State of the Art: Bridging to lung transplantation using artificial organ support technologies

The Roles of Venopulmonary Arterial Extracorporeal Membrane Oxygenation

OBJECTIVES

Concise definitive review of the use of venopulmonary arterial extracorporeal membrane oxygenation (V-PA ECMO) support in patients with cardiopulmonary failure.

DATA SOURCES

Original investigations identified through a PubMed search with search terms "percutaneous right ventricular assist device," "oxy-RVAD," "V-PA ECMO," and "veno-pulmonary arterial ECMO" were reviewed and evaluated for relevance.

STUDY SELECTION

Studies that included more than three patients supported with V-PA ECMO were included.

DATA EXTRACTION

Clinically relevant data from included studies, including patient-important outcomes, were summarized and discussed.

DATA SYNTHESIS

We identified four groups of patients where V-PA ECMO has been studied: acute respiratory distress syndrome, right ventricular dysfunction after left ventricular assist device placement, bridge to lung transplantation, and pulmonary embolism. Most identified works are small, single center, and retrospective in nature, precluding definitive conclusions regarding the efficacy of V-PA ECMO. There have been no clinical trials evaluating the efficacy of V-PA ECMO for any indication.

CONCLUSIONS

V-PA ECMO is a promising form of extracorporeal support for patients with right ventricular dysfunction. Future work should focus on identifying the optimal timing and populations for the use of V-PA ECMO.

Extracorporeal membrane oxygenation bridge to pediatric lung transplantation: Modern era analysis

BACKGROUND

Survival outcomes of children on extracorporeal membrane oxygenation (ECMO) at time of lung transplant (LTx) remain unclear.

METHODS

Pediatric first-time LTx recipients transplanted between January 2000 and December 2020 were identified in the United Network for Organ Sharing Registry to compare post-transplant survival according to ECMO support at time of transplant. For a comprehensive analysis of the data, univariate analysis, multivariable Cox regression, and propensity score matching were performed.

RESULTS

During the study period, 954 children under 18 years of age underwent LTx with 40 patients on ECMO. We did not identify a post-LTx survival difference between patients receiving ECMO when compared to those that did not. A multivariable Cox regression model (Hazard ratio = 0.83; 95% confidence interval: 0.47, 1.45; p = .51) did not demonstrate an increased risk for death post-LTx. Lastly, a propensity score matching analysis, retaining 33 ECMO and 33 non-ECMO patients, further confirmed no post-LTx survival difference comparing ECMO to no ECMO cohorts (Hazard ratio = 0.98; 95% confidence interval: 0.48, 2.00; p = .96).

CONCLUSIONS

In this contemporary cohort of children, the use of ECMO at the time of LTx did not negatively impact post-transplant survival.

Discontinuation of ECMO-a review with a note on Indian scenario

Extracorporeal membrane oxygenation (ECMO) has strikingly progressed over the last 20 years in the management of adult and pediatric severe respiratory and cardiac dysfunctions refractory to conventional management. In this review, we will discuss the weaning strategies of veno-venous and veno-arterial ECMO including the bridge to recovery and bridge to transplant along with post-ECMO care. We will also discuss the futility and the management of bridge to nowhere from Indian perspectives.

State of the art - Extracorporeal membrane oxygenation as a bridge to thoracic transplantation

BACKGROUND

Extracorporeal membrane oxygenation (ECMO) has revolutionized the treatment of refractory cardiac and respiratory failure, and its use continues to increase, particularly in adults. However, ECMO-related morbidity and mortality remain high.

MAIN TEXT

In this review, we investigate and expand upon the current state of the art in thoracic transplant and extracorporeal life support (ELS). In particular, we examine recent increase in incidence of heart transplant in patients supported by ECMO; the potential changes in patient care and selection for transplant in the years prior to updated United Network for Organ Sharing (UNOS) organ allocation guidelines versus those in the years following, particularly where these guidelines pertain to ECMO; and the newly revived practice of heart-lung block transplants (HLT) and the prevalence and utility of ECMO support in patients listed for HLT.

CONCLUSIONS

Our findings highlight encouraging outcomes in patients bridged to transplant with ECMO, considerable changes in treatment surrounding the updated UNOS guidelines, and complex, diverse outcomes among different centers in their care for increasingly ill patients listed for thoracic transplant.

Early career scientists converse on the future of soft robotics

During the recent decade, we have witnessed an extraordinary flourishing of soft robotics. Rekindled interest in soft robots is partially associated with the advances in manufacturing techniques that enable the fabrication of sophisticated multi-material robotic bodies with dimensions ranging across multiple length scales. In recent manuscripts, a reader might find peculiar-looking soft robots capable of grasping, walking, or swimming. However, the growth in publication numbers does not always reflect the real progress in the field since many manuscripts employ very similar ideas and just tweak soft body geometries. Therefore, we unreservedly agree with the sentiment that future research must move beyond "soft for soft's sake." Soft robotics is an undoubtedly fascinating field, but it requires a critical assessment of the limitations and challenges, enabling us to spotlight the areas and directions where soft robots will have the best leverage over their traditional counterparts. In this perspective paper, we discuss the current state of robotic research related to such important aspects as energy autonomy, electronic-free logic, and sustainability. The goal is to critically look at perspectives of soft robotics from two opposite points of view provided by early career researchers and highlight the most promising future direction, that is, in our opinion, the employment of soft robotic technologies for soft bio-inspired artificial organs.

Intraoperative Circulatory Support in Lung Transplantation: Current Trend and Its Evidence

Lung transplantation has a high risk of haemodynamic complications in a highly vulnerable patient population. The effects on the cardiovascular system of the various underlying end-stage lung diseases also contribute to this risk. Following a literature review and based on our own experience, this review article summarises the current trends and their evidence for intraoperative circulatory support in lung transplantation. Identifiable and partly modifiable risk factors are mentioned and corresponding strategies for treatment are discussed. The approach of first identifying risk factors and then developing an adjusted strategy is presented as the ERSAS (early risk stratification and strategy) concept. Typical haemodynamic complications discussed here include right ventricular failure, diastolic dysfunction caused by left ventricular deconditioning, and reperfusion injury to the transplanted lung. Pre- and intra-operatively detectable risk factors for the occurrence of haemodynamic complications are rare, and the therapeutic strategies applied differ considerably between centres. However, all the mentioned risk factors and treatment strategies can be integrated into clinical treatment algorithms and can influence patient outcome in terms of both mortality and morbidity.

Ambulatory extracorporeal membrane oxygenation (ECMO) as a bridge to lung transplantation

Ambulatory extracorporeal membrane oxygenation (ECMO) has shown promise as a bridge to lung transplantation. The primary goal of ambulatory ECMO is to provide enough gas exchange to allow patients to participate in preoperative physical therapy. Various strategies of ambulatory ECMO are utilized depending upon patients’ need. A wide spectrum of ECMO configurations is available to tackle this situation. We discuss those configurations in this article.

Critical Care Management of the Patient with Pulmonary Hypertension

Pulmonary hypertension patients admitted to the intensive care unit have high mortality, and right ventricular failure typically is implicated as cause of or contributor to death. Initial care of critically ill pulmonary hypertension patients includes recognition of right ventricular failure, appropriate monitoring, and identification and treatment of any inciting cause. Management centers around optimization of cardiac function, with a multipronged approach aimed at reversing the pathophysiology of right ventricular failure. For patients who remain critically ill or in shock despite medical optimization, mechanical circulatory support can be used as a bridge to recovery or lung transplantation.

ProtekDuo as a bridge to lung transplant and heart-lung transplant

Recent advances in technology have led to significantly greater use of extracorporeal membrane oxygenation (ECMO) as a bridge to lung transplantation with better outcomes. The novel ProtekDuo veno-venous ECMO (CardiacAssist, Inc.) has gained significance as it facilitates effective decompression of the right heart in patients with acute decompensation, while also providing consistent and effective gas exchange by eliminating recirculation. Here, we report two cases of effectively using ProtekDuo veno-venous ECMO: one case as a bridge to lung transplantation and another case as a bridge to heart-lung transplantation.

Artificial lungs--Where are we going with the lung replacement therapy?

Lung transplantation may be a final destination therapy in lung failure, but limited donor organ availability creates a need for alternative management, including artificial lung technology. This invited review discusses ongoing developments and future research pathways for respiratory assist devices and tissue engineering to treat advanced and refractory lung disease. An overview is also given on the aftermath of the coronavirus disease 2019 pandemic and lessons learned as the world comes out of this situation. The first order of business in the future of lung support is solving the problems with existing mechanical devices. Interestingly, challenges identified during the early days of development persist today. These challenges include device-related infection, bleeding, thrombosis, cost, and patient quality of life. The main approaches of the future directions are to repair, restore, replace, or regenerate the lungs. Engineering improvements to hollow fiber membrane gas exchangers are enabling longer term wearable systems and can be used to bridge lung failure patients to transplantation. Progress in the development of microchannel-based devices has provided the concept of biomimetic devices that may even enable intracorporeal implantation. Tissue engineering and cell-based technologies have provided the concept of bioartificial lungs with properties similar to the native organ. Recent progress in artificial lung technologies includes continued advances in both engineering and biology. The final goal is to achieve a truly implantable and durable artificial lung that is applicable to destination therapy.

Treatment of right ventricular dysfunction and heart failure in pulmonary arterial hypertension

Right heart dysfunction and failure is the principal determinant of adverse outcomes in patients with pulmonary arterial hypertension (PAH). In addition to right ventricular (RV) dysfunction, systemic congestion, increased afterload and impaired myocardial contractility play an important role in the pathophysiology of RV failure. The behavior of the RV in response to the hemodynamic overload is primarily modulated by the ventricular interaction and its coupling to the pulmonary circulation. The presentation can be acute with hemodynamic instability and shock or chronic producing symptoms of systemic venous congestion and low cardiac output. The prognostic factors associated with poor outcomes in hospitalized patients include systemic hypotension, hyponatremia, severe tricuspid insufficiency, inotropic support use and the presence of pericardial effusion. Effective therapeutic management strategies involve identification and effective treatment of the triggering factors, improving cardiopulmonary hemodynamics by optimization of volume to improve diastolic ventricular interactions, improving contractility by use of inotropes, and reducing afterload by use of drugs targeting pulmonary circulation. The medical therapies approved for PAH act primarily on the pulmonary vasculature with secondary effects on the right ventricle. Mechanical circulatory support as a bridge to transplantation has also gained traction in medically refractory cases. The current review was undertaken to summarize recent insights into the evaluation and treatment of RV dysfunction and failure attributable to PAH.

In Vivo 5 Day Animal Studies of a Compact, Wearable Pumping Artificial Lung

Recent studies show improved outcomes in ambulated lung failure patients. Ambulation still remains a challenge in these patients. This necessitates development of more compact and less cumbersome respiratory support specifically designed to be wearable. The Paracorporeal Ambulatory Assist Lung (PAAL) is being designed for providing ambulatory support in lung failure patients during bridge to transplant or recovery. We previously published in vitro and acute in vivo results of the PAAL. This study further evaluates the PAAL for 5 days. Five-day in vivo studies with the PAAL were conducted in 50-60 kg sheep after heparinization (activated clotting time range: 190-250 s) and cannulation with a 27 Fr. Avalon Elite dual-lumen cannula. The animals were able to move freely in a stanchion while device flow, resistance, and hemodynamics were recorded hourly. Oxygenation and hemolysis were measured daily. Platelet activation, blood chemistry, and comprehensive blood counts are reported for preoperatively, on POD 0, and POD 5. Three animals survived for 5 days. No study termination resulted from device failure. One animal was terminated on POD 0 and one animal was terminated at POD 3. The device was operated between 1.93 and 2.15 L/min. Blood left the device 100% oxygenated. Plasma-free hemoglobin ranged 10.8-14.5 mg/dl. CD62-P expression was under 10%. Minimal thrombus was seen in devices at explant. Chronic use of the PAAL in awake sheep is promising based on our study. There were no device-related complications over the study course. This study represents the next step in our pathway to eventual clinical translation.

Extracorporeal membrane oxygenation as a bridge to lung transplantation may not impact overall mortality risk after transplantation: results from a 7-year single-centre experience

OBJECTIVES

Extracorporeal membrane oxygenation (ECMO) has an important role in bridging patients to lung transplantation. In this study, we present our experience with pretransplant ECMO during the last 7 years and investigate its impact on graft outcomes.

METHODS

Records of all lung-transplanted patients at our institution between January 2010 and April 2017 were retrospectively reviewed. Graft survival was compared between patients who required pretransplant ECMO (pre-Tx ECMO+) and patients who did not (pre-Tx ECMO-). Risk factors for in-hospital mortality and graft survival were identified using a binary logistic regression and the Cox regression analyses, respectively.

RESULTS

Among the 917 patients transplanted during the study period, 68 (7%) required ECMO as a bridge to transplantation [awake strategy, n = 57 (84%) patients]. Median bridging time was 9 days. Among pre-Tx ECMO+ patients, the need for haemodialysis at any point during bridging emerged as an independent risk factor for in-hospital mortality (odds ratio 7.79, 95% confidence interval 1.21-50.24; P = 0.031). Although in-hospital mortality was significantly higher in pre-Tx ECMO+ versus pre-Tx ECMO- patients (15% vs 5%, P = 0.003), overall graft survival did not differ between groups (79% vs 90% and 61% vs 68% at 1 and 5 years, respectively, P = 0.13). Pretransplant ECMO did not emerge as a risk factor for graft survival in the multivariable analysis.

CONCLUSIONS

If applied in selected patients in a high-volume centre, pretransplant ECMO as a bridge to transplantation results in impaired, but still high in-hospital, survival and does not impact graft survival.

Intensive care, right ventricular support and lung transplantation in patients with pulmonary hypertension

Intensive care of patients with pulmonary hypertension (PH) and right-sided heart failure includes treatment of factors causing or contributing to heart failure, careful fluid management, and strategies to reduce ventricular afterload and improve cardiac function. Extracorporeal membrane oxygenation (ECMO) should be considered in distinct situations, especially in candidates for lung transplantation (bridge to transplant) or, occasionally, in patients with a reversible cause of right-sided heart failure (bridge to recovery). ECMO should not be used in patients with end-stage disease without a realistic chance for recovery or for transplantation. For patients with refractory disease, lung transplantation remains an important treatment option. Patients should be referred to a transplant centre when they remain in an intermediate- or high-risk category despite receiving optimised pulmonary arterial hypertension therapy. Meticulous peri-operative management including the intra-operative and post-operative use of ECMO effectively prevents graft failure. In experienced centres, the 1-year survival rates after lung transplantation for PH now exceed 90%.

Critical Care before Lung Transplantation

Lung transplantation is widely accepted as the only viable treatment option for patients with end-stage lung disease. However, the imbalance between the number of suitable donor lungs available and the number of possible candidates often results in intensive care unit (ICU) admission for the latter. In the ICU setting, critical care is essential to keep these patients alive and to successfully bridge to lung transplantation. Proper management in the ICU is also one of the key factors supporting long-term success following transplantation. Critical care includes the provision of respiratory support such as mechanical ventilation (MV) and extracorporeal life support (ECLS). Accordingly, a working knowledge of the common critical care issues related to these unique patients and the early recognition and management of problems that arise before and after transplantation in the ICU setting are crucial for long-term success. In this review, we discuss the management and selection of candidates for lung transplantation as well as existing respiratory support strategies that involve MV and ECLS in the ICU setting.

Extracorporeal support, during and after lung transplantation: the history of an idea

During recent years, continuous technological innovation has provoked an increase of extracorporeal life support (ECLS) use for perioperative cardiopulmonary support in lung transplantation. Initial results were disappointing, due to ECLS-specific complications and high surgical risk of the supported patients. However, the combination of improved patient management, multidisciplinary team work and standardization of ECLS protocols has recently yielded excellent results in several case series from high-volume transplant centres. Therein, it was demonstrated that, although the prevalence of complications remains higher in supported patients, there may be no difference in long-term graft function between supported and non-supported patients. These results are important, because most of the patients who require ECLS support in lung transplantation are young and have no other chance to survive, but to be transplanted. Moreover, there is no device for "bridging to destination" therapy in lung transplantation. Of note, the evidence in favour of ECLS support in lung transplantation was never validated by randomized controlled trials, but by everyday experience at the patient bed-side. Here, we review the state-of-the-art ECLS evidence for intraoperative and postoperative cardiopulmonary support in lung transplantation.

Mechanical Ventilation and Extracorporeal Membrane Oxygenation as a Bridging Strategy to Lung Transplantation: Significant Gains in Survival

Mechanical ventilation (MV) and extracorporeal membrane oxygenation (ECMO) are increasingly used to bridge patients to lung transplantation. We investigated the impact of using MV, with or without ECMO, before lung transplantation on survival after transplantation by performing a retrospective analysis of 826 patients who underwent transplantation at our high-volume center. Recipient characteristics and posttransplant outcomes were analyzed. Most lung transplant recipients (729 patients) did not require bridging; 194 of these patients were propensity matched with patients who were bridged using MV alone (48 patients) or MV and ECMO (49 patients). There was no difference in overall survival between the MV and MV+ECMO groups (p = 0.07). The MV+ECMO group had significantly higher survival conditioned on surviving to 1 year (median 1,811 days ([MV] vs. not reached ([MV+ECMO], p = 0.01). Recipients in the MV+ECMO group, however, were more likely to require ECMO after lung transplantation (16.7% MV vs. 57.1% MV+ECMO, p < 0.001). There were no differences in duration of postoperative MV, hospital stay, graft survival, or the incidence of acute rejection, renal failure, bleeding requiring reoperation, or airway complications. In this contemporary series, the combination of MV and ECMO was a viable bridging strategy to lung transplantation that led to acceptable patient outcomes.

Pediatric lung transplantation and end of life care in cystic fibrosis: Barriers and successful strategies

Pediatric lung transplantation has advanced over the years, providing a potential life-prolonging therapy to patients with cystic fibrosis. Despite this, many challenges in lung transplantation remain and result in worse outcomes than other solid organ transplants. As CF lung disease progresses, children and their caregivers are often simultaneously preparing for lung transplantation and end of life. In this article, we will discuss the current barriers to success in pediatric CF lung transplantation as well as approaches to end of life care in this population.

Bridging to lung transplantation with extracorporeal circulatory support: when or when not?

Patients with end-stage lung disease who are candidates for lung transplantation may acutely decompensate before a donor organ becomes available. In this scenario, extracorporeal life support (ECLS) may be considered as a bridge to transplant or as a bridge to decision. In the current chapter, we review the indications, techniques, and outcomes for bridging to lung transplantation with ECLS.

Extracorporeal membrane oxygenation in the pre and post lung transplant period

Evolution in technology has resulted in rapid increase in utilization of extracorporeal membrane oxygenation (ECMO) as a bridge to recovery and/or transplantation. Although there is limited evidence for the use of ECMO, recent improvements in ECMO technology, personnel training, ambulatory practices on ECMO and lung protective strategies have resulted in improved outcomes in patients bridged to lung transplantation. This review provides an insight into the current outcomes and best practices for utilization of ECMO in the pre- and post-lung transplantation period.