The nature of chronic rejection after lung transplantation: a murine orthotopic lung transplant study.

Introduction: Chronic rejection is a major complication post-transplantation. Within lung transplantation, chronic rejection was considered as airway centred. Chronic Lung Allograft Dysfunction (CLAD), defined to cover all late chronic complications, makes it more difficult to understand chronic rejection from an immunological perspective. This study investigated the true nature, timing and location of chronic rejection as a whole, within mouse lung transplantation. Methods: 40 mice underwent an orthotopic left lung transplantation, were sacrificed at day 70 and evaluated by histology and in vivo µCT. For timing and location of rejection, extra grafts were sacrificed at day 7, 35, 56 and investigated by ex vivo µCT or single cell RNA (scRNA) profiling. Results: Chronic rejection originated as innate inflammation around small arteries evolving toward adaptive organization with subsequent end-arterial fibrosis and obliterans. Subsequently, venous and pleural infiltration appeared, followed by airway related bronchiolar folding and rarely bronchiolitis obliterans was observed. Ex vivo µCT and scRNA profiling validated the time, location and sequence of events with endothelial destruction and activation as primary onset. Conclusion: Against the current belief, chronic rejection in lung transplantation may start as an arterial response, followed by responses in venules, pleura, and, only in the late stage, bronchioles, as may be seen in some but not all patients with CLAD.

Computed tomography-based machine learning for donor lung screening before transplantation.

BACKGROUND: Assessment and selection of donor lungs remain largely subjective and experience based. Criteria to accept or decline lungs are poorly standardized and are not compliant with the current donor pool. Using ex vivo computed tomography (CT) images, we investigated the use of a CT-based machine learning algorithm for screening donor lungs before transplantation. METHODS: Clinical measures and ex situ CT scans were collected from 100 cases as part of a prospective clinical trial. Following procurement, donor lungs were inflated, placed on ice according to routine clinical practice, and imaged using a clinical CT scanner before transplantation while stored in the icebox. We trained and tested a supervised machine learning method called dictionary learning, which uses CT scans and learns specific image patterns and features pertaining to each class for a classification task. The results were evaluated with donor and recipient clinical measures. RESULTS: Of the 100 lung pairs donated, 70 were considered acceptable for transplantation (based on standard clinical assessment) before CT screening and were consequently implanted. The remaining 30 pairs were screened but not transplanted. Our machine learning algorithm was able to detect pulmonary abnormalities on the CT scans. Among the patients who received donor lungs, our algorithm identified recipients who had extended stays in the intensive care unit and were at 19 times higher risk of developing chronic lung allograft dysfunction within 2 years posttransplant. CONCLUSIONS: We have created a strategy to ex vivo screen donor lungs using a CT-based machine learning algorithm. As the use of suboptimal donor lungs rises, it is important to have in place objective techniques that will assist physicians in accurately screening donor lungs to identify recipients most at risk of posttransplant complications.

The hemodynamic interplay between pulmonary ischemia-reperfusion injury and right ventricular function in lung transplantation: a translational porcine model.

Lung transplantation (LTx) is a challenging procedure. Following the process of ischemia-reperfusion injury, the transplanted pulmonary graft might become severely damaged, resulting in primary graft dysfunction. In addition, during the intraoperative window, the right ventricle (RV) is at risk of acute failure. The interaction of right ventricular function with lung injury is, however, poorly understood. We aimed to address this interaction in a translational porcine model of pulmonary ischemia-reperfusion injury. Advanced pulmonary and hemodynamic assessment was used, including right ventricular pressure-volume loop analysis. The acute model was based on clamping and unclamping of the left lung hilus, respecting the different hemodynamic phases of a clinical lung transplantation. We found that forcing entire right ventricular cardiac output through a lung suffering from ischemia-reperfusion injury increased afterload (pulmonary vascular resistance from baseline to end experiment P < 0.0001) and induced right ventricular failure (RVF) in 5/9 animals. Notably, we identified different compensation patterns in failing versus nonfailing ventricles (arterial elastance P = 0.0008; stroke volume P < 0.0001). Furthermore, increased vascular pressure and flow produced by the right ventricle resulted in higher pulmonary injury, as measured by ex vivo CT density (correlation: pressure r = 0.8; flow r = 0.85). Finally, RV ischemia as measured by troponin-T was negatively correlated with pulmonary injury (r = -0.76); however, troponin-T values did not determine RVF in all animals. In conclusion, we demonstrate a delicate balance between development of pulmonary ischemia-reperfusion injury and right ventricular function during lung transplantation. Furthermore, we provide a physiological basis for potential benefit of extracorporeal life support technology.NEW & NOTEWORTHY In contrast to the abundant literature of mechanical pulmonary artery clamping to increase right ventricular afterload, we developed a model adding a biological factor of pulmonary ischemia-reperfusion injury. We did not only focus on the right ventricular behavior, but also on the interaction with the injured lung. We are the first to describe this interaction while addressing the hemodynamic intraoperative phases of clinical lung transplantation.

Structural and functional analysis of aquaporin-2 mutants involved in nephrogenic diabetes insipidus.

Aquaporins are water channels found in the cell membrane, where they allow the passage of water molecules in and out of the cells. In the kidney collecting duct, arginine vasopressin-dependent trafficking of aquaporin-2 (AQP2) fine-tunes reabsorption of water from pre-urine, allowing precise regulation of the final urine volume. Point mutations in the gene for AQP2 may disturb this process and lead to nephrogenic diabetes insipidus (NDI), whereby patients void large volumes of highly hypo-osmotic urine. In recessive NDI, mutants of AQP2 are retained in the endoplasmic reticulum due to misfolding. Here we describe the structural and functional characterization of three AQP2 mutations associated with recessive NDI: T125M and T126M, situated close to a glycosylation site and A147T in the transmembrane region. Using a proteoliposome assay, we show that all three mutants permit the transport of water. The crystal structures of T125M and T126M together with biophysical characterization of all three mutants support that they retain the native structure, but that there is a significant destabilization of A147T. Our work provides unique molecular insights into the mechanisms behind recessive NDI as well as deepens our understanding of how misfolded proteins are recognized by the ER quality control system.

The Effect of Prone Positioning After Lung Transplantation.

BACKGROUND: Prone positioning has become a standard therapy in acute respiratory distress syndrome to improve oxygenation and decrease mortality. However, little is known about prone positioning in lung transplant recipients. This large, singe-center analysis investigated whether prone positioning improves gas exchange after lung transplantation. METHODS: Clinical data of 583 patients were analyzed. Prone position was considered in case of impaired gas exchange Pao2/fraction of oxygen in inhaled air (<250), signs of edema after lung transplantation, and/or evidence of reperfusion injury. Patients with hemodynamic instability or active bleeding were not proned. Impact of prone positioning (n = 165) on gas exchange, early outcome and survival were determined and compared with patients in supine positioning (n = 418). RESULTS: Patients in prone position were younger, more likely to have interstitial lung disease, and had a higher lung allocation score. Patients were proned for a median of 19 hours (interquartile range,15-26) hours). They had significantly lower Pao2/fraction of oxygen in inhaled air (227 ± 96 vs 303 ± 127 mm Hg, P = .004), and lower lung compliance (24.8 ± 9.1 mL/mbar vs 29.8 ± 9.7 mL/mbar, P < .001) immediately after lung transplantation. Both values significantly improved after prone positioning for 24 hours (Pao2/fraction of oxygen ratio: 331 ± 91 mm Hg; lung compliance: 31.7 ± 20.2 mL/mbar). Survival at 90 days was similar between the 2 groups (93% vs 96%, P = .105). CONCLUSIONS: Prone positioning led to a significant improvement in lung compliance and oxygenation after lung transplantation. Prospective studies are needed to confirm the benefit of prone positioning in lung transplantation.

CT-based Machine Learning for Donor Lung Screening Prior to Transplantation.

Background: Assessment and selection of donor lungs remains largely subjective and experience based. Criteria to accept or decline lungs are poorly standardized and are not compliant with the current donor pool. Using ex vivo CT images, we investigated the use of a CT-based machine learning algorithm for screening donor lungs prior to transplantation. Methods: Clinical measures and ex-situ CT scans were collected from 100 cases as part of a prospective clinical trial. Following procurement, donor lungs were inflated, placed on ice according to routine clinical practice, and imaged using a clinical CT scanner prior to transplantation while stored in the icebox. We trained and tested a supervised machine learning method called dictionary learning , which uses CT scans and learns specific image patterns and features pertaining to each class for a classification task. The results were evaluated with donor and recipient clinical measures. Results: Of the 100 lung pairs donated, 70 were considered acceptable for transplantation (based on standard clinical assessment) prior to CT screening and were consequently implanted. The remaining 30 pairs were screened but not transplanted. Our machine learning algorithm was able to detect pulmonary abnormalities on the CT scans. Among the patients who received donor lungs, our algorithm identified recipients who had extended stays in the ICU and were at 19 times higher risk of developing CLAD within 2 years post-transplant. Conclusions: We have created a strategy to ex vivo screen donor lungs using a CT-based machine learning algorithm. As the use of suboptimal donor lungs rises, it is important to have in place objective techniques that will assist physicians in accurately screening donor lungs to identify recipients most at risk of post-transplant complications.

Can we attenuate ischaemia-reperfusion injury of allografts in a porcine left lung transplant models by adsorption of cytokines?

OBJECTIVES: Primary graft dysfunction resulting from ischaemia-reperfusion injury remains a major obstacle after lung transplantation (LTx) and is associated with morbidity and mortality. Continuous release of inflammatory cytokines, due to the process of ischaemia and reperfusion, triggers a complex cascade of apoptosis and necrosis resulting in graft dysfunction. Previous studies demonstrated successful graft improvement by cytokine filtration during ex vivo lung perfusion. We hypothesize that plasma cytokine filtration with CytoSorb® during in vivo graft perfusion immediately after implantation may attenuate ischaemia-reperfusion injury after left LTx in a porcine model. METHODS: Left porcine LTx was performed with allografts preserved for 24 h at 4°C. In the treatment group [T] (n = 7), a veno-venous shunt was created to insert the cytokine filter (CytoSorbents, Berlin, Germany). In the sham group [S] (n = 4), the shunt was created without the filter. Haemodynamic parameters, lung mechanics, blood gases and plasma cytokines were assessed during 6 h in vivo reperfusion. RESULTS: During 6 h of reperfusion, significant differences in plasma pro-inflammatory cytokine [interferon (IFN)-α, IFN-γ and interleukin (IL)-6] concentrations were observed between [T] and [S], but surprisingly with higher plasma levels in the [T] group. Plasma concentrations of other pro-inflammatory cytokines (IL-1ß, IL-12p40, IL-4, IL-6, IL-8, IFN-α, IFN-γ and tumour necrosis factor-α) and anti-inflammatory cytokines (IL-10) did not find any evidence for a difference. Furthermore, our study failed to show meaningful difference in haemodynamics and blood gases. Also, no statistically significant differences were found between [T] and [S] in biopsies and wet-to-dry ratio at the end of the experiment. CONCLUSIONS: In our porcine left LTx model cytokine filtration did not achieve the intended effect. This is in contrast to previous studies with CytoSorb use during ex vivo lung perfusion as a surrogate LTx model. Our findings might highlight the fact that the theoretical benefit of inserting an additional cytokine adsorber to improve graft function in clinical practice should be critically evaluated with further studies.

Effect of mode of intraoperative support on primary graft dysfunction after lung transplant.

OBJECTIVE: To clarify the relationship between the use of extracorporeal life support during lung transplantation and severe primary graft dysfunction (PGD), we developed and analyzed a novel multicenter international registry. METHODS: The Extracorporeal Life Support in Lung Transplantation Registry includes double-lung transplants performed at 8 high-volume centers (>40/year). Multiorgan transplants were excluded. We defined severe PGD as grade 3 PGD (PGD3) observed 48 or 72 hours after reperfusion. Modes of support were no extracorporeal life support (off-pump), extracorporeal membrane oxygenation (ECMO), and cardiopulmonary bypass (CPB). To assess the association between mode of support and PGD3, we adjusted for demographic and intraoperative factors with a stepwise, mixed selection, multivariable regression model, ending with 10 covariates in the final model. RESULTS: We analyzed 852 transplants performed between January 2016 and March 2020: 422 (50%) off-pump, 273 (32%) ECMO, and 157 (18%) CPB cases. PGD3 rates at time point 48-72 were 12.1% (51 out of 422) for off-pump, 28.9% for ECMO (79 out of 273), and 42.7% (67 out of 157) for CPB. The adjusted model resulted in the following risk profile for PGD3: CPB versus ECMO odds ratio, 1.89 (95% CI, 1.05-3.41; P = .033), CPB versus off-pump odds ratio, 4.24 (95% CI, 2.24-8.04; P < .001), and ECMO versus off-pump odds ratio, 2.24 (95% CI, 1.38-3.65; P = .001). CONCLUSIONS: Venoarterial ECMO is increasingly used at high-volume centers to support complex transplant recipients during double-lung transplantation. This practice is associated with more risk of PGD3 than off-pump transplantation but less risk than CPB. When extracorporeal life support is required during lung transplantation, ECMO may be the preferable approach when feasible.

Lung transplantation for acute respiratory distress syndrome: A multicenter experience.

Acute respiratory distress syndrome (ARDS) is a rapidly progressive lung disease with a high mortality rate. Although lung transplantation (LTx) is a well-established treatment for a variety of chronic pulmonary diseases, LTx for acute lung failure (due to ARDS) remains controversial. We reviewed posttransplant outcome of ARDS patients from three high-volume European transplant centers. Demographics and clinical data were collected and analyzed. Viral infection was the main reason for ARDS (n = 7/13, 53.8%). All patients were admitted to ICU and required mechanical ventilation, 11/13 were supported with ECMO at the time of listing. They were granted a median LAS of 76 (IQR 50-85) and waited for a median of 3 days (IQR 1.5-14). Postoperatively, median length of mechanical ventilation was 33 days (IQR 17-52.5), median length of ICU and hospital stay were 39 days (IQR 19.5-58.5) and 54 days (IQR 43.5-127). Prolongation of peripheral postoperative ECMO was required in 7/13 (53.8%) patients with a median duration of 2 days (IQR 2-7). 30-day mortality was 7.7%, 1 and 5-year survival rates were calculated as 71.6% and 54.2%, respectively. Given the lack of alternative treatment options, the herein presented results support the concept of offering live-saving LTx to carefully selected ARDS patients.

Functional outcome after single-stage laryngotracheal reconstruction with rib cartilage grafting.

OBJECTIVE: Single-stage laryngotracheal reconstruction (SSLTR) provides a definite surgical treatment for patients with complex glotto-subglottic stenosis. To date, the influence of SSLTR on the functional outcome after surgery has not been analyzed. METHODS: A retrospective analysis of all patients receiving a SSLTR between November 2012 and October 2019 was performed. Preoperatively and 3 months postoperatively, patients received a full functional evaluation, including spirometry; voice measurements (eg, fundamental frequency; dynamic range, singing voice range, and perceptual voice evaluation using the Roughness-Breathiness-Hoarseness [RBH] score, and fiberoptic endoscopic evaluation of swallowing [FEES]). RESULTS: A total of 15 patients with a mean age of 45 ± 17 years underwent SSTLR. Two (13%) patients were men and 13 (87%) were women. The majority of patients (67%) had undergone previous surgical or endoscopic treatment attempts that had failed. At the 3-month follow-up visit, none of the patients had signs of penetration or aspiration in their swallowing examination. Voice measurements revealed a significantly lower fundamental voice frequency (201.0 Hz vs 155.5 Hz; P = .006), whereas voice range (19.1 semitones vs 14.9 semitones; P = .200) and dynamic range (52.5 dB vs 53.0 dB; P = .777) was hardly affected. The median RBH score changed from R1 B0 H1 to R2 B1 H2. In spirometry, breathing capacity increased significantly (peak expiratory flow, 44% vs 87% [P < .001] and mean expiratory flow at 75% of vital capacity, 48% vs 90% [P < .001]). During a median follow-up of 32.5 months (range, 7-88 months), none of the patients developed re-stenosis. CONCLUSIONS: For complex glotto-subglottic stenoses, durable long-term airway patency together with reasonable voice quality and normal deglutition can be achieved by SSLTR.

Difficulties in the differential diagnosis of large solitary pulmonary cysts.

Large solitary cystic lesions are a rare finding, and their differential diagnosis includes cystic airspaces associated with lung cancer, congenital pulmonary airway malformations and pneumatoceles. Here, we report 3 consecutive patients who presented with a large solitary pulmonary cyst on chest computed tomography. All underwent surgical resection, and the histopathological findings were different in all 3 cases. In one patient, a very rare finding of squamous cell carcinoma arising from the cystic lesion in the left lower lobe was confirmed. Therefore, in carefully selected cases, pulmonary cysts should be resected based on the potential risk for recurrent infection and the development of malignancy.

Mobility during and after training: autobiography and advice to early career colleagues.

Mobility programs can be a valuable enhancement to medical formation and career, either during or after training as part of an internship or as a fellowship. In the case of surgery, the opportunity to visit departments who offer a broader range of operations than the home institution, learn new clinical and surgical techniques are unique possibilities to expand surgical and clinical daily routine practice but also to meet colleagues and exchange experiences for future collaboration and networking.

Genomic comparison of carbapenem-resistant Enterobacteriaceae from humans and gulls in Alaska.

OBJECTIVES: Wildlife may harbour clinically important antimicrobial-resistant bacteria, but the role of wildlife in the epidemiology of antimicrobial-resistant bacterial infections in humans is largely unknown. In this study, we aimed to assess dissemination of the blaKPC carbapenemase gene among humans and gulls in Alaska. METHODS: We performed whole-genome sequencing to determine the genetic context of blaKPC in bacterial isolates from all four human carbapenemase-producing Enterobacteriaceae (CPE) infections reported in Alaska between 2013-2018 and to compare the sequences with seven previously reported CPE isolates from gull faeces within the same region and time period. RESULTS: Genomic analysis of CPE isolates suggested independent acquisition events among humans with no evidence for direct transmission of blaKPC between people and gulls. However, some isolates shared conserved genetic elements surrounding blaKPC, suggesting possible exchange between species. CONCLUSION: Our results highlight the genomic plasticity associated with blaKPC and demonstrate that sampling of wildlife may be useful for identifying clinically relevant antimicrobial resistance not observed through local passive surveillance in humans.

Laryngotracheal resection can be performed safely without a guardian Chin stitch-a single-centre experience including 165 consecutive patients.

OBJECTIVES: A tension-free anastomosis is crucial to minimize the risk of airway complications after laryngotracheal surgery. The 'guardian' chin stitch is placed to prevent hyperextension of the neck in the early postoperative period. This manoeuvre was introduced early in tracheal surgery and is now routinely performed by many airway surgeons. However, the evidence for or against is sparse. METHODS: We performed a retrospective analysis of all adult patients receiving a (laryngo-)tracheal resection at our department from October 2011 to December 2019. According to our institutional standard, none of the patients received a chin stitch. Instead, a head cradle was used to obtain anteflexion of the neck during the first 3 days and patients were instructed to avoid hyperextension of the neck during the hospital stay. The postoperative outcome and the rate of anastomotic complications were analysed. RESULTS: A total of 165 consecutive patients were included in this study. Median age at surgery was 53 years (18-80). Seventy-four patients received a tracheal resection, 24 a cricotracheal resection, 52 an extended cricotracheal resection including dorsal mucosectomy and 15 a single-stage laryngotracheal reconstruction. The median resection length was 25 mm (range 10-55 mm). One hundred and sixty-two out of 165 (98.2%) patients had an unremarkable postoperative course. One patient (0.6%) had partial anastomotic rupture after a traumatic reintubation, which required revision surgery and re-anastomosis. Two patients (1.2%) after previous radiation therapy (>60 Gy) developed a partial necrosis of the anastomosis, resulting in prolonged airleak and fistulation. At follow-up, bronchoscopy 3 months after surgery, 92.7% (127/137) of the patients had a proper anastomosis, 6.6% (9/137) had minor granuloma formations at the site of the anastomosis, which were all treated successfully by endoscopic removal. One patient received dilatation for restenosis (0.7%). CONCLUSIONS: After sufficient mobilization of the central airways, postoperative anteflexion of the neck supported by a head cradle is sufficient to prevent excessive anastomotic tension and dehiscence. Considering the risk for severe neurological complications associated with the chin stitch, the routine use of this manoeuvre in laryngotracheal surgery should not be recommended.

A novel experimental porcine model to assess the impact of differential pulmonary blood flow on ischemia-reperfusion injury after unilateral lung transplantation.

BACKGROUND: Primary graft dysfunction (PGD) remains a major obstacle after lung transplantation. Ischemia-reperfusion injury is a known contributor to the development of PGD following lung transplantation. We developed a novel approach to assess the impact of increased pulmonary blood flow in a large porcine single-left lung transplantation model. MATERIALS: Twelve porcine left lung transplants were divided in two groups (n = 6, in low- (LF) and high-flow (HF) group). Donor lungs were stored for 24 h on ice, followed by left lung transplantation. In the HF group, recipient animals were observed for 6 h after reperfusion with partially clamping right pulmonary artery to achieve a higher flow (target flow 40-60% of total cardiac output) to the transplanted lung compared to the LF group, where the right pulmonary artery was not clamped. RESULTS: Survival at 6 h was 100% in both groups. Histological, functional and biological assessment did not significantly differ between both groups during the first 6 h of reperfusion. injury was also present in the right native lung and showed signs compatible with the pathophysiological hallmarks of ischemia-reperfusion injury. CONCLUSIONS: Partial clamping native pulmonary artery in large animal lung transplantation setting to study the impact of low versus high pulmonary flow on the development of ischemia reperfusion is feasible. In our study, differential blood flow had no effect on IRI. However, our findings might impact future studies with extracorporeal devices and represent a specific intra-operative problem during bilateral sequential single-lung transplantation.

Early protein expression profile in bronchoalveolar lavage fluid and clinical outcomes in primary graft dysfunction after lung transplantation.

OBJECTIVES: Primary graft dysfunction (PGD) remains a major post-transplant complication and is associated with increased morbidity and mortality. Mechanisms evoking PGD are not completely clear, but inflammation plays a central role. We investigated the association between PGD and inflammatory proteins present in immediate postoperative bronchoalveolar lavage. METHODS: All double-lung recipients transplanted at our institution from 2002 to 2018 were included in our study. We retrospectively selected 80 consecutive lung transplant recipients with different PGD grades (n = 20 for each PGD grades 0-1 to 2-3). In bronchoalveolar lavage performed within the first 24 h after donor aortic cross-clamping following lung transplantation, concentrations of 30 cytokines, chemokines and growth factors were assessed by enzyme-linked immunosorbent assay (ELISA) and correlated with donor and recipient demographics and outcomes. For analysis, 2 groups were defined: 'mild' PGD (grade 0-1) and 'severe' PGD (grades 2-3). RESULTS: Significant differences between mild and severe PGD were found in 8 biomarkers [interleukin (IL)-6, IL-10, IL-13, eotaxin, granulocyte colony-stimulating factor, interferon γ, macrophage inflammatory protein 1α, surfactant protein D (SP-D); P < 0.05]. Increased IL-10 and IL-13, but none of the other proteins, were associated with short-term outcome (longer time to extubation; P = 0.005 and P < 0.0001; increased intensive care unit stay; P = 0.012 and P < 0.0001; and hospital stay; P = 0.041 and P = 0.002). There were no significant differences in donor and recipient characteristics between the groups. CONCLUSIONS: Expression profiles of key inflammatory mediators in bronchoalveolar lavage fluid differed significantly between lung transplant recipients with severe versus mild PGD and correlated with clinical outcome variables. Further research should focus on the early mechanisms leading to PGD.

Training curriculum for European thoracic surgeons: a joint initiative of the European Society of Thoracic Surgeons and the European Respiratory Society.

Because of the differing definitions of the margins of thoracic surgery as a specialty and the variability in the training curricula among European countries, the European Society of Thoracic Surgeons formed a task force to elaborate a consensual proposal. The first step comprised creating a harmonized syllabus that was completed and published in 2018. This publication presents a proposal for a curriculum upon which the task force and the external expert reviewers have agreed. The curriculum was developed by the task force: each module and item describe the expected level of knowledge, skills and attitudes to be attained by the participants; learning opportunities, assessment tools and minimal clinical exposures have been defined as well. Competence in terms of non-technical skills has been defined for each module according to the CanMEDS (http://www.royalcollege.ca/rcsite/canmeds/canmeds-framework-e) glossary. The different modules were subsequently submitted to an internal and an external review process and re-edited accordingly before final validation. The authors hope that this document will serve as a roadmap for both thoracic surgical trainees and mentors. It should further guide continuous professional development. However, evolving scientific and technological advances are expected to modify the diagnosis and treatment of diseases and disorders in the future and hence will mandate periodical revisions of the document.