**3. Results**

#### *3.1. Overall Results: Primary Outcomes*

In the RDN and LDN groups, most kidney donors were female (63–68%), 51–54 years old, and had a BMI of 25.4–25.9 (see Table 1). Donor characteristics only differed concerning the individual history of smoking, as there were more smokers in the LDN group (52.7 vs. 9.6%, *p* < 0.001). Donor organs were 20% right-sided and had a split-renal function of 50%. The number of organs with multiple

arteries was no di fferent between RDN and LDN (11.5% vs. 18.5%), but significantly more grafts in the LDN group had multiple veins (12.7% vs. none, *p* < 0.01). The groups did not di ffer regarding recipient characteristics. Most were male (67–70%), 42–45 years old, and had a BMI of 24.7–25.3. For more than 90% of recipients, it was their first kidney transplantation.


**Table 1.** Comparison of donor, graft, and recipient characteristics.

Concerning primary outcomes, neither the median operating time (RDN 223.5 vs. LDN 213 min), WIT (3 vs. 2.45 min), nor intraoperative complication rate (5.7 vs. 2.9%) were significantly di fferent between groups (see Table 2). One RDN had to be converted to open surgery because of massive obesity and multiple trocar dislocations. In two other cases, a malfunction of the stapler and a lumbal vein caused bleeding, which could be managed robotically without the need for blood transfusions. In the LDN group, in one case, bleeding from a dorsal branch of the renal vein could not be controlled laparoscopically, leading to a conversion to open surgery. In another LDN case, the renal vein was torn during kidney removal, but could be reconstructed. Once, the donor's spleen and the renal parenchyma were accidentally cut, and a small hole in the descending colon had to be sutured. A previously undetected obstructed ureteropelvic junction made one pyelovesicostomy necessary for a recipient in the LDN group.

The median length of stay of five days was no di fferent between the LDN and RDN groups, nor was the postoperative major complication rate. In the RDN group, one patient had an ileus that dissolved after gastroscopy. In the LDN group, a bronchoscopy had to be performed because of dyspnea, and a retention of chylous ascites had to be punctured. In another case, continuous arterial bleeding from the abdominal internal oblique muscle made electrocoagulation necessary in the LDN group.

#### *3.2. Learning Curve*

When comparing the first half of the RDNs with the second half to analyze for inherent learning effects, the WIT, intra- and postoperative complication rate, and length of stay remained unchanged (see Table 3). Operating time significantly increased from 185 to 265 min in the RDN group (*p* < 0.001). This di fference no longer remained significant when the last 18 RDN cases were excluded; in these

cases, RDN was followed by robot-assisted kidney transplantation (185 vs. 226 min, n.s.). In the LDN group, the surgical results remained unchanged over time.


**Table 2.** Outcomes of 257 donor nephrectomies.

**Table 3.** Assessment for the inherent learning curves in RDN and LDN by comparing the first with the second half of cases within each group.


1 When excluding the last 18 cases, where RDN was followed by robot-assisted kidney transplantation, the difference was no longer significant (185 vs. 226 min, n.s.).

#### *3.3. Kidney Function of the Donor and Recipient: Secondary Outcomes*

The type of surgical approach of DN did not impact the postoperative kidney function either of the donor or the recipient (see Figure 1). Among the donors, kidney function did not di ffer preoperatively or at discharge between groups. For recipients, kidney function significantly improved after transplantation, irrespective of the type of DN, and stayed stable thereafter.

DGF rates were 6.3 to 11.5% (LDN vs. RDN), and did not significantly di ffer between groups and did not change over time (see Tables 2 and 3). In the RDN group, DGF was caused by three (5.7%) suspected transplant renal artery stenoses, one (1.9%) perirenal hematoma due to double anticoagulation of the mechanic aortic valve and prolonged serum creatinine decline (no dialysis needed), one (1.9%) prolonged CIT (cold ischemia time) due to vascular complications during transplantation, and one (1.9%) insu fficient serum creatinine decline without other cause. In the LDN group, DGF resulted from

seven (3.4%) acute rejections, one (0.5%) lesion of the arterial anastomosis after the Fogarty maneuver, and one (0.5%) case of donor-related pre-existing vascular damage. One (0.5%) patient needed dialysis for depletion of potassium only, and in three (1.5%) other cases, the cause for DGF in the LDN group was unknown.

**Figure 1.** Follow-up of kidney function of the donor (**a**) and graft (**b**). The kidney function did not differ between robot-assisted (RDN) and laparoscopic donor nephrectomy (LDN).

In the multivariate regression analysis, only patient-specific factors were found to have an impact on postoperative kidney function, but not surgical factors (see Table 4). Concerning the kidney function of the donor at discharge, male patient gender was predictive for worse kidney function (*B*-value 0.14, *p* < 0.001). Furthermore, worse preoperative kidney function was associated with worse postoperative function (*B*-value 1.0, *p* < 0.001). A history of smoking only had an impact on postoperative kidney function in the univariate analysis. No other (surgical) factors such as approach (LDN vs. RDN), operating time, intraoperative complications, WIT, kidney side, or number of arteries or veins, had an impact on the kidney function of the donor at discharge.


**Table 4.** Multivariable regression analysis to predict the serum creatinine (1) of the donor at discharge ("donor kidney function") or (2) of the recipient one week after transplantation ("graft function").

A history of donor smoking also had a significant impact on the kidney function of the recipient in the multivariate regression analysis: a kidney donor with a history of smoking caused worse graft function one week after transplantation (*B*-value 0.63, *p* < 0.05, see Table 4). Again, the preoperative kidney function of the recipient was predictive for their postoperative graft function (*B*-value 0.22, *p* < 0.001). In the univariate, but not the multivariate analysis, a preemptive kidney transplantation predicted better graft function (*B*-value −0.72, *p* < 0.05). Again, no surgical factors, either the type of donor nephrectomy (LDN vs. RDN) or the type of transplantation (open vs. robot-assisted), had an impact on graft function one week after transplantation.
