As part of the TRANSPLANT’AFUF group led by the AFUF (Association Française des Urologues en Formation), a multicenter French retrospective database involving 13 centers was established. Inclusions were carried out successively from 2022 until 2011 for some centers. In all these healthcare facilities, kidney transplant surgeries are exclusively performed by urologists. Nevertheless, there is a lack of consensus regarding the operational protocols for managing renal transplantation.

Patients were divided into two groups based on the timing of the graft incision: daytime grafts (8:00 a.m.–8:00 p.m.) (DG) and nighttime grafts (8:00 p.m.–8:00 a.m.) (NG). 8:00 a.m. was chosen as the cut-off time because it corresponds to the change of anesthetists and OR nurses. All time points (including the moment of skin incision, the duration of the anastomosis, and the overall procedure duration) were electronically recorded during surgery and available on operative schedule. To perform a secondary analysis, a deep night graft (DNG) (11:00 p.m.–4:00) subgroup was also established.

Evaluated parameters included donor, graft, and recipient characteristics, graft incision and closure times, and vascular anastomosis times (time between the beginning of the first anastomosis to the end of the last anastomosis). Cold ischemia time was calculated between organ retrieval clamp and transplantation. According to the “Agence de Biomédecine” protocol, all extended criteria and Maastricht 3 kidneys must be put on hypothermic Perfusion Machine. All Maastricht 3 protocols in France are made using a normothermic extracorporeal circulation between the cardiac arrest and the retrievals of the organs [15].

The primary outcome measure was graft survival, the graft was considered non-functional in case of patient death, return to dialysis, or removal of the graft. Secondary outcome measures included graft function assessed by creatinine levels, delayed graft function (DGF, defined by the necessity of dialysis during the seven first day after transplantation), early complications (within the first postoperative month), and late complications assessed using the Clavien-Dindo classification. All these data were available on patient files.

We have distinguished between junior and senior surgeons for the analysis of complications. In our French centers, a senior surgeon has completed his or her post-internship formation.

Statistical analyses were performed using SPSS software. Univariate comparison was made using Chi-squared test and Fisher’s exact test for categorical variables. Continuous variables were compared using Student’s t-test or Mann–Whitney U-test (when assumptions of Gaussian distribution were not met). Graft survival was estimated using Kaplan-Meier method. A significance level of p < 0.05 was considered for all statistical data.

The study was a retrospective analysis and involved already available data on human participants and followed the 1964 Declaration of Helsinki and its later amendments. Data collection followed the French legislation concerning prospective non-interventional studies to evaluate routine care (Article Art.L1121-1-2 of French Public Health Code).

Out of the 2,972 patients in the TRANSPLANT’AFUF database, 118 patients were excluded due to missing graft timing data, resulting in the inclusion of 2,854 patients between 01 January 2011 and 31 December 2022. Of these, 2,043 were daytime grafts (DG—8:00 a.m.–8:00 p.m.) and 811 were nighttime grafts (NG—8:00 p.m.–8:00 a.m.). 218 grafts were realized in deep night (DNG—11:00 p.m.–4:00 a.m.) (Figure 1).

Table 1 displays the characteristics of donors, showing significant differences in donor type with Maastricht 3 kidneys being more frequently transplanted at night (21.45% NG vs. 5.53% DG, p < 0.0001). Additionally, 20.80% of DG were from living donors. No differences were observed in preoperative creatinine, expanded criteria kidneys, or donor age. Regarding transplanted kidney characteristics (Table 2), NG kidneys were more often placed on machines (54.38% NG vs. 37.98% DG, p < 0.0001) and exhibited more arterial calcifications (27.37% NG vs. 22.47% DG, p < 0.017). However, no differences were found in the number of arteries or veins.

Regarding recipients, only preemptive transplantation was statistically significant (14.05% for DG vs. 6.29% for NG, p < 0.0001). There were no differences in terms of gender, age, BMI, cause of renal insufficiency, type of dialysis, residual diuresis, or the number of transplants. There was no difference between the mean follow up between DG and NG (30 months for DG; 28 months for NG; p = 0.2064) (Table 3).

Regarding surgery, there were more Lich-Gregoir (LG) ureteric anastomoses performed at night and more pyelo-ureteral (PU) anastomoses during the day (LG 78.56% for DG and 92.11% for NG; PU 14.93% for DG and 3.70% for NG; p < 0.0001). The duration of vascular anastomosis was significantly shorter during the day (50.5 min for DG vs. 55 min for NG, p < 0.005). The duration of cold ischemia was not statistically different between the two groups [777 min for DG (493–1,052) vs. 810 min for NG (570–1,005); p = 0.0541] (Table 4).

In a sub-group analysis, we found that, compared with DG, seniors realized significantly more DNG (40.72% DG vs. 49.08% DNG; p = 0.0172).

Graft survival was observed, considering the graft non-functional in case of patient death, return to dialysis, or removal of the graft. There was no significant difference in graft survival between DG and NG. The time of 75% survival was 67.5 months for DG and 63.5 for NG [p = 0.1749; HR (day/night): 0.8695; 95% CI (0.7049; 1.073)] (Figure 2).

Creatinine levels at 1-year post-transplant did not significantly differ between the two groups [DG: 137 μmol/L (101–157); NG: 140 μmol/L (103–158); p = 0.3019].

Regarding DGF, there was no statistically significant difference observed between the daytime and nighttime groups [410 DGF for DG (20.21%); 173 DGF for NG (21.54%); p = 0.4276] (Table 5). The occurrence of DGF was found to be correlated with prolonged anastomosis timing, irrespective of whether it occurred during the daytime (no DGF 52 min vs. DGF 64 min; p < 0.0001) or nighttime (no DGF 55 min vs. DGF 63 min; p = 0.0024).

No significant difference was observed in surgical complications based on graft timing, either for early complications <30 days (Clavien I-II DG 20.95% vs. NG 20.10%; Clavien III-IV-V DG 15.42% vs. NG 12.94%; p = 0.0889) or late >30 days (Clavien I-II DG 6.80% vs. NG 5.67%; Clavien III-IV-V DG 12.78% vs. NG 12.82%; p = 0.2444). Looking in detail at early and late Clavien III complications (IIIa vs. IIIb), we also found no difference between DG and NG (<30 days: DG Clavien IIIa 1.57%—Clavien IIIb 9.83% vs. NG Clavien IIIa 0.97%—Clavien IIIb 8.75%; p = 0.4072. >30 day: DG Clavien IIIa 1.81%—Clavien IIIb 9.15% vs. NG Clavien IIIa 0.97%—Clavien IIIb 9.73%; p = 0.1217) (Table 5).

There was also no difference in surgical complications: immediate postoperative transfusion, graft removal, thrombosis, surgical reintervention, urinoma or ureteric stenosis (Table 5). In subgroup analysis, no significant difference was observed in surgical complications Clavien III-V for early complication <30 days (16.06% DNG vs. 12.78% DG; p = 0.1724).

Figures 3, 4 show the association between surgical complications with cold ischemia time and transplantation timing, which revealed no difference between the two groups.