2 The condition, current treatments and procedure
2.1 Lung transplant is usually done in patients with non-malignant advanced or end-stage pulmonary diseases (such as severe pulmonary fibrosis, cystic fibrosis, pulmonary hypertension and obliterative bronchiolitis) that is minimally responsive or unresponsive to treatment and who have a life expectancy of less than a year. This improves patients' quality of life and prolongs survival.
2.2 On average, 20% of potential deceased donor lungs in the UK are used for transplant. The rest are considered unsuitable, usually because of complications associated with attempts to save the donor or injury which happens in association with death. Limited availability of deceased donor lungs that meet standard criteria for transplant results in up to 30% of patients clinically deteriorating and dying while waiting for a lung transplant.
2.3 Standard lung transplant protocol involves cold preservation to maintain the donor lungs. Various other strategies are used to increase the available pool of deceased donor lungs and these include brain death donor lungs from extended criteria donors and donors after circulatory death. Living donor lobal or lung transplant is another option.
2.4 Ex-situ machine perfusion for extracorporeal preservation of lungs (ex-vivo lung perfusion, EVLP) is a technique of lung preservation that may allow donor lungs to be preserved for longer in better physiologic conditions, and may allow marginal donor lungs or pulmonary grafts which are working poorly to be improved and reconditioned so that they can be used in lung transplant.
2.5 Ex-situ machine perfusion for extracorporeal preservation of lungs is done once the lungs have been removed from the donor after cold pulmonary flush using surgical techniques. An adequate donor left atrial cuff and pulmonary artery are preserved to allow anastomosis to the recipients' organs.
2.6 After being transferred in cold solution and being ischemic for a period of time, the lungs are placed in a specially designed organ chamber and connected to a modified heart–lung bypass machine, a ventilator and filtration or EVLP system. A specialised nutrient solution (perfusate) is pumped from the filtration or EVLP system through a perfusion circuit (gas exchange membrane, heat exchanger and leukocyte filter) under optimal colloid pressure through the pulmonary artery to the lungs. Pulmonary effluent from the pulmonary veins drains back to the EVLP system and is recirculated. Perfusion flow is then gradually increased, pulmonary artery pressure is carefully monitored, and protective controlled mechanical lung ventilation with low tidal volume and positive end expiratory pressure is started. The lungs are gradually rewarmed to body temperature while reaching a targeted flow. EVLP is possible for a number of hours after removal from the donor. During this period, the lungs can be assessed and, if necessary, treated to remove unwanted fluid, and to re‑expand areas of lung that have collapsed (atelectatic areas). If EVLP-treated lungs recover well enough, they may be considered suitable for transplant in the conventional way.
2.7 Ex-situ machine perfusion can be done using different devices or machines and protocols. The perfusate composition, perfusion and ventilation settings (target flow, temperature, pressure) may vary.