Author Affiliations: Ochsner Multi-Organ Transplant Institute, Ochsner Medical Center, 1514 Jefferson Highway, New Orleans, LA 70121, USA (Reichman TW, Fiorello B, Carmody I, Bohorquez H, Cohen A, Seal J, Bruce D and Loss GE)

Corresponding Author: Trevor W Reichman, MD, PhD, FACS, Division of Transplantation, Department of Surgery, Virginia Commonwealth University, P. O. Box 980057, Richmond, VA 23298, USA (Tel: +1-804-828-2461; Fax: +1-804-828-4858; Email: trevor.reichman@vcuhealth.org)

 

© 2016, Hepatobiliary Pancreat Dis Int. All rights reserved.

doi: 10.1016/S1499-3872(16)60155-8

Published online November 4, 2016.

 

 

Contributors: RTW proposed the study. RTW and FB performed the research and wrote the first draft. FB collected the data. RTW, CI, and BH performed the data analysis. All authors contributed to the design and interpretation of the study and to further drafts and revisions of the manuscript. RTW is the guarantor.

Funding: None.

Ethical approval: This study was approved by the IRB Committee of Ochsner Medical Center.

Competing interest: No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.

 

 

BACKGROUND: Split liver transplantation increases the number of grafts available for transplantation. Pre-recovery assessment of liver graft volume is essential for selecting suitable recipients. The purpose of this study was to determine the ability and feasibility of constructing a 3-D model to aid in surgical planning and to predict graft weight prior to an in situ division of the donor liver.

 

METHODS: Over 11 months, 3-D volumetric reconstruction of 4 deceased donors was performed using Pathfinder Scout^© liver volumetric software. Demographic, laboratory, operative, perioperative and survival data for these patients along with donor demographic data were collected prospectively and analyzed retrospectively.

 

RESULTS: The average predicted weight of the grafts from the adult donors obtained from an in situ split procedure were 1130 g (930-1458 g) for the extended right lobe donors and 312 g (222-396 g) for left lateral segment grafts. Actual adult graft weight was 92% of the predicted weight for both the extended right grafts and the left lateral segment grafts. The predicted and actual graft weights for the pediatric donors were 176 g and 210 g for the left lateral segment grafts and 308 g and 280 g for the extended right lobe grafts, respectively. All grafts were transplanted except for the right lobe from the pediatric donors due to the small graft weight.

 

CONCLUSIONS: On-site volumetric assessment of donors provides useful information for the planning of an in situ split and for selection of recipients. This information may expand the donor pool to recipients previously felt to be unsuitable due to donor and/or recipient weight.

 

(Hepatobiliary Pancreat Dis Int 2016;15:587-592)

 

KEY WORDS: split liver transplantation; reduced-size liver transplantation; 3-D reconstruction

Donor shortage remains one of the major rate-limiting steps to the growth and expansion of liver transplantation.^[1] One potential source of additional liver grafts is split liver transplantation (SLT) which permits one liver graft to be shared and transplanted into two suitably sized recipients.^[2] Several large series have demonstrated good outcomes from SLT, dividing the liver into a left lateral segment graft for a small pediatric patient and an extended right graft suitable for most average size adults.^[3-7] One study using matched recipients of extended right lobe grafts to whole liver grafts demonstrated equivalent outcomes between the two groups.^[8] In addition, a multi-center effort to optimize the use of SLT effectively resulted in a decrease in the drop-rates for listed patients in both pediatric and adult waiting lists.^[3] The “split” technique was modified by Colledan et al to divide the liver along Cantlie’s line in an attempt to create similar sized grafts suitable for two adults.^[9] However, prior to the commencement of any split operation, potential donors suitable for SLT need to be carefully assessed and matched to potential recipients based on donor anatomy, graft weights and recipient size. In addition, recipient selection and operating room logistics are important for optimal outcomes.

 

Pediatric liver transplants account for 5% of all transplants performed in the world, but due to their small size particularly for the youngest of recipients, the number of whole-organ deceased donor grafts size-matched for this population is minimal. SLT and partial liver transplantation have made the largest impact in pediatric liver transplantation due to the difficulty in finding a significant number of suitably sized liver grafts.^[10] Recent data also suggest that with experience, the partial liver grafts yield similar outcomes to full liver grafts.^[11]

 

Three dimensional (3-D) liver reconstruction and volume calculation have been used extensively in liver resections and living donor liver transplantations to carefully calculate liver remnants and liver donor graft weights.^{[12, 13]} Current data suggest that preoperative volumetric analysis of the percentage of liver that remains after resection is 98% specific in predicting liver dysfunction postoperatively.^[14] Pathfinder Scout^© liver volumetric software is a commercially available, laptop-based software program used in preoperative planning of liver resections that provides 3-D visualization and measurement of liver anatomy. Volumetric measurements are performed utilizing CT and/or MR imaging studies. The resulting 3-D model allows for rotation, surgical planning and evaluation of the functional liver remnant. After using this software for oncologic liver resections and living donor liver transplantations, we hypothesized that on-site donor volumetric analysis could be a useful tool to determine donor suitability and donor liver volumes for in situ SLT.

 

The purpose of this study was to determine the ability and feasibility of constructing a 3-D model to aid in surgical planning and to predict graft weights following an in situ division of the donor liver. Data obtained using this technique can enhance the ability of surgeons to better match partial donor grafts to potential recipients following an in situ donor liver resection for SLT.

 

 

From February 2014 through December 2014, a prospective study was carried to assess the feasibility of constructing a 3-D model and calculating liver volumes prior to performing in an in situ liver division for SLT. Potential recipients were allocated donor liver grafts according to their pediatric end-stage liver disease (PELD)/model for end-stage liver disease (MELD) and United Network for Organ Sharing (UNOS) policy. Donors were assessed to determine suitability for splitting which included: donors less than 40 years old, single vasopressor or less, peak aminotranferases no greater than three times of normal with a downward trend at the time of organ recovery, and a BMI 28 kg/m² or less. Potential recipient was also evaluated for suitability to receive whole or partial liver graft. Recipient selection was conducted based on the presumed graft weight to recipient weight (GWRW) ratio, severity of portal hypertension, and medical urgency. After the decision was finalized to proceed with the SLT, the remnant liver was offered to a secondary recipient according to the UNOS MELD based allocation system. In all cases for this study, the pediatric recipient was initially allocated the liver.

 

Pathfinder Scout^© liver volumetric software (Analogic Corporation, Peabody, MA, USA) was available on a portable laptop computer and used in preoperative planning for potential in situ division of donor livers. Liver volumetric software provides 3-D visualization of structures within the liver that may be of interest and aids in planning the resection plane. It also allows for the calculation of graft weight that was used to predict a preliminary GWRW ratio. In many cases, CT scans were performed as part of the donor’s care (i.e. trauma workup). When no CT scan was present and after the donor chart was reviewed, a discussion with the local organ procurement organization (OPO) was carried out with regard to performing a CT scan. When requested for splitting, a liver protocol (triple phase) CT scan was performed. In all cases, OPOs were more than willing to perform a scan if there was interest in splitting the liver for two recipients and there was little concern to administering intravenous contrast. Care was taken to adequately hydrate the patient to protect the kidneys as in all cases the kidneys were also recovered. In no case, did performing a CT scan for our protocol adversely affect the placement of other donor organs (e.g. kidneys, lungs, or heart). After the scan was performed, a discussion was then carried out with the on-site radiologist to try to rule out any aberrant liver anatomy that might preclude splitting the liver such as a replaced left hepatic artery. We have typically not split liver grafts with replaced left artery due to the concern of compromising the arterial flow to the left lateral graft. In the case of a full left/right split, the accessory/replaced left would not be a contraindication. Once completed, CT scan files were copied onto a CD and used for further analysis. These DICOM files were subsequently used for processing after uploading onto the laptop computer; a process that takes less than 5 minutes. Images were processed and planning was performed in approximately 20 to 30 minutes. The proposed resection was performed on the 3-D model and then compared with the actual graft weight once removed from the donor. For comparison, the total liver volume was also calculated using the weight-based formula: total liver volume (TLV)=191.80+18.51×weight (kg).^[15] The “Vauthey formula” was developed at a Western center and was thought to be the most applicable to calculating liver volumes from donors in this study. The DICOM images were processed while the donor operating room was getting ready prior to the start of the organ recovery and never delayed the commencement of this procedure. Extensive experience was gained by our center using this software and its accuracy was verified in both our living donor liver transplant and hepatobiliary oncology programs prior to using this technology for this study.

 

Intraoperative assessment of the donor liver was carried out. Biopsy was performed if there was concern for the quality of the liver graft. Liver anatomy was carefully assessed and feasibility for SLT was confirmed. A cholangiogram was also performed when feasible. Once the decision was made to proceed with SLT, the liver parenchyma was divided along the proposed line determined by preoperative 3-D planning and performed using a combination of electrocautery and a bipolar tissue-sealing device (LigaSure™, Covidien). Once completed, the donor organs were flushed with University of Wisconsin solution and removed from the donor. On the backtable, the parenchymal division was completed (if necessary) and the vessels divided to completely separate the two liver grafts. Grafts were then weighed, packaged, and transported back to the transplanting facility. Transplants for both the pediatric and adult recipients were performed simultaneously using standard transplant techniques.

 

Recipients that underwent SLT were identified. Demographic, laboratory, operative, perioperative and survival data for these patients along with donor demographic data were collected prospectively and analyzed retrospectively.

 

 

Potential recipients were allocated donor livers based on UNOS and local Organ Procurement and Transplantation Network (OPTN) criteria. During the indicated time period, 4 donors were identified that met criteria for splitting (Table 1). In all cases, the pediatric patient was the index case. Mean donor age was 18.3 years and BMI ranged between 19 and 23 kg/m². Mean age of the recipients of the left segmental grafts was 2.7 years and for the right lobe was 55.3 years (Table 2). Mean PELD/MELD at the time of transplant was 7.4 and 21.0 for the pediatric and adult cases, respectively. The average GWRW ratio for the pediatric recipients was 2.1 and 1.8 for the adult recipients. The right lobe graft from the pediatric donor was offered out but discarded secondary to inadequate volume for any potential available recipients. One of the pediatric patients also received a kidney and two of the adult recipients also underwent simultaneous liver and kidney transplants. One of the pediatric patients developed a biliary stricture post-transplant that was managed with a percutaneous transhepatic catheter followed by surgical revision and the recipient’s alkaline phosphatase and bilirubin returned to normal. One of the adult patients developed hepatic artery stenosis that was managed using endovascular balloon dilation and stent placement. No other complications were recorded in either the adult or pediatric patients. Graft and patient survival is 100% for both the right and left lobe grafts. Average follow-up time was 13 months (range 8-18).

 

3-D reconstruction and volumetric analysis were carried out with Pathfinder software using the donor CT scans available at the designated donor sites (Fig.). Calculated weights were compared with actual weights (Table 3).

 

 

Since SLT was first reported in 1989, the technique has evolved and outcomes have continued to improve.^[3-7] However, one of the limitations to more wide spread use of SLT continues to be matching partial grafts to recipients because of size restrictions. 3-D modeling is feasible and allows for the accurate calculation of split liver graft weights. This was easily performed using information provided at the donor hospital and software available on a portable laptop computer. Using this information, we were able to verify that the selected recipients were of appropriate size for the presumed graft weights. This resulted in short cold ischemia time, good early graft function, and expansion of the donor pool to patients normally ruled out due to size restrictions.

 

3-D images can be created and also used for surgical planning prior to commencement of the split operation. This information is useful for both in situ or ex situ splitting as slight variations can be planned in order to adjust graft size and volume based on recipient characteristics. As demonstrated recently, the resection plane can be altered in SLT for left lateral segment and left lateral segment grafts for living donation. The best resection plane is still a matter of debate and depends on the underlying anatomy of the donor.^{[16, 17]} Dividing livers along different resection planes inherently results in grafts of different weights. Accurate calculation of these weights is critical prior to preforming the in situ division of the liver in order to accurately select recipients such that the graft is not too small (in the case of potential adult recipients) nor too large (the case of potential pediatric recipients).

 

The routine use of 3-D modeling and volumetrics might have the largest impact on true right-left SLT. These grafts potentially can be used in two adult patients or in an adult and larger pediatric patient. There have been several studies that have shown good outcomes using grafts split into a full left and full right lobe.^[18-21] However, there are reported cases of small-for-size syndrome especially using the smaller left lobe grafts, further supporting the importance of graft weight in SLT.^[18-21] Accurate calculation of the potential graft sizes prior to the donor operation would reduce cold ischemia time and also aid in appropriately matching these organs to recipients, avoiding small grafts in larger patients but also not excluding patients that would previously be excluded due to their larger size.

 

In addition to GWRW ratio for full right-left lobe SLT, reduction in the portal inflow and improvement in the venous outflow of the liver are also thought to improve outcomes using smaller grafts.^{[22, 23]} Modification of the technique to “split” the middle hepatic vein theoretically improves drainage of both split liver grafts, and decreases the amount of non-functioning liver.^{[24, 25]} 3-D imaging could yield better information regarding the drainage of each of the hemiliver grafts leading to better decision making with regards to the fate of the middle hepatic vein, and the need for further reconstruction to improve drainage of the hemigraft.

 

Prior to 3-D modeling, other groups have used different techniques to estimate graft weights. Past studies have used whole liver weight as 2% of donor’s body weight which was then split into estimates for lobar weight: 35% for the left and 65% for the right. However, in 10%-20% of cases the grafts were oversized after reperfusion despite using the donor’s weight to predict graft size.^[26] Several equations have also been developed that estimate total liver volume based on body weight or body surface area of the patients with fairly good accuracy.^{[15, 27, 28]} However, these calculations are limited to calculating the volume of the whole organ and does not allow for calculation of the potential graft sizes. Lee et al and Wang et al were able to accurately calculate potential volumes based on the donors body surface area and the maximal portal vein diameter of right and left portal veins. This was used successfully to predict graft sizes for both adult right lobe living donor grafts and for SLT in adults for full right and left lobe grafts.^{[29, 30]} Tongyoo et al^[31] also published a similar report calculating the total graft weight based on body surface area and also using portal vein diameter to estimate right lobe graft weights. This technique was not used to calculate graft weights for the classic SLT (left lateral segment graft/extended right lobe graft) that were used in this study and does not allow for changes in the resection plane. In addition, in our experience, calculating graft weight based on body weight is not as accurate as the 3-D model (Table 3).

 

Although 3-D modeling and volumetrics can be used for both in situ and ex vivo division of the liver, the advantages to in situ division of the liver are well known. These include: shorter cold ischemia time and less blood loss with reperfusion. Initially, improved perioperative outcomes were also found to translate into better long-term survival for recipients of partial grafts.^[32] With improvement in technique, outcomes using ex vivo split techniques have improved long-term survival,^{[33, 34]} but short-term, perioperative complications (e.g. blood loss) still persist.^[33]

 

In conclusion, these results were proof of concept that 3-D volumetrics is feasible, easy and can be done prior to the commencement of a split operation. Analysis of potential donor liver grafts is useful for surgical planning and also predicts graft weights that are accurate and can be used to more appropriately select transplant recipients. With the improvement in technology and access to imaging remotely, the utility of 3-D reconstruction might be even more applicable and analysis is able to be performed on web-based portals prior to leaving for the donor hospital.

 

 

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