Current research review. Lung transplantation

Risk factors of bronchial dehiscence after primary lung transplantation

Complications of the bronchial anastomosis in lung transplantation, once the Achilles heel of the procedure, have become quite rare. The surgical technique is well established and safe. Risks contributing to anastomotic complications are primarily related to patients pre-existing conditions. The key factor is good blood flow to the bronchial stump. Postoperative infection can also contribute to the breakdown of the anastomosis. This may be the reason why different immunosuppressive regimes lead to differences in the incidence of bronchial dehiscence.

China lung transplantation developing: past, present and future

Lung transplantation in China has been developing for almost 40 years (1979-2019). The pioneers of this procedure experienced struggles and obstacles upon accomplishment of the initial 20 cases of lung transplantation. Like the expanding process of transplant programs elsewhere in western countries and other regions in Asia, transplant teams in China have found their own way to step forward, with the establishment of the two largest centers in Beijing and Wuxi. Since 2015, which was a novel start and milestone for transplant affairs in China, the pace of transplant volume and comparable quality of care for lung transplant recipients have increased noticeably. We reviewed the advancement of lung transplantation programs and registry setup in China and indicated that more socioeconomic factors and human care aspects needed to be considered to benefit Chinese recipients, which may further inspire the modification of criteria of listing and organ utilization based on East Asian cultural and traditional origins.

Historical perspectives of lung transplantation: connecting the dots

Lung transplantation is now a treatment option for many patients with end-stage lung disease. Now 55 years since the first human lung transplant, this is a good time to reflect upon the history of lung transplantation, to recognize major milestones in the field, and to learn from others' unsuccessful transplant experiences. James Hardy was instrumental in developing experimental thoracic transplantation, performing the first human lung transplant in 1963. George Magovern and Adolph Yates carried out the second human lung transplant a few days later. With a combined survival of only 26 days for these first 2 lung transplant recipients, the specialty of lung transplantation clearly had a long way to go. The first "successful" lung transplant, in which the recipient survived for 10.5 months, was reported by Fritz Derom in 1971. Ten years later, Bruce Reitz and colleagues performed the first successful en bloc transplantation of the heart and one lung with a single distal tracheal anastomosis. In 1988, Alexander Patterson performed the first successful double lung transplant. The modern technique of sequential double lung transplantation and anastomosis performed at the mainstem bronchus level was originally described by Henri Metras in 1950, but was not reintroduced into the field until Pasque reported it again in 1990. Since then, lung transplantation has seen landmark changes: evolving immunosuppression regimens, clarifying the definition of primary graft dysfunction (PGD), establishing the lung allocation score (LAS), introducing extracorporeal membrane oxygenation (ECMO) as a bridge to transplant, allowing donation after cardiac death, and implementing ex vivo perfusion, to name a few. This article attempts to connect the historical dots in this field of research, with the hope that our effort helps summarize what has been achieved, and identifies opportunities for future generations of transplant pulmonologists and surgeons alike.

Normal bronchial healing without bronchial wrapping in canine lung transplantation

The deleterious effect of steroids on bronchial healing in lung transplantation has led to the development of techniques to protect the anastomosis and to the exclusion of steroid-dependent patients from transplantation. The effect of steroids on bronchial healing was tested in a canine single-lung allotransplantation model. Twenty size-matched mongrel dogs (20 to 30 kg) underwent left lung transplantation without anastomotic wrap or direct revascularization. Postoperatively, all received daily doses of cyclosporine (15 mg/kg) and azathioprine (1 mg/kg) and were subdivided into three steroid dosage groups. Group A (n = 10) animals received 1.5 mg/kg of prednisone per day whereas groups B (n = 5) and C (n = 5) received 5.0 mg/kg of prednisone per day for 28 postoperative days. In addition, group C received prednisone (5.0 mg.kg-1.day-1) for 1 month preoperatively. In group A, 8 of 10 dogs survived 28 days without evidence of respiratory compromise, with anastomotic bursting pressure greater than 510 mm Hg. In group B, all 5 dogs survived to 28 days without evidence of respiratory compromise and with intact bronchial anastomoses (bursting pressures greater than 510 mm Hg). In group C, 3 of 5 animals survived to 28 days with intact anastomoses. Histological examination demonstrated normal bronchial healing in all anastomoses. These data suggest that preoperative steroid dependence should not be a contraindication to lung transplantation and that bronchial anastomotic wrapping with vascular tissue may not be essential.

Glutathione decreases the pulmonary reimplantation response in canine lung autotransplants

The pulmonary reimplantation response (PRR) is a form of membrane permeability pulmonary edema occurring in lung transplants. The severity of the PRR reflects the quality and duration of lung graft preservation. Free radicals formed during ischemia with reperfusion in the autotransplanted dog lung may play a role in producing PRR. We hypothesized that the addition of reduced glutathione (GSH) to the preservative solution could decrease PRR if hydroperoxides are being formed. Six dogs underwent left lung autotransplantation after the lung was flushed with Euro-Collins solution (EC). These dogs demonstrated radiographic and histopathologic evidence of bilateral pulmonary edema, greatest in the transplanted left lung. They also had increases in lung wet to dry weight (W/D) ratios in both lungs (left, 12.0 +/- 0.9; right, 10.1 +/- 0.8) as compared with a group of five unmanipulated control animals (left, 6.0 +/- 0.5; right, 7.0 +/- 0.4). Malondialdehyde (MDA) concentrations were significantly increased in the transplanted left lungs (14 +/- 4) from this group as compared with the controls (5 +/- 7). Five additional dogs underwent left lung autotransplantation with GSH added to the EC cryopreservation fluid. These animals did not develop histologic or radiographic evidence of pulmonary edema, and W/D ratios as well as MDA concentrations were not different from those in controls. To evaluate the effect of ischemia alone on changes in lung GSH concentrations, ten additional dogs underwent left pneumonectomy. Left lungs were cryopreserved in EC + GSH. In five of the animals, the right lung was removed and preserved in EC alone. In the other five animals, the right lung remained in vivo for 3 h and was then removed. Lung GSH concentrations were doubled after 3 h of ischemia when incubated in EC + GSH compared to in vivo controls and to EC-treated lungs. These data suggest that GSH added to the preservation fluid prevents PRR following transplantation and that lung GSH concentrations actually increase during preservation prior to reimplantation and reperfusion if the lung graft is exposed to GSH in the preservation fluid.

Lung and heart-lung transplantation

Unilateral lung transplantation has become a successful method for the treatment of end-stage pulmonary disease, whereas double-lung transplantation has provided benefit to patients with nonfibrotic lung disease such as emphysema and cystic fibrosis. In the past 5 years, 16 single-lung and 13 double-lung transplantations have been performed by the Toronto Lung Transplant Group in patients with end-stage lung disease. Seven perioperative and two late deaths have been recorded so far. Since the introduction of heart-lung transplantation at Stanford in 1981 and at Pittsburgh in 1982 for the treatment of Eisenmenger's syndrome and terminal pulmonary vascular disease, more than 350 combined heart-lung transplantations have been carried out throughout the world. Presently, the 2-year actuarial survival is about 62%. The long-term results have not yet reached the same level of success as those of cardiac transplantation alone. Although several factors have played a role in this difference, a prominent cause has been the lack of a reliable and simple method for pulmonary protection against prolonged ischemia. Most of the techniques proposed against ischemia can be classified as normothermic or static hypothermic cardiopulmonary preservation. The use of the normothermic method has not always been successful. For this reason, interest has now been directed toward the potential for hypothermic preservation of the heart-lung bloc and the use of free-radical scavenger therapy in the reduction of reperfusion injury.

Reduced-size lung transplantation in neonatal swine: technique and short-term physiological response

Lung transplantation is now a clinical reality in adults but is limited by the scarcity of appropriate donors. The donor shortage is even more acute for neonatal and pediatric patients. Reduced-size lung grafts would expand the pool of appropriate cadaveric donors and allow HLA-matched living related lobar or segmental lung transplants. To evaluate this experimentally, we developed a model of pulmonary lobar transplantation in neonatal pigs and studied the acute hemodynamic response after transplanting the left lower lobe from a more mature donor to a neonatal recipient. Technical considerations included using the recipient atrial appendage for the pulmonary venous anastomosis. Nine pairs of pigs underwent left lateral thoracotomy. The recipient left atrial and pulmonary arterial pressures, cardiac output, and pulmonary vascular resistance were measured before pneumonectomy and after left lower lobe transplantation. Although the left atrial and pulmonary arterial pressures remained unchanged after transplantation, there was a 15% increase in pulmonary vascular resistance and a 23% reduction in cardiac output. Neither change was statistically significant. The distribution of blood flow through the left and right pulmonary arteries was unchanged after transplantation. We conclude that lobar transplantation is technically feasible in immature animals and that the pulmonary venous anastomosis to the left atrial appendage facilitates the procedure. This model may prove useful in studying lung transplantation in immature recipients and expedite implementation of reduced-size lung transplantation in neonatal and pediatric patients.

Pulmonary lobar transplantation in neonatal swine: a model for treatment of congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) babies born with severe pulmonary hypoplasia are unsalvageable despite maximal therapy including extracorporeal membrane oxygenation (ECMO). Lung transplantation is a potential treatment for these otherwise doomed infants using ECMO as a bridge to transplantation. Cadaveric, or living related donation of a more mature reduced size lung (pulmonary lobe or segment) may help solve the critical donor shortage problem. We evaluated the physiological response of mature left lower lobe (LLL) transplants in neonatal swine with the hemodynamic conditions of CDH simulated by occlusion of the right pulmonary artery (PA), and also studied the pulmonary function of the mature lobar graft compared with the neonatal lung. LLL transplantation was well tolerated and resulted in minimal alteration in hemodynamic parameters. The response to right PA occlusion was similar pre- and posttransplantation with a fall in cardiac output and a significant rise in pulmonary vascular resistance. Compared with the contralateral native lung, the lobar graft was preferentially ventilated with resultant higher pH (7.65 +/- 0.17 v 7.41 +/- 0.08, P less than .01) and lower pCO2 (17 +/- 6 v 36 +/- 5, P less than .001). The more mature lobar graft was preferentially ventilated due to the increased compliance compared with the neonatal right lung (8.16 +/- 1.28 v 5.48 +/- 0.82 mL/cm, P less than .0001). Reduced size lung transplantation is technically feasible and may help solve the donor problem for severe CDH neonates for whom no effective therapy is currently available.

Lung transplantation

Over the past 20 years, many advances in surgical methods, transplantation immunology, donor organ procurement and preservation techniques, and postsurgical care regimens have influenced greatly the field of lung transplantation. The single remaining obstacle to widespread clinical success is donor lung availability. Improved methods of ex vivo lung preservation, organ donor maintenance, and donor lung retrieval after the completion of cardiac donation should help to ameliorate this problem.

Bronchial omentopexy in canine lung allotransplantation

Impaired bronchial healing has been a major source of morbidity and mortality following clinical lung transplantation. Bronchial ischemia secondary to division of the systemic bronchial blood supply may be an important cause of these complications. Bronchial omentopexy was performed in conjunction with lung allotransplantation in 6 dogs. Revascularization of the distal bronchial circulation through the omental pedicle was demonstrated in all instances by postmortem injection studies done through the celiac artery. Bronchostenosis occurred in 1 dog. No other complications were encountered. In view of the frequency of bronchial anastomotic complications following human lung transplantation, the technique of bronchial omentopexy warrants serious consideration.

Pulmonary reimplantation response

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Pathological findings after right lung transplantation in a patient with fibrosing alveolitis

The pathological findings in a patient who died two months after right lung transplantation for fibrosing alveolitis are reported. The cause of death was haemoptysis, due to penetrating ulceration causing a fistula between the surface of the cartilagenous part of the main bronchus of the donor lung and the right upper lobe pulmonary artery. The opening in the donor bronchus was immediately distal to the line of the bronchial anastomosis and through an actively inflamed area. Other parts of the donor bronchus had microscopic changes suggesting ischaemia, emphasizing that inadequacy of blood supply to the donor extrapulmonary bronchus is one of the most serious hazards of lung transplantation. Within the lung, histological features of rejection were mild and there was minimal evidence of infection. Another question raised by this case is whether the donor lung was in the process of developing the original disease, evidence for which was sought electron microscopically but was not proven.