Extension of Cold Static Donor Lung Preservation at 10°C

How do we expand the lung donor pool?

PURPOSE OF REVIEW

Lung transplantation activity continues to be limited by the availability of timely quality donor lungs. It is apparent though that progress has been made. The steady evolution of clinical practice, combined with painstaking scientific discovery and innovation are described.

RECENT FINDINGS

There have been successful studies reporting innovations in the wider use and broader consideration of donation after circulatory death donor lungs, including an increasing number of transplants from each of the controlled, uncontrolled and medically assisted dying donor descriptive categories. Donors beyond age 70 years are providing better than expected long-term outcomes. Hepatitis C PCR positive donor lungs can be safely used if treated postoperatively with appropriate antivirals. Donor lung perfusion at a constant 10 degrees appears capable of significantly improving donor logistics and ex-vivo lung perfusion offers the potential of an ever-increasing number of novel donor management roles. Bioartificial and xenografts remain distant possibilities only at present.

SUMMARY

Donor lungs have proved to be surprisingly robust and combined with clinical, scientific and engineering innovations, the realizable lung donor pool is proving to be larger than previously thought.

Extended ischemic time (>15 hours) using controlled hypothermic storage in lung transplantation: A multicenter experience

Static ice storage has long been the standard-of-care for lung preservation, although freezing injury limits ischemic time (IT). Controlled hypothermic storage (CHS) at elevated temperature could safely extend IT. This retrospective analysis assesses feasibility and safety of CHS with IT > 15 hours. Three lung transplant (LuTx) centers (April-October 2023) included demographics, storage details, IT, and short-term outcome from 13 LuTx recipients (8 male, 59 years old). Donor lungs were preserved in a portable CHS device at 7 (5-9.3)°C. Indication was overnight bridging and/or long-distance transport. IT of second-implanted lung was 17.3 (15.1-22) hours. LuTx were successful, 4/13 exhibited primary graft dysfunction grade 3 within 72 hours and 0/13 at 72 hours. Post-LuTx mechanical ventilation was 29 (7-442) hours. Intensive care unit stay was 9 (5-28) and hospital stay 30 (16-90) days. Four patients needed postoperative extracorporeal membrane oxygenation (ECMO). One patient died (day 7) following malpositioning of an ECMO cannula. This multicenter experience demonstrates the possibility of safely extending IT > 15 hours by CHS.

Donor Lung Preservation at 10°C: Clinical and Logistical Impact

INTRODUCTION

Cold static donor lung preservation at 10°C appears to be a promising method to safely extend the cold ischemic time (CIT) and improve lung transplant (LTx) logistics.

METHODS

LTx from November 2021 to February 2023 were included in this single institution, prospective, non-randomized study comparing prolonged preservation at 10°C versus standard preservation on ice. The inclusion criteria for 10°C preservation were suitable grafts for LTx without any donor retrieval concerns.

PRIMARY ENDPOINT

primary graft dysfunction (PGD) grade-3 at 72-h. Secondary endpoints: clinical outcomes, cytokine profile and logistical impact.

RESULTS

Thirty-three out of fifty-seven cases were preserved at 10°C. Donor and recipient characteristics were similar across the groups. Total preservation times (h:min) were longer (p<0.001) in the 10°C group [1st lung: median 12:09 (IQR 9:23-13:29); 2nd: 14:24 (12:00-16:20)] vs. standard group [1st lung: median 5:47 (IQR 5:18-6:40); 2nd: 7:15 (6:33-7:40)]. PGD grade-3 at 72-h was 9.4% in 10°C group vs. 12.5% in standard group (p=0.440). Length of mechanical ventilation (MV), ICU and hospital stays were similar in both groups. Thirty and ninety-day mortality rates were 0% in 10°C group (vs. 4.2% in standard group). IL-8 concentration was significantly higher 6-h post-LTx in the standard group (p=0.025) and IL-10 concentration was increased 72-h post-LTx in the 10°C group (p=0.045).

CONCLUSIONS

Preservation at 10°C may represent a safe and feasible strategy to intentionally prolong the CIT. In our center, extending the CIT at 10°C may allow for semi-elective LTx and improve logistics with similar outcomes compared to the current standard preservation on ice.

Technical Advances Targeting Multiday Preservation of Isolated Ex Vivo Lung Perfusion

Indications for ex vivo lung perfusion (EVLP) have evolved from assessment of questionable donor lungs to treatment of some pathologies and the logistics. Yet up to 3 quarters of donor lungs remain discarded across the globe. Multiday preservation of discarded human lungs on EVLP platforms would improve donor lung utilization rates via application of sophisticated treatment modalities, which could eventually result in zero waitlist mortality. The purpose of this article is to summarize advances made on the technical aspects of the protocols in achieving a stable multiday preservation of isolated EVLP. Based on the evidence derived from large animal and/or human studies, the following advances have been considered important in achieving this goal: ability to reposition donor lungs during EVLP; perfusate adsorption/filtration modalities; perfusate enrichment with plasma and/or donor whole blood, nutrients, vitamins, and amino acids; low-flow, pulsatile, and subnormothermic perfusion; positive outflow pressure; injury specific personalized ventilation strategies; and negative pressure ventilation. Combination of some of these advances in an automatized EVLP device capable of managing perfusate biochemistry and ventilation would likely speed up the processes of achieving multiday preservation of isolated EVLP.

Controlled Hypothermic Storage for Lung Preservation: Leaving the Ice Age Behind

Controlled hypothermic storage (CHS) is a recent advance in lung transplantation (LTx) allowing preservation at temperatures higher than those achieved with traditional ice storage. The mechanisms explaining the benefits of CHS compared to conventional static ice storage (SIS) remain unclear and clinical data on safety and feasibility of lung CHS are limited. Therefore, we aimed to provide a focus review on animal experiments, molecular mechanisms, CHS devices, current clinical experience, and potential future benefits of CHS. Rabbit, canine and porcine experiments showed superior lung physiology after prolonged storage at 10°C vs. ≤4°C. In recent molecular analyses of lung CHS, better protection of mitochondrial health and higher levels of antioxidative metabolites were observed. The acquired insights into the underlying mechanisms and development of CHS devices allowed clinical application and research using CHS for lung preservation. The initial findings are promising; however, further data collection and analysis are required to draw more robust conclusions. Extended lung preservation with CHS may provide benefits to both recipients and healthcare personnel. Reduced time pressure between procurement and transplantation introduces flexibility allowing better decision-making and overnight bridging by delaying transplantation to daytime without compromising outcome.

The Advent of Semi-Elective Lung Transplantation-Prolonged Static Cold Storage at 10°C

Since the early days of clinical lung transplantation the preservation of donor organs has become a fairly standardized procedure and most centers do follow similar processes. This includes the use of low-potassium high dextran flush solutions and static cold storage (SCS) in a cooler filled with ice. Depending on the length of SCS, organs usually arrive at the recipient hospital at a temperature of 0°C-4°C. The question of the optimal storage temperature for donor lung preservation has been revisited as data from large animal experiments demonstrated that organs stored at 10°C experience less mitochondrial damage. Thus, prolonged cold ischemic times can be better tolerated at 10°C-even in pre-damaged organs. The clinical applicability of these findings was demonstrated in an international multi-center observational study including three high-volume lung transplant centers. Total clinical preservation times of up to 24 hrs have been successfully achieved in organs stored at 10°C without hampering primary organ function and short-term outcomes. Currently, a randomized-controlled trial (RCT) is recruiting patients with the aim to compare standard SCS on ice with prolonged SCS protocol at 10°C. If, as anticipated, this RCT confirms data from previous studies, lung transplantation could indeed become a semi-elective procedure.