Twenty-Four-Hour Ex Vivo Perfusion with Acellular Solution Enables Successful Replantation of Porcine Forelimbs

Machine Perfusion Enables 24-h Preservation of Vascularized Composite Allografts in a Swine Model of Allotransplantation

The current gold standard for preserving vascularized composite allografts (VCA) is 4°C static cold storage (SCS), albeit muscle vulnerability to ischemia can be described as early as after 2 h of SCS. Alternatively, machine perfusion (MP) is growing in the world of organ preservation. Herein, we investigated the outcomes of oxygenated acellular subnormothermic machine perfusion (SNMP) for 24-h VCA preservation before allotransplantation in a swine model. Six partial hindlimbs were procured on adult pigs and preserved ex vivo for 24 h with either SNMP (n = 3) or SCS (n = 3) before heterotopic allotransplantation. Recipient animals received immunosuppression and were followed up for 14 days. Clinical monitoring was carried out twice daily, and graft biopsies and blood samples were regularly collected. Two blinded pathologists assessed skin and muscle samples. Overall survival was higher in the SNMP group. Early euthanasia of 2 animals in the SCS group was linked to significant graft degeneration. Analyses of the grafts showed massive muscle degeneration in the SCS group and a normal aspect in the SNMP group 2 weeks after allotransplantation. Therefore, this 24-h SNMP protocol using a modified Steen solution generated better clinical and histological outcomes in allotransplantation when compared to time-matched SCS.

Design of a Multiparametric Perfusion Bioreactor System for Evaluating Sub-Normothermic Preservation of Rat Abdominal Wall Vascularized Composite Allografts

Static cold storage (SCS), the current clinical gold standard for organ preservation, provides surgeons with a limited window of time between procurement and transplantation. In vascularized composite allotransplantation (VCA), this time limitation prevents many viable allografts from being designated to the best-matched recipients. Machine perfusion (MP) systems hold significant promise for extending and improving organ preservation. Most of the prior MP systems for VCA have been built and tested for large animal models. However, small animal models are beneficial for high-throughput biomolecular investigations. This study describes the design and development of a multiparametric bioreactor with a circuit customized to perfuse rat abdominal wall VCAs. To demonstrate its concept and functionality, this bioreactor system was employed in a small-scale demonstrative study in which biomolecular metrics pertaining to graft viability were evaluated non-invasively and in real time. We additionally report a low incidence of cell death from ischemic necrosis as well as minimal interstitial edema in machine perfused grafts. After up to 12 h of continuous perfusion, grafts were shown to survive transplantation and reperfusion, successfully integrating with recipient tissues and vasculature. Our multiparametric bioreactor system for rat abdominal wall VCA provides an advanced framework to test novel techniques to enhance normothermic and sub-normothermic VCA preservations in small animal models.

Machine Perfusion Deters Ischemia-Related Derangement of a Rodent Free Flap: Development of a Model

INTRODUCTION

Machine perfusion can enable isolated support of composite tissues, such as free flaps. The goal of perfusion in this setting is to preserve tissues prior to transplantation or provide transient support at the wound bed. This study aimed to establish a rodent model of machine perfusion in a fasciocutaneous-free flap to serve as an affordable testbed and determine the potential of the developed support protocol to deter ischemia-related metabolic derangement.

METHODS

Rat epigastric-free flaps were harvested and transferred to a closed circuit that provides circulatory and respiratory support. Whole rat blood was recirculated for 8 h, while adjusting the flow rate to maintain arterial-like perfusion pressures. Blood samples were collected during support. Extracellular tissue lactate and glucose levels were characterized with a microdialysis probe and compared with warm ischemic, cold ischemic, and anastomosed-free flap controls.

RESULTS

Maintenance of physiologic arterial pressures (85-100 mmHg) resulted in average pump flow rates of 360-430 μL/min. Blood-based measurements showed maintained glucose and oxygen consumption throughout machine perfusion. Average normalized lactate to glucose ratio for the perfused flaps was 5-32-fold lower than that for the warm ischemic flap controls during hours 2-8 (P < 0.05).

CONCLUSIONS

We developed a rat model of ex vivo machine perfusion of a fasciocutaneous-free flap with maintained stable flow and tissue metabolic activity for 8 h. This model can be used to assess critical elements of support in this setting as well as explore other novel therapies and technologies to improve free tissue transfer.

Normothermic Ex Situ Machine Perfusion of Vascularized Composite Allografts with Oxygen Microcarriers for 12 Hours Using Real-Time Mitochondrial Redox Quantification

BACKGROUND

Normothermic ex situ perfusion of vascularized composite allografts (VCAs) necessitates high oxygen demand and, thus, increased metabolic activity, which, in turn, requires the use of blood-based perfusion solutions. However, blood-derived perfusates, in turn, constitute an antigenic load. To circumvent this immunogenic problem, we used a perfusate enriched with acellular dextrane oxygen microcarriers to perfuse rat hindlimbs.

METHODS

Rat hindlimbs (n = 11) were perfused with either (non-), oxygenated dextrane-enriched Phoxilium, or Phoxilium enriched with dextrane oxygen microcarriers (MO2) for 12 h at 37 °C or stored on ice. Oxygenation of the skeletal muscle was assessed with Raman spectroscopy, tissue pO2-probes, and analysis of the perfusate. Transmission electronic microscopy was utilized to assess the ultrastructure of mitochondria of the skeletal muscle.

RESULTS

For all evaluated conditions, ischemia time until perfusion was comparable (22.91 ± 1.64 min; p = 0.1559). After 12 h, limb weight increased significantly by at least 81%, up to 124% in the perfusion groups, and by 27% in the static cold storage (SCS) group. Raman spectroscopy signals of skeletal muscle did not differ substantially among the groups during either perfusion or static cold storage across the duration of the experiment. While the total number of skeletal muscle mitochondria decreased significantly compared to baseline, mitochondrial diameter increased in the perfusion groups and the static cold storage group.

CONCLUSION

The use of oxygen microcarriers in ex situ perfusion of VCA with acellular perfusates under normothermic conditions for 12 h facilitates the maintenance of mitochondrial structure, as well as a subsequent recovery of mitochondrial redox status over time, while markers of muscle injury were lower compared to conventional oxygenated acellular perfusates.

Long-Term Survival and Functional Recovery of Cryopreserved Vascularized Groin Flap and Below-the-Knee Rat Limb Transplants

Effective cryopreservation of large tissues, limbs, and organs has the potential to revolutionize medical post-trauma reconstruction options and organ preservation and transplantation procedures. To date, vitrification and directional freezing are the only viable methods for long-term organ or tissue preservation, but are of limited clinical relevance. This work aimed to develop a vitrification-based approach that will enable the long-term survival and functional recovery of large tissues and limbs following transplantation. The presented novel two-stage cooling process involves rapid specimen cooling to subzero temperatures, followed by gradual cooling to the vitrification solution (VS) and tissue glass transition temperature. Flap cooling and storage were only feasible at temperatures equal to or slightly lower than the VS Tg (i.e., -135°C). Vascularized rat groin flaps and below-the-knee (BTK) hind limb transplants cryopreserved using this approach exhibited long-term survival (>30 days) following transplantation to rats. BTK-limb recovery included hair regrowth, normal peripheral blood flow, and normal skin, fat, and muscle histology. Above all, BTK limbs were reinnervated, enabling rats to sense pain in the cryopreserved limb. These findings provide a strong foundation for the development of a long-term large-tissue, limb and organ preservation protocol for clinical use.

The heart-lung machine in major limb replantation: Report of two cases

Replantation of amputated limbs after long ischemic hours almost always comes with reperfusion syndrome and poor outcomes. An ischemic time of greater than 6 h is often considered unsuitable for major limb replantation. However, usage of extracorporeal perfusion has been shown to prolong the viability of major limbs in animal studies. The aim of this report is to show that extracorporeal perfusion with cardiopulmonary bypass machine (CPBM) is a safe and reliable technique in improving limb survival as illustrated by our cases. We report two cases of successful major limb replantation with late presentation. One case involved a 31-year-old man with shoulder disarticulation and the other involved a 30-year-old man sustained proximal transtibial amputation. Both patients, who were generally fit, were involved in major road traffic accidents. The amputated segments were connected to a CPBM to expedite reperfusion and to flush away anaerobic metabolic products. The major vessels were cannulated and connected to a bypass machine that was initially primed with heparinized saline and perfused with packed cells at 100% oxygen concentration. The perfusion was carried out at 35°C with low pressure to prevent edema and low flow to reduce reperfusion injury. Venous blood was drained completely before replantation. Total ischemia times were 7 h 40 min and 9 h, respectively. No evidences of perioperative reperfusion syndrome were seen. Both of the replanted limbs survived and patients had regained better-than-expected limb functional outcomes at 5-year and 2-year follow-up, respectively. CPBM may be safely used in major replantation surgery to enhance limb survival and therefore warrants further research.

Continuous versus Pulsatile Flow in 24-Hour Vascularized Composite Allograft Machine Perfusion in Swine: A Pilot Study

INTRODUCTION

Multiple perfusion systems have been investigated on vascularized composite allografts, with various temperatures and different preservation solutions, most using continuous flow (CF). However, physiological flow is pulsatile and provides better outcomes in kidney and lung ex vivo perfusions. The objective of this pilot study is to compare pulsatile flow (PF) with CF in our 24-h subnormothermic machine perfusion protocol for swine hindlimbs.

METHODS

Partial hindlimbs were harvested from Yorkshire pigs and perfused with a modified Steen solution at 21°C for 24 h either with CF (n = 3) or with pulsatile flow (PF) at 60 beats/min (n = 3). Perfusion parameters, endothelial markers, and muscle biopsies were assessed at different timepoints.

RESULTS

Overall, lactate levels were significantly lower in the PF group (P = 0.001). Glucose uptake and potassium concentration were similar in both groups throughout perfusion. Total nitric oxide levels were significantly higher in the PF group throughout perfusion (P = 0.032). Nitric oxide/endothelin-1 ratio also tends to be higher in the PF group, reflecting a potentially better vasoconductivity with PF, although not reaching statistical significance (P = 0.095). Arterial resistances were higher in the PF group (P < 0.001). Histological assessment did not show significant difference in muscular injury between the two groups. Weight increased quicker in the CF group but reached similar values with the PF after 24 h.

CONCLUSIONS

This pilot study suggests that PF may provide superior preservation of vascularized composite allografts when perfused for 24 h at subnormothermic temperatures, with potential improvement in endothelial function and decreased ischemic injury.

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.

Proof of Concept Study for a Closed Ex-Vivo Limb Perfusion System for 24-hour Subnormothermic Preservation Using Acellular Perfusate

BACKGROUND

The two approaches to vascularized tissue machine perfusion utilize either the open (non-pressurized) or closed (pressurized) perfusion system. Most studies describing isolated limb perfusion preservation rely on open perfusion systems and report tissue edema exceeding 40% after 12-14 hours of preservation.A variant of machine perfusion places the limb and perfusate into a reservoir closed to atmosphere. It is hypothesized that the reservoir pressure, acting as a transmural pressure, has the advantage of reducing edema formation by counteracting the hydrostatic pressure gradient from the perfusion pressure.This proof-of-concept study aim was to demonstrate feasibility of the ULiSSESTM device (closed, vertical perfusion system) to preserve forelimbs of Sus Scrofa swine for 24 hours of subnormothermic perfusion compared to an open, horizontal perfusion system. The ULiSSES™ is a compact, practical device that applies pulsatile, pressurized perfusion through the novel use of a diaphragm pump powered by compressed oxygen.

METHODS

Forelimbs from swine were preserved in ULiSSES™ device (closed perfusion system) (n = 9) and in an open perfusion system (n = 4) using sub-normothermic modified Krebs-Henseleit Solution. Physiological parameters were measured at the start and every 3 hours for 24 hours. Limbs were weighed prior to and post perfusion to compare weight gain. Edema and cellular integrity were evaluated using histopathology pre and post perfusion.

RESULTS

Closed perfusion system showed superiority compared to the open perfusion system in terms of oxygen consumption, reduction in vascular resistance, and overall tissue integrity. The closed perfusion system demonstrated a 21% reduction in weight gain compared to the open perfusion system and significantly reduced intracellular edema.

CONCLUSION

The ULiSSES™ closed, pressurized perfusion technology has translatable military applications with the potential to preserve porcine limbs for 24 hours with improved results compared to an open perfusion system.

LEVEL OF EVIDENCE

N/A.

24-hour Perfusion of Porcine Myocutaneous Flaps Mitigates Reperfusion Injury: A 7-day Follow-up Study

Background:

Static cold storage is the gold standard of preservation in vascularized composite allotransplantation and allows a preservation time of 4–6 hours. Machine preservation is a promising technique for prolonged preservation; however, studies on extended preservation that compare different preservatives are scarce. This study aims to assess the feasibility of 24-hour acellular perfusion and compares different preservation solutions in a porcine myocutaneous flap replantation model.

Methods:

Six harvested bilateral myocutaneous flaps of three Dutch Landrace pigs were perfused hypothermically for 24 hours with University of Wisconsin machine perfusion solution (UW-MPS; n = 2) or histidine-tryptophan-ketoglutarate solution (HTK; n = 2) or preserved on ice for 4 hours (n = 2) before orthotopic replantation. Animals were observed for 7 days after replantation. Skeletal muscle injury was assessed by biochemical markers during perfusion, and muscle biopsies were analyzed for ischemia reperfusion injury directly after preservation and at 1, 3, and 7 days after replantation.

Results:

Markers of muscle damage varied during perfusion, but decreased overall in both perfusion groups. Flap weight increased 60% and 97% in the HTK-perfused flaps, compared with -6% and -7% in the UW-MPS-perfused flaps after 24 hours. Histopathologic evaluation demonstrated decreased muscle damage in flaps perfused with HTK compared with the UW-MPS-perfused flaps at 1 week after replantation.

Conclusions:

Machine perfusion of myocutaneous flaps for 24 hours with subsequent replantation is feasible, but warrants further research. Perfusion with HTK solution seemed to result in better histological outcomes 7 days after reperfusion compared with UW-MPS.

Renal hemofiltration prevents metabolic acidosis and reduces inflammation during normothermic machine perfusion of the vascularized composite allograft-A preclinical study

INTRODUCTION

Recent experimental evidence suggests normothermic machine perfusion of the vascularized composite allograft results in improved preservation compared to static cold storage, with less reperfusion injury in the immediate post-operative period. However, metabolic acidosis is a common feature of vascularized composite allograft perfusion, primarily due to the inability to process metabolic by-products. We evaluated the impact of combined limb-kidney perfusion on markers of metabolic acidosis and inflammation in a porcine model.

METHODS

Ten paired pig forelimbs were used for this study, grouped as either limb-only (LO, n = 5) perfusion, or limb-kidney (LK, n = 5) perfusion. Infrared thermal imaging was used to determine homogeneity of perfusion. Lactate, bicarbonate, base, pH, and electrolytes, along with an inflammatory profile generated via the quantification of cytokines and cell-free DNA in the perfusate were recorded.

RESULTS

The addition of a kidney to a limb perfusion circuit resulted in the rapid stabilization of lactate, bicarbonate, base, and pH. Conversely, the LO circuit became progressively acidotic, correlating in a significant increase in pro-inflammatory cytokines. Global perfusion across the limb was more homogenous with LK compared to LO.

CONCLUSION

The addition of a kidney during limb perfusion results in significant improvements in perfusate biochemistry, with no evidence of metabolic acidosis.

Rectus Abdominis Flap Replantation after 18 h Hypothermic Extracorporeal Perfusion-A Porcine Model

Cold storage remains the clinical standard for composite tissue preservation but is time-limited. A long ischemia time during surgery will adversely affect postoperative outcomes due to ischemia-reperfusion injury. Extracorporeal perfusion (ECP) seems to be a promising alternative for prolonged preservation, but more evidence is needed to support its use and to identify optimal perfusion fluids. This article assessed musculocutaneous flap vitality after prolonged ECP and compared outcomes after replantation to short static cold storage (SCS). Unilateral musculocutaneous rectus abdominis flaps were raised from 15 pigs and preserved by 4 h SCS (n = 5), 18 h mid-thermic ECP with Histidine–Tryptophan–Ketoglutarate (HTK, n = 5) or University of Wisconsin solution (UW, n = 5). Flaps were replanted and observed for 12 h. Skeletal muscle histology was assessed (score 0–12; high scores equal more damage), blood and perfusate samples were collected and weight was recorded as a marker for oedema. Mean histological scores were 4.0 after HTK preservation, 5.6 after UW perfusion and 5.0 after SCS (p = 0.366). Creatinine kinase (CK) was higher after ECP compared to SCS (p < 0.001). No weight increase was observed during UW perfusion, but increased 56% during HTK perfusion. Following 12 h reperfusion, mean weight gain reduced 39% in the HTK group and increased 24% in the UW group and 17% in the SCS group. To conclude, skeletal muscle seemed well preserved after 18 h ECP with HTK or UW perfusion, with comparable histological results to 4 h SCS upon short reperfusion. The high oedema rate during HTK perfusion remains a challenge that needs to be further addressed.

Comparison of Acellular Solutions for Ex-situ Perfusion of Amputated Limbs

INTRODUCTION

Hypothermic ex-situ machine perfusion (MP) has been shown to be a promising alternative to static cold storage (SCS) for preservation of solid organs for transplantation and vascularized composite allotransplantation. Perfusion with blood-based perfusion solutions in austere environments is problematic due to their need for appropriate storage and short shelf life, making it impractical for military and emergency use. Acellular perfusion has been shown to be effective, but the ideal perfusate solution for MP of amputated limbs is yet to be determined. The purpose of this study is to evaluate the efficacy of alternative perfusate solutions, such as dextran-enriched Phoxilium, Steen, and Phoxilium in ex-vivo hypothermic MP of amputated limbs in a porcine model.

MATERIALS AND METHODS

Amputated forelimbs from Yorkshire pigs (n = 8) were preserved either in SCS (n = 2) at 4°C for 12 hours or machine-perfused at 10°C for 12 hours with oxygenated perfusion solutions (n = 6) at a constant flow rate. The perfusates used include modified Steen-solution, Phoxilium (PHOX), or Phoxilium enriched with dextran-40 (PHODEX). The perfusate was exchanged after 1 and 6 hours of perfusion. Machine data were recorded continuously. Perfusate samples for clinical chemistry, blood gas analysis, and muscle biopsies were procured at specific timepoints and subsequently analyzed. In this semi in-vivo study, limb replantation has not been performed.

RESULTS

After amputation, every limb was successfully transferred and connected to our perfusion device. The mean total ischemia time was 77.5 ± 5.24 minutes. The temperature of the perfusion solution was maintained at 10.18 ± 2.01°C, and perfusion pressure at 24.48 ± 10.72 mmHg. Limb weight increased by 3% in the SCS group, 36% in the PHODEX group, 25% in the Steen group, and 58% in the PHOX group after 12 hours. This increase was significant in the PHOX group compared with the SCS group. All perfusion groups showed a pressure increase of 10.99 mmHg over time due to edema. The levels of HIF-1a decreased over time in all groups except the Steen and the PHODEX group. The biomarkers of muscle injury in the perfusate samples, such as creatine kinase and lactate-dehydrogenase, showed a significant difference between groups, with highest values in the PHODEX group. No significant differences were found in the results of the blood gas analysis.

CONCLUSION

With the exception of significantly higher levels of creatine kinase and lactate dehydrogenase, MP with dextran-enriched Phoxilium provides similar results as that of the commercially available perfusates such as Steen, without the need for cold storage, and at circa 5% of the cost of the Steen solution. Further large-scale replantation studies are necessary to evaluate the efficacy of dextran-enriched Phoxilium as an alternate perfusate solution.

Successful 18-h acellular extracorporeal perfusion and replantation of porcine limbs - Histology versus nerve stimulation

The current standard for composite tissue preservation is static cold storage (SCS) and is limited to 6 h until irreversible muscle damage occurs. Extracorporeal perfusion (ECP) is a promising technique for prolonged preservation, however, functional results have been scarcely researched. This article assessed neuromuscular function and compared results to histological alterations to predict muscle damage after ECP. Forelimbs of twelve Dutch landrace pigs were amputated and preserved by 4 h SCS at 4–6 °C (n = 6) or 18 h mid‐thermic ECP with University of Wisconsin solution (n = 6). Limbs were replanted and observed for 12 h. Sham surgery was performed on contralateral forelimbs (n = 12). Histology analysis scored four subgroups representing different alterations (higher score equals more damage). Muscle contraction after median nerve stimulation was comparable between ECP, SCS, and sham limbs (P = 0.193). Histology scores were higher in ECP limbs compared to SCS limbs (4.8 vs. 1.5, P = 0.013). This was mainly based on more oedema in these limbs. In‐vivo muscle contraction was well preserved after 18 h ECP compared to short SCS, although histology seemed inferior in this group. Histology, therefore, did not correlate to muscle function at 12 h after replantation. This leads to the question whether histology or neuromuscular function is the best predictor for transplant success.

Tissue Viability of Free Flaps after Extracorporeal Perfusion Using a Modified Hydroxyethyl Starch Solution

BACKGROUND

In free flap surgery, tissue is stored under hypothermic ischemia. Extracorporeal perfusion (EP) has the potential to extend storage time and the tissue's perspective of survival. In the present study, the aim is to improve a recently established, simplified extracorporeal perfusion system.

METHODS

Porcine musculus rectus abdominis were stored under different conditions. One group was perfused continuously with a simplified one-way perfusion system for six hours, while the other received only a single flush but no further treatment. A modified hydroxyethyl starch solution was used as a perfusion and flushing solution. Vitality, functionality, and metabolic activity of both groups were analyzed.

RESULTS

Perfused muscles, in contrast to the ischemically stored ones, showed no loss of vitality and significantly less functionality loss, confirming the superiority of storage under continuous perfusion over ischemic storage. Furthermore, in comparison to a previous study, the results were improved even further by using a modified hydroxyethyl starch solution.

CONCLUSION

The use of EP has major benefits compared to the clinical standard static storage at room temperature. Continuous perfusion not only maintains the oxygen and nutrient supply but also removes toxic metabolites formed due to inadequate storage conditions.

Hypothermic Ex Situ Perfusion of Human Limbs With Acellular Solution for 24 Hours

BACKGROUND

Machine perfusion (MP) has evolved as a promising approach for the ex situ preservation in organ transplantation. However, the literature on the use of MP in human vascularized composite allografts is scarce. The aim of this study was to evaluate the effects of hypothermic MP with an acellular perfusate in human upper extremities and compare with the current gold standard of static cold storage (SCS).

METHODS

Six upper extremities were assigned to either MP (n = 3) or SCS (n = 3) conditions for 24 h. MP-extremities were perfused with oxygenated Steen solution at a constant pressure of 30 mm Hg and 10°C.

RESULTS

Median total ischemia time was 213 min (range, 127-222 min). Myoglobin, creatine-kinase (CK) showed increased levels at the start of MP (medians: myoglobin: 4377 ng/mL, CK: 1442 U/L), peaking 6 h after perfusate exchange (medians: myoglobin: 9206 ng/mL, CK: 3995 U/L) at timepoint 24. Lactate levels decreased from a median of 6.9-2.8 mmol/L over time. Expression of hypoxia-inducible factor 1-alpha peaked in the SCS-group after 8 h, followed by a decrease. Increased hypoxia-inducible factor 1-alpha expression in the MP group was delayed until 20 h. Perfusion pressure, temperature, and circuit flow were maintained at median of 30.88 mm Hg, 9.77°C, and 31.13 mL/min, respectively. Weight increased 1.4% in the SCS group and 4.3% in the MP group over 24 h.

CONCLUSIONS

Hypothermic ex situ perfusion with an oxygenated acellular Steen solution may extend the allowable extracorporeal preservation time by a factor of 4-6 compared to SCS and holds promise to be beneficial for vascularized composite allograft recipients and victims of traumatic major limb amputation.