The first successful liver transplantation was performed by Starzl et al in 1967. Since then, the procedure has become the gold standard treatment for liver diseases that have progressed to end-stage liver failure.¹ In North American and European countries, most transplanted livers are obtained from cadaveric donors. In Turkey and some Asian countries, most liver grafts are from living donors.² In most cadaveric transplant procedures, vascular reconstruction is uncomplicated, because the structure of the donated liver has been preserved. On the other hand, vascular reconstruction in living donor grafts can be challenging if vascular grafts are needed.

Grafts used for vascular reconstruction may be autogeneic, allogeneic, or manufactured from synthetic materials, such as polytetrafluoroethylene. Allogeneic grafts must be obtained prior to any transplantation procedure in which they are used. Thus, for active liver transplantation centers, having a continuous source of allogeneic grafts depends on effective storage methods. The key challenges to this procedure include ensuring that grafts remain free of endothelial injury, protecting the viability or patency of the graft, and maintaining absolute sterility. In this report, we describe an allogeneic vascular graft storage method that was developed in our high-volume liver transplant center and has proven to be successful.

Materials and Methods

Vascular reconstruction models

From 2002 to mid-2012, 875 liver transplantations were performed at the Inonu University School of Medicine's Liver Transplant Institute (Malatya, Turkey). Of these, 77% were living donor liver transplantations, and the remaining 23% were cadaveric. Several vascular reconstruction models were used during these procedures, including iliac artery, iliac vein, and saphenous vein grafts (Fig. 1A–1C). In some cases, inferior vena cava and abdominal aorta grafts were used. To obtain optimal venous drainage of the transplanted liver, all V5, V8, and short hepatic veins having a diameter ≥5 mm were integrated to a common large opening model. In cases with impaired hepatic artery flow or intimal dissection, arterial reconstruction was performed using allogeneic vascular grafts. Allogeneic vascular grafts were also used for portal vein reconstruction (Fig. 1D).

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Results

The study analyzed data from 29 recipients (age range, 12–64 years; 22 male and 7 female recipients) and 29 donors (10 male and 19 female donors). The demographic and clinical characteristics of the recipients and donors are summarized in Table 1. Right lobe hepatectomy was performed in 25 of the living donors, and left lobe hepatectomy was performed in the remaining 4. All 29 vascular grafts were applied as venous reconstructions on the operating room back-table. Among the allogeneic grafts, 16 were from the saphenous vein, 10 were from the iliac vein, and 3 were from the iliac artery. The saphenous veins grafts were obtained during variceal surgery. The iliac artery and vein grafts were obtained from cadaveric donors. Vascular grafts preserved with the simple storage technique described above were used within an average of 40 days (range, 15–85 days). All of the tissue samples obtained from stored vascular grafts were free of bacterial contamination. All of the vascular graft donors were seronegative for HBV, HCV, and HIV. No allogeneic vascular graft–related complications, including graft patency (100%), occurred in any recipient during the 5 months of follow-up.

Table 1  Demographic and clinical features of both organ recipient and donor patients

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Discussion

Living donor liver transplantation is an alternative treatment option in countries without an adequate availability of cadaveric livers.³ It should be noted that cadaveric grafts have advantages over grafts from living donors that are important both surgically and for postoperative graft function. Being able to harvest the retrohepatic inferior vena cava, the portal vein extending as far as inferior mesenteric vein, and the hepatic artery together with the celiac trunk, along with the donor liver, simplifies the ability to establish vascular anastomoses during transplantation. Living donor grafts, on the other hand, can be technically difficult if the hepatic vein, portal vein, and hepatic artery segments present in the transplanted liver are relatively short. In such cases, vascular reconstruction may require several vascular grafts, especially in cases with intimal dissection of the recipient hepatic artery. Reconstruction of hepatic outflow may also require several vascular grafts.

Homologous (allogeneic), autologous, and artificial (synthetic) grafts may all be used for vascular reconstruction. Recipient left portal, paraumbilical, and saphenous vein autografts have also been successfully applied.⁴ The most frequent allogeneic vascular grafts are saphenous and iliac veins, iliac arteries, inferior vena cava, and aortae obtained from cadaveric donors. Some transplant centers use homologous grafts harvested during variceal surgery. Synthetic vascular grafts, most often those made from polytetrafluoroethylene, are generally used when suitable allogeneic grafts are not available, and they are often used for reconstruction of V5, V8, and the middle hepatic vein.^5–7

A consensus exists on reuse of synthetic grafts following resterilization by various techniques. However, optimal preservation techniques and storage time for allogeneic vascular grafts are controversial. Hwang et al⁵ successfully used cryopreserved allogeneic vascular grafts that had been stored for a mean of 3 months (range, 4 days to 15 months) for hepatic vein reconstruction.⁵ In our institution, allogeneic vascular grafts are used for reconstruction of hepatic outflow at nearly every back-table stage. The grafts are stored as described above, with a maximum storage period of 3 months.

Graft storage using various antimicrobial and preservation solutions is becoming more common in the field; cryopreservation, cold storage, and glutaraldehyde treatment methods have also been improved recently.⁸ A graft storage technique that uses slow freezing, with the temperature falling from +1°C to −40°C, has also been reported.⁹ Cryopreservation using liquid nitrogen and dimethylsulfoxide keeps tissues at a temperature between −120°C and −190°C. Cold storage techniques keep grafts immersed in saline solutions at +4°C. The objective of all of these storage methods is to maintain the allogeneic vascular graft without inducing damage, immunologic changes, or changes in graft aperture, while also maintaining sterility, for as long a time as possible. The storage protocol described herein does not include any preservation solutions or antimicrobial agents. Microbiologic analysis revealed no sign of contamination prior to graft use, and 5 months of follow-up did not reveal any graft-related infections or problems related to vascular graft patency.

Most previous studies evaluated storage effects on the viability of graft tissue, patency rates, and endothelial injury. To our knowledge, this is the first report to include results from testing for bacterial contamination in stored vascular grafts. Second, the storage method described herein has not been reported previously, is simple and inexpensive, and requires only simple reagents, microbiologic techniques, and a readily available laboratory freezer for storing the graft tissues. In summary, the freezing storage procedure involves 2 regular sterile, disposable surgical gloves, 1 regular sterile, disposable specimen storage container, and 1 label for each vascular graft tissue obtained from the donor. Therefore, the biggest cost of this storage method may involve the space and energy required in the hospital freezers.

The risk of viral transmission is another potential challenge for safely transplanting vascular grafts. In a recent article from the Centers for Disease Control and Prevention (CDC), organ transplantation centers are discouraged from storing vascular grafts obtained from donors who were positive for hepatitis B surface antigen (HbsAg) or anti-HCV antibodies, or had detectable HBV or HCV sequence by nucleic acid test.¹⁰ Furthermore, the CDC reported that grafts obtained from seropositive donors should be stored in separate freezers from grafts obtained from seronegative donors. In addition, to further prevent technical mistakes, for both living and cadaveric sources, the donor's features and viral marker results should be labeled on the storage containers. Our hospital employs such strict storage methods, which likely played a beneficial role in our study recipients avoiding viral transmission, as well as the more than 700 living donor liver transplantations that have been performed at our hospital over time.

For the series of vascular reconstruction grafts stored using this protocol and described in this study, the results demonstrate that allogeneic vascular grafts can be stored without need of expensive materials and complex methods, and without risk of bacterial contamination. However, future larger-scale prospective randomized studies should be carried out to confirm our findings and further optimize the simplified system.