In situ normothermic regional perfusion versus ex situ normothermic machine perfusion in liver transplantation from donation after circulatory death

INTRODUCTION

Liver transplantation (LT) from controlled donation after circulatory death (cDCD) donors has been developed during the past two decades in an attempt to address the organ shortage but at the cost of inferior outcomes.^[1] Several studies have reported higher rates of early graft loss and increased rates of biliary complications in cDCD LT recipients compared with those receiving a donation after brain death (DBD) allograft.^[1-3] These inferior outcomes are attributed to allograft injury caused by prolonged donor warm ischemia (DWI) occurring after the withdrawal of life-sustaining therapies and before organ retrieval. Various dynamic preservation strategies have been developed to ameliorate this damage, including in situ normothermic regional perfusion (NRP) and ex situ normothermic machine perfusion (NMP).^{[4, 5]}

The NRP approach consists of cannulating donor iliac vessels and commencing perfusion of the abdominal compartment organs shortly after donor circulatory arrest. This strategy has been adopted by countries including France and Spain.^{[4, 6]} Large retrospective studies from these programs suggested that NRP was associated with superior posttransplant outcomes in cDCD allografts compared with super-rapid recovery with static cold storage (SCS), achieving results similar to DBD livers.^{[4, 7]}

In contrast, NMP involves the ex situ perfusion of livers with oxygenated blood and medications at body temperature to preserve the liver in a physiological, functioning state. This preservation strategy can be commenced at the donor hospital or at the recipient center after a period of SCS. NMP commenced at the donor hospital was compared with SCS in a randomized controlled trial conducted by the Consortium for Organ Preservation in Europe (COPE). The study demonstrated lower posttransplant peak aspartate aminotransferase (AST) levels and lower rates of early allograft dysfunction in the NMP group, with these benefits being greatest in the cDCD subgroup.^[8]

NRP and NMP have not yet been compared directly; this study is the first to compare the results of LT using these two different strategies in the context of LT from cDCD.

PATIENTS AND METHODS

RESULTS

Graft use rates

Of the 249 cDCD donors in the NRP cohort that were considered for procurement, 224 proceeded to asystole. Of these, 31 livers were not procured because of technical failure or dramatic postperfusion peak AST, whereas 193 livers were eventually procured, resulting in 157 transplants and 36 discarded livers, mainly as a result of steatosis or poor macroscopic aspect (Figure 1). In the NMP cohort, of the 63 cDCD donations that were considered for procurement, 40 proceeded to asystole. Normothermic perfusion was commenced in all 40 cases and resulted in 34 transplants. The corresponding organ use rates were 70% and 85% (p = 0.052) in the NRP and NMP cohort, respectively (Figure 1).

Survival rates

The 1- and 2-year graft survival rates were 93.9% versus 88.2% and 89.4% versus 88.2% (hazard ratio [HR], 0.67; 95% confidence interval [CI], 0.20–2.23; p = 0.516) for the NRP and NMP groups, respectively (Table 5). The 1- and 2-year patient survival rates were 98.5% versus 94.1% and 96.4% versus 90.9% (HR, 0.38 [95% CI, 0.06–2.30]; p = 0.275) for the NRP and NMP groups, respectively. Because of the high incidence of the HCC in the NRP group, we also calculated survival rates with censoring of recipients with HCC recurrence and found similar graft and patient survival rates (Table 5, Figures 2 and 3).

TABLE 5. Survival rates

Variables	NMP, %	NRP, %	p value
Graft survival rates			0.516
1 year	88.2	93.9
2  years	88.2	89.4
Tumor-censored graft survival rates			0.523
1 year	88.2	94.1
2  years	88.2	91.5
Patient survival rates			0.275
1 year	94.1	98.5
2  years	90.9	96.4
Tumor-censored patient survival rates			0.255
1 year	94.1	100
2  years	94.1	97.9

• Abbreviations: NMP, ex situ normothermic machine perfusion; NRP, in situ normothermic regional machine perfusion.

DISCUSSION

This is the first study comparing NRP and NMP strategies in cDCD LT. The results show patient and graft outcomes that are comparable with benchmarks established for DBD and much lower rates of NAS than contemporary cDCD series preserved by SCS.^{[2, 11-13]} Our findings suggest that the NMP procedure allows longer total preservation times and may achieve higher organ use rates. The NRP intervention achieved similar posttransplant results and also potentially improves the quality of other donated abdominal organs.^[14]

As a result of the historically poorer outcomes of cDCD livers, the selection criteria are usually more restrictive, resulting in lower organ use and higher discard rates compared with DBD donors. An important objective of machine perfusion is to recover graft quality and increase use rates. In the randomized COPE trial, the organ discard rate was 50% lower for the NMP compared with the SCS group and yet, despite the increased use of suboptimal cDCD livers, the results were superior to the SCS group.^[8] This suggests that NMP allows increased organ use without compromising outcomes. Conversely, studies comparing the use of NRP with the standard cDCD super-rapid recovery have not yet demonstrated improvement in terms of cDCD graft use rates. In the study by Hessheimer et al., the liver use rates from withdrawal of life-sustaining therapies were 34% and 38% after NRP and super-rapid recovery, respectively.^[4] These findings seem to be confirmed by our results, which suggest that the use rate might be higher after super-rapid recovery followed by NMP commenced at the donor center than after NRP.

Although open-abdomen cannulation is preferred in some countries, as it appears to be technically less demanding and results in very low rates of technical failure,^[15] other countries advocate the use of percutaneous femoral performed in the ITU. Because open-abdominal aortic cannulation for cDCD donation is not allowed in France,^16] the NRP cannulas needs to be inserted percutaneously by ITU doctors, which represents a demanding procedure associated with a steep learning curve.^[7] Technical failure to commence NRP was encountered in 19 of 224 donors in the NRP group, contributing to the reported use rates. The rates of technical success may be improved when cannulation is performed by skilled and well-trained operators^[17] or by using premortem cannulation, the latter of which is not allowed in several countries, including France.

Posttransplant AST or ALT are surrogate markers of hepatocyte injury used in definitions for early allograft dysfunction^{[9, 18, 19]} and also may predict the development of NAS in cDCD grafts.^[20] In comparison with SCS, both NMP and NRP are associated with a decreased AST peak after the LT of cDCD grafts. In the COPE trial, the peak AST was the primary endpoint that was found to be significantly lower in both the cDCD and DBD subgroups.^[8] In the first comparative study of NRP versus ex situ hypothermic oxygenated machine perfusion (HOPE) LT from cDCD donors, the peak AST in the NRP group was significantly lower than in the HOPE group.^[21] This might suggest that commencing perfusion early in the cDCD liver preservation pathway is more efficient in preventing the graft damage compared with perfusion initiated at the recipient center. However, such an explanation must be taken with caution because of the hazardous interpretation of transaminase level variations after machine perfusion, the retrospective nature of these comparisons, and other differences between the studies. The present study also suggests that clinicians feel more confident in extending the preservation time during NMP than with NRP. Indeed, NRP protocol applied herein required not to exceed a 4-h perfusion time while there is no data suggesting any deleterious effects of prolonged NRP (>4 h).

The biliary tract represents tissue that is most vulnerable to prolonged ischemia/reperfusion injury. The majority of studies assessing the outcome of cDCD versus DBD LT have reported increased rates of biliary complications in cDCD livers^[2] resulting either in decreased graft and patient survival ^22] or in more stringent selection criteria resulting in lower use rates.^[23] One of the main objectives of the use of machine perfusion in cDCD LT is to decrease the rate of NAS.^[24] The COPE trial was not powered to demonstrate any difference between SCS and NMP in terms of biliary complications; although it showed lower rates of radiologically diagnosed NAS in the NMP arm (11% vs. 26%), this difference did not achieve statistical significance, and the majority of these cases were clinically asymptomatic.^[8] In the Spanish cDCD transplant experience comparing super-rapid recovery versus NRP, the rates of both NAS and overall biliary complications were significantly reduced in the NRP group.^[4] All of these findings suggest that dynamic liver preservation strategies decrease the incidence of NAS in cDCD LT. In the present study, the rate of clinically manifest NAS was similar among the two groups (1.5% in the NRP group vs. 2.9% in the NMP group). This is considerably lower compared with the cDCD preserved by cold storage only,^24] which suggests that both perfusion technologies are clinically efficacious in reducing biliary complications in cDCD LT.

DCD livers represent a valuable source of allografts that has helped to address the shortage of organs in several countries albeit at the cost of the inferior outcomes. In addition to the NAS that may lead to graft loss, the cDCD livers have also been associated with increased rates of posttransplant acute kidney failure and inferior patient survival rates.^{[2, 22, 24, 25]} In the present study, recipients in both groups achieved a 90-day graft loss of less than 10% (4.4% after NRP, 8.8% after NMP), and 2-year graft and patient survival rates higher than 85%, thus achieving outcomes similar to those expected after LT from DBD nonmarginal grafts.^[12]

There are clear limitations to this study in relation to its retrospective nature and nonrandomized design. The two compared perfusion strategies were performed in different trials and in the context of different organ allocation policies, graft selection criteria, and health care systems. Use rates are also affected by waitlist pressure, which may vary across countries and centers. Despite some differences in recipient and donor baseline characteristics, the two groups were similar with respect to variables that could have an influence on the analyzed outcomes, and we performed an inverse probability treatment weighting adjustment, which allowed us to obtain two cohorts that were comparable for the most relevant variables, such as donor age, donor risk index, UK-DCD score, and recipient laboratory MELD score. The main difference between the groups was a higher proportion of recipients who received transplants for HCC in the NRP group; we avoided the risk of a tumor-related survival bias by presenting both overall and tumor-censored graft and patient survival rates. The other shortcoming is the relatively small size of the NMP cohort.

In conclusion, the present study is the first to compare two different machine perfusion strategies applied to cDCD livers at a donor hospital. The results suggest that both interventions, NRP and continuous NMP, improve outcomes to a level expected for DBD livers in terms of 1- and 2-year graft and patient survival rates. On the other hand, we have produced no good evidence that either technology is superior and therefore propose that this state of equipoise might be the basis for a formal prospective, randomized, controlled clinical trial to compare not only the effectiveness of these two approaches to perfusion of DCD livers but also the logistic and cost elements.

CONFLICT OF INTEREST

Darius F. Mirza owns stock in OrganOx. M. Thamara P. R. Perera is on the speakers’ bureau for OrganOx. Xavier Muller received grants from Intitut Georges Lopez. Peter J. Friend is the cofounder of, owns stock in, is employed by, consults for, advises, received grants from, and is an inventor on a licensed patent for OrganOx.

ETHICS APPROVAL

The COPE study approval was obtained from the London–Dulwich National Research Ethics Committee and the Medicines and Healthcare Regulatory Agency in the United Kingdom and research ethics committees and medical device regulatory bodies in Belgium, Spain, and Germany. The NRP program was approved by the French institutional local and national ethics committee. The presented study was approved by the COPE steering committee and by the Hospices Civils de Lyon ethics committee (approval number: CSE-HCL_21_360).