The study was conducted in accordance with the Declaration of Helsinki. The study was approved by the Ethics Review Committee of Peking Union Medical College Hospital (PUMCH) with a registration number of HS-2410. Informed consent was obtained from all patients. Included in this prospective study were patients aged between 18 and 75 years, who underwent RAPA for adrenal mass in PUMCH from November 2020 to May 2022. Indications for RAPA were clinically benign adrenal tumors with a long diameter of <5 cm on imaging. Exclusion criteria included: (1) pregnancy; (2) severe systemic diseases; (3) combined with other urological diseases which may interfere the operation such as tumors, malformations and tuberculosis; (4) malignant or recurrent tumors.

All patients underwent enhanced abdomen computed tomography (CT) or magnetic resonance imaging (MRI) to assess location and size of the mass. Laboratory tests including complete blood count, liver function test, renal function test, coagulation test, electrolyte test as well as a full set of endocrine tests were performed before surgery. Perioperative managements of hormone-active tumors were performed according to guidelines (11–13).

The KD-SR-01® robotic system passed the special channel of National Medical Products Administration (NMPA) for innovative medical devices and was allowed to enter the clinical trial in 2019. KD-SR-01® has been approved for registration by NMPA of in June 2022.

The KD-SR-01® robotic system is composed of a surgical console, a patient cart and a 3D imaging system (Figures 1A–1C). The surgical console is integrated with two master manipulators and a 3D high-definition monitor, combined with passive polarizing glasses, enabling surgeons to precisely and synchronously control the surgical arms and instruments without flexion of the neck (10) The patient cart is designed as a three-arm system, which has seven degrees of freedom for movements and can filter out tremors of the hands. The imaging system adopts a modular interface, which can match various 3D laparoscopic display systems. In this study, Karl Storz IMAGE1 SD3-LinkTM laparoscopic systems were used with 30° 10-mm three-dimensional video laparoscopes.

The surgical team contained two expert surgeons, who have altogether performed more than 300 cases of RAPA using the DaVinci® system. Prior to the initiation of the study, two surgeons and two operating room nurses were exclusively trained for three days by performing surgical procedures on porcine models utilizing the KD-SR-01® robotic system.

All surgeries were performed via a retroperitoneal approach. After general anesthesia induction, the patient was placed in a lateral flank position (Figure 2A). A 2-cm incision was made at the midaxillary line 2 cm above the iliac crest, through which the retroperitoneal cavity was created by balloon dilation. After a pneumoperitoneum of 14 mmHg was established, a 30° 3D video laparoscope was introduced through the first incision. Then, two 10-mm robotic cannulas used as monopolar curved scissor and bipolar curved forceps were placed under direct vision at the anterior and posterior axillary lines above the iliac crest, respectively. Another assistant 10-mm trocar was placed between the camera port and the anterior port (Figure 2B). Robotic arms were then docked and were advanced into the extraperitoneal space under direct vision by an assistant surgeon. The operation was then conducted by the lead surgeon at the open console (Figure 2C). After dissociation of the kidney, the ventral side of the adrenal gland was then dissected between the superior renal pole fat sac and the Gerota fascia with the aim of exposing the adrenal mass (Figure 3A). The mass was then progressively mobilized at the level of the upper pole of the kidney and from the dorsal side, respectively (Figure 3B). After the mass is sufficiently exposed, it is completely enucleated from surrounding adrenal tissues with an integrated tumor margin (Figure 3C). For masses adjacent to the central vein of adrenal gland, the adrenal vein was ligated and excised. The surgical bed was checked for hemostasis and the remnant adrenal margins were sutured (Figure 3D) before the removal of the excised tumor with a specimen bag.

Study data were collected from the electronic medical record system of PUMCH. Collected perioperative data were demographic variables including age, sex, body mass index (BMI) and American Society of Anesthesiologists (ASA) score (14); baseline physical examination results including systolic blood pressure (SBP), diastolic blood pressure (DBP) and body temperature; baseline laboratory results including complete blood count, liver and renal function tests, electrolyte test as well as a full set of endocrine tests.

Collected intraoperative data were preparation time, docking time, console time, total operative time (OT), estimated blood loss (EBL) and intraoperative complications. The docking time was defined as the interval from the movement of the robotic cart to docking of the last canula to the corresponding arm. The console time was defined as the time from robot docking to robot undocking.

Collected postoperative data were pathology findings including tumor size, histology and margin status, postoperative physical examination results, postoperative laboratory results, admission to intensive care unit (ICU) and ventilator use, postoperative complications, time to first flatus and defecation, time to removal of urinary catheter and drainage tube, use of analgesics and antibiotics, length of stay (LOS) and 30-day readmission.

The estimated glomerular filtration rate (eGFR) was calculated by the CKD-EPI formula (15). Complications were graded using the Clavien-Dindo classification system and grade III-IV complications were defined as major complications (16). Diagnosis and outcome measures of hormone-active tumors were assessed according to relevant consensus and guidelines (11, 13, 17, 18).

The ergonomics were assessed by using the Subjective Mental Effort Questionnaire (SMEQ) and the Local Experienced Discomfort (LED) scale after each surgery by the surgical team (19). The SMEQ score ranges from 0 to 150 and lower scores indicated less mental effort. The LED scale evaluates user comfort with a score of 0 to 10 points and lower scores indicated less discomfort.

Continuous variables were described as median [interquartile range (IQR), p25–p75] or median (range). Categorical variables were described as absolute value and percentages. Continuous variables were compared by Mann-Whitney U test. Analyses were performed using SPSS 25.0 for windows (SPSS institute, Chicago, IL, USA) and P value < 0.05 was considered statistically significant.

Altogether, 23 patients, including 10 male and 13 female patients met the inclusion and exclusion criteria and were thus enrolled, whose baseline characteristics were summarized in Table 1. The median age, BMI and preoperative eGFR were 49.0 years (range, 22–67), 23.8 kg/m² [interquartile range (IQR), 20.8–27.0] and 94.0 ml/min/1.73 m² (IQR, 82.4–105.7), respectively. Six (26.1%) patients had a history of abdominal surgery. Nine (39.1%) patients had hormone-active tumor, including five (21.7%) aldosterone-producing adenoma (APA), two (8.7%) cortisol-producing adenoma (CPA) and two (8.7%) pheochromocytoma (PHEO). The median long diameter of tumors was 2.8 cm (IQR, 1.5–3.5).

All patients received partial adrenalectomy via the retroperitoneal approach. The median OT was 86.5 min (IQR, 60–112.5), of which the median preparation time, docking time and console time were 15.3 (IQR, 10.0–17.3), 4.3 (IQR, 3.4–5.6), 46.5 (IQR, 35.1–59.0) minutes, respectively (Table 2). The median EBL was 50 ml (range, 20–400). No case was converted to open or received intraoperative transfusion. Two (8.7%) patients with PHEO were routinely transferred to ICU for one day.

Altogether, three (13.0%) patients developed postoperative complications, including one (4.3%) grade II complication of one patient requiring antibiotic treatment due to postoperative fever. 17 (73.9%) patients underwent incisional pain, and two (8.7%) of them received weak opioids for analgesia. During hospitalization, the median time to first flatus and stool dropping were 2 days (range, 1–3) and 3 days (range, 2–4). The median time of urinary catheter placement and perirenal drainage was 1 day (range, 1–3) and 3 days (range, 2–4). The overall perirenal drainage volume was 90.0 ml (IQR, 65.0–131.0), which declined from 50.0 ml (IQR, 30.0–95.0) on postoperative day 1 to 25.0 ml (IQR, 15.0–50.0) on postoperative day 2. The median LOS and postoperative LOS were 10.0 days (IQR, 8.0–12.0) and 4.0 days (IQR, 3.0–5.0), respectively. No patient was readmitted within 30 days.

According to the pathology findings, all surgical margins are negative. The removed masses, including 19 (82.6%) adenoma, two (8.7%) pheochromocytoma and two (8.7%) adrenocortical nodular hyperplasia pathologically.

The short-term postoperative follow-up for hormone-active patients was performed at a median of 3.3 months (2.4–3.9) after discharge (Table 3). The follow-up was available in seven (77.8%) patients and two were unable to come for their visit due to personal reasons.

In the five APA patients, the postoperative SBP (175 mmHg (IQR, 180–190) vs. 135 mmHg (IQR, 133–143), P = 0.042) and DBP (100 mmHg (IQR, 100–120) vs. 85 mmHg (IQR, 78–90), P = 0.042) decreased significantly compared to baseline. One patient stopped taking antihypertensive drug, and the remaining four patients underwent reductions in number or dose of antihypertensive drugs to varying degrees. Serum potassium elevated from 2.6 mmol/L (IQR, 2.1–2.9) to 4.0 mmol/L (IQR, 3.6–4.4) (P = 0.042). One patient still received potassium supplementation discontinuously. For the three APA patients who came for follow-up, the aldosterone-renin ratio (ARR) declined from 1,714 to 59, 617 to 29 and 2,132 to 277, respectively.

In the two CPA patients, the postoperative blood pressure decreased from 130/85 to 120/70 mmHg and 145/85 to 135/70 mmHg, respectively. The cortisol (8 am) level decreased from 20.7 to 14.6 μg/ml and 26.1 to 21.9 μg/ml, respectively. The urinary cortisol level decreased from 374.4 to 81.9 μg/24 h and 641.5 to 152.7 μg/24 h, respectively. The adreno-cortico-tropic-hormone (ACTH) level increased accordingly.

In the two PHEO patients, the postoperative blood pressure (SBP/DBP) decreased from 170/105 to 120/80 mmHg and 160/100 to 120/70 mmHg, respectively. One patient still takes antihypertensive drug. Relevant endocrine measures declined to the normal range.

The median SMEQ score (scoring from 0 to 150 points) was 45 points (range, 20–90), indicating some efforts. The median LED score (scoring from 0 to 10 points) was 1.7 (range, 0–7), indicating some discomforts.