This study is a single-institution, prospective cohort trial (ClinicalTrial.gov: NCT02061462). We wanted to verify the safety of lung transplantations performed with organs from DCD donors procured with an original protocol. We compared clinical and functional outcomes of patients undergoing lung transplantation who received grafts from DCD donors (DCD Group) with those of recipients of lungs from DBD donors (DBD Group) in our centre in the same period. We also performed an analysis comparing the outcomes of the DCD Group with those of recipients of lungs from DBD donors requiring machine perfusion (DBD-EVLP Group).

Since November 2014 all subjects provided written informed consent to participate in the trial at the time of enlisting, in accordance with the protocol approved by the local Ethics Committee. Recipients were selected sequentially, based on blood group, size match (total lung capacity) and waiting-list status (i.e., lung allocation score (LAS) or emergency program) (10,11). The type of donor (DBD vs. DCD) did not represent a criterion for donor-recipient matching, thus maintaining randomness of recipients group distribution. Recipients of a DCD lung were asked to renew their consent to receive organs from a DCD donor closely ahead of transplantation. During and after surgery, standard care was provided in both groups, according to our protocol (see Supplementary Material). Recipients’ and respective donors’ variables of interest were recorded in a dedicated electronic database from the date of waiting-list entry to the date of the last follow-up. Institutional board approval for data use was obtained (number 749_2016bis). The follow-up period was concluded on 31st July 2020.

All patients enlisted for bilateral lung transplantation older than 14 years were deemed eligible. Candidates for multi-organ transplantation or re-transplantation were excluded. Donors aged 65 and older, as well as DCD category I or IV donors, were also excluded.

The lungs, from both DBD and DCD donors, were offered to our centre by the regional and national organ procurement organizations: the North Italian Transplant program (NITp) and the National Transplantation Centre (CNT), respectively (10,12). Notably, Italian law requires 6 h of observation, or 20 min of flat EKG to declare the patient’s death according to neurological or cardiocirculatory criteria, respectively.

Primary endpoint was the 30-day mortality after transplantation. The secondary endpoints were the duration of MV, ICU length of stay, the occurrence of primary graft dysfunction (PGD) of grade 3 within the first 72 h after transplantation (17), and the onset of chronic lung allograft dysfunction (CLAD) (18).

Continuous data are presented as median and inter quartile range (IQR). Binary variables are shown as absolute and percentages frequencies. The Mann-Whitney or Chi-square tests were performed, as appropriate. Pulmonary function parameters were measured at 3, 6, and 12 months. The repeated measures for pulmonary function data were analysed using the “mean response profile” method through generalized estimating equations (GEE) by employing time as a categorical variable and logit link function (19). GEE standard errors were calculated with a sandwich estimator. We used the unstructured working correlation matrix selected by correlation information criterion (20). The GEE regression model was adjusted by donor smoking history, donor age, donor-recipient sex mismatch, surgical incision, recipient medical diagnosis, LAS, grade 3 PGD, TIT and WIT for both first and second lung, airway complications.

We chose GEE because it allows a population-averaged interpretation of the regression coefficients. The null hypothesis was that the difference of pulmonary function between the two study groups was constant over time. This was verified using the multivariate Wald test, testing time × group interaction in the GEE regression model. Profile likelihood confidence intervals (CIs) at 95% confidence level were computed. Univariate Wald test for each GEE-estimated parameter was performed. The non-parametric Kaplan-Meier estimator was used to analyse time-to-event data related to overall survival and CLAD onset. Confidence intervals (CIs) were at 95% and 2-sided p-values were calculated. A p-value of <0.05 was considered statistically significant; the inference should be intended for exploratory purposes. All analyses and graphs were carried out using an R software (version 3.2.2) (21).

From November 2014 to July 2019, we performed 143 lung transplantations. Out of these, 22 cases were excluded from the study: ten single-lung transplantations, eight donors ≥65 years-old, two re-transplantations, one DCD category IV donor, one recipient <14 years-old (Figure 1). The remaining 121 patients were enrolled in the study: 110 in the DBD Group and 11 in the DCD Group (five patients received lungs procured from DCD II donors and six from DCD III donors). The complete results of our DCD program are shown in Figure 2.

Recipients’ diseases leading to lung transplantation were distributed homogeneously in the two groups; notably, in the DCD and DBD groups, 72.7% and 61.9% of patients suffered from cystic fibrosis (CF), respectively. Recipients were similar in terms of number of urgent transplants, LAS, preoperative mean pulmonary artery pressure (PAPm), and preoperative arterial partial pressure of carbon dioxide (PaCO₂). Sex mismatch (female recipient with male donor) occurred more often in the DCD Group (p = 0.009) (Table 1). There were no statistically significant differences between the DBD and DCD groups in terms of donors’ sex, age, comorbidities, duration of MV, smoking history, percentage of abnormal chest X-ray, PaO₂/FiO₂ ratio, and secretions at bronchoscopy. Donor BMI was significantly higher in the DCD Group (p = 0.022). The percentage of grafts from DBD undergoing machine perfusion was 15.5%; all grafts from DCD donors underwent ex-vivo evaluation. With regard to perioperative variables, the two groups were similar in terms of type of incision, need for both intraoperative and post-operative extra-corporeal support, and packed red blood cell, plasma and platelet intraoperative transfusion.

CIT, TIT, and preservation times were significantly higher in the DCD Group (p < 0.001), while intraoperative WIT was similar between the two groups. Table 2 shows the ischemia times of procurement and preservation in the DCD Group, in details.

Post-operative data and outcomes are shown in Table 3. No adverse events related to our protocol were recorded in the DCD Group. In the first 30 days 1 patient (0.9%) died in the DBD Group, none in the DCD Group (p = NS). There was a statistically significant difference in median duration of MV (2 days for DCD and 1 day for DBD, p = 0.011). The prevalence of PGD3 within the first 72 h was 27.3% in the DCD Group and 18.2% in the DBD Group (p = 0.742).

Airway complications occurred in two recipients of DCD Group (18.2%) and seven of the DBD Group (6.4%): the difference, however, did not reach statistical significance (p = 0.154). No bronchial anastomotic dehiscence occurred in both groups, but only stenosis. Both cases and the 71.4% of patients required endoscopic treatment in the DCD Group and DBD Group, respectively.

The incidence of both histology-proven acute rejection (AR) and acute lung allograft dysfunction (ALAD) was similar between the two groups (22). The median follow-up period after transplantation was 605 days in the DCD Group and 895 days in the DBD Group. None of the patients receiving lungs from a circulatory death donor experienced CLAD during the period of the study. The probability of CLAD free survival in the DBD Group at 1, 3 and 5 years after transplantation was 0.96, 0.68, and 0.60, respectively (Figure 3). There were no deaths in the DCD Group, while overall survival in the DBD Group at 1, 3 and 5 years after surgery was 0.88, 0.75 and 0.70, respectively (Figure 4).

At 3 months, pulmonary function values were similar in both groups for Forced Expiratory Volume in the first second (FEV1), forced vital capacity (FVC) and Tiffeneau index. Mean percentage of predicted FEV1 at 3, 6 and 12 months was 76.3%, 78.5%, and 81.7% in the DCD Group and 77%, 83.5%, and 86% in the DBD Group, respectively (Supplementary Table S1). The difference in mean FEV1 was statistically significant only at 6 months (p = 0.046), as shown in Figure 5. Mean FVC and Tiffeneau index were not significantly different at all time points (Figure 6).

The results of the adjusted GEE regression analysis for pulmonary function tests cohort are shown in Supplementary Table S2. At the test baseline (3 months), lower FEV1 and FVC were associated with grade 3 PGD and clamshell incision. Moreover, grade 3 PGD, donor age, and airway complications significantly reduced the Tiffeneau index.

Data regarding best FEV1 reached within the first year after transplantation and throughout the follow-up period are shown in Table 4. There were no statistically significant differences between the two groups. In both sets of patients, best FEV1 was reached during the first year after surgery: in the DCD Group, the median time to achieve best FEV1 was 217 days, whereas in the DBD Group, it was 333 days.

When comparing the DCD Group with the subset of DBD grafts undergoing EVLP, the difference in terms of duration of MV did not reach statistical significance. The incidence of PGD3 in the DBD-EVLP Group was 23.5% vs. 27.3% in the DCD Group. Also, there was no statistically significant difference regarding airway complications, even though the incidence was higher in the DCD Group (18.2% vs. 5.8% in the DBD-EVLP Group).

The punctual estimates and regression as a function of time of FEV1, FVC, and Tiffeneau index are presented for the DCD Group and DBD-EVLP Group in Supplementary Table S3 in the Supplementary material. No difference was detected between the two groups.