Retroperitoneal Robot-Assisted Partial Nephrectomy in Obese Patients

Abstract

Objectives:

To report our experience with retroperitoneal robotic-assisted partial nephrectomy (RAPN) in obese patients.

Patients and Methods:

From April 2012 to December 2018, 127 patients with body mass index (BMI) ≥30 kg/m² underwent RAPN, of whom 110 patients had retroperitoneal RAPN. We reviewed the patients' demographic, operative data, perioperative and postoperative complications, and postoperative histology.

Results:

The median BMI was 33.1 kg/m² (interquartile range [IQR] 31.5–36.6). The median age of the patients was 59 years. The mean histological size of tumor was 32.2 mm (IQR 23.8–40). The median total surgical time was 130 minutes (IQR 110–176) with a median warm ischemia time of 22.0 minutes. The tumor was located anteriorly in 25% of the cases. The median R.E.N.A.L.* nephrometry score was 6. The median estimated blood loss was 30 mL (IQR 10–80). Three cases were converted to open partial nephrectomy because of bleeding (2.7%). Four patients and one patient returned within 30 days with postoperative complications Clavien-Dindo classification grade 2 and 3a, respectively. Two patients needed perioperative blood transfusion because of bleeding. The median length of stay was 1 day (IQR 1–2).

Conclusion:

Retroperitoneal RAPN is feasible in patients with high BMI and provides good surgical access to treat nonanterior renal masses. Retroperitoneal RAPN is associated with less blood loss, shorter surgical time, and warm ischemia time when compared with transperitoneal RAPN studies.

Introduction

The chronic risks of obesity on health are widely voiced in the public domain. Cancer Research United Kingdom recently reported that obesity could cause more cancer cases than smoking among women in the United Kingdom in the next few decades.¹ Obesity has a long-established strong association with an increased risk of renal cell cancer (RCC) among men and women.^2–4 The rate of obesity has increased from 15% in 1993 to 26% in 2010, remaining at a similar level since 2010.⁵ It is interesting that we have also seen a rise in the number of patients diagnosed with renal cancer. Although kidney cancer is the seventh most common cancer in the United Kingdom, representing 3% of all newly diagnosed cancer cases,⁶ the incidence rates of kidney cancer are projected to rise by 26% in the United Kingdom between 2014 and 2035.⁷ There is no doubt that obesity is by no means the only or indeed even the most important risk factor in the development of renal cancer. However, it is clear that a substantial proportion of those diagnosed are clinically obese and given that surgical intervention is the predominant treatment option, the impact of the patient's body mass index (BMI) is an important issue in terms of surgical risk.

Nephron sparing surgery is the gold standard treatment for clinically diagnosed T1a renal masses.⁸ The use of robotic platforms in performing this complex surgery has become increasingly widespread around the developed world. Recent studies evaluated the advantage of robotic-assisted partial nephrectomy (RAPN) over the conventional open partial nephrectomy (PN), demonstrating advantage in blood loss and transfusion rate, postoperative complications, length of hospital stay, but with the same cancer outcomes.^9,10 Though far more commonly performed via the transperitoneal approach, RAPN may also be performed by the extra- or retroperitoneal approach. There are a number of reports of transperitoneal RAPN in the obese patient; however, no studies in the literature have evaluated the role of RAPN in obese patients by using the retroperitoneal approach.

The aim of this study is to report the outcome of retroperitoneal RAPN in obese patients and to compare our findings with conventional transperitoneal RAPN reported in the literature.

Patients and Methods

At our institution, retroperitoneal RAPN is the standard approach for treating patients with small renal masses, with transperitoneal RAPN reserved for anterior hilar renal tumors.

We reviewed our prospectively maintained RAPN database at our institution. Overall, 474 patients underwent RAPN for small renal masses between June 2010 and December 2018. Sixty-two patients were excluded from our study because their BMI was not recorded. We identified 127 patients with BMI ≥30 kg/m² who underwent RAPN, of whom 110 patients did so via the retroperitoneal approach (Fig. 1).

FIG. 1.

Flow diagram showing patients undergoing RAPN classified according to BMI. RAPN, robotic-assisted partial nephrectomy; BMI, body mass index.

Collected data included the patients' demographic, preoperative, and perioperative complications. We examined tumor characteristics and tumor complexity.

Obesity was defined as BMI ≥30 kg/m². The degree of obesity was further defined by using the WHO classification: class 1 (30–34.9 kg/m²), class 2 (35–39.9 kg/m²), and class 3 (≥40 kg/m²). Tumor complexity was classified according to R.E.N.A.L.^* nephrometry score: low (4–6), moderate (7–9), and high (10–12).¹¹ Complications were graded based on the Clavien-Dindo classification system.¹²

The total operating time corresponds to the time from port insertion, console time, and port skin closure.

We use the same technique for retroperitoneal access for all patients undergoing RAPN, including obese patients using the da Vinci^® Si HD Surgical System. The patient is placed in the modified flank position. The table is fully flexed to increase the space between the iliac crest and 12th rib. A 12-mm incision is made 3.5 cm (2 finger-breadths) above the iliac crest in the mid-axillary line. A 12-mm PDB™ Auto Suture Round-Shape Balloon (Covidien™, Mansfield, MA) is inserted and inflated to create the retroperitoneal space. The dilator device is exchanged for a 12-mm Kii^® Balloon Blunt Tip System (Applied Medical, Rancho Santa Margarita, CA). An 8-mm da Vinci S port is inserted in the superior lumbar (Grynfeltt-Lesshaft) triangle under direct vision. Another 8-mm da Vinci S port is placed 8 cm from the camera port in the anterior axillary line cephalad to the anterior superior iliac spine. A 12-mm Airseal^® Access port (SurgiQuest, Milford, CT) is placed midway between the camera port and the most medial robotic port (Fig. 2).

FIG. 2.

Diagram showing the position of the camera port, robotic ports, and the assistant port.

Results

A total of 474 patients underwent RAPN during the study period, of whom 127 patients were obese (BMI of 30 kg/m² or more). One hundred ten of these underwent retroperitoneal RAPN. Baseline demographics and radiographic information are summarized in Table 1. The median BMI was 33.1 kg/m² (interquartile range [IQR] 31.5–36.6). Within this group, 8% of patients were morbidly obese (BMI class III). The median R.E.N.A.L. nephrometry score was 6 (range 4–11). Less than one-third of renal masses were classified as anterior masses.

Table 1.

Patients' Demographics and Radiological Characteristics of Renal Tumors

BMI	≥30 kg/m² (n = 110)	30–34.9 kg/m² (n = 68)	35–39.9 kg/m² (n = 33)	≥40 kg/m² (n = 9)
Sex
Male, n (%)	71 (64.5)	42 (61.8)	24 (72.7)	5 (55.6)
Female, n (%)	39 (35.5)	26 (38.2)	9 (27.3)	4 (44.4)
Age (years)
Median	59	57.9	56	61
SD	11.3	11.7	48–63	9.8
BMI (kg/m²)
Median	33.1	32	37	45.37
IQR	31.5–36.6	30.9–32.9	36.1–37.9	41.8–47.86
ASA
Median	2	2	2	3
ASA I, n (%)	22 (20)	17 (22.1)	7 (21.2)	0
ASA II, n (%)	66 (60)	43 (63.2)	19 (57.5)	4 (44.4)
ASA III, n (%)	16 (14.6)	6 (8.8)	5 (15.2)	5 (55.6)
Unknown, n (%)	6 (5.4)	4 (5.9)	2 (6.1)	0
Side
Rt, n (%)	59 (53.6)	33 (48.5)	20 (60.6)	6 (66.7)
Lt, n (%)	51 (46.4)	35 (51.5)	13 (39.4)	3 (33.3)
R.E.N.A.L. nephrometry
Low, n (%)	56 (51)	35 (51.5)	16 (48.5)	5 (55.5)
Medium, n (%)	38 (34.5)	25 (36.7)	9 (27.3)	4 (44.5)
High, n (%)	11 (10)	4 (5.9)	7 (21.2)	0
Unknown, n (%)	5 (4.5)	4 (5.9)	1 (3)
Localization
a, n (%)	27 (24.6)	15 (22)	8 (24.3)	4 (44.4)
p, n (%)	48 (43.6)	27 (39.7)	18 (54.5)	3 (33.4)
x, n (%)	27 (24.6)	19 (27.9)	6 (18.2)	2 (22.2)
ph, n (%)	1 (0.9)	1 (1.5)	0	0
ah, n (%)	1 (0.9)	1 (1.5)	0	0
xh, n (%)	1 (0.9)	1 (1.5)	0	0
Unknown, n (%)	5 (4.5)	4 (5.9)	1 (3)	0

ASA, American Society of Anesthesiologists; BMI, body mass index; IQR, interquartile range; Lt, left; Rt, right; R.E.N.A.L., Radius, Exophytic/endophytic, Nearness, Anterior/Posterior, Location; SD, standard deviation.

The median operating time was 130 minutes (IQR 110–176). The median warm ischemia time was 22 minutes (IQR 17.5–25.5). The median estimated blood loss (EBL) was 30 mL (mean 94.4 mL, IQR 10–80) (Table 2).

Table 2.

Perioperative Outcomes, Postoperative Complications, and Length of Stay

BMI	≥30 kg/m² (n = 110)	30–34.9 kg/m² (n = 68)	35–39.9 kg/m² (n = 33)	≥40 kg/m² (n = 9)
Operative time (minutes)
Mean	139.6	137.9	147	125.3
Median	130	127.5	160	125
IQR	110–176	105–178.8	120–180	125–156.5
WIT (minutes)
Mean	21.8	21.6	22.15	23.7
Median	22	22	22.5	23
IQR	17.5–25.5	16.3–25.3	19.5–25.5	17.25–27.5
EBL (mL)
Mean	94.4	43.3	147	296.7
Median	30	20	50	125
IQR	10–80	0–50	15–100	20–1600
Perioperative transfusion
No, n (%)	108 (97.1)	67 (98.5)	33 (97)	9 (100)
Yes, n (%)	2 (1.8)	1 (1.5)	1 (3)	0
Complications
Grade 2, n (%)	4 (3.6)	3 (4.4)	1 (3)	0
Grade 3a, n (%)	1 (0.9)	0	1 (3)	0
Grade 3b, n (%)	0	0	0	0
LOS (days)
Mean	2.1	2.06	1.88	3.5
Median	1	1	2	1
IQR	1–2	1–2	1–2.5	1–6

BMI, body mass index; EBL, estimated blood loss; IQR, interquartile range; LOS, length of stay; WIT, warm ischaemia time.

In relation to perioperative and postoperative complications, two patients (1.8%) required blood transfusion. Three RAPN cases were converted to open PN because of bleeding. Four patients (3.6%) and one patient returned within 30 days with postoperative complications Clavien-Dindo classification grade 2 and 3a, respectively. The median length of stay was 1 day (IQR 1–2) (Table 2).

With respect to surgical specimens, 67.2% of resected tumors were clear cell RCC and 17.2% were benign pathology (oncocytoma and angiomyolipoma). The mean histological size of the tumors was 32.2 mm (IQR 23.8–40). Pathological stagings were 74.7%, 16.5%, and 8.8% for pT1a, pT1b, and pT3a, respectively (Table 3). There was one true positive margin (1%). The tumor was enucleated in 11 patients (12%); therefore, tumor cells were seen on histological analysis up to surgical margins. Up to now, there has been no evidence of local or distant recurrence in this group of patients (median follow-up 33 months).

Table 3.

Histological Analysis of Excised Renal Tumors

BMI	≥30 kg/m² (n = 110)	30–34.9 kg/m² (n = 68)	35–39.9 kg/m² (n = 33)	≥40 kg/m² (n = 9)
Histological classification, n (%)
RCC	74 (67.2)	50 (73.6)	18 (54.5)	6 (66.7)
Oncocytoma	13 (11.8)	6 (8.8)	6 (18.2)	1 (11.1)
Chromophobe	5 (4.6)	3 (4.4)	2(6.1)	0
AML	4 (3.6)	2(2.9)	1 (3)	1 (11.1)
Papillary 1 and 2	12 (11)	6 (8.8)	5 (15.2)	(11.1)
Other benign	2 (1.8)	1 (1.5)	1 (3)	0
Size (mm)
Mean	32.2	29.8	34.5	41.1
Median	32	30	34	40
IQR	23.8–40	22–37.7	27–41.5	36.5–43
Stage, n (%)
pT1a	68 (74.7)	47 (79.6s)	17 (68)	4 (57.1)
pT1b	15 (16.5)	7 (11.9)	5 (20)	3 (42.9)
pT3a	8 (8.8)	5 (8.5)	3 (12)	0

AML, angiomyolipoma; BMI, body mass index; IQR, interquartile range; RCC, renal cell cancer.

We performed further analysis of our data according to BMI classes. The BMI did not have an impact on the total operating time (P = .735), warm ischemia time (P = .5), postoperative complications, and length of stay (P = .178) (Table 2). On univariate analysis, obese patients (BMI class III, class II, and class I) had higher estimated mean blood loss (296.7, 147, and 43.3 mL respectively) (P = .036).

The rate of achieving Trifecta (negative surgical margin, no postoperative complications, and warm ischemia time of <25 minutes) was 69.1%.

Discussion

As for many types of surgery, it is also well established that surgical time and operative blood loss is higher in obese patients undergoing open PN.¹³ Previous studies have confirmed the role of minimally invasive robotic-assisted surgery in treating obese patients with small renal masses.^14–17

Colombo et al.¹⁸ examined the role of transperitoneal and retroperitoneal laparoscopic PN in obese patients. They found that in the retroperitoneal group there was a shorter operative time and hospital stay when compared with the transperitoneal group. This cohort study is the first, to our knowledge, to evaluate the role of retroperitoneal RAPN in treating small renal masses in patients with BMI ≥30 kg/m² and appears to reflect similar potential advantages to this surgical approach over the much more widely employed transperitoneal approach in a number of areas as described in the published literature.

Operating and warm ischemia time:

A large multicentre study published preoperative outcomes of 1836 patients undergoing RAPN via the transperitoneal approach, of whom 806 patients were classified as obese. The median operating time was reported as 176 minutes, and the median warm ischemia time was reported as 19 minutes. The median preoperative tumor size was 29 mm.¹⁴ Another group reported similar results with regards to median operating time and warm ischemia time.¹⁵ Naeem et al.¹⁶ reported significantly longer operating time (265 minutes). An examination of our data employing the retroperitoneal approach suggests that the median warm ischemia time was consistent with other studies; however, our operating time was significantly shorter (130 minutes versus 176 minutes).

Peri- and postoperative morbidity

A recent study by Malkoc et al.¹⁵ confirmed transperitoneal RAPN to be a less morbid procedure than open PN in obese patients with a median EBL 150 mL and rate of blood transfusion of 3.4%. Never the less, Isac et al.¹⁷ reported that EBL was higher in morbidly obese patients compared with obese patients (250 mL versus 200 mL) using this surgical approach. With regards to postoperative complications, published studies have described the incidence of major complications (Clavien-Dindo classification grade 3 or more) to be around 4%–5.6%.^14–17 In our study, we again confirmed the association between higher BMI class and higher blood loss, with the median and mean EBL being 30 and 95 mL, respectively, in patients with BMI ≥30 kg/m². These figures are not only significantly less than those reported in previous transperitoneal series for obese patients but also significantly less than for the nonobese patients in the same series. Similar comparative outcomes are seen as regards significant surgical complications, that although two patients (1.8%) needed blood transfusion, only one patient (0.9%) had Grade 3a complication (Table 4).

Table 4.

Series of Transperitoneal Robot-Assisted Partial Nephrectomy Versus Retroperitoneal Robot-Assisted Partial Nephrectomy (Present Study) in Obese Patients

	Present study (n = 110)	Isac et al. (n = 103)	Abdullah et al. (n = 806)	Malkoc et el. (n = 177)	Naeem et al. (n = 49)
≥Grade 3a complications, %	0.9	4.9	4.4	5.6	4.0
Median EBL (mL)	30	150	150	150	150
Transfusion rate, %	1.8	12.6	4.5	3.4	4
Total surgical time (minutes)	130	180	176	180	265

EBL, estimated blood loss.

Inpatient hospital stay

Two studies found that the median length of stay was 3 days for obese patients undergoing transperitoneal RAPN.^15,17 One study in the literature reported a shorter hospital stay (2 days) in line with our results (median stay 1 day).

Impact of BMI class

Interestingly, our study found that the median tumor size increased with higher BMI class (29.5, 34.4, and 41.1 mm for BMI class I, class II, and class III, respectively); however, this did not translate into a difference in R.E.N.A.L. nephrometry score. These results were consistent with findings reported by Isac et al.¹⁷

While describing prospectively collected data in a high-volume tertiary referral center, this retrospective report represents the experience of a single institution, which inherently represents a limitation to the study, and what conclusions may be drawn. Nevertheless, other published series have suggested potential advantage to patients of the retroperitoneal approach over the more standard transperitoneal approach in laparoscopic surgery, regarding both radical nephrectomy and PN.^19–22 Our experience would suggest that similar advantages may remain true for RAPN in the obese patient. The retroperitoneal approach is associated with a significantly shorter operating time, fewer postoperative complications, a shorter hospital stay, less blood loss, and lower rates of blood transfusion compared with transperitoneal RAPN with no evidence of compromise on “cancer cure.”

Epidemiological data suggest an ever more obese society and higher rates of diagnoses of renal cancer. The vast majority of these diagnoses are likely to be incidental, as the driving force in the rise of renal cancer incidence is the small renal mass (<4 cm).²³ As such, there will probably be more obese patients than ever who are likely to find themselves offered an RAPN for a small renal tumor/cancer.

In conclusion, the apparent advantages of the retroperitoneal approach over the vastly more commonly performed transperitoneal surgery are relevant to both patients and health care systems alike and reinforce the need for the future-facing specialist urologist to have the skill set to allow the delivery of a safe and effective RAPN via whichever approach is most appropriate, determined by both patient and tumor factors, not limited by surgical experience.

Footnotes

Acknowledgments

The authors thank the following people for their assistance: Mr. Georg Müller, Mr. Amr Emara, and Mr. Surayne Segaran.

Disclosure Statement

No competing financial interests exist.

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