KONOS collects the underlying disease in the following 12 categories: idiopathic pulmonary fibrosis (IPF), sarcoidosis, bronchiectasis, bronchiolitis obliterans after transplant, emphysema, lymphangioleiomyomatosis, asbestosis, primary pulmonary hypertension, cystic fibrosis, Eisenmenger syndrome, other, and unknown. We classified the underlying disease into the following 5 categories: chronic obstructive pulmonary disease (COPD; emphysema), interstitial lung disease (ILD, idiopathic pulmonary fibrosis, sarcoidosis, lymphangioleiomyomatosis, asbestosis), primary pulmonary hypertension, bronchiectasis (cystic fibrosis), and other (Eisenmenger syndrome, bronchiolitis obliterans after transplant, other and unknown).

Before the implementation of the system in July 2017, all donor lungs were allocated according to an urgency tier system. Patients were classified as status 0, 1, 2, 3 and 7 (Supplementary Table 1). Patients with status 0 were defined as those who require mechanical ventilation or extracorporeal membrane oxygenation (high urgent status). Those with status 1 (urgent status) were defined as having one or more of the following conditions: 1) New York Heart Association (NYHA) IV and PaO₂ < 55 mmHg on arterial blood gas test measured without oxygen administration, 2) NYHA IV and mean pulmonary arterial pressure > 65 mmHg or mean right atrial pressure > 15 mmHg, and 3) cardiac index < 2 L/min/m². Status 2 were defined as having one or more of the following conditions: 1) In the pulmonary function test, forced expiratory volume at 1 second (FEV1) < 25%, 2) PaO₂ < 60 mmHg in arterial blood gas test measured without oxygen, 3) When the average right atrial blood pressure is 10–15 mmHg, 4) When the average pulmonary arterial pressure is 55–65 mmHg, 5) Cardiac index < 2–2.5 L/min/m². Status 3 were defined as having one or more of the following conditions: 1) When a single lung transplant is required, 2) Emphysema, pulmonary hypertension, diffuse interstitial lung disease, 3) Forced expiratory volume < 30% in pulmonary function test, 4) If hospitalized more than 3 times for respiratory failure. Status 7 was defined as whose status does not meet 0–3. Status from 2 to 7 was considered an elective status. Patients with status 0 (high urgent status) were prioritized over those with status 1 to 7. Moreover, within the same urgency tier, patients with the longest waiting period received the lung donation first. In July 2017, the Korea organ commission of the Korea medical council decided to change the system. The changed system was primarily based on urgency, blood type, and distance between donor and recipient. Urgency was the most prioritized variable, followed by same region, same blood type, waiting times, past history or family history of organ donation and age in order. Furthermore, the following criteria were added to status 1: 1) arterial blood gas analysis with PCO₂ ≥ 80 mmHg and 2) patients with high-flow nasal cannula 30 L and FiO₂ ≥ 0.6 for more than 2 weeks. The region was divided into regions 1–3, where region 1 included Seoul, Incheon, Gyeonggi, Gangwon, and Jeju. Region 2 included Gwangu, Daejeon, Jeonbuk, Jeonnam, Chungbuk, and Ghungnam, and region 3 included Busan, Daegu, Ulsan, Geyongbuk, and Gyeongnam.

A marginal donor was defined as when any of the following parameters was fulfilled: age ≥ 55 years, PF ratio ≤ 300, smoking history ≥ 20 pack-years, consolidation or collapse in the chest radiograph, organisms in sputum cultures, and purulent secretion or inflammation on bronchoscopy.8

Donor, recipient, and transplant factors are expressed as either total number and percentage or mean and standard deviation. Categorical variables were analyzed using a χ² test, and continuous variables were assessed using the Mann-Whitney U test. To adjust urgent status and marginal donor usage, we performed a propensity score matching analysis (1:1). Univariate analysis was performed to determine the donor and recipient factors affecting 1-year mortality. Multivariate analysis was conducted on all factors with P < 0.05 using a logistic regression model. All statistical analyses were accomplished using SPSS version 21 (IBM corporation, Armonk, NY, USA). P < 0.05 was considered to be statistically significant for all analyses.

The present study protocol was reviewed and approved by the Institutional Review Board of Pusan National University Yangsan Hospital (approval No. 05-2020-004). Informed consent was waived because of the retrospective nature of the study.

Table 1 summarizes the characteristics of all lung transplant candidates registered during the 4 years before (n = 210) and after (n = 417) the introduction of the revised system. The primary diagnosis was ILD (47.4%). No differences were noted related to the primary diagnosis and the blood type among the candidates listed for transplant between the two periods. In addition, there were no significant differences in age, gender, and urgency between the two periods. The total waiting list size increased by 98.6%, from 210 in period 1 to 417 in period 2 (Fig. 1). Regarding the urgency status, there were no differences among the candidates listed for transplantation between the two periods (Fig. 1). A total of 35.4% of candidates were in the high urgent status requiring mechanical ventilation and/or extracorporeal membrane oxygenation support (37.1% vs. 34.5%, P = 0.519).

The number of transplant patients also increased by 32.7%, from 171 in period 1 to 227 in period 2 (Fig. 1A). The number of donors decreased from 1,042 to 878, whereas the usage rate, i.e., the number of donor lungs used for transplantation among the total number of reported donor lungs, increased from 16.4% to 25.9%. Table 2 shows the baseline characteristics of the lung transplantations performed during the study period. The primary disease for which lung transplantation was performed was ILD. No significant difference was detected in the diagnosis profile between the two periods. There was also no significant difference in the blood type, except a very slight trend toward significance indicating that the proportion of patients with blood type A decreased from 40.9% to 30.8%, otherwise that of type O increased from 19.9% to 24.7%, between the two periods. The proportion of patients with high urgent status at transplantation increased from 45% to 60.4%, whereas those with urgent status decreased from 46.8% to 35.7% (P = 0.006, Fig. 2). No significant difference was observed in the waiting time from registration to transplantation, although it showed an increasing tendency among those with urgent status. The use of marginal donor lungs was strikingly increased from 29.8% to 53.7% (P < 0.001). To adjust urgency status and marginal donor usage between two groups, we conducted a propensity score matching analysis (Supplementary Table 2). No significant differences were detected in 1-, 6-month and 1-year survival rates between the two periods after propensity score matching (1-month survival 96.5% vs. 95.3%, P = 0.585, 6-month survival 81.2% vs. 82.4%, P = 0.779, 1-year survival 70.6% vs. 71.2%, P = 0.905). In the subgroup analysis for high urgent patients, 1-year survival tended to decrease from 72.7% to 61.3% (P = 0.127). Conversely, 1-year survival tended to increase from 70.9% to 80.2% (P = 0.168) in the urgent patients (Fig. 3).

The univariate analysis revealed that recipient age (≥ 65 years) (odds ratio [OR], 2.44; 95% confidence interval [CI], 1.40–4.25; P = 0.002) and donor age (≥ 55 years) (OR, 1.81; 95% CI, 1.01–3.25; P = 0.045) were significantly associated with 1-year mortality (Supplementary Table 3). However, in the multivariate analysis, only recipient age (≥ 65 years) was found to be significantly associated with 1-year mortality (OR, 2.44; 95% CI, 1.40–4.25; P = 0.002).

Table 3 shows the baseline characteristics of the patients who died while waiting for lung transplantation. No significant differences were observed in the mortality rate on the waiting list between the two periods (17.1% vs. 19.4%, P = 0.489). The proportion of patients with ILD increased from period 1 to period 2 (30.6% vs. 54.3%, P = 0.024). The proportion of patients with blood type A increased from 33.3% to 46.9%, whereas that of type O decreased from 44.4% to 32.1%, with no statistical significance (P = 0.531). There was a significant difference in the urgency at the time of registration. The proportion of patients with urgent status significantly increased from 19.4% to 43.2% (P = 0.039). There was no significant difference in the cause of death on the waiting list between the two periods (Supplementary Table 4).

The status of used donor lungs is presented in Table 4. The mean age of the patients was 40.1 ± 13.1 years, with no difference in donor age between the two periods. The proportion of patients aged ≥ 55 years tended to increase from 11.1% to 16.3%. Smoking habit and PF ratio showed no differences among the patients. However, the proportion of patients with consolidation or collapse in the chest radiograph significantly increased from 14.0% to 34.8% (P < 0.001).

The causes of unused donor lungs are presented in Supplementary Table 5. The major cause was poor donor lung condition. The proportion of marginal donor lungs among the unused donor lungs was 81.7%, with no difference between the two periods (80.5% vs. 83.4%, P = 0.146). The mean age of donor patients whose lungs were unused was 49.1 ± 16.4 years, and the proportion of those aged ≥ 55 years was 41.8%, and 43.1% of patients had smoking habit. The mean PF ratio was 271.8 ± 128.7 mmHg, and chest X-ray abnormality was observed in 22.1% of patients. The difference in each factor between the two periods is presented in Supplementary Table 6. The mean age of donor patients whose lungs were unused increased from 48.2 ± 16.8 to 50.2 ± 15.8 years (P = 0.015), and no significant differences were detected in other factors between the two periods.