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.

Primary Graft Dysfunction

Primary graft dysfunction (PGD) is a form of acute lung injury after transplantation characterized by hypoxemia and the development of alveolar infiltrates on chest radiograph that occurs within 72 hours of reperfusion. PGD is among the most common early complications following lung transplantation and significantly contributes to increased short-term morbidity and mortality. In addition, severe PGD has been associated with higher 90-day and 1-year mortality rates compared with absent or less severe PGD and is a significant risk factor for the subsequent development of chronic lung allograft dysfunction. The International Society for Heart and Lung Transplantation released updated consensus guidelines in 2017, defining grade 3 PGD, the most severe form, by the presence of alveolar infiltrates and a ratio of PaO₂:FiO₂ less than 200. Multiple donor-related, recipient-related, and perioperative risk factors for PGD have been identified, many of which are potentially modifiable. Consistently identified risk factors include donor tobacco and alcohol use; increased recipient body mass index; recipient history of pulmonary hypertension, sarcoidosis, or pulmonary fibrosis; single lung transplantation; and use of cardiopulmonary bypass, among others. Several cellular pathways have been implicated in the pathogenesis of PGD, thus presenting several possible therapeutic targets for preventing and treating PGD. Notably, use of ex vivo lung perfusion (EVLP) has become more widespread and offers a potential platform to safely investigate novel PGD treatments while expanding the lung donor pool. Even in the presence of significantly prolonged ischemic times, EVLP has not been associated with an increased risk for PGD.

Inhaled Pulmonary Vasodilators and Thoracic Organ Transplantation: Does Evidence Support Its Use and Cost Benefit?

In heart transplantation, pulmonary hypertension and increased pulmonary vascular resistance followed by donor right ventricular dysfunction remain a major cause of perioperative morbidity and mortality. In lung transplantation, primary graft dysfunction remains a major obstacle because it can cause bronchiolitis obliterans and mortality. Pulmonary vasodilators have been used as an adjunct therapy for heart or lung transplantation, mainly to treat pulmonary hypertension, right ventricular failure, and associated refractory hypoxemia. Among pulmonary vasodilators, inhaled nitric oxide is unique in that it is selective in pulmonary circulation and causes fewer systemic complications such as hypotension, flushing, or coagulopathy. Nitric oxide is expected to prevent or attenuate primary graft dysfunction by decreasing ischemia-reperfusion injury in lung transplantation. However, when considering the long-term benefit of these medications, little evidence supports their use in heart or lung transplantation. Current guidelines endorse inhaled vasodilators for managing immediate postoperative right ventricular failure in lung or heart transplantation, but no guidance is offered regarding agent selection, dosing, or administration. This review presents the current evidence of inhaled nitric oxide in lung or heart transplantation as well as comparisons with other pulmonary vasodilators including cost differences in consideration of economic pressures to contain rising pharmacy costs.

Inhaled nitric oxide

Nitric oxide (NO) is a gas that induces relaxation of smooth muscle cells in the vasculature. Because NO reacts with oxyhaemoglobin with high affinity, the gas is rapidly scavenged by oxyhaemoglobin in red blood cells and the vasodilating effects of inhaled NO are limited to ventilated regions in the lung. NO therefore has the unique ability to induce pulmonary vasodilatation specifically in the portions of the lung with adequate ventilation, thereby improving oxygenation of blood and decreasing intrapulmonary right to left shunting. Inhaled NO is used to treat a spectrum of cardiopulmonary conditions, including pulmonary hypertension in children and adults. However, the widespread use of inhaled NO is limited by logistical and financial barriers. We have designed, developed and tested a simple and economic NO generation device, which uses pulsed electrical discharges in air to produce therapeutic levels of NO that can be used for inhalation therapy. LINKED ARTICLES: This article is part of a themed section on Nitric Oxide 20 Years from the 1998 Nobel Prize. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.2/issuetoc.

Perioperative Management of the Lung Graft Following Lung Transplantation

Perioperative management of patients undergoing lung transplantation is one of the most complex in cardiothoracic surgery. Certain perioperative interventions, such as mechanical ventilation, fluid management and blood transfusions, use of extracorporeal mechanical support, and pain management, may have significant impact on the lung graft function and clinical outcome. This article provides a review of perioperative interventions that have been shown to impact the perioperative course after lung transplantation.

Treatment of primary graft dysfunction after lung transplantation with orally inhaled AP301: A prospective, randomized pilot study

BACKGROUND

Primary graft dysfunction (PGD) after lung transplantation (LTx) carries significant morbidity and mortality in the early post-operative period and is associated with the development of chronic lung allograft dysfunction. AP301, an activator of epithelial sodium channel-mediated Na+ uptake represents a new concept for prevention and treatment of pulmonary edema and has shown promising results in the pre-clinical setting. This pilot study investigated the clinical effect of inhaled AP301 on patients with development of PGD > 1 according to International Society of Heart and Lung Transplantation criteria after primary LTx in a high-volume center and was conducted as a randomized, placebo-controlled, single-center pilot-study including 20 patients. All consecutive patients fulfilling inclusion criteria were screened for PGD at arrival on the intensive care unit (ICU) after LTx. After randomization, inhaled AP301 or placebo was administered by nebulizer twice daily for 7 days or until extubation. Otherwise, patients were treated according to routine clinical protocol. Partial pressure of arterial oxygen (Pao2)/fraction of inspired oxygen (Fio2) values were obtained until extubation and assessed as a primary outcome parameter. Patients were monitored for 30 days within the study protocol.

RESULTS

From July 2013 to August 2014, 20 patients were randomized 1:1 to AP301 (Group 1) or placebo (Group 2). Both groups were comparable with regard to sex (40% women/60% men vs 50% women/50% men), mean age (55 ± 13 vs 54 ± 6 years), comorbidities, and diagnosis leading to LTx. The Pao2/Fio2 ratio at the time of inclusion was comparable in both groups, with a mean 235.65 ± 90.78 vs 214.2 ± 95.84 (p = 0.405), and there was no significant difference in the extravascular lung water index (13.88 ± 5.28 vs 16 ± 6.29 ml/kg, p = 0.476). The primary end point was mean Pao2/Fio2 ratio values between baseline and Day 3. In the AP301 group, only 1 patient was ventilated at Day 4 and no patients were ventilated after Day 4. In the placebo group, 5 patients were ventilated on Day 4 and 2 patients on Days 5, 6, and 7. The mean increase in the Pao2/Fio2 ratio was significantly higher in Group 1 patients, and the mean between baseline and at 72 hours was 365.6 ± 90.4 in Group 1 vs 335.2 ± 42.3 in Group 2 (p = 0.049). The duration of intubation was shorter in Group 1 than in Group 2 patients (2 ± 0.82 vs 3.7 ± 1.95 days; p = 0.02). ICU stay was 7.5 ± 3.13 days in Group 1 vs 10.8 ± 8.65 days in group 2 (p = 0.57). Survival at 30 days was 100%. No severe adverse events were recorded.

CONCLUSIONS

This study was designed as a proof-of-concept pilot study. Although it was not powered to achieve statistical significances, the study demonstrated relevant clinical effects of inhaled AP301 on patients with PGD after primary LTx. The improved gas exchange led to a significantly shorter duration of mechanical ventilation and a trend towards a shorter ICU stay. Further investigation of AP301 for treatment of PGD in larger studies is warranted.

TRIAL REGISTRATION

The trial is registered at https://www.clinicaltrialsregister.eu/ctr-search/trial/2013-000716-21/AT.

Primary graft dysfunction: pathophysiology to guide new preventive therapies

INTRODUCTION

Primary graft dysfunction (PGD) is a common complication of lung transplantation characterized by acute pulmonary edema associated with bilateral pulmonary infiltrates and hypoxemia in the first 3 post-operative days. Development of PGD is a predictor of poor short- and long-term outcomes after lung transplantation, but there are currently limited tools to prevent its occurrence. Areas covered: Several potentially modifiable donor, recipient, and operative risk factors for PGD have been identified. In addition, basic and translational studies in animals and ex vivo lung perfusion systems have identified several biomarkers and mechanisms of injury in PGD. In this review, we outline the clinical and genetic risk factors for PGD and summarize experimental data exploring PGD mechanisms, with a focus on strategies to reduce PGD risk and on potential novel molecular targets for PGD prevention. Expert commentary: Because of the clinical importance of PGD, development of new therapies for prevention and treatment is critically important. Improved understanding of the pathophysiology of clinical PGD provides a framework to explore novel agents to prevent or reverse PGD. Ex vivo lung perfusion provides a new opportunity for rapid development of therapeutics that target this devastating complication of lung transplantation.

Primary graft dysfunction: lessons learned about the first 72 h after lung transplantation

PURPOSE OF REVIEW

In 2005, the International Society for Heart and Lung Transplantation published a standardized definition of primary graft dysfunction (PGD), facilitating new knowledge on this form of acute lung injury that occurs within 72 h of lung transplantation. PGD continues to be associated with significant morbidity and mortality. This article will summarize the current literature on the epidemiology of PGD, pathogenesis, risk factors, and preventive and treatment strategies.

RECENT FINDINGS

Since 2011, several manuscripts have been published that provide insight into the clinical risk factors and pathogenesis of PGD. In addition, several transplant centers have explored preventive and treatment strategies for PGD, including the use of extracorporeal strategies. More recently, results from several trials assessing the role of extracorporeal lung perfusion may allow for much-needed expansion of the donor pool, without raising PGD rates.

SUMMARY

This article will highlight the current state of the science regarding PGD, focusing on recent advances, and set a framework for future preventive and treatment strategies.

Beneficial effects of inhaled NO on apoptotic pneumocytes in pulmonary thromboembolism model

BACKGROUND

Lung ischemia-reperfusion injury (LIRI) may occur in the region of the affected lung after reperfusion therapy. Inhaled NO may be useful in treating acute and chronic pulmonary thromboembolism (PTE) due to the biological effect property of NO.

METHODS

A PTE canine model was established through selectively embolizing blood clots to an intended right lower lobar pulmonary artery. PaO2/FiO2, the mPAP and PVR were investigated at the time points of 2, 4, 6 hours after inhaled NO. Masson's trichrome stain, apoptotic pneumocytes and lung sample ultrastructure were also investigated among different groups.

RESULTS

The PaO2/FiO2 in the Inhaled NO group increased significantly when compared with the Reperfusion group at time points of 4 and 6 hours after reperfusion, mPAP decreased significantly at point of 2 hours and the PVR decreased significantly at point of 6 hours after reperfusion. The amounts of apoptotic type II pneumocytes in the lower lobar lung have negative correlation trend with the arterial blood PaO2/FiO2 in Reperfusion group and Inhaled NO group. Inhaled nitric oxide given at 20 ppm for 6 hours can significantly alleviate the LIRI in the model.

CONCLUSIONS

Dramatic physiological improvements are seen during the therapeutic use of inhaled NO in pulmonary thromboembolism canine model. Inhaled NO may be useful in treating LIRI in acute or chronic PTE by alleviating apoptotic type II pneumocytes. This potential application warrants further investigation.

Postoperative complications in the intensive care unit following lung transplantation in adults: results in University Hospital Reina Sofia

The postoperative period following lung transplantation remains critical because of several complications. Infection, primary graft failure, acute rejection, and surgical complications are risk factors for mortality and morbidity. The recognition and early treatment of these complications is important to optimize outcomes. This article provides an overview of postoperative complications observed in our center during the last year. We were particularly interested in the influence of variables, such as inotrope usage and Acute Physiology and Chronic Health Evaluation (APACHE II) score, a well-known, and validated mortality prediction model for general intensive care unit (ICU) patients only infrequently reported in the transplantation literature. High APACHE II scores were significantly associated with prolonged mechanical ventilation (P = 0.041) and a tracheostomy requirement (P = .035). The factors significantly associated with an early postoperative death were older donor age (P = .005), prolonged donor ICU period (P = .004), need for cardiopulmonary bypass (CB; P = .005), and high inotrope requirements in the ICU (P = .034). CB data were biased because we selected the worst case patients. Donor age and high inotrope requirements in the ICU have been reported previously to be prognostic factors for poor graft function. We believe that control of these variables may improve outcomes.

Lung Ischemia Reperfusion Injury

Lung ischemia reperfusion injury (LIRI) is a pathologic process occurring when oxygen supply to the lung has been compromised followed by a period of reperfusion. The disruption of oxygen supply can occur either via limited blood flow or decreased ventilation termed anoxic ischemia and ventilated ischemia, respectively. When reperfusion occurs, blood flow and oxygen are reintroduced to the ischemic lung parenchyma, facilitating a toxic environment through the creation of reactive oxygen species, activation of the immune and coagulation systems, endothelial dysfunction, and apoptotic cell death. This review will focus on the mechanisms of LIRI, the current supportive treatments used, and the many therapies currently under research for prevention and treatment of LIRI.