A CLUE for better assessment of donor lungs: Novel technique in clinical ex vivo lung perfusion

Real-time lung weight measurement during clinical ex vivo lung perfusion

BACKGROUND

Real-time lung weight (LW) measurement is a simple and non-invasive technique for detecting extravascular lung water during ex vivo lung perfusion (EVLP). We investigated the feasibility of real-time LW measurement in clinical EVLP as a predictor of transplant suitability and post-transplant outcomes.

METHODS

In our clinical acellular EVLP protocol, real-time LW was measured in 117 EVLP cases from June 2019 to June 2022. The estimated LW gain at each timepoint was calculated using a scale placed under the organ chamber. The lungs were classified into four categories based on LW adjusted for height and compared between suitable and unsuitable cases. The relationship between estimated LW gain and primary graft dysfunction was also investigated.

RESULTS

The estimated LW gain during the EVLP significantly correlated with the LW gain (post EVLP LW - pre EVLP LW) measured on the back table (R2=0.61, P<0.01). In the adjusted LW categories 2-4, the estimated LW gain at 0-1 h after EVLP was significantly higher in unsuitable cases than in suitable cases. The area under the curve for the estimated LW gain was ≥0.80. Primary graft dysfunction grade 0-1 had a significantly lower estimated LW gain at 60 min than grades 2-3 (-43 vs. 1 g, P<0.01).

CONCLUSIONS

Real-time lung measurements can predict transplant suitability and post-transplant outcomes by the early detection of extravascular lung water during the initial 1 h of EVLP.

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.

Ex vivo lung perfusion and the Organ Care System: a review

With the increasing prevalence of heart failure and end-stage lung disease, there is a sustained interest in expanding the donor pool to alleviate the thoracic organ shortage crisis. Efforts to extend the standard donor criteria and to include donation after circulatory death have been made to increase the availability of suitable organs. Studies have demonstrated that outcomes with extended-criteria donors are comparable to those with standard-criteria donors. Another promising approach to augment the donor pool is the improvement of organ preservation techniques. Both ex vivo lung perfusion (EVLP) for the lungs and the Organ Care System (OCS, TransMedics) for the heart have shown encouraging results in preserving organs and extending ischemia time through the application of normothermic regional perfusion. EVLP has been effective in improving marginal or borderline lungs by preserving and reconditioning them. The use of OCS is associated with excellent short-term outcomes for cardiac allografts and has improved utilization rates of hearts from extended-criteria donors. While both EVLP and OCS have successfully transitioned from research to clinical practice, the costs associated with commercially available systems and consumables must be considered. The ex vivo perfusion platform, which includes both EVLP and OCS, holds the potential for diverse and innovative therapies, thereby transforming the landscape of thoracic organ transplantation.

Intermittent Ex Vivo Lung Perfusion in a Porcine Model for Prolonged Lung Preservation

BACKGROUND

Ex vivo lung perfusion expands the lung transplant donor pool and extends preservation time beyond cold static preservation. We hypothesized that repeated regular ex vivo lung perfusion would better maintain lung grafts.

METHODS

Ten pig lungs were randomized into 2 groups. The control underwent 16 h of cold ischemic time and 2 h of cellular ex vivo lung perfusion. The intermittent ex vivo lung perfusion group underwent cold ischemic time for 4 h, ex vivo lung perfusion (first) for 2 h, cold ischemic time for 10 h, and 2 h of ex vivo lung perfusion (second). Lungs were assessed, and transplant suitability was determined after 2 h of ex vivo lung perfusion.

RESULTS

The second ex vivo lung perfusion was significantly associated with better oxygenation, limited extravascular water, higher adenosine triphosphate, reduced intraalveolar edema, and well-preserved mitochondria compared with the control, despite proinflammatory cytokine elevation. No significant difference was observed in the first and second perfusion regarding oxygenation and adenosine triphosphate, whereas the second was associated with lower dynamic compliance and higher extravascular lung water than the first. Transplant suitability was 100% for the first and 60% for the second ex vivo lung perfusion, and 0% for the control.

CONCLUSIONS

The second ex vivo lung perfusion had a slight deterioration in graft function compared to the first. Intermittent ex vivo lung perfusion created a better condition for lung grafts than cold static preservation, despite cytokine elevation. These results suggested that intermittent ex vivo lung perfusion may help prolong lung preservation.

Expanding Donor Options for Lung Transplant: Extended Criteria, Donation After Circulatory Death, ABO Incompatibility, and Evolution of Ex Vivo Lung Perfusion

Only using brain-dead donors with standard criteria, the existing donor shortage has never improved in lung transplantation. Currently, clinical efforts have sought the means to use cohorts of untapped donors, such as extended criteria donors, donation after circulatory death, and donors that are ABO blood group incompatible, and establish the evidence for their potential contribution to the lung transplant needs. Also, technical maturation for using those lungs may eliminate immediate concerns about the early posttransplant course, such as primary graft dysfunction or hyperacute rejection. In addition, recent clinical and preclinical advances in ex vivo lung perfusion techniques have allowed the safer use of lungs from high-risk donors and graft modification to match grafts to recipients and may improve posttransplant outcomes. This review summarizes recent trends and accomplishments and future applications for expanding the donor pool in lung transplantation.

Ventilation during ex vivo lung perfusion, a review

Evidence suggests that ventilation during ex vivo lung perfusion (EVLP) with a 'one-size-fits-all' strategy has the potential to cause lung injury which may only become clinically relevant in marginal lung allografts. EVLP induced- or accelerated lung injury is a dynamic and cumulative process reflecting the interplay of a number of factors. Stress and strain in lung tissue caused by positive pressure ventilation may be exacerbated by the altered properties of lung tissue in an EVLP setting. Any pre-existing injury may alter the ability of lung allografts to accommodate set ventilation and perfusion techniques on EVLP leading to further injury. This review will examine the effects of ventilation on donor lungs in the setting of EVLP. A framework for developing a protective ventilation technique will be proposed.

Perioperative fluid management for lung transplantation is challenging

Lung transplantation is the definitive end-stage treatment for many lung diseases, and postoperative pulmonary oedema severely affects survival after lung transplantation. Optimizing perioperative fluid management can reduce the incidence of postoperative pulmonary oedema and improve the prognosis of lung transplant patients by removing the influence of patient, donor's lung and ECMO factors. Therefore, this article reviews seven aspects of lung transplant patients' pathophysiological characteristics, physiological characteristics of fluids, the influence of the donor lung on pulmonary oedema as well as current fluid rehydration concepts, advantages or disadvantages of intraoperative monitoring tools or types of fluids on postoperative pulmonary oedema, while showing the existing challenges in section 7. The aim is to show the specificity of perioperative fluid management in lung transplant patients and to provide new ideas for individualised fluid management in lung transplantation.

Clinical performance of lung ultrasound in predicting time-dependent changes in lung aeration in ARDS patients

To evaluate whether lung ultrasound is reliable bedside tool to monitor changes of lung aeration at the early and late stages of ARDS. LUS was performed in ARDS patients that underwent at least two consecutive CT scan at ICU admission and at least 1 week after admission. Twelve fields were evaluated and graded from 0 (normal) to 3 (consolidation). Changes of LUS score in twelve fields (ΔLUStot) and in four ventral (ΔLUSV), intermediate (ΔLUSI) and dorsal (ΔLUSD) zones were calculated at each time points. Three categories were described: Improve (ΔLUS < 0), Equal (ΔLUS = 0) or Worse (ΔLUS > 0). LUS scores were correlated with total changes in lung CT aeration (ΔCTair) and with normally, poorly and not aerated regions (ΔCTnorm, ΔCTpoor and ΔCTnot, respectively). Eleven patients were enrolled. ΔLUStot had significant correlation with ΔCTair (r = - 0.74, p < 0.01). ΔLUSV, ΔLUSI and ΔLUSD showed significant correlations with ΔCTair (r = - 0.66, r = - 0.69, r = - 0.63, respectively; p < 0.05). Compared to Equal, Improve and Worse categories had significantly higher (p < 0.01) and lower (p < 0.05) ΔCTair values, respectively. Compared to Equal, Improve and Worse categories had lower (p < 0.01) and higher (p < 0.01) ΔCTnot values, respectively. LUS score had a good correlation with lung CT in detecting changes of lung aeration.

Thoracic Ultrasound in Lung Transplantation—Insights in the Field

The use of thoracic ultrasound (TUS) is a novel and dynamic diagnostic and monitoring modality that has shown remarkable advances within the last decade, with several published papers investigating its role within the field of lung transplantation. The aim of this current opinion review is to review the existing literature on the role of TUS in all stages of LTx, from in-donor lung evaluation to graft assessment on ex vivo lung perfusion and in the short- and long-term follow-up after LTx.

Emerging Imaging Modalities for Functional Assessment of Donor Lungs Ex Vivo

The severe shortage of functional donor lungs that can be offered to recipients has been a major challenge in lung transplantation. Innovative ex vivo lung perfusion (EVLP) and tissue engineering methodologies are now being developed to repair damaged donor lungs that are deemed unsuitable for transplantation. To assess the efficacy of donor lung reconditioning methods intended to rehabilitate rejected donor lungs, monitoring of lung function with improved spatiotemporal resolution is needed. Recent developments in live imaging are enabling non-destructive, direct, and longitudinal modalities for assessing local tissue and whole lung functions. In this review, we describe how emerging live imaging modalities can be coupled with lung tissue engineering approaches to promote functional recovery of ex vivo donor lungs.

Real-time Lung Weight Measurement During Cellular Ex Vivo Lung Perfusion: An Early Predictor of Transplant Suitability

BACKGROUND

Increased extravascular lung water during ex vivo lung perfusion (EVLP) is associated with ischemia reperfusion injury and poor pulmonary function. A non-invasive technique for evaluating extravascular lung water during EVLP is desired to assess the transplant suitability of lungs. We investigated real-time lung weight measurements as a reliable method for assessing pulmonary functions in cellular EVLP using a porcine lung model.

METHODS

Fifteen pigs were randomly divided into 3 groups: control (no warm ischemia) or donation after circulatory death groups with 60 or 90 min of warm ischemia (n = 5, each). Real-time lung weight gain was measured by load cells positioned at the bottom of the organ chamber.

RESULTS

Real-time lung weight gain at 2 h was significantly correlated with lung weight gain as measured on a back table ( R  = 0.979, P  < 0.01). Lung weight gain in non-suitable cases (n = 6) was significantly higher than in suitable cases (n = 9) at 40 min (51.6 ± 46.0 versus -8.8 ± 25.7 g; P  < 0.01, cutoff = +12 g, area under the curve = 0.907). Lung weight gain at 40 min was significantly correlated with PaO 2 /FiO 2 , peak inspiratory pressure, shunt ratio, wet/dry ratio, and transplant suitability at 2 h ( P  < 0.05, each). In non-suitable cases, lung weight gain at 66% and 100% of cardiac output was significantly higher than at 33% ( P  < 0.05).

CONCLUSIONS

Real-time lung weight measurement could potentially be an early predictor of pulmonary function in cellular EVLP.

Single-center experience of ex vivo lung perfusion and subsequent lung transplantation

BACKGROUND

The safety of lung transplantation using ex vivo lung perfusion (EVLP) has been confirmed in multiple clinical studies; however, limited evidence is currently available regarding the potential effects of EVLP on posttransplant graft complications and survival with mid- to long-term follow-up. In this study, we reviewed our institutional data to better understand the impact of EVLP.

METHODS

Lungs placed on EVLP from 2014 through 2020 and transplant outcomes were retrospectively analyzed. Data were compared between lungs transplanted and declined after EVLP, between patients with severe primary graft dysfunction (PGD3) and no PGD3 after EVLP, and between matched patients with lungs transplanted with and without EVLP.

RESULTS

In total, 98 EVLP cases were performed. Changes in metabolic indicators during EVLP were correlated with graft quality and transplantability, but not changes in physiological parameters. Among 58 transplanted lungs after EVLP, PGD3 at 72 h occurred in 36.9% and was associated with preservation time, mechanical support prior to transplant, and intraoperative transfusion volume. Compared with patients without EVLP, patients who received lungs screened with EVLP had a higher incidence of PGD3 and longer ICU and hospital stays. Lung grafts placed on EVLP exhibited a significantly higher chance of developing airway anastomotic ischemic injury by 30 days posttransplant. Acute and chronic graft rejection, pulmonary function, and posttransplant survival were not different between patients with lungs screened on EVLP versus lungs with no EVLP.

CONCLUSION

EVLP use is associated with an increase of early posttransplant adverse events, but graft functional outcomes and patient survival are preserved.

Optical oxygen saturation imaging in cellular ex vivo lung perfusion to assess lobular pulmonary function

Ex vivo lung perfusion (EVLP) is an emerging tool to evaluate marginal lungs in lung transplantation. However, there is no objective metric to monitor lobular regional oxygenation during EVLP. In this study, we developed oxygen saturation (SaO₂) imaging to quantitatively assess the regional gas exchange potential of the lower lobes. Ten porcine lungs were randomly divided into control and donation after circulatory death (DCD) groups (n = 5, each). Lungs were perfused in cellular EVLP for 2 h, and multispectral images were continuously collected from the dorsal sides of the lower lobes. We examined whether lower lobe SaO₂ correlated with PaO₂/FiO₂ (P/F) ratios in lower pulmonary veins (PV). The wet/dry ratio in lower lobes was measured and Monte Carlo simulations were performed to investigate the method's feasibility. There was a significant correlation between lower lobe SaO₂ and the P/F ratio in lower PV (r = 0.855, P < 0.001). The DCD group was associated with lower SaO₂ and higher wet/dry ratio than the control group (P < 0.001). The error of estimated SaO₂ was limited according to Monte Carlo simulations. The developed technology provides a noninvasive and regional evaluative tool of quantitative lobular function in EVLP.

The Year in Cardiothoracic Transplant Anesthesia: Selected Highlights From 2020 Part I - Lung Transplantation

This special article focuses on the highlights in cardiothoracic transplantation literature in the year 2020. Part I encompasses the recent literature on lung transplantation, including the advances in preoperative assessment and optimization, donor management, including the use of ex-vivo lung perfusion, recipient management, including those who have been infected with coronavirus disease 2019, updates on the perioperative management, including the use of extracorporeal membrane oxygenation, and long-term outcomes.