Kidney transplantation is the best available option for the management of end stage renal disease (ESRD). ¹ Transplantation reduces the risk of cardiovascular and mortality events, while also improving quality of life compared to chronic hemodialysis. ² Living donor transplantation is preferred over deceased donor, as it has better survival rates and less delayed graft function. ^{3 , 4} Laparoscopic living donor nephrectomy (LLDN) is the standard surgical practice due to fewer complications associated with the treatment. ⁵ This technique includes standard laparoscopic, hand-assisted laparoscopic, hand-assisted retroperitoneoscopic, pure retroperitoneoscopic, and robot-assisted live donor nephrectomy. ^{6 – 9}

Previous studies have shown that the retroperitoneal approach to LLDN has more advantages than the transperitoneal approach; namely shorter access to renal arteries and veins, better visualization during donor nephrectomy, and prevention of injuries of the liver, spleen, and bowel. ^{10 – 13} However, some adjustments to the techniques require additional training for the operators performing the technique. Evaluation of surgical practice performances could be done using the learning curve. ¹⁴ However, there has only a few studies regarding the learning curve of the retroperitoneal approach of LLDN. Moreover, a previous study only analyzed learning curve on a single operator, although LLDN is usually performed by a team. ¹⁵

Therefore, this study aims to investigate the learning curve for retroperitoneal approach in LLDN among urologists in an individual and team-based approach.

A retrospective analysis of laparoscopic living donor nephrectomy (LLDN) procedures was done on four different urologists (operators) with different levels of experience from January 2019 to January 2022 at Cipto Mangunkusumo National General Hospital, Indonesia. All of the operators in our kidney donor team were included in this study. The date was determined as the first LLDN in our center was performed in January 2019 while the endpoint was the most recent date that the yearly review of the procedure was carried out.

Ethical Approval to conduct this study was issued by the ethics committee of the Faculty of Medicine Universitas Indonesia–Cipto Mangunkusumo Hospital (KET-720/UN2.F1/ETIK/2018). All patients had received detailed preoperative counselling and their decision to undergo the procedure was taken with written informed consent prior to the surgery. Meanwhile, the data used in this study were collected from the medical records of the patients. The written permission was granted by the ethics committee of the Faculty of Medicine Universitas Indonesia–Cipto Mangunkusumo Hospital for the publication of the study results.

Demographical data was collected from the electronic medical record, including age, sex, and body mass index (BMI, calculated as weight in kilograms divided by square of height in meters). Preoperative data included number of arteries involved and side of the donor kidney. Intraoperative data included surgery duration, warm ischemic time (WIT), and estimated blood loss (EBL). Surgery duration was determined as the length of time from the first incision to renal artery clamping, as the final closure was sometimes done by the residents due to the study location being a teaching hospital. WIT was documented as the length of time from clamping to cold ischemic time. Postoperative complication was documented in accordance to the pre-existing data in the medical records.

A total of 127 patients underwent LLDN during the three years [30], with 31 operations done by S1, 30 operations by S2, 38 operations by S3, and 28 operations by S4. There was no conversion to open nephrectomy during the surgeries performed in this study.

Minimally invasive techniques are the preferred technique for donor nephrectomy compared to open nephrectomy. Studies found that a minimally invasive approach is associated with perioperative lower blood loss, lower morbidity, ¹⁹ reduced analgesia use, shorter length of stay, and faster recovery. ⁵ Retroperitoneal approach or retroperitoneoscopic provides direct access to renal hilum without moving abdominal organs. Therefore, injury or bleeding of the organs could be avoided and bowel function may return rapidly following the surgery. ^{10 , 20} The crucial disadvantage of this procedure was the difficulty to orient the landmark due to the limited working space of the retroperitoneal approach in LLDN. ²¹ In terms of the learning curve, retroperitoneal approach is more technically demanding and has a steeper learning curve than the transperitoneal approach. ^{22 – 24}

Learning curves represent the relationship between learning repetition and practice performance. ²⁵ There are several methods that can be used to analyze the learning curves other than CUSUM analysis, such as graphical visual inspection, split-group method, and regression techniques. CUSUM method is considered the sensitive method adopted by surgical practice for self-and supervisor assessment. This method uses plotted graph and gives accurate progression and level of performance, thus, it can be used to show a process of achieving and maintaining a surgical technique proficiency. ¹⁴

A comparison study of retroperitoneoscopic donor nephrectomy by a single surgeon between a high volume and a low volume hospital by van der Merwe et al. describes the learning curve differences in surgery time and WIT. This study shows the improvement based on the graph decline. ¹¹ Meanwhile, a learning curve study of retroperitoneoscopic donor nephrectomy by Pal et al. analyzes the performance changes between three groups using the split-group method. However, this method has several biases based on its arbitrary group size option and uncertain changes. ²⁶

In our CUSUM analysis study, on an individual level, an average of 16.5 procedures was needed to achieve proficiency and 28 procedures to acquire mastery in the transition from transperitoneal to retroperitoneal approach. There were some differences between the results of this study and other learning curve studies of the retroperitoneal approach of LLDN. Pal et al. ²⁶ found a significantly reduced surgery time after 34 pure laparoscopic retroperitoneal nephrectomies. Chin et al., ¹⁵ though, observed a substantial difference in surgery time after 150 cases, although this study did not use the CUSUM model analysis. The second reduction of operation time or mastery is found after 300 laparoscopic nephrectomies in a study by Nakajima et al. ²⁷ However, the procedures needed to achieve both proficiency and mastery in our study differed on each operator. Operator 1 who had more experience in other surgeries only needed 12 procedures before achieving proficiency, while other operators needed more procedures in accordance with their prior experiences.

Based on the CUSUM analysis, it was found that 66 procedure was needed to achieve proficiency (phase 2) and 106 procedures to acquire mastery (phase 3) for team-based approach of the transition from transperitoneal to retroperitoneal LLDN. Team-based analysis shows a more gradual improvement in operation time compared an individual surgeon-based analysis. A study by van der Merwe et al. shows that the subgroup analysis of a single surgeon shows a more graphically evident improvement in operation time than the team-based analysis. ²⁴ However, LLDN is usually approached by several operators, as it is technically demanding and require a significant amount of time.

Several variables could affect the learning curve of the retroperitoneal approach of LLDN. The technical skills of each surgeon are related to shorter surgery time and lesser complications. The advantages of the retroperitoneal approach may relate to the surgeon’s experience as the vessel injury, or surgical complications were lower in the more experienced surgeon. ^{10 , 19} In this study, urologists that have more experience achieve proficiency in operation time in fewer procedures. A study by Zhang et al. showed that senior surgeons had a better learning curve for laparoscopic procedures. Operation time was also significantly faster, with a lower conversion rate to open surgeries. ²⁸ Proficiency-based guidance, part-task training, and assigning practice over time might optimize the learning curve. ²⁹ There were other problematic factors, such as obese donors prolonged the surgery time then affected the learning curve. ⁶ A few millimeters of perinephric fat would significantly prolong the surgery time. ³⁰

A limitation of the study is in the methodology as it is a retrospective study based on pre-existing medical records and done in a single center. Therefore, information bias may occur due to the data input, processing, and collection. Moreover, being a teaching hospital, the performance of urology residents as the operative assistant may create another bias, especially for the operative time. However, we have limited the calculated operative time to only from the first incision to renal artery clamping, as the final closure was sometimes done by the residents.

Transition from transperitoneal to retroperitoneal approach in laparoscopic living donor nephrectomy has a certain learning curve time to achieve proficiency and mastery, both on the individual and team-based analysis. Prior experience and focused training may improve the learning process. The transition to retroperitoneal approach is a feasible option to improve the outcome of LLDN.

IW involved in conceptualization, protocol development, administration of the study, data collection, funding, manuscript writing, and manuscript finalization.

IAA involved in conceptualization, protocol development, administration of the study, data collection, and manuscript finalization.

KY involved in conceptualization, protocol development, administration of the study, data collection, and manuscript finalization.

FW involved in protocol development, study conceptualization, patient recruitment, and manuscript editing and finalization.

ARAH contributed in protocol development, study conceptualization, patient recruitment, and manuscript editing and finalization.

CAM contributed in protocol development, study conceptualization, patient recruitment, and manuscript editing and finalization.

All authors read and approved the final manuscript.

Ethical Approval to conduct this study was issued by the ethics committee of the Faculty of Medicine Universitas Indonesia–Cipto Mangunkusumo Hospital (KET-720/UN2.F1/ETIK/2018). Written informed consent was obtained from the patient for the surgery performed in this study. Written informed consent was obtained from a guardian for participants under 18 years old. Written permission was granted by the ethics committee of the Faculty of Medicine Universitas Indonesia–Cipto Mangunkusumo Hospital for the publication of the study results.