Ex vivo normothermic preservation of amputated limbs with a hemoglobin-based oxygen carrier perfusate

A meta-analysis of perfusion parameters affecting weight gain in ex vivo perfusion

BACKGROUND

Ex vivo machine perfusion (EVMP) has been established to extend viability of donor organs. However, EVMP protocols are inconsistent. We hypothesize that there is a significant relationship between specific parameters during EVMP and perfusion outcomes.

METHODS

A meta-analysis of literature was conducted in accordance with the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) Statement. The search encompassed articles published before July 25, 2023. PubMed, Embase, and CENTRAL databases were screened using search terms "ex-vivo," "ex-situ," "machine," and "perfusion." Weight gain, an indicator of organ viability, was chosen to compare outcomes. Extracted variables included perfused organ, warm and cold ischemia time before perfusion, perfusion duration, perfusate flow, pressure, temperature, perfusate composition (presence of cellular or acellular oxygen carrier, colloids, and other supplements) and percent weight change. Data were analyzed using SPSS statistical software.

RESULTS

Overall, 44 articles were included. Red blood cell-based perfusates resulted in significantly lower weight gain compared to acellular perfusates without oxygen carriers (11.3% vs. 27.0%, p < 0.001). Hemoglobin-based oxygen carriers resulted in significantly lower weight gain compared to acellular perfusates (16.5% vs. 27%, p = 0.006). Normothermic perfusion led to the least weight gain (14.6%), significantly different from hypothermic (24.3%) and subnormothermic (25.0%) conditions (p < 0.001), with no significant difference between hypothermic and subnormothermic groups (24.3% vs. 25.0%, p = 0.952). There was a positive correlation between flow rate and weight gain (ß = 13.1, R = 0.390, p < 0.001).

CONCLUSIONS

Oxygen carriers, low flow rates, and normothermic perfusate temperature appear to improve outcomes in EVMP. These findings offer opportunities for improving organ transplantation outcomes.

A Guide to the Implementation and Design of Ex Vivo Perfusion Machines for Vascularized Composite Allotransplantation

Background

Ex vivo machine perfusion (EVMP) is a versatile platform utilized in vascularized composite allotransplantation (VCA) to prolong preservation, salvage tissue, and evaluate graft viability. However, there is no consensus on best practices for VCA. This article discusses the common components, modifications, and considerations necessary for a successful VCA perfusion.

Methods

A systematic literature review was performed in several databases (PubMed, Scopus, Embase, Web of Science, Cochrane Library, and ClinicalTrials.gov) to identify articles published on VCA EVMP (face, limb, abdominal wall, uterus, penis, and free flaps) before August 2022. Graft type and animal model, general perfusion parameters, core components of the circuit, and optional components for enhanced monitoring were extracted from the articles.

Results

A total of 1370 articles were screened, and 46 articles met inclusion criteria. Most articles (84.8%) were published in the last 10 years. Pigs were the main model used, but 10 protocols used human grafts. Free flaps were the most common graft type (41.3%), then upper extremities/forelimbs (28.3%), uteruses (17.4%), and hindlimbs (13.0%). Postperfusion replantation occurred in 15.2% of studies. Normothermic perfusion predominated (54.1%), followed by hypothermic (24.3%), and subnormothermic (21.6%). The majority of studies (87.0%) oxygenated their systems, most commonly with carbogen.

Conclusions

EVMP is a rapidly growing area of research. Leveraging EVMP in VCA can optimize VCA procedures and allow for expansion into replantation, flap salvage, and other areas of plastic surgery. Currently, VCA EVMP is achieved through a variety of approaches, but standardization is necessary to advance this technology and attain clinical translation.

Study on the preservation effects of the amputated forelimb by machine perfusion at physiological temperature

PURPOSE

Ischemia and hypoxia are the main factors limiting limb replantation and transplantation. Static cold storage (SCS), a common preservation method for tissues and organs, can only prolong limb ischemia time to 4 - 6 h. The normothermic machine perfusion (NMP) is a promising method for the preservation of tissues and organs, which can extend the preservation time in vitro by providing continuous oxygen and nutrients. This study aimed to evaluate the difference in the efficacy of the 2 limb preservation methods.

METHODS

The 6 forelimbs from beagle dogs were divided into 2 groups. In the SCS group (n = 3), the limbs were preserved in a sterile refrigerator at 4 °C for 24 h, and in the NMP group (n = 3), the perfusate prepared with autologous blood was used for the oxygenated machine perfusion at physiological temperature for 24 h, and the solution was changed every 6 h. The effects of limb storage were evaluated by weight gain, perfusate biochemical analysis, enzyme-linked immunosorbent assay, and histological analysis. All statistical analyses and graphs were performed using GraphPad Prism 9.0 one-way or two-way analysis of variance. The p value of less than 0.05 was considered to indicate statistical significance.

RESULTS

In the NMP group, the weight gained percentage was 11.72% ± 4.06%; the hypoxia-inducible factor-1α contents showed no significant changes; the shape of muscle fibers was normal; the gap between muscle fibers slightly increased, showing the intercellular distance of (30.19 ± 2.83) μm; and the vascular α-smooth muscle actin (α-SMA) contents were lower than those in the normal blood vessels. The creatine kinase level in the perfusate of the NMP group increased from the beginning of perfusion, decreased after each perfusate change, and remained stable at the end of perfusion showing a peak level of 4097.6 U/L. The lactate dehydrogenase level of the NMP group increased near the end of perfusion and reached the peak level of 374.4 U/L. In the SCS group, the percentage of weight gain was 0.18% ± 0.10%, and the contents of hypoxia-inducible factor-1α increased gradually and reached the maximum level of (164.85 ± 20.75) pg/mL at the end of the experiment. The muscle fibers lost their normal shape and the gap between muscle fibers increased, showing an intercellular distance of (41.66 ± 5.38) μm. The contents of vascular α-SMA were much lower in the SCS group as compared to normal blood vessels.

CONCLUSIONS

NMP caused lesser muscle damage and contained more vascular α-SMA as compared to SCS. This study demonstrated that NMP of the amputated limb with perfusate solution based on autologous blood could maintain the physiological activities of the limb for at least 24 h.

Orthotopic forelimb transplantation in a Yucatan minipig model: Anatomic and in vivo study

INTRODUCTION

Above elbow transplants represent 19% of the upper extremity transplants. Previous large-animal models have been too distal or heterotopic, did not use immunosuppression and had short survival. We hypothesize that an orthotopic forelimb transplant model, under standard immunosuppression, is feasible and can be used to address questions on peri-transplant ischemia reperfusion injury, and post-transplantation vascular, immunologic, infectious, and functional outcomes.

MATERIALS AND METHODS

Four forelimbs were used for anatomical studies. Four mock transplants were performed to establish technique/level of muscle/tendon repairs. Four donor and four recipient female Yucatan minipigs were utilized for in-vivo transplants (endpoint 90-days). Forelimbs were amputated at the midarm and preserved through ex vivo normothermic perfusion (EVNP) utilizing an RBC-based perfusate. Hourly perfusate fluid-dynamics, gases, electrolytes were recorded. Contractility during EVNLP was graded hourly using the Medical Research Council scale. EVNP termination criteria included systolic arterial pressure ≥115 mmHg, compartment pressure ≥30 mmHg (at EVNP endpoint), oxygen saturation reduction of 20%, and weight change ≥2%. Indocyanine green (ICG) angiography was performed after revascularization. Limb rejection was evaluated clinically (rash, edema, temperature), and histologically (BANFF classification) collecting per cause and protocol biopsies (POD 1, 7, 30, 60 and endpoint). Systemic infections were assessed by blood culture and tissue histology. CT scan was used to confirm bone bridging at endpoint.

RESULTS

Animals 2, 4 reached endpoint with grade 0-I rejection. Limbs 1, 3 presented grade III rejection on days 6, 61. CsA troughs averaged 461 ± 189 ng/mL. EVNLP averaged 4.3 ± 0.52 h. Perfusate lactate, PO2 , and pH were 5.6 ± 0.9 mmol/L, 557 ± 72 mmHg and 7.5 ± 0.1, respectively. Muscle contractions were 4 [1] during EVNLP. Transplants 2, 3, 4 showed bone bridging on CT.

CONCLUSION

We present preliminary evidence supporting the feasibility of an orthotopic, mid-humeral forelimb allotransplantation model under standard immunosuppression regimen. Further research should validate the immunological, infectious, and functional outcomes of this model.

Normothermic Machine Perfusion Systems: Where Do We Go From Here?

Normothermic machine perfusion (NMP) aims to preserve organs ex vivo by simulating physiological conditions such as body temperature. Recent advancements in NMP system design have prompted the development of clinically effective devices for liver, heart, lung, and kidney transplantation that preserve organs for several hours/up to 1 d. In preclinical studies, adjustments to circuit structure, perfusate composition, and automatic supervision have extended perfusion times up to 1 wk of preservation. Emerging NMP platforms for ex vivo preservation of the pancreas, intestine, uterus, ovary, and vascularized composite allografts represent exciting prospects. Thus, NMP may become a valuable tool in transplantation and provide significant advantages to biomedical research. This review recaps recent NMP research, including discussions of devices in clinical trials, innovative preclinical systems for extended preservation, and platforms developed for other organs. We will also discuss NMP strategies using a global approach while focusing on technical specifications and preservation times.

Review of machine perfusion studies in vascularized composite allotransplant preservation

The applications of Vascularized composite allotransplantation (VCA) are increasing since the first successful hand transplantation in 1998. However, the abundance of muscle tissue makes VCA's vulnerable to ischemia-reperfusion injury (IRI), which has detrimental effects on the outcome of the procedure, restricting allowable donor-to-recipient time and limiting its widespread use. The current clinical method is Static cold storage (SCS) and this allows only 6 h before irreversible damage occurs upon reperfusion. In order to overcome this obstacle, the focus of research has been shifted towards the prospect of ex-vivo perfusion preservation which already has an established clinical role in solid organ transplants especially in the last decade. In this comprehensive qualitative review, we compile the literature on all VCA machine perfusion models and we aim to highlight the essentials of an ex vivo perfusion set-up, the different strategies, and their associated outcomes.

Weight gain is an early indicator of injury in ex vivo normothermic limb perfusion (EVNLP)

PURPOSE

There are no established criteria for discontinuing ex vivo normothermic limb perfusion (EVNLP) before irreversible damage occurs. This study evaluates weight gain as an indicator of injury during EVNLP.

METHODS

Sixteen Yorkshire pig forelimbs were procured and preserved using EVNLP with a hemoglobin-based oxygen carrier (HBOC-201) or static cold storage. EVNLP continued until termination criteria were met: arterial pressure ≥ 115 mm Hg, compartment pressure > 30 mm Hg, or 20% reduction of oxygen saturation. Limb weight, contractility, hemodynamics, perfusate electrolytes, metabolites and gases were recorded. Muscles were biopsied 6-h, and muscle injury scores (MIS) calculated. Forearm compartment pressures and indocyanine green (ICG) angiography were recorded at endpoint. Outcomes were compared at 2%, 5%, 10%, and 20% limb weight gain.

RESULTS

EVNLP lasted 20 ± 3 h. Weight gain was observed after 13 ± 5 h (2%), 15 ± 6 h (5%), 16 ± 6 h (10%), and 19 ± 4 h (20%). Weight correlated positively with MIS (ρ = 0.92, p < 0.0001), potassium (ρ = -1.00, p < 0.0001), pressure (ρ = 0.78, p < 0.0001), and negatively with contractility (ρ = -0.96, p = 0.011). At 5% weight gain, MIS (p < 0.0001), potassium (p = 0.03), and lactate (p < 0.0001) were significantly higher than baseline. Median muscle contractility was 5 [3-5] at 2% weight gain, 4 [1-5] at 5%, 3 [0-4] and 2 [0-2] at 10% and 20%, respectively. At 20% weight gain, contractility was significantly lower than baseline (p = 0.003). Percent weight gain correlated negatively with endpoint ICG hoof fluorescence (r = -0.712, p = 0.047).

CONCLUSIONS

Weight gain correlated with microscopic muscle injury and was the earliest evidence of limb dysfunction. Weight gain may serve as a criterion for discontinuation of EVNLP.

Improving the ischemia-reperfusion injury in vascularized composite allotransplantation: Clinical experience and experimental implications

Long-time ischemia worsening transplant outcomes in vascularized composite allotransplantation (VCA) is often neglected. Ischemia-reperfusion injury (IRI) is an inevitable event that follows reperfusion after a period of cold static storage. The pathophysiological mechanism activates local inflammation, which is a barrier to allograft long-term immune tolerance. The previous publications have not clearly described the relationship between the tissue damage and ischemia time, nor the rejection grade. In this review, we found that the rejection episodes and rejection grade are usually related to the ischemia time, both in clinical and experimental aspects. Moreover, we summarized the potential therapeutic measures to mitigate the ischemia-reperfusion injury. Compare to static preservation, machine perfusion is a promising method that can keep VCA tissue viability and extend preservation time, which is especially beneficial for the expansion of the donor pool and better MHC-matching.