A simplified experimental model of large-for-size liver transplantation in pigs

Experimental Clinical Model of Liver Transplantation in Large White Pigs Without Venovenous Bypass: Pre-, Intra-, and Maintenance Care

BACKGROUND

Liver transplantation in an animal model is challenging due to hemodynamics and intraoperative anesthetic care. Several models are described in the literature employing different techniques such as venovenous bypass or aortic cross-clamping to maintain hemodynamic stability, although few groups keep the animal alive in the postoperative period. This study aims to evaluate a liver transplantation clinical model in pigs without venovenous bypass or aortic cross-clamping.

METHODS

Male pigs weighing 20 to 35 kg underwent liver transplantation surgery without using venovenous bypass or aorta cross-clamping. Protocols were approved by the Animal Care and Use Committee of the University of São Paulo, Brazil.

RESULTS

Ten LTs were performed. Cold ischemia and warm ischemia were 119 ± 33.28 minutes and 26 ± 9.6 minutes, respectively. Hemodynamic changes were significantly higher after the postrevasculazation phase: heart rate (P < .001), medium arterial pressure (P < .001), and cardiac output (P = .03). Hypotension was treated with intravenous fluids and, in some cases, with vasoactive drugs especially during the post-reperfusion period. No animals died during the procedure and almost survival until the first postoperative day. Serum aspartate aminotransferase and lactate increased their values in the post-reperfusion phase.

CONCLUSIONS

Practice-based on laboratory animals improves surgical skills and the development of experimental models aimed at new advances in this field. Perfecting our technique on the swine model, we could move forward to create a small-for-size model, test new therapeutic strategies, and define the boundaries for safely performing an enlarged liver resection or a partial liver graft transplant.

Does Arterialization of Portal Vein Have Any Effects in Large-for-Size Liver Transplantation? Hemodynamic, Histological, and Biomolecular Experimental Studies

BACKGROUND

In pediatric liver transplantation, the optimal size of the transplanted liver ranges between 0.8% and 4.0% of the recipient's weight. Sometimes, the graft weight exceeds this upper limit, characterizing the large-for-size condition potentially associated with reduced blood flow and worsening of ischemia-reperfusion injury. Therefore, it would be beneficial to increase the portal flow through arterialization of the portal vein. Materials and methods: Fifteen pigs underwent large-for-size liver transplants. They were divided into two groups: control (CTRL 6 animals - conventional technique) and arterialization - a shunt was established between the portal vein and the splenic artery (ART 9 animals). Hemodynamic, biochemical, histological, and molecular variables were compared. Results: Arterialization resulted in a significant increase in portal vein pressure but no changes in other hemodynamic variables, as shown in the analysis of variance. It was observed lower ALT values (p = 0.007), with no differences regarding the values of blood pH and lactate (p = 0.54 and p = 0.699 respectively) or histological variables (edema, steatosis, inflammation, necrosis, and IRI - p = 1.0, p = 0.943, p = 0.174, p = 0.832, p = 0.662, respectively). The molecular studies showed significantly increased expression of IL6 after 3 hours of reperfusion (p = 0.048) and decreased expression of ICAM immediately after reperfusion (p = 0.03). The regression analysis suggested a positive influence of portal flow and pressure on biochemical parameters. Conclusion: Arterialization of the portal vein showed no histological, biochemical, or molecular benefits in large-for-size transplantation.

Impact of Three Methods of Ischemic Preconditioning on Ischemia-Reperfusion Injury in a Pig Model of Liver Transplantation

BACKGROUND

Ischemic preconditioning (IPC), either direct (DIPC) or remote (RIPC), is a procedure aimed at reducing the harmful effects of ischemia-reperfusion (I/R) injury.

OBJECTIVES

To assess the local and systemic effects of DIPC, RIPC, and both combined, in the pig liver transplant model.

MATERIALS AND METHODS

Twenty-four pigs underwent orthotopic liver transplantation and were divided into 4 groups: control, direct donor preconditioning, indirect preconditioning at the recipient, and direct donor with indirect recipient preconditioning. The recorded parameters were: donor and recipient weight, graft-to-recipient weight ratio (GRWR), surgery time, warm and cold ischemia time, and intraoperative hemodynamic values. Blood samples were collected before native liver removal (BL) and at 0 h, 1 h, 3 h, 6 h, 12 h, 18 h, and 24 h post-reperfusion for the biochemical tests: aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), gamma-glutamyl transferase (GGT), creatinine, BUN (blood urea nitrogen), lactate, total and direct bilirubin. Histopathological examination of liver, gut, kidney, and lung fragments were performed, as well as molecular analyses for expression of the apoptosis-related BAX (pro-apoptotic) and Bcl-XL (anti-apoptotic) genes, eNOS (endothelial nitric oxide synthase) gene, and IL-6 gene related to inflammatory ischemia-reperfusion injury, using real-time polymerase chain reaction (RT-PCR).

RESULTS

There were no differences between the groups regarding biochemical and histopathological parameters. We found a reduced ratio between the expression of the BAX gene and Bcl-XL in the livers of animals with IPC versus the control group.

CONCLUSIONS

DIPC, RIPC or a combination of both, produce beneficial effects at the molecular level without biochemical or histological changes.

Long-Term Outcomes of Abdominal Wall Reconstruction with Expanded Polytetrafluoroethylene Mesh in Pediatric Liver Transplantation

Background: Large-for-size syndrome caused by organ size mismatch increases the risk of abdominal compartment syndrome. Massive transfusion and portal vein clamping during liver transplantation may cause abdominal compartment syndrome (ACS) related to mesenteric congestion. In general pediatric surgery—such as correcting gastroschisis—abdominal wall reconstruction for the reparation of defects using expanded polytetrafluoroethylene is an established method. The purpose of this study is to describe the ePTFE-Gore-Tex closure method in patients with or at a high risk of ACS among pediatric liver transplant patients and to investigate the long-term prognosis and outcomes. Methods: From March 1988 to March 2018, 253 pediatric liver transplantation were performed in Seoul National University Hospital. We retrospectively reviewed the cases that underwent abdominal wall reconstruction with ePTFE during liver transplantation. Results: A total of 15 cases underwent abdominal closure with ePTFE-GoreTex graft. We usually used a 2 mm × 10 cm × 15 cm sized Gore-Tex graft for extending the abdominal cavity. The median follow up was 59.5 (17–128.7) months and there were no cases of ACS after transplantation. There were no infectious complications related to ePTFE implantation. The patient and graft survival rate during the study period was 93.3% (14/15). Conclusions: Abdominal wall reconstruction using ePTFE is feasible and could be an alternative option for patients with a high risk of ACS.

Large-for-Size Orthotopic Liver Transplantation: a Systematic Review of Definitions, Outcomes, and Solutions

BACKGROUND

We systematically reviewed the literature on definitions and outcomes of large-for-size (LFS) syndrome in orthotopic liver transplantation (LT).

METHODS

This systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The Cochrane Library, PubMed, and Embase were searched (January 1990-January 2019) for studies reporting LFS in LT. Primary outcomes were definitions and mortality of LFS LT.

RESULTS

Eleven studies reporting patients with LFS LT were identified. Four different formulas (graft-to-recipient weight ratio (GRWR), body surface area index (BSAi), donor standardized total liver volume (sTLV)-to-recipient sTLV ratio, and graft weight/right anteroposterior distance (RAP) ratio) with their critical thresholds were found. There were 81 patients (54% women) with a median weight and height of 62.5 kg (range, 40-105 kg) and 165 cm (range, 145-180 cm). The median graft weight was 1772 g (range, 1290-2400 g), and the median GWRW was 2.77% (range, 2.1-4.00%). Graft venous outflow obstruction was described in seven patients (8.6%). At the time of LT, fascial closure was not achieved in 24 patients (29.6%) and the graft size was reduced by a liver resection in three patients (3.7%). Thirteen deaths (16%) were reported in the first 90 postoperative days with two patients undergoing re-transplant.

CONCLUSIONS

LFS LT remains heterogeneously defined but characterized by high mortality rates despite the use of tailored surgical solutions (graft reduction and open abdomen). A composite definition is proposed in order to better describe LFS clinical syndrome.

Long-term Functional Maintenance of Exteriorized Portal Venous Catheters in a Porcine Animal Model

BACKGROUND

Portal venous access for blood sampling, infusion therapy, and measurement of portal venous pressure is of special interest for experimental studies in surgery, pharmacology, and hepatology. Chronic animal models with continuous portal venous access are rare and especially thrombosis or clotting of permanent catheters is a frequent complication. Aim of this study was to establish a preclinical pig model with a permanent portal venous catheter (PVC).

MATERIALS AND METHODS

PVC implantation was performed in 21 LEWE mini pigs. The catheter was inserted in the distal part of the superior mesenteric vein and fixated with a tobacco-pouch suture. Animals were followed up for 4 wk, directly after implantation of the PVC. Blood gas analyses and portal venous pressures were recorded. Three different groups with continuous infusion via the catheters were defined: NaCl solution (2 mL/h) (group 1), NaCl solution (2 mL/h) + enoxaparin sodium injection (anti-Xa levels of 0.3-0.8 U/mL) (group 2) and heparinized NaCl (2 I.E./mL, 2 mL/h) (group 3).

RESULTS

All 21 PVC implantations were performed without any complications. Application of continuous perfusion with heparinized NaCl (group 3) enabled portal venous access for the entire experiment in 8 of 10 cases (mean of 23.7 d) without any signs of dysfunction. However, for use of NaCl alone or in combination with enoxaparin sodium, catheters were only functional for 6.8 d and 6.9 d, respectively.

CONCLUSIONS

Permanent portal venous access through PVC in mini pigs is achievable by continuous infusion of low-dose heparinized NaCl solution.

Serial volumetric assessment of large for size liver grafts after whole cadaveric liver transplant in adults: do large liver grafts shrink in size?

BACKGROUND

After whole graft orthotopic liver transplantation (OLT), adaptation of the large grafts' volume to recipient weight is widely accepted despite the paucity of evidence on this subject.

METHODS

Thirty nine patients with GRWR > 2.5% were included in this study and subsequently divided into two groups with 3 ≥ GRWR > 3%. Patients had CT scans at three predetermined time points after OLT used for measuring the liver volume. The objective of this study is to evaluate the volumetric changes of whole large liver grafts after adult OLT.

RESULTS

At LT, the mean graft recipient body weight ratio (GRWR) was 3.1 ± 0.4%. The mean liver weight was 1881 ± 68 g at LT, 2014 ± 99 ml at one week, 1725 ± 126 ml at 3 months, and 1632 ± 117 (ml) at >6 months. There is an initial increase at 1 week after LT and a subsequent decrease of liver volume on later measurements. None of the late volume measurements were significantly different from the initial graft volume at liver transplant in pair wise comparisons ANOVA repeated measures (p > 0.05). Similarly, the mean GRWR did not change significantly between the initial calculation at transplantation date and the subsequent measurements during the different study time points (F = 0.04, p = 0.96) with a mean of 3.1% (95% CI = 2.2-4.2). AUC ROC discriminated a cutoff of 3% for the initial GRWR above which grafts tend to decrease in size over time (c statistics = 0.74, p = 0.036). In a Clustered ANOVA repeated measures, there was no significant difference in the changes of liver volume between both groups. However, patients with GRWR > 3 showed a trend towards a latent reduction in volume over the tracing period. There was a tendency, but none significant; towards a higher bilirubin, AST, ALT levels over the first postoperative days in recipients with GRWR > 3.

CONCLUSION

Large grafts do not significantly decrease in size. Nonetheless, grafts weighing >3% of the GRWR show a different trend towards decrease in size over time.

Swine model in transplant research: Review of anaesthesia and perioperative management

Pigs are one of most common animal species to be used in biomedical models due to their many anatomical visceral similarities with humans, particularly with regards to transplantation. Despite this use, in many of the researches in which pigs are selected for transplantation, the anaesthesia used is an adaptation of human anaesthesia and presents some limitations such as a reduced analgesia a limited control in perioperative period. In this review we show some of the most important conditions in the preanaesthetic management and of swine as well as we review of anaesthetic protocols for the most common types of swine model of transplantation.

Effects of ischemic preconditioning in a pig model of large-for-size liver transplantation

OBJECTIVE

In most cases of pediatric liver transplantation, the clinical scenario of large-for-size transplants can lead to hepatic dysfunction and a decreased blood supply to the liver graft. The objective of the present experimental investigation was to evaluate the effects of ischemic preconditioning on this clinical entity.

METHODS

Eighteen pigs were divided into three groups and underwent liver transplantation: a control group, in which the weights of the donors were similar to those of the recipients, a large-for-size group, and a large-for-size + ischemic preconditioning group. Blood samples were collected from the recipients to evaluate the pH and the sodium, potassium, aspartate aminotransferase and alanine aminotransferase levels. In addition, hepatic tissue was sampled from the recipients for histological evaluation, immunohistochemical analyses to detect hepatocyte apoptosis and proliferation and molecular analyses to evaluate the gene expression of Bax (pro-apoptotic), Bcl-XL (anti-apoptotic), c-Fos and c-Jun (immediate-early genes), ischemia-reperfusion-related inflammatory cytokines (IL-1, TNF-alpha and IL-6, which is also a stimulator of hepatocyte regeneration), intracellular adhesion molecule, endothelial nitric oxide synthase (a mediator of the protective effect of ischemic preconditioning) and TGF-beta (a pro-fibrogenic cytokine).

RESULTS

All animals developed acidosis. At 1 hour and 3 hours after reperfusion, the animals in the large-for-size and large-for-size + ischemic preconditioning groups had decreased serum levels of Na and increased serum levels of K and aspartate aminotransferase compared with the control group. The molecular analysis revealed higher expression of the Bax, TNF-alpha, I-CAM and TGF-beta genes in the large-for-size group compared with the control and large-for-size + ischemic preconditioning groups. Ischemic preconditioning was responsible for an increase in c-Fos, IL-1, IL-6 and e-NOS gene expression.

CONCLUSION

Ischemia-reperfusion injury in this model of large-for-size liver transplantation could be partially attenuated by ischemic preconditioning.

Large-for-size liver transplantation: a flowmetry study in pigs

BACKGROUND

Ischemia-reperfusion injury is partly responsible for morbidity in pediatric liver transplantation. Large-for-size (LFS) liver transplantation has not been fully studied in the pediatric population, and the effects of reperfusion injury may be underestimated.

MATERIALS AND METHODS

Thirteen Landrace-Large white pigs weighing 23 kg (range, 17-38 kg) underwent orthotopic liver transplantation. They were divided into two groups according to the size of the donor body: LFS and control (CTRL). After transplantation, the abdominal cavity of the recipient was kept open and portal venous flow (PVF) was measured after 1 h. The ratio of recipient PVF (PVFr) to donor PVF was used to establish correlations with ischemia and reperfusion parameters. Liver biopsies were taken 1 h after transplantation to assess ischemia and reperfusion and to quantify the gene expression of endothelial nitric oxide synthase, interleukin 6, BAX, and BCL.

RESULTS

Recipient weight, total ischemia time, and warm ischemia time were similar between groups. Among hemodynamic and metabolic analyses, pH, central arteriovenous PCO2 difference, and AST were statistically worse in the LFS group than in the CTRL group. The same was found with endothelial nitric oxide synthase (0.41 ± 0.18 versus 1.56 ± 0.78; P = 0.02) and interleukin 6 (4.66 ± 4.61 versus 16.21 ± 8.25; P = 0.02). In the LFS group, a significant decay in the PVFr was observed in comparison with the CTRL group (0.93 ± 0.08 and 0.52 ± 0.11, respectively; P < 0.001).

CONCLUSIONS

The implantation of a graft was responsible for poor hemodynamic status of the recipient 1 h after transplantation. Furthermore, the LFS group demonstrated markers of ischemia and reperfusion that were worse when compared with the CTRL group and exhibited a more significant decrease in PVF from donor to recipient.