease has long been associated with the hypothesis of hypersplenism, where portal hypertension causes pooling and sequestration of all corpuscular elements of the blood, predominantly thrombocytes, in the enlarged and congested spleen. Other mechanisms of importance include bone marrow suppression by toxic substances, such as alcohol or viral infection, and immunological removal of platelets from the circulation. However, insufficient platelet recovery after relief of portal hypertension by shunt procedures or minor and transient recovery after splenic artery embolization have caused many to question the importance and relative contribution of this mechanism to thrombocytopenia. The discovery of the cytokine thrombopoietin has led to the elucidation of a central mechanism. Thrombopoietin is predominantly produced by the liver and is reduced when liver cell mass is severely damaged. This leads to reduced thrombopoiesis in the bone marrow and consequently to thrombocytopenia in the peripheral blood of patients with advanced-stage liver disease. Restoration of adequate thrombopoietin production post-liver transplantation leads to prompt restoration of platelet production. A number of new treatments that substitute thrombopoietin activity are available or in development.

Immature platelet fraction values predict recovery of platelet counts following liver transplantation

BACKGROUND

Thrombocytopenia after orthotopic liver transplantation (OLT) is a well-recognized and prevalent early postoperative complication. In the current study, we assessed the clinical utility of the immature platelet fraction (expressed as a percent of total platelets, IPF %) to predict platelet count recovery following OLT.

METHODS

We analyzed the changes in peripheral platelet counts, IPF values, and liver function before OLT, and 21 days after transplantation in 30 patients with liver cirrhosis. All patients were followed up for at least six months.

RESULTS

The nadir in the peripheral platelet counts most commonly occurred on the 5th day after post-transplant. Platelets counts gradually rose again to exceed pre-transplant levels by the 3rd to 4th day after the IPF % reached its peak.

CONCLUSION

The IPF % increased prior to the elevation of platelet counts in patients with OLT suggesting that the IPF % may reflect production of platelets. These findings suggest IPF% could be useful as a predictor of platelet recovery in patients with OLT.

Development of a Hyperactive Primary Hemostatic System During Off-Pump Lung Transplantation Resulting From an Unbalance Between von Willebrand Factor and Its Cleaving Protease ADAMTS13

An unbalance between the platelet-adhesive protein von Willebrand factor (VWF) and its cleaving protease ADAMTS13 is a risk factor for thrombosis. Here, we assessed levels and functionality of VWF and ADAMTS13 in patients undergoing off-pump lung transplantation. We analyzed plasma of 10 patients and distinguished lung transplantation-specific effects from those generally accompanying open-chest surgeries by comparing results with 11 patients undergoing off-pump coronary bypass graft (CABG) surgery. Forty healthy volunteers were included for reference values. VWF antigen levels as well as the VWF ristocetin cofactor activity/VWF antigen ratio increased during lung transplantation and after CABG surgery. An increase in VWF propeptide levels was paralleled by a decrease in ADAMTS13 activity. This was more pronounced during lung transplantation. Similarly, the capacity of plasma to support platelet aggregation under shear flow conditions in vitro was more increased during lung transplantation. The proportion of high molecular weight VWF multimers was elevated in both groups without evidence for ultra-large VWF. VWF's collagen binding activity remained unchanged. In conclusion, a hyperactive primary hemostatic system develops during lung transplantation resulting both from a pronounced (functional) increase of the VWF molecule and decrease of ADAMTS13. This may increase the risk of platelet thrombosis within the allograft.

Thrombocytopenia, Platelet Transfusion, and Outcome Following Liver Transplantation

Thrombocytopenia affects patients undergoing liver transplantation. Intraoperative platelet transfusion has been shown to independently influence survival after liver transplantation at 1 and 5 years. We examined the impact of thrombocytopenia and intraoperative platelet transfusion on short-term graft and overall survival after orthotopic liver transplantation (OLT). A total of 399 patients undergoing first OLT were studied. Graft and overall survival in patients with different degrees of thrombocytopenia and with or without intraoperative platelet transfusion were described. The degree of thrombocytopenia prior to OLT did not affect graft or overall survival after transplant. However, graft survival in patients receiving platelets was significantly reduced at 1 year (P= .023) but not at 90 days (P= .093). Overall survival was significantly reduced at both 90 days (P= .040) and 1 year (P= .037) in patients receiving platelets. We conclude that a consistently lower graft and overall survival were observed in patients receiving intraoperative platelet transfusion.

No increase in blood transfusions during liver transplantation since the withdrawal of aprotinin

The aims of this study were to determine whether the withdrawal of aprotinin (APRO) led to an increased bleeding risk in patients undergoing orthotopic liver transplantation (OLT). A retrospective analysis compared consecutive patients undergoing OLT and treated with aprotinin (APRO group; n = 100) with a group in which aprotinin was not used (no-APRO group; n = 100). Propensity score matching was then performed for each group to identify 2 matched cohorts. Patients were matched by their primary diagnoses and Model for End-Stage Liver Disease scores. This resulted in 2 matched cohorts with 55 patients in each group. None of the patients in the APRO group had significant fibrinolysis. In the no-APRO group, 23.6% of the patients developed fibrinolysis (P < 0.003). Tranexamic acid was used in 61.5% of the patients (n = 8) in the no-APRO group in whom lysis was present, and this resolved the fibrinolysis in all but 1 of these patients. There were no differences in red blood cell, fresh frozen plasma, platelet concentrate, or cryoprecipitate transfusions between the 2 groups. In conclusion, we have shown a significant increase in the prevalence of fibrinolysis during OLT since the withdrawal of APRO. However, there has been no increase in transfusion requirements.

Hepatic sinusoidal endothelium avidly binds platelets in an integrin-dependent manner, leading to platelet and endothelial activation and leukocyte recruitment

Platelets have recently been shown to drive liver injury in murine models of viral hepatitis and promote liver regeneration through the release of serotonin. Despite their emerging role in inflammatory liver disease, little is known about the mechanisms by which platelets bind to the hepatic vasculature. Therefore, we referenced public expression data to determine the profile of potential adhesive receptors expressed by hepatic endothelium. We then used a combination of tissue-binding and flow-based endothelial-binding adhesion assays to show that resting platelets bind to human hepatic sinusoidal endothelial cells and that the magnitude of adhesion is greatly enhanced by thrombin-induced platelet activation. Adhesion was mediated by the integrins Gp1b, αIIbβIII, and αvβ3, as well as immobilized fibrinogen. Platelet binding to hepatic endothelial cells resulted in NF-κB activation and increased chemokine secretion. The functional relevance of platelet binding was confirmed by experiments that showed markedly increased binding of neutrophils and lymphocytes to hepatic endothelial cells under shear conditions replicating those found in the hepatic sinusoid, which was in part dependent on P-selectin expression. Thus the ability of platelets to activate endothelium and promote leukocyte adhesion may reflect an additional mechanism through which they promote liver injury.

Thrombocytopenia after pig-to-baboon liver xenotransplantation: where do platelets go?

BACKGROUND

In baboons with orthotopic pig liver xenografts, profound thrombocytopenia was observed within 1 h after reperfusion. Assessment of the fate of platelets may shed light on the underlying mechanisms leading to thrombocytopenia and may allow preventive therapies to be introduced.

METHODS

Platelet-white blood cell (WBC) aggregation was studied in two baboons that received orthotopic liver xenografts from α1,3-galactosyltransferase gene-knockout pigs transgenic for human CD46 (GTKO/CD46). Percentages of CD42a-positive platelet aggregates with WBC-subtypes were determined by flow cytometry, and absolute numbers (per mm(3) ) were calculated. Platelet aggregates in the liver xenografts were identified by immunofluorescence and electron microscopy. Mean platelet volume (MPV) was determined before and after transplantation.

RESULTS

After pig liver reperfusion, profound thrombocytopenia was associated with aggregation of platelets with WBC-subtypes. Increasing aggregation of platelets with WBC-subtypes was detected throughout the post-transplant period until the recipient was euthanized. Significant negative correlation was found between platelet counts in the blood and aggregation of platelets with monocytes (P < 0.01) and neutrophils (P < 0.01), but not with lymphocytes. MPV remained within the normal range. Two hours after reperfusion, platelet and fibrin deposition were already detected in the liver xenografts by immunofluorescence and by electron microscopy.

CONCLUSIONS

Following liver xenotransplantation, the early disappearance of platelets from the circulation was at least in part due to their aggregation with circulating WBC, which may augment their deposition in the liver xenograft and native lungs. Prevention of platelet aggregation with monocytes and neutrophils is likely beneficial in reducing their subsequent sequestration in the liver xenograft and native organs.

Factors predicting persistent thrombocytopenia after living donor liver transplantation in pediatric patients

Thrombocytopenia is common after LT for pediatric end-stage liver diseases. Seventy-six pediatric patients (≤15 yr old) who underwent LDLT were evaluated for the incidence and predictive factors of post-transplant thrombocytopenia (PLT <100, 000/mm(3) ). The prevalence of thrombocytopenia at two wk and at 12 months post-transplant was 22/76 (28.9%) and 11/62 (17.7%), respectively. Thrombocytopenia at two wk after LDLT was significantly associated with age at transplant, preoperative PLT, GRWR, acute rejection, and CMV infection in univariate analysis. Moreover, preoperative PLT, GRWR, and acute rejection had a strong correlation in multivariate analysis. Thrombocytopenia at 12 months after LDLT was associated only with preoperative PLT. We also demonstrated that vascular complications caused thrombocytopenia and that successful treatment recovered the PLT. These results showed that, in addition to considering the preoperative PLT, post-operative monitoring of platelets is very helpful for the early detection of adverse events related to the graft liver in pediatric liver transplant patients.

No evidence for systemic platelet activation during or after orthotopic liver transplantation

Platelet function is thought to deteriorate during liver transplantation as a result of platelet activation and proteolysis of platelet receptors by plasmin following reperfusion. However, this hypothesis has never been formally tested. Twenty patients undergoing a first or second liver transplant were included in the study. Blood samples were taken at standardized time points during transplantation and up to 10 days after transplantation. Platelet activation was assessed by detection of the activation markers P-selectin and activated integrin alphaIIbbeta3 with flow cytometry. Proteolytic cleavage of platelet receptors was assessed by flow cytometry measurement of the constitutively expressed platelet receptors glycoprotein Ibalpha and integrin alphaIIbbeta3. In addition, using enzyme-linked immunosorbent assay techniques, we measured plasma levels of platelet activation products beta-thromboglobulin and platelet factor 4 and plasma levels of cleaved fragments of glycoproteins Ibalpha and V. Flow cytometry analyses provided no evidence of substantial platelet activation during transplantation. In fact, the expression of activated integrin alphaIIbbeta3 decreased postoperatively; this indicated that platelets were in a slightly activated state prior to surgery. Plasma levels of beta-thromboglobulin and platelet factor 4 also substantially decreased after transplantation. In addition, no changes were observed in the constitutively expressed platelet receptors or in the plasma levels of platelet receptor fragments, and this indicated a lack of substantial receptor proteolysis. In conclusion, no evidence was found for significant activation of circulating blood platelets or the proteolysis of key platelet receptors during liver transplantation. These findings suggest that the platelet functional capacity does not decrease during liver transplantation. Liver Transpl 15:956-962, 2009. (c) 2009 AASLD.

Development of a severe von Willebrand factor/ADAMTS13 dysbalance during orthotopic liver transplantation

Patients with liver disease show profound changes in their hemostatic system, which may further change during liver transplantation. We previously demonstrated that highly elevated levels of the platelet adhesive protein von Willebrand factor (VWF) in patients with cirrhosis lead to an increased VWF-dependent platelet deposition under flow as compared to healthy controls. In this study we examined VWF parameters during the course of liver transplantation. We collected serial plasma samples from 20 patients undergoing liver transplantation in which we determined plasma levels of VWF and the VWF-cleaving protease ADAMTS13. Furthermore, we performed functional tests of VWF-dependent platelet adhesion. We found persistently elevated levels of VWF during and after liver transplantation. The capacity of VWF to interact with platelets normalized during the course of transplantation, and flow-mediated VWF-dependent platelet adhesion remained at levels far exceeding those observed in healthy individuals during and after transplantation. Plasma levels of ADAMTS13 dropped during transplantation, and in four patients levels below 10% of normal were observed after reperfusion. We observed the development of a hyperreactive primary hemostatic system, as evidenced by high levels of fully functional VWF and a temporary ADAMTS13 deficiency, during liver transplantation, and speculate that these changes contribute to postoperative thrombotic complications.

Soluble p-selectin and the risk of primary graft dysfunction after lung transplantation

BACKGROUND

Platelet activation with subsequent neutrophilic adherence to the vasculature initiates ischemia-reperfusion injury. We hypothesized that higher plasma P-selectin levels reflecting platelet activation would therefore be associated with primary graft dysfunction (PGD) after lung transplantation.

METHODS

In a prospective, multicenter cohort study of 376 patients who had undergone lung transplantation between 2002 and 2007, we measured soluble P-selectin levels before lung transplantation and at 6 and 24 h after lung reperfusion in 20 patients with grade III PGD (Pao(2)/fraction of inspired oxygen, < 200 mm Hg [with alveolar infiltrates seen on chest radiographs]) at 72 h after transplantation and 61 control subjects without PGD.

RESULTS

Higher postoperative soluble P-selectin levels were associated with an increased risk of PGD at 72 h after transplantation (odds ratio [OR] per 1 natural log increase in soluble P-selectin at 6 h after lung allograft reperfusion, 3.5; 95% confidence interval [CI], 1.01 to 11.8; p = 0.048) and at 24 h after lung allograft reperfusion (OR, 4.8; 95% CI, 1.4 to 16.1; p = 0.01). Higher preoperative mean pulmonary artery pressure and the use of cardiopulmonary bypass were also associated with an increased risk of PGD.

CONCLUSION

Higher postoperative soluble P-selectin levels were associated with an increased risk of PGD at 72 h following lung transplantation.

The impact of intraoperative transfusion of platelets and red blood cells on survival after liver transplantation

BACKGROUND

Intraoperative transfusion of red blood cells (RBC) is associated with adverse outcome after orthotopic liver transplantation (OLT). Although experimental studies have shown that platelets contribute to reperfusion injury of the liver, the influence of allogeneic platelet transfusion on outcome has not been studied in detail. In this study, we evaluate the impact of various blood products on outcome after OLT.

METHODS

Twenty-nine variables, including blood product transfusions, were studied in relation to outcome in 433 adult patients undergoing a first OLT between 1989 and 2004. Data were analyzed using uni- and multivariate stepwise Cox's proportional hazards analyses, as well as propensity score-adjusted analyses for platelet transfusion to control for selection bias in the use of blood products.

RESULTS

The proportion of patients receiving transfusion of any blood component decreased from 100% in the period 1989-1996 to 74% in the period 1997-2004. In uni- and multivariate analyses, the indication for transplantation, transfusion of platelets and RBC were highly dominant in predicting 1-yr patient survival. These risk factors were independent from well-accepted indices of disease, such as the Model for End-Stage Liver Disease score and Karnofsky score. The effect on 1-yr survival was dose-related with a hazard ratio of 1.377 per unit of platelets (P = 0.01) and 1.057 per unit of RBC (P = 0.001). The negative impact of platelet transfusion on survival was confirmed by propensity-adjusted analysis.

CONCLUSION

This retrospective study indicates that, in addition to RBC, platelet transfusions are an independent risk factor for survival after OLT. These findings have important implications for transfusion practice in liver transplant recipients.

Platelets in liver transplantation: friend or foe?

Apart from the well-known role of blood platelets in hemostasis, there is emerging evidence that platelets have various nonhemostatic properties that play a critical role in inflammation, angiogenesis, tissue repair and regeneration, and ischemia/reperfusion (I/R) injury. All these processes may be involved in the (patho)physiological alterations occurring in patients undergoing liver transplantation. Experimental and clinical research points toward a dualistic role of platelets in patients undergoing liver transplantation, resulting in both beneficial and detrimental effects. Although a low platelet count is generally considered a risk factor for perioperative bleeding, recent studies have indicated that platelet function in patients with cirrhosis may not be as abnormal as previously assumed. Platelet transfusions are frequently considered in liver transplant recipients to correct low platelet counts and to prevent bleeding; however, evidence-based transfusion thresholds are lacking, and the other detrimental and nonhemostatic properties of platelets are generally not weighed in this respect. First, platelets have been shown to contribute to I/R injury of the liver graft via induction of sinusoidal endothelial cell apoptosis. Second, platelet transfusion has been identified as an independent risk factor for reduced survival via mechanisms that are not completely understood yet. On the other hand, recent studies indicate that platelets are critically involved in restoration after liver injury and in liver regeneration via serotonin-mediated mechanisms. These findings make platelets both friend and foe in liver transplantation. The scientific challenge will be to further dissect the mechanisms and clinical relevance of these contrasting roles of platelets in liver transplantation.

Acute thrombocytopenia after liver transplant: role of platelet activation, thrombopoietin deficiency and response to high dose intravenous IgG treatment

BACKGROUND/AIMS

Thrombocytopenia is common after liver transplantation due to platelet sequestration secondary to hypersplenism. The aim of this study was to further investigate the causes of this condition, as well as the response of thrombocytopenia to high dose intravenous immunoglobulins.

METHODS

We retrospectively studied 73 patients who underwent liver transplantation. Out of these 73 patients, 27 had severe thrombocytopenia and were treated with high dose intravenous immunoglobulin. Additionally, we retrospectively studied 8 patients undergoing liver transplantation.

RESULTS

Our data suggest that splenomegaly is not the only factor responsible for thrombocytopenia after liver transplantion and two additional phenomena, namely, reduced platelet production due to reduced thrombopoietin levels and sustained platelets activation take part in the pathogenesis of this condition. The infusion of high dose immunoglobulins induced a safe, prompt, complete and persistent resolution of severe thrombocytopenia in more than 70% of patients.

CONCLUSIONS

Based on these findings, treatment with high dose intravenous immunoglobulins should be considered in the management of severe thrombocytopenia after liver transplant, although additional randomized trials are warranted.

Efficacy and safety of antifibrinolytic drugs in liver transplantation: a systematic review and meta-analysis

Although several randomized controlled trials (RCTs) have shown the efficacy of antifibrinolytic drugs in liver transplantation, their use remains debated due to concern for thromboembolic complications. None of the reported RCTs has shown a higher incidence of these complications in treated patients; however, none of the individual studies has been large enough to elucidate this issue completely. We therefore performed a systematic review and meta-analysis of efficacy and safety endpoints in all published controlled clinical trials on the use of antifibrinolytic drugs in liver transplantation. Studies were included if antifibrinolytic drugs (epsilon-aminocaproic acid, tranexamic acid (TA) or aprotinin) were compared with each other or with controls/placebo. Intraoperative red blood cell and fresh frozen plasma requirements, the perioperative incidence of hepatic artery thrombosis, venous thromboembolic events and mortality were analyzed. We identified 23 studies with a total of 1407 patients which met the inclusion criteria. Aprotinin and TA both reduced transfusion requirements compared with controls. No increased risk for hepatic artery thrombosis, venous thromboembolic events or perioperative mortality was observed for any of the investigated drugs. This systematic review and meta-analysis does not provide evidence for an increased risk of thromboembolic events associated with antifibrinolytic drugs in liver transplantation.

Plasma ADAMTS13 activity may predict early adverse events in living donor liver transplantation: observations in 3 cases

A disintegrin-like and metalloproteinase with thrombospondin type-1 motifs 13 (ADAMTS13) is a metalloproteinase that specifically cleaves the multimeric von Willebrand factor (VWF). Deficiency of ADAMTS13 increases the unusually large VWF multimers (UL-VWFM), which leads to platelet clumping and/or thrombus formation, resulting in microcirculatory disturbance. We serially determined the activity of plasma ADAMTS13, together with VWF antigen (VWF:Ag) and UL-VWFM, in association with the development of early graft dysfunction in 3 liver transplant recipients and 4 patients with major hepatectomy as controls. In case 1, ADAMTS13 activity decreased markedly from 108% to less than 3% with concomitant thrombocytopenia on posttransplantation day 7, when acute rejection occurred. Simultaneously, UL-VWFM were detected. During the second episode of rejection, VWF:Ag increased to 368% with the appearance of UL-VWFM, while ADAMTS13 activity was as low as 18%, indicating an imbalance between a large amount of UL-VWFM and low activity of ADAMTS13. Administration of fresh frozen plasma (FFP) together with treatment for acute rejection resulted in an improvement of ADAMTS13 activity and disappearance of the UL-VWFM. In case 2, ADAMTS13 activity promptly decreased to 9% with thrombocytopenia on day 1, when ischemia-reperfusion injury occurred. Subsequently, the ADAMTS13 activity increased steadily without appearance of UL-VWFM, and the patient recovered uneventfully. ADAMTS13 activity decreased to 15% immediately after transplantation in case 3 as well. In contrast, ADAMTS13 activity never decreased below 20% in 4 patients with major hepatectomy as controls. In conclusion, these results indicate that the kinetics of ADAMTS13 and UL-VWFM could be good indicators of adverse events after liver transplantation. Our findings not only suggest a novel mechanism for thrombocytopenia, but also provide a useful tool for diagnosis of graft dysfunction in the early stage after transplantation.

Measuring platelet aggregation to estimate small intestinal ischemia-reperfusion injury

BACKGROUND

The success of intestinal transplantation is affected by the extreme susceptibility of the small bowel to ischemia-reperfusion (I/R) injury. Currently, there is no quick, convenient method to estimate the extent of small bowel I/R injury. Although histological evaluation is reliable and accurate, it takes too long to allow favorable intervention in I/R injury. I/R causes the production of arachidonic acid products, oxygen free radicals, cytokines, and nitric oxide, which affect platelet function.

OBJECTIVE

This study determined whether measuring platelet aggregation is useful for evaluating small bowel I/R injury.

METHODS

Eighteen mongrel dogs were divided into three groups. In group A both the superior mesenteric artery (SMA) and vein (SMV) were occluded for 120 min. In group B the SMA was occluded for 60 min. Group C underwent a sham operation. Platelet aggregation was measured using a whole blood aggregometer (WBA analyzer), which readily handles small samples. Histological examination was performed. The correlation between platelet aggregation and histology was analyzed.

RESULTS

Platelet aggregation was similar in all groups before reperfusion. After reperfusion, platelet aggregation was significantly lower in group A than in groups B and C (P < 0.05), and mucosal damage was most severe in group A (P < 0.05). After 1 and 3 h of reperfusion, there was a significant negative correlation between platelet aggregation and histological damage.

CONCLUSIONS

Measuring platelet aggregation is rapid, easy, and useful for evaluating small bowel I/R injury.

Platelet P-selectin and GPIIb/IIIa expression after liver transplantation and resection

Platelet dysfunction contributes to haemostatic defects, possibly leading to bleeding complications. We hypothesised that liver transplantation and liver resection, together with portal clamping time, might be a potential stimulus for platelet activation. Therefore, we determined the expression of platelet GPIIb/IIIa and P-selectin, representing important platelet activation markers, and the thrombopoietin (TPO) serum level after transplantation and resection. Twenty patients [ten that had undergone orthotopic liver transplantation (OLT), ten with liver resection (LRX)] were included in the study. From sequential venous blood samples, surface expression of GPIIb/IIIa and P-selectin was quantified by flow cytometry, and TPO serum levels were determined by ELISA. Baseline GPIIb/IIIa receptor expression on circulating platelets was significantly reduced in the OLT group compared to the LRX group and healthy volunteers. GPIIb/IIIa expression after activation with TRAP-6 increased significantly ( P<0.001) in the LRX group but not in the OLT group. P-selectin expression after TRAP-6 stimulation increased significantly ( P<0.001) in the LRX group, being comparable to that in healthy volunteers, whereas only a very low increase in the OLT group was found. In the OLT group, TPO serum levels were in the lower normal range and rose above the upper limit of normal values 24 h after reperfusion. These data indicate that neither liver transplantation nor liver resection influences GPIIb/IIIa and P-selectin expression on circulating platelets. There was a lack of expression in cirrhotic patients and unimpaired baseline expression and functional reserve in non-cirrhotic liver-resection patients. After liver transplantation, increasing serum TPO levels, which indicated a recovering graft function, resulted in rising peripheral platelet counts.

Hypersplenism

Cytopenias in liver disease are a common finding. In the past they have mostly been attributed to pooling and/or destruction of blood cells in the enlarged spleen, leading to the term 'hypersplenism'. With recent advances in the understanding of the physiology of blood formation, in particular with the discovery of several haematopoietic growth factors, new insight into the pathophysiology of blood cell derangements in liver disease has been obtained. Recombinant haematopoietic growth factors present new opportunities for support of the haematopoietic system, which is required because of toxic antiviral therapies or surgical interventions in these patients.

Blunted rise in platelet count in critically ill patients is associated with worse outcome

OBJECTIVE

To test the hypothesis that a low rate of change of platelet counts (PCs) after admission to the intensive care unit (ICU) is associated with mortality. Low PCs are known to be associated with disease severity in critically ill patients, but the relevance of time-dependent changes of PCs has not been investigated.

DESIGN

Retrospective study.

SETTING

A 12-bed surgical ICU of a university hospital.

PATIENTS

All adult patients admitted to the ICU for at least 4 days during a 7-yr period.

INTERVENTIONS

At admission, Acute Physiology and Chronic Health Evaluation scores were calculated. PCs and leukocyte counts were analyzed from admission to day 10. The daily rise of the PCs (deltaPC/deltat from day 2 to day 10 was calculated. Rates for 30-day mortality as well as hospital mortality were determined.

MEASUREMENTS AND MAIN RESULTS

A total of 1,415 admissions were studied. Median PCs (interquartile range) initially decreased and subsequently increased, with a higher PC in 1,203 survivors than in 212 nonsurvivors from day 2 onward (302 [range,181-438] x 10(3)/mm3/day vs. 129 [range, 62-228] x 10(3)/mm3 at day 10; p < 0.001). After stratification of patients per type of surgery, within each group PC was also higher in survivors. Mean deltaPC/deltat was more than five times higher in survivors compared with nonsurvivors: 30 +/- 46 x 10(3)/mm3/day vs. 6 +/- 28 x 10(3)/mm3/day (p < 0.001). The area under the receiving operating characteristic curve of deltaPC/deltat for 30-day survival was 0.743 compared with 0.728 for the Acute Physiology and Chronic Health Evaluation. Leukocyte counts showed marginal differences between nonsurvivors and survivors.

CONCLUSION

A blunted or absent rise in PCs in critically ill patients is associated with increased mortality. deltaPC/deltat is a readily available and simple parameter to improve assessment of critically ill patients.

Thrombopoietin induces rapid resolution of thrombocytopenia after orthotopic liver transplantation through increased platelet production

Thrombopoietin (TPO) deficiency has been proposed as an important etiologic factor for thrombocytopenia in advanced-stage liver disease. To clarify the contributions of platelet production, platelet consumption, coagulation activation, and splenic sequestration to thrombocytopenia in liver disease, we studied TPO serum levels and markers of platelet production, platelet activation, and coagulation activation before and 14 days after orthotopic liver transplantation (OLT) in 18 patients with advanced liver cirrhosis. Thrombocytopenia before transplantation occurred with low-normal serum levels of TPO, normal levels of platelet and coagulation activation markers, and no increase in bone marrow production of platelets. TPO serum levels increased significantly on the first day after OLT, preceding the increase of reticulated platelets by 3 days and peripheral platelets by 5 days. Normalization of the peripheral platelet count occurred in most patients within 14 days of OLT, irrespective of the change in spleen size assessed by computed tomography volumetry. Normalization of platelet counts was not hampered by a certain degree of platelet activation observed during the steepest increase in the peripheral platelet count. Bone marrow production of platelets increased significantly within 2 weeks of transplantation. Low TPO serum levels with low platelet counts and without platelet consumption suggests low TPO production in end-stage liver disease. The rapid increase in TPO serum levels after transplantation induces an increase in the bone marrow production of platelets. Decreased TPO production in the cirrhotic liver is an important etiologic factor for thrombocytopenia in liver disease that is rapidly reversed by transplantation.

Thrombocytopenia in liver transplant recipients: predictors, impact on fungal infections, and role of endogenous thrombopoietin

BACKGROUND

Thrombocytopenia is a frequent and potentially serious complication in liver transplant recipients. The role of endogenous thrombopoietin level in posttransplant thrombocytopenia, has not been fully defined in liver transplant recipients. Additionally, there is accumulating evidence to suggest that platelets play a important role in antimicrobial host defense.

METHODS

There were 50 consecutive liver transplant recipients studied. Variables predictive of thrombocytopenia, its impact on infectious morbidity and outcome, and serial thrombopoietin (TPO) serum concentration were assessed.

RESULTS

The median pretransplant platelet count was 67 x 10(3)/cmm. After the liver transplantation, the median nadir platelet count was 33 x 10(3)/cmm and was reached a mean of 6 days after the transplant. A lower pretransplant platelet count (r= +.068, P=.0001), lower serum albumin before the transplants (r=+0.39, P=.014), longer operation time (r=0.27, P=.05), higher intraoperative packed red cells (r=0.28, P=.049) and fresh frozen plasma transfusions (r=0.42, P=.004), higher bilirubin at Day 7 (r=-.386, P=.005), and higher serum creatinine at Day 7 after the transplants (r=-.031, P=.025) correlated significantly with a lower nadir in platelets after the transplant. Nadir in platelet count was significantly lower in nonsurvivors compared with survivors (16 vs. 36 x 10(3)/cmm, P=.0001). Forty-three percent (9 of 21) of the patients with nadir platelet counts of < or =30 x 10(3)/cmm had a major infection within 30 days of the transplant compared with 17% (5 of 29) with nadir platelet counts > 30 x 10(3)/cmm (P=.04). Fungal infections occurred in 14% of the patients with nadir platelet counts of < or =30 x 10(3)/cmm versus 0% in those with nadir platelet counts of > 30 x 10(3)/cmm (P=.06); all patients with fungal infections had nadir platelet counts of < or =30 x 10(3)/cmm before fungal infection. Nadir in platelet count preceded the first major infection by a median of 7 days. Pretransplant TPO level did not differ between survivors (mean 103 pg/ml) or nonsurvivors (mean 144 pg/ml). After the transplantation, TPO levels increased in both groups. TPO level peaked at Day 7 and subsequently declined in survivors. Nonsurvivors had persistent thrombocytopenia despite a progressive rise in TPO level; TPO level was significantly higher at Day 7 (P=.02), Day 9 (P=.0019), and Day 14 (P=.04) in nonsurvivors compared with survivors.

CONCLUSION

Persistent thrombocytopenia portended a poor outcome in liver transplant recipients and was not related to low TPO levels. Thrombocytopenia preceded infections and identified a subgroup of liver transplant patients susceptible to early major infections; its precise role in fungal infections warrants validation in larger studies.

Platelets induce sinusoidal endothelial cell apoptosis upon reperfusion of the cold ischemic rat liver

BACKGROUND & AIMS

Sinusoidal endothelial cell (SEC) apoptosis is a central feature of reperfusion injury in liver transplantation. Platelet sequestration occurs after transplantation with possible deleterious effects. We tested the hypothesis that platelets mediate SEC apoptosis.

METHODS

Livers were perfused after 24 hours of cold preservation in University of Wisconsin solution in an isolated perfused rat liver model. The perfusate contained isolated syngeneic red blood cells and purified platelets. Effects of inhibiting platelet adhesion on SEC apoptosis was tested using sialyl Lewis-X oligosaccharide (sLe(x)), a natural ligand of selectin adhesion molecules. Reperfusion injury was assessed by established markers of injury. Apoptosis was determined by TUNEL and electron microscopy.

RESULTS

A third of the circulating platelets was rapidly sequestered in the liver after reperfusion. This was associated with increased graft injury. Single platelets were adherent to sinusoidal lining without morphological or dynamic evidence of impairment of microcirculation. TUNEL staining revealed a 6-fold increase in the number of apoptotic SECs at 1 hour of reperfusion. No hepatocyte death or evidence of necrosis was detected up to 3 hours of reperfusion. Addition of sLe(x) inhibited adhesion and significantly reduced SEC apoptosis.

CONCLUSIONS

Platelets cause SEC apoptosis upon reperfusion of liver grafts. Prevention of adhesion is protective.

Functional, life-threatening disorders and splenectomy following liver transplantation

Splenectomy (SPL) in cirrhotic patients undergoing liver transplantation (LTx) may resolve specific problems related to the procedure itself, in case of functional and life-threatening clinical situations often occurring as a result of liver cirrhosis and portal hypertension.

METHOD

A single-center experience of ten splenectomies in a series of 180 consecutive adult liver transplant patients over a period of 6 yr is reported. The mean patient age was 46.8 +/- 9.5 yr (range 25 57 yr). Indications for SPL were post-operative massive ascitic fluid loss (n = 3), severe thrombocytopenia (n = 3), acute intra-abdominal hemorrhage (n = 2), infarction of the spleen (n = 1), and multiple splenic artery aneurysms (n = 1).

RESULTS

Extreme ascites production due to functional graft congestion disappeared post-SPL, with an improvement of the hepatic and renal functions. SPL was also effective in cases of thrombocytopenia persistence post-LTx, leading to an increase in the platelet count after about 1 wk. Bleeding episodes related to left-sided portal hypertension or trauma were also resolved. The rejection rate during hospitalization was 0%, and no other episodes were recorded in the course of the long-term follow-up. However, sepsis with a fatal outcome occurred in 4 patients, i.e. between 2 and 3 wk post-SPL in three cases and 1 yr after the procedure as a result of pneumococcal infection in the last case. Fatal traumatic cranial injury occurred 3 yr post-LTx in another case. Five patients (50%) are still alive and asymptomatic after a median follow-up period of 36 months.

CONCLUSION

The lowering of the portal flow appears to resolve unexplained post-operative ascitic fluid loss as a result of functional graft congestion following LTx. However, because of the enhanced risk of SPL-related sepsis, a partial splenic embolization (PSE) or a spleno-renal shunt could be used as an alternative procedure because it allows us to preserve the immunological function of the spleen. SPL is indicated in case of post-transplant bleeding due to left-sided portal hypertension and trauma, spleen infarction, and to enable prevention of hemorrhage in liver transplant patients with multiple splenic artery aneurysms. Severe and persistent thrombocytopenia could be treated with PSE. Because the occurrence of fatal sepsis post-SPL is a major complication in LTx, functional disorders, such as ascites and thrombocytopenia, should be treated with a more conservative approach.

Thrombocytopenia after liver transplantation

BACKGROUND

Thrombocytopenia after orthotopic liver transplantation (OLT) is a well recognized and prevalent early postoperative complication. The etiology, as well as the effect of this phenomenon on transplant outcome, however, are vague. The aims of this study are to identify factors contributing to thrombocytopenia and to ascertain whether there is any correlation with early rejection and ultimate survival.

METHODS

This study examines 541 OLTs (541 grafts in 494 patients) that were transplanted at the University of Miami during the 3-year period from June 1994 to September 1997. The patients with severe postoperative thrombocytopenia (nadir platelet count [PLT] < 20,000/mm3), as well as the whole group of patients, were analyzed. The preoperative PLT, intra-operative platelet transfusion requirements, cross-match, recipient and donor cytomegalovirus (CMV) status, infusion of donor bone marrow cells (DBMC), occurrence of early rejection episodes (in the first posttransplant month), and re-transplantation were factors examined for any association with thrombocytopenia. Total bilirubin (TB) and direct bilirubin (dB), hematocrit, white blood cell count (WBC), aspartate aminotransferase and alanine aminotransferase, determined on the day that platelets reached a nadir (nadir day), were also analyzed.

RESULTS

In 90.9% of the cases, there was a 56.5%+/-23.5% fall in platelets in the immediate posttransplant period (first 2 weeks), but the mean PLT exceeded preoperative levels during the 3rd and 4th postoperative weeks. The nadir of the drop in the PLT most commonly occurred on posttransplant day 4. For preoperative PLT, platelet transfusions during the operation, re-transplantation, early rejection, cross-match, and recipient CMV status, there was significant statistical correlation with any degree of postoperative thrombocytopenia. Four of these factors, preoperative PLT, intra-operative platelet transfusions, re-transplantation, and early rejection, were found to be independently associated with thrombocytopenia in general. None of them was found to be independently correlated with severe thrombocytopenia. A statistically significant correlation between bilirubin and WBC on the nadir day and the degree of thrombocytopenia was observed. No correlation was found between infusion of DBMC or donor CMV serology and thrombocytopenia. Both the nadir PLT and the percentage of the platelet fall were independent predictive factors (p<0.01 and 0.005, respectively) of patient and graft survival.

CONCLUSIONS

Thrombocytopenia in the immediate posttransplant period is correlated with low preoperative PLT, massive platelet transfusions, and re-transplantation. These factors reflect a poor preoperative condition. There is also a correlation with allograft dysfunction, rejection, and poorer patient and graft survival. A rise in the mean PLT after the 2nd postoperative week reflects proper graft function.

Megakaryocytes and platelets in alpha-granule disorders

This chapter summarizes research data contributing to current understanding of disorders affecting alpha-granules of megakaryocytes and platelets. Diagnostic features of the gray platelet syndrome are well defined. Combined evidence suggests a defect, specific to the megakaryocyte cell lineage, causing a cytoskeletal abnormality and defective targeting of endogenously synthesized proteins to the alpha-granule. The abnormalities linked by signal transduction pathways. von Willebrand disease and afibrinogenaemia are disorders which highlight the functional importance of platelet storage pools of von Willebrand factor and fibrinogen, essential ligands in the process of adhesion and aggregation. The abnormality in the factor V Quebec disorder leads to a degradation of most proteins contained within the alpha-granule. The familial platelet disorder Paris-Trousseau thrombocytopenia is the only alpha-granule disorder associated with a cytogenetic abnormality, and it presents a useful model for exploring the genetic influence on regulation of thrombopoiesis. Study of these syndromes has elucidated aspects of the physiology of normal megakaryocyte maturation and platelet formation, including storage organelle biosynthesis.