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

Authors


  • This study was presented as an oral presentation at the 18th Annual International Congress of the International Liver Transplantation Society (May 16-19, 2012).

  • The authors have no grants, financial support, or conflicts of interest to report.

Abstract

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. Liver Transpl 20:584-590, 2014. © 2014 AASLD.

Orthotopic liver transplantation (OLT) for end-stage liver disease can be associated with large amounts of bleeding and blood component transfusions. Portal hypertension, platelet dysfunction, and coagulopathy mean that patients undergoing OLT are at increased risk for bleeding. End-stage liver disease is associated with increased fibrinolytic activity, and this can be exacerbated during OLT, particularly during the anhepatic and early postreperfusion periods, and lead to excess bleeding.[1] Since the late 1980s, aprotinin (APRO), a serine protease an inhibitor of plasmin and, at higher doses, kallikrein, have been used at many institutions to reduce the incidence of bleeding caused by fibrinolysis during OLT.[2] The first multicenter, randomized study by Porte et al.[3] showed that the intraoperative use of APRO in patients undergoing OLT significantly reduced blood transfusion requirements, and other groups have reported similar findings.[4]

The 2006 publication of a large multicenter analysis demonstrating a doubling of the risk of renal failure and a significantly increased risk of major adverse cardiac events and stroke in patients who received APRO for complex cardiac surgery raised major questions about the safety of the drug.[5] In 2008, Blood Conservation Using Antifibrinolytics in a Randomized Trial[6] showed a strong and consistent negative mortality trend associated with APRO in comparison with other lysine analogues, and the study was terminated early because of this increased mortality. This resulted in the product license for this drug being withdrawn in many countries and the cessation of use.

The abrupt withdrawal of APRO from clinical use led to the concern that this could lead to an increased risk of bleeding and increased transfusion requirements. This seemed to be confirmed by a study of more than 100 patients who had received prophylactic APRO and a more recent cohort of 39 patients who had no prophylactic antifibrinolytic therapy; the study demonstrated increased red blood cell transfusion requirements for the no-APRO group.[7] Previous studies have shown that tranexamic acid is comparable to APRO in terms of reducing blood loss[8, 9] with negligible changes in clinical and operative outcomes. A systematic review and meta-analysis of the safety and efficacy of antifibrinolytic drugs in liver transplantation did not provide any evidence of an increased risk of thromboembolic events associated with these drugs.[10] However, none of these studies were sufficiently powered to conclusively answer the question. The possibility of adverse thrombotic effects associated with the use of APRO in liver surgery has been known for some time,[11, 12] and other potential complications such as renal injury are also concerns, although a large, retrospective, observational study of more than 1000 liver transplant patients showed an association only with early renal dysfunction and no long-term morbidity.[13] There is a growing sense that as transfusion requirements for liver transplantation continue to fall and the number of patients undergoing the procedure without any red blood cell transfusions at all increases, the risk-benefit balance of antifibrinolytic therapy in liver transplantation is changing, and at many institutions, there is a move away from routine prophylactic use to more select prophylaxis or treatment only.

PATIENTS AND METHODS

The routine use of APRO was stopped at our institution in 2007. Consecutive patients treated with APRO before 2007 (APRO group; n = 100) were directly compared with a post-2008 group in which APRO was not used (no-APRO group; n = 100). Patients before 2008 were excluded if APRO had not been used or there were incomplete data for the analysis. Patients from a crossover period of 1 year were not included because there was sporadic use of APRO during this period.

During the first time period (05/19/2004 to 12/06/2007), 188 liver transplants were performed. During the second time period (01/10/2009 to 12/26/2010), 121 transplants were performed. Propensity score matching was performed for each group to identify 2 matched cohorts. Patients were matched by primary diagnoses and Model for End-Stage Liver Disease (MELD) scores. This resulted in 2 matched cohorts with 55 patients in each group; the groups were then analyzed.

Before the analysis of the data, advice was sought from the local ethics committee, which advised that formal institutional approval was not required because these were anonymized data routinely collected in the liver transplant database and because all patients had consented a priori to data collection for research purposes when they had consented to liver transplantation.

At our institution, intraoperative thromboelastography (TEG; Haemonetics, Braintree, MA) is performed by dedicated, trained staff throughout the procedure according to a standard protocol; in addition, blood component transfusions are recorded by the stage of the procedure. Cell saver blood conservation is used during all liver transplants. The transfusion protocols were the same for both groups of patients. The algorithm for blood transfusions is based on TEG and point-of-care hemoglobin and platelet counts. A transfusion trigger of 80 g/L is used for red blood cell transfusions. Blood products (fresh frozen plasma, platelet concentrates, and cryoprecipitates) are administered only in the presence of diffuse bleeding and abnormal TEG findings or during massive, uncontrollable hemorrhaging. A prolonged reaction time (R-time) is treated with fresh frozen plasma (or a prothrombin complex concentrate), and a reduced maximum amplitude is treated with either cryoprecipitates (or fibrinogen concentrates) or platelet concentrates (according to the cause of the reduced clot strength). The anesthetic and surgical teams were largely unchanged over the period, and the intraoperative management remained similar.

APRO was administered according to the standard cardiac regimen of 2,000,000 KIU,[14] which was followed by an infusion of 500,000 KIU per hour. Patients with hypercoagulable TEG, cholestatic liver disease, or a previous history of thrombotic complications were not given prophylactic APRO unless the baseline TEG result was obviously hypocoagulable.

Tranexamic acid was the antifibrinolytic used during the second time period. The protocol was to administer it only in the presence of fibrinolysis according to TEG analysis and/or microvascular ooze; however, the decision to treat fibrinolysis was left to the discretion of the physician. This was influenced by the presence of diffuse bleeding, the disease process, the severity of the fibrinolysis, and the stage of the operation (fibrinolysis commencing before reperfusion rarely is corrected spontaneously). Tranexamic acid was administered as a 1- to 2-g bolus; this depended on the patient's weight.

Information was gathered from the hospital liver transplant database and case note reviews. Blood product usage by the stage of the procedure was recorded, and TEG data were reviewed. The presence of fibrinolysis [clot lysis index (CLI) at 30 minutes] was reviewed in all heparinase samples. Fibrinolysis was graded as none (CLI < 15%), mild (CLI = 15%-30%), moderate (CLI = 30.1%-60%), or severe (CLI > 60%). The timing, usage, and doses of alternative antifibrinolytics (tranexamic acid) were correlated with TEG findings and the stage of surgery. Wilcoxon matched pairs were used for the nonparametric transfusion data analysis of the 2 groups. Fisher's exact 2-tailed test (2 × 2) was used to compare the presence of lysis in the 2 groups. For the comparison of transfusions to lysis, a 4-group Kruskal-Wallis test was used. Parametric data were analyzed with an unpaired t test. P values < 0.05 were considered statistically significant. The statistical analysis was performed with GraphPad software (GraphPad Software, Inc., La Jolla, CA).

RESULTS

Demographics

Fifty-five patients treated with APRO were compared with a matched group in which APRO was not used (the no-APRO group). Patient demographics and reasons for transplantation are shown in Tables 1 and 2. There was no significant difference between the groups with respect to age, body mass index, or MELD or Child-Pugh scores. There were equal numbers of donation after cardiac death (DCD) grafts in the 2 groups, and there were no significant differences in cold ischemia times.

Table 1. Baseline Characteristics of the 2 Groups
DemographicsAPRO GroupNo-APRO GroupP Value
  1. NOTE: The data are presented as means and standard deviations.

Age (year)51.04 ± 9.6552.96 ± 10.950.37
MELD score15.51 ± 7.1616.22 ± 7.920.62
Child-Pugh score8.47 ± 2.128.45 ± 2.350.97
Height (m)1.69 ± 0.081.71 ± 0.090.18
Weight (kg)74.22 ± 16.0379.24 ± 16.060.10
Body mass index (kg/m2)25.98 ± 4.9327.26 ± 4.950.18
Cold ischemia time (minutes)532.44 ± 149.52475.22 ± 176.610.07
DCD/DBD (n/n)2/532/53NS
Table 2. Primary and Secondary Diagnoses for the 2 Groups
Primary DiagnosisAPRONo-APRO GroupSignificance
Alcoholic liver disease20 (36.4)19 (34.5)NS
Hepatitis C14 (25.5)15 (27.3)NS
Primary biliary cirrhosis6 (10.9)6 (10.9)NS
Hepatitis B4 (7.3)4 (7.3)NS
Cryptogenic cirrhosis3 (5.5)3 (5.5)NS
Acute liver failure3 (5.5)3 (5.5)NS
Primary sclerosing cholangitis3 (5.5)3 (5.5)NS
Chronic rejection1 (1.8)1 (1.8)NS
Primary graft nonfunction1 (1.8)1 (1.8)NS
Secondary DiagnosisAPRONo-APRO GroupSignificance
  1. NOTE: The data are presented as numbers and percentages.

Hepatocellular carcinoma9 (16.4)9 (16.4)NS

Fibrinolysis

No patient in the APRO group developed lysis (CLI < 15%) during transplantation. In the no-APRO group, 23.6% of the patients (n = 13) developed lysis at some stage during the operative period: 5 patients had mild lysis, 6 had moderate lysis, and 2 had severe lysis (Table 3). This difference in fibrinolysis between the groups was statistically significant (P < 0.003). When the presence of lysis was analyzed by the stage of the operation, we found that 33.3% occurred during the dissection phase, 26.7% occurred during the anhepatic phase, and 40% occurred during the reperfusion stage. In the no-APRO group of patients who developed lysis, 84.6% (n = 11) had only 1 episode of lysis, and 15.4% (n = 2) showed lysis on 2 samples, which were consecutive. Tranexamic acid was used as an antifibrinolytic 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 (1- to 2-g dose). In all but 1 of the patients with TEG evidence of fibrinolysis for whom the decision was made not to administer tranexamic acid, the fibrinolysis resolved spontaneously by the time of the next measurement.

Table 3. Presence of Lysis
Degree of LysisAPRO GroupNo-APRO Group
  1. NOTE: The data are presented as numbers and percentages.

Mild lysis0 (0)5 (9.1)
Moderate lysis0 (0)6 (10.9)
Severe lysis0 (0)2 (3.6)

In the no-APRO group, there were no significant differences in the amounts of red blood cell or other blood component transfusions between patients with no lysis and patients with mild, moderate, or severe fibrinolysis (Table 4).

Table 4. Comparison of Blood Component Transfusions in the No-APRO Group With Respect to the Degree of Lysis
 Red Blood Cells (units)Fresh Frozen Plasma (units)Platelets (units)Cryoprecipitates (units)
  1. NOTE: The data are presented as medians and interquartile ranges.

No lysis (n = 42)4 (1.25-7.5)4 (2-6)2 (0-2)0 (0-0)
Severe lysis (n = 2)12.5 (8.25-16.75)

P = 0.2

7 (5.5-8.5)

P = 0.32

3 (1.5-4.5)

P = 0.61

0 (0-0)

P = 0.5

Moderate lysis (n = 6)3 (1.25-5.5)

P = 0.94

3.5 (2.25-5.5)

P = 0.88

0 (0-0.75)

P = 0.19

0 (0-1.5)

P = 0.37

Mild lysis (n = 5)3 (2-3)

P = 0.64

2 (2-4)

P = 0.34

1 (1-1)

P = 0.86

0 (0-0)

P = 0.9

All lysis (n = 13)3 (2-6)

P = 0.81

4 (2-4)

P = 0.78

1 (0-1)

P = 0.45

0 (0-0)

P = 0.69

Blood Product Transfusion

There was no significant difference in red blood cell transfusions between the APRO and no-APRO groups (Table 5). There were no significant differences in the amounts of other transfused blood components between the groups (Table 5). Similar numbers in each group received no transfusions (19.61% in the APRO group and 18.18% in the no-APRO, P = 0.39).

Table 5. Comparison of Blood Component Transfusions in the 2 Groups
 APRO GroupNo-APRO GroupP Value
  1. NOTE: The data are presented as medians and interquartile ranges.

Total red blood cells (units)3 (1-5.5)4 (2-6)0.27
Total fresh frozen plasma (units)4 (3-7)4 (2-6)0.72
Total platelets (units)1 (0-2)1 (0-2)0.07
Total cryoprecipitates (units)0 (0-0)0 (0-0)0.25

TEG and Other Blood Results

TEG and hematology blood results at the start and end of the cases were compared. Baseline fibrinogen levels were not routinely available until 2010. At the start of the cases, there were no significant differences in the TEG and other blood results except for a lower native maximum amplitude in the no-APRO group [32.15 mm (±15.12 mm) versus 42.41 mm (±16.92 mm), P = 0.02; Table 6].

Table 6. Comparison of the Baseline Hematology and TEG Parameters at the Start of Surgery
Start of CaseAPRO GroupNo-APRO GroupP Value
  1. a

    P < 0.05.

  2. NOTE: The data are presented as means and standard deviations.

Hemoglobin (g/L)102.8 ± 1.68104.2 ± 0.980.95
International normalized ratio1.76 ± 1.061.87 ± 1.010.57
Platelets (×109)70.58 ± 29.7787.44 ± 47.050.15
Native reaction time (seconds)34.14 ± 23.4538.65 ± 36.460.53
Native maximum amplitude (mm)42.41 ± 16.9232.15 ± 15.120.02a
Native lysis (CLI %)0.98 ± 1.700.93 ± 3.460.94
Heparinase reaction time (seconds)21.71 ± 11.7917.27 ± 9.430.09
Heparinase maximum amplitude (mm)46.62 ± 14.1040.23 ± 12.350.06
Heparinase lysis (CLI %)1.17 ± 1.540.53 ± 1.310.07

At the end of the cases, there were significantly lower hemoglobin and platelet concentrations in the APRO group and a significantly higher international normalized ratio. There was also a significantly higher native reaction time for the APRO group (Table 7).

Table 7. Comparison of Hematology and TEG Parameters at the End of Surgery
End of CaseAPRO GroupNo-APRO GroupP Value
  1. a

    P < 0.05.

  2. NOTE: The data are presented as means and standard deviations.

Hemoglobin (g/L)85.0 ± 1.23100.7 ± 2.10<0.001a
International normalized ratio3.03 ± 1.961.83 ± 1.410.01a
Platelets (×109)67.75 ± 34.8191.07 ± 54.660.12
Native reaction time (seconds)31.57 ± 15.5720.92 ± 10.490.005a
Native maximum amplitude (mm)31.46 ± 14.3541.59 ± 15.590.06
Native lysis (CLI %)0.54 ± 0.540.44 ± 0.770.78
Heparinase reaction time (seconds)20.59 ± 9.1021.31 ± 10.570.92
Heparinase maximum amplitude (mm)39.5 ± 6.0955.43 ± 63.650.39
Heparinase lysis (CLI %)1.41 ± 1.240.36 ± 0.770.15

DISCUSSION

Increased fibrinolytic potential has been well described for patients with chronic liver disease, and it is known that enhanced fibrinolytic activity occurs during the anhepatic period of liver transplantation, mainly because of the high levels of tissue-type plasminogen activator as hepatic clearance is compromised.[15] This is followed by a dramatic increase in tissue-type plasminogen activator immediately after reperfusion and can be associated with explosive primary hyperfibrinolysis,[1] with some patients developing diffuse, uncontrolled bleeding. Usually, hyperfibrinolysis subsides within an hour, but in the presence of a poorly functional or marginal graft, it may persist.[16]

The routine use of prophylactic antifibrinolytic agents was common in the early history of OLT because massive blood loss was relatively common and any risk associated with the use of antifibrinolytics was small in comparison. Concerns have always existed about the potential for thromboembolic complications when prophylactic antifibrinolytic therapy is routinely used. However, a review of more than 1400 OLT patients found no significant difference in arterial or venous thromboembolisms between patients receiving APRO and patients receiving no treatment.[17] In addition, a systematic review and meta-analysis of antifibrinolytic therapy in liver transplantation found no increase in thrombotic complications.[10] However, the lack of a difference in thromboembolic events does not necessarily mean that there is no increased risk associated with the use of antifibrinolytic drugs in a specific subset of patients because relevant subgroups can be missed in a meta-analysis. In addition, different drug dosages were used in different studies. Although epsilon-aminocaproic acid is widely used in the United States as the antifibrinolytic of choice, there has been only 1 randomized control trial, and no benefit was shown in comparison with a placebo.[18]

We have shown a significant increase in the prevalence of fibrinolysis on TEG analysis in our patients undergoing liver transplantation since the withdrawal of prophylactic APRO in 2007. However, the clinical significance of this is less clear. Indeed, the incidence of fibrinolysis (26.3%) since 2007 is much less than we had expected, so we question the need for prophylactic tranexamic acid. In all but 1 of the patients in this study to whom no antifibrinolytic was administered, the fibrinolysis was resolved by the next measurement point. We also have shown that tranexamic acid is an effective alternative to APRO: it led to the resolution of fibrinolysis in approximately 85% of the cases, and this confirms the findings of other institutions.[8] In the presence of good graft function, fibrinolysis is usually self-limiting after reperfusion and does not always require treatment,[5, 19] as shown by our data: all but 1 case resolved spontaneously without treatment. The decision to treat should be based on the presence of diffuse bleeding, the disease process, the severity of the fibrinolysis, and the stage of the operation. Fibrinolysis occurring during the dissection and early anhepatic phase of surgery is more likely to require treatment because it is unlikely to resolve spontaneously. After the reperfusion of a marginal graft, fibrinolysis is more common and can be severe, and we now routinely give tranexamic acid before reperfusion when a DCD graft is used.[20]

We looked at early fibrinolysis (30 minutes) with TEG measurements: data about lysis at 60 minutes were not always available because the TEG test was terminated before this period. It is often not practical to wait for up to 60 minutes before an antifibrinolytic is administered in the presence of diffuse bleeding, and during the perioperative period, lysis at 30 minutes is normally used to guide therapy. Less is known about the presence of late fibrinolysis; however, this would be a useful area for further study.

In contrast to other groups, we have shown no increase in red blood cell or other blood component transfusion requirements since the withdrawal of APRO from our routine practice.[4, 7, 17] A recent Cochrane systematic review also showed that APRO, recombinant factor VIIa, and TEG may potentially reduce blood loss and transfusion requirements, but there was no difference in transfusion requirements when APRO and tranexamic acid were compared.[21] It is notable that there was a trend toward increased amounts of red blood cell transfusions as the degree of lysis increased, but this was not significant (NS), possibly because of the small number of patients who had developed severe lysis, but a type II error cannot be excluded. This is likely to be a useful area for further study because it appears that more severe degrees of lysis warrant treatment with antifibrinolytic drugs, and indeed, this is a factor in our decision to treat fibrinolysis.

The numbers of patients receiving no transfusions were also similar for the 2 groups, and this suggests that the change in our antifibrinolytic strategy has not had a detrimental effect with respect to bleeding and transfusion requirements.

Notably, at the end of surgery, there was a significantly lower hemoglobin count for the APRO group (85.0 versus 100.7 g/L), and this increased the likelihood of more blood component transfusions being required after the completion of surgery.

There was also a longer native reaction time for the APRO group (31.57 versus 20.92 seconds), and this has been previously described as an effect of APRO.[22]

Study Limitations

This study compared data from 2 nonoverlapping cohorts in different but adjacent time periods. Therefore, the risk of unrecognized changes in practice could not be excluded completely, but the study design and the fact that the known variables were comparable minimized this risk. Our observational study enrolled a relatively large number of consecutive patients. However, the study did not have enough power to detect all important differences between the treatment groups.

In conclusion, we have shown that the withdrawal of APRO from use in liver transplantation surgery has not had the predicted deleterious effects with respect to red blood cell and other blood component transfusion requirements. We have shown that a viscoelastic test–guided strategy tailored to the individual patient's risk of bleeding is as effective as the routine administration of APRO to all high-risk patients undergoing OLT. Factors that may contribute to an increased risk of bleeding include the degree of lysis, the stage of the operation, ongoing bleeding, and the disease process. Further study is needed to validate individual risk factors for bleeding.

Abbreviations
APRO

aprotinin

CLI

clot lysis index

DBD

donation after brain death

DCD

donation after cardiac death

MELD

Model for End-Stage Liver Disease

NS

not significant

OLT

orthotopic liver transplantation

TEG

thromboelastography

Ancillary