Perioperative Outcomes of Laparoscopic Partial Nephrectomy Stratified by Body Mass Index

Abstract

Background and Purpose:

Increased body mass index (BMI) has been shown to have inferior perioperative outcomes in patients undergoing laparoscopic partial nephrectomy (LPN). The aim of this study was to determine the differences in perioperative outcomes for patients undergoing LPN in normal, overweight, and obese persons using established BMI risk categories.

Methods:

A retrospective review of 488 patients undergoing LPN was performed stratifying patients according to BMI of <25 kg/m², 25 to 30 kg/m², and >30 kg/m². The analysis of variance test, chi-square analysis, and bivariate regression models were used to compare comorbidities and perioperative outcomes among the groups.

Results:

One hundred and eighty nine of 369 patients were identified as being obese. Obese patients were found to have a significantly higher American Society of Anesthesiologists class (2.4 vs 2.1) than normal weight patients (P=0.03). No significant differences were demonstrated in estimated blood loss, operative time, transfusion requirement, or rate of conversion between the groups. In addition, there was no significant difference in cardiovascular, pulmonary, thromboembolic, or infectious complications between the groups. Obesity was significantly associated with bleeding necessitating angioembolization (P=0.033).

Conclusion:

LPN demonstrates equivalent perioperative outcomes in normal, overweight, and obese patients. The minimally invasive approach achieves equivalent outcomes in patients undergoing major abdominal surgery although further studies of alternate procedures are needed to validate our findings.

Introduction

Data collected through the Centers for Disease Control and Prevention's Behavioral Risk Factor Surveillance System have shown that only one U.S. state has a prevalence of obesity less than 20%. Over the last 10 years, obesity has continued to rise among adults in the United States with rates exceeding 30% for most age and sex groups.¹ The obesity epidemic has important implications, because obesity and its comorbidities have been demonstrated as modifiable risk factors in the development of renal-cell carcinoma (RCC).² Increased body mass index (BMI) has been demonstrated as a risk factor for RCC and, consequently, urologists are increasingly faced with a greater proportion of obese patients needing definitive extirpative therapy.^3,4 With the current trends of RCC management shifting toward minimally invasive surgery, use of laparoscopic renal surgery in obese patients should be clearly evaluated.

Obesity has been considered by some to be a relative contraindication to laparoscopic surgery, with certain surgical series demonstrating inferior outcomes for renal surgery in obese patients.⁵ Obesity has been demonstrated as an independent risk factor for death and cardiac complications after vascular procedures.⁶ A recent study of 42,426 obese patients undergoing open versus laparoscopic appendectomy demonstrated lower overall complications (including deep venous thrombosis, pulmonary embolism, wound infection, respiratory failure), mortality rate, mean hospital charges, and mean length of stay (LOS) in the laparoscopic cohort.⁷ Early studies have demonstrated higher complication rates for urologic laparoscopic surgery in obese patients, and recent series have demonstrated BMI as a predictor of surgical site infections after laparoscopic urologic surgery.^8,9 Major advances in laparoscopic techniques combined with increasing surgeon experience have allowed these rates to significantly improve, necessitating reassessment of outcomes in contemporary surgical series. Obese patients often have significant comorbidities, including cardiovascular disease and insulin resistance, placing them at higher risk for suboptimal surgical outcomes. Increased BMI places patients at risk throughout the entire surgical procedure, including general anesthesia, with obesity being a predictor for adverse respiratory outcomes.¹⁰ Laparoscopic management of renal-cell carcinoma (RCC) in the obese patient is complicated by increased intraperitoneal pressure requirements, reducing ventilation, and resulting in greater CO₂ absorption, enhanced venous stasis, and decreased respiratory compliance, among others.¹¹ Obese patients are also at a higher risk of postoperative complications including nosocomial infections, particularly surgical-site infections, and fascial dehiscence.^12,13 A number of subsequent studies, however, have found similar morbidity and mortality rates between obese and nonobese patients undergoing urologic laparoscopic surgery.^14,15

Current series in the literature assessing outcomes in obese patients undergoing laparoscopic urologic procedures have been limited by small sample size, without comprehensive inclusion of contributing preoperative patient factors or detailed accounting of postoperative complications. This study, to our knowledge, represents the largest cohort of obese patients undergoing laparoscopic urologic surgery with analysis performed across established BMI risk groupings with known prognostic differences. The objective of the study is to describe the perioperative outcomes of obese versus nonobese patients undergoing laparoscopic partial nephrectomy (LPN) with respect to intraoperative parameters and early postoperative outcomes in a contemporary cohort of patients.

Methods

Once Institutional Review Board approval was obtained, a retrospective review of 488 patients who underwent LPN by a single surgeon (LRK) was performed. Patient demographic and clinical information including comorbidities were gathered and maintained. Patients were excluded from the study if information about their height and/or weight or perioperative course was not available. Four hundred and thirty-five patients met the inclusion criteria for our study.

A transperitoneal approach was used in all cases. Our surgical technique used to perform LPN has been described previously.^16

–19 An intraperitoneal pressure of 15 mm Hg was used in all patients, and a lateral shift in trocars was used to account for the obese patient's body habitus as described by Fugita and associates.²⁰ We obtained patient data including preoperative creatinine and hematocrit levels, operative time, blood loss, volume of intravenous fluid administered, intraoperative transfusions, and 6-month serum creatinine levels. Estimated glomerular filtration rate (eGFR) was calculated using the Cockcroft-Gault formula. In addition, we collected data on perioperative complications, postoperative transfusions, and recurrences. The modified Clavien classification system was used to report complications.²¹

Patients were divided into three groups based on BMI for statistical analysis. Patients were stratified into groups, based on World Health Organization (WHO) classification of obesity of BMI <25 kg/m² (group 1, normal), BMI 25 to 29.99 kg/m² (group 2, overweight), and BMI >30 kg/m² (group 3, obese).²² Statistical analysis using the analysis of variance test was used to compare the groups. Statistical significance was defined as P<0.05. All analyses were performed using commercially available statistical software (SPSS version 16.0, SPSS, Inc, Cary, NC).

Results

A total of 435 patients were identified with complete data for analysis, all of whom underwent transperitoneal LPN for renal masses. After stratifying patients for BMI according to the WHO criteria, sex (male) and American Society of Anesthesiologists class were found to be associated with increasing BMI. Patient characteristics are presented in Table 1. The majority of obese patients were male (69%) with an average age of 58.9 years and mean BMI of 35.7 kg/m². Additional variables collected and analyzed included comorbidities (hypertension, hyperlipidemia, diabetes mellitus, cardiac disease, smoking history), and previous abdominal surgery, none of which achieved statistical significance when comparing the three groups.

Table 1.

Patient Characteristics

	Group 1 (BMI <25 kg/m²) n=74	Group 2 (BMI 25–29.9 kg.m²) n=180	Group 3 (BMI >30) n=181	P value
Mean age (y) (range)	58.9 (33–79)	58.6 (21–84)	58.9 (26–81)	NS
Sex
# Female (%)	54% (40)	31% (56)	31% (57)	0.008
# Male (%)	46% (34)	69% (124)	69% (124)
Mean ASA score (range)	2.0 (1–4)	2.3 (1–4)	2.4 (1–3)	<0.001
Mean BMI (range)	22.0 (13.5–24.9)	27.4 (25–29.9)	35.7 (30–70.5)	-
Estimated preoperative GFR (min) (range)^a	77.7 (31.6–156.7)	95.6 (28.0–201.0)	120.8 (43.9–292.7)	<0.001

BMI=body mass index; ASA=American Society of Anesthesiologists; GFR=glomerular filtration rate.

eGFR was calculated using the Cockcroft-Gault equation

Tumor characteristics are illustrated in Table 2. There was no significant difference in mean tumor size or tumor volume between the groups. The mean tumor size ranged from 3.0 cm in the obese cohort to 3.6 cm in the normal cohort. Tumor complexity is reported using the R.E.N.A.L. (radius; exophytic/endophytic; nearness; anterior/posterior; location) nephrometry scoring system (Table 3). The majority of tumors in all three groups were of low (36%–47%) and moderate complexity (40%–50%). Tumors were found to be mostly clear-cell RCC on final pathologic evaluation (54%–60%) with papillary RCC being the second most prevalent at 20% in all groups. There were no significant differences in final pathologic determination between the three groups.

Table 2.

Tumor Characteristics

	Group 1 (BMI <25 kg/m²) n=74	Group 2 (BMI 25–29.9 kg.m²) n=180	Group 3 (BMI >30) n=181	P value
Mean tumor size (cm) (range)	3.6 (1–11)	3.1 (0.9–13.5)	3.0 (0.4–12.2)	NS
Mean tumor (cm³) (range)	31.3 (1–357)	29.8 (2.5–567)	28.9 (3.3–469.7)	NS
Histology
Clear-cell RCC	58% (38)	60% (100)	54% (89)	NS
Papillary RCC	20% (13)	20% (33)	20% (33)
Chromophobe RCC	12% (8)	3% (5)	7% (11)
Oncocytoma	3% (2)	8% (14)	10% (16)
Angiomyolipoma	3% (2)	7% (11)	3% (5)
Other	3% (2)	2% (4)	6% (10)
Unavailable	8	54	17

BMI=body mass index; RCC=renal-cell carcinoma.

Table 3.

Comparison of Tumor Complexity Using the R.E.N.A.L. Scoring System

	Low complexity score 4–6	Moderate complexity score 7–9	High complexity score 10–12
Group 1 (BMI <25)	42%	50%	8%
Group 2 (BMI 25–29.9)	36%	47%	17%
Group 3 (BMI >30)	47%	40%	13%

R.E.N.A.L.=radius; exophytic/endophytic; nearness; anterior/posterior; location; BMI=body mass index.

Perioperative characteristics and postoperative outcomes of our cohort are illustrated in Table 4. There was a trend toward longer operating room (OR) time with increasing BMI; group 1 had a mean OR time of 137.6 minutes and group 3 with an OR time of 147.1 minutes, although this difference was not significant. Estimated blood loss (EBL), transfusion requirement, conversion rate, clamp time, and intravenous fluid administration were not significantly different between the groups. Two conversions were noted in group 3, one of which was attributed to bleeding for a hilar tumor and the second for renal cooling to decrease warm ischemia time during difficult dissection. A significant difference was noted in 6-month postoperative percent change in eGFR (P=0.020), although this difference was not seen when comparing change in the absolute serum creatinine level. Postoperatively, a lower BMI was associated with a greater LOS in group 1 (3 days, P=0.031), but this was because of a single outlier with a LOS of 29 days, which when excluded demonstrated no difference between the three groups. Complications are outlined in Table 5. There was no difference in overall complication rates between the groups, or any significant differences by Clavien grade. Only postoperative hematuria/bleeding necessitating angioembolization was associated with obesity because 11 patients in group 3 versus 2 patients each in groups 1 and 2 needed a secondary procedure (P=0.033). There was no significant difference in cardiovascular, respiratory, thromboembolic, or infectious events between the groups.

Table 4.

Comparison of Perioperative Factors

	Group 1	Group 2	Group 3
	(BMI <25 kg/m²)	(BMI 25–29.9 kg.m²)	(BMI >30)
	n=74	n=180	n=181	P value
Mean operative time (min) (range)	136.9 (59–280)	139.5 (35–441)	142.5 (31–308)	NS
Mean estimated blood loss (mL) (range)	274.7 (50–1500)	290.3 (5–1700)	318.7 (5–1500)	NS
Mean warm ischemia time (min) (range)	14.4 (0–51)	18.5 (0–60)	16.7 (0–53)	NS
Mean length of stay (d) (range)	3.0 (1–29)	2.5 (1–10)	2.3 (1–14)	0.031
Transfusion
Intraoperative	0% (0)	1% (2)	0% (0)	NS
Postoperative	5% (3)	3% (5)	3% (5)	NS
# Postoperative complications	15% (11)	14% (26)	23% (42)	0.070
Δ Estimated GFR 6 mos (range)	−12.5 (−49.7–13.6)	−9.9 (−74.2–19.6)	−8.5 (−80.2–181.5)	NS
%Δ Estimated GFR 6 mos (range)	−15.6 (−50.2–14.3)	−9.9 (−48.3–17.5)	−6.8 (−45.8–124)	0.043

BMI=body mass index; GFR=glomerular filtration rate.

Table 5.

Clavien-Dindo Classification of Postoperative Complications

	Group 1	Group 2	Group 3
	(BMI <25 kg/m²)	(BMI 25–29.9 kg.m²)	(BMI >30)
	n=74	n=180	n=181	P value
Overall	11	26	42	NS
Clavien I	5	10	19	NS
Trocar hematoma	1		1
Fever	1		2
Wound infection/separation	1	1	3
Bleeding	1	1	1
Urine leak (observed)	1	1	1
Ileus		3	3
Neuropraxia		1
Urinary retention		1	4
Hypoxia		2	3
Renal failure			1
Clavien II	1	9	8	NS
Transfusion		1	1
Wound infection		1	1
C. difficile infection	1	2	1
Cardiac arrythmia		3	2
Pulmonary embolus		1	1
Pneumonia		1
UTI			1
Hydronephrosis			1
Clavien III	4	7	14	NS
Bleeding necessitating angiogram/embolization	2	2	11	0.033
Port site hernia	1	1
GI bleeding	1	1	1
DVT (IVC filter)		1
Pneumothorax		1
Urine leak		1	2
Clavien IV			1	NS
Clavien V	1			NS

BMI=body mass index; UTI=urinary tract infection; GI=gastrointestinal; DVT=deep venous thrombosis; IVC=inferior vena cava.

Discussion

The prevalence of obesity is increasing at an alarming rate, and the health risks associated with being overweight have stimulated a considerable amount of research regarding its clinical sequelae. Because urologists are seeing a greater proportion of obese patients, it is compelling to analyze outcomes of interventions in this population, who are presumably at higher risk for poorer outcomes and greater cost to the healthcare system. A recent study revealed that open partial nephrectomy in obese patients cost almost $4000 more than their nonobese counterparts, mainly because of increased LOS, although no differences were noted in the laparoscopic groups.²³ Minimally invasive renal surgery has repeatedly demonstrated superior outcomes to open surgery, and the question of whether its advantages carry over to obese persons has been a topic of recent interest. The prevalence of obesity in patients undergoing surgery for RCC has been steadily increasing, and our data revealed an astounding 51% of patients meeting the criteria of being clinically obese.

Early reports of laparoscopic surgery in urology were met with tepid results, with greater complications, greater OR times, and generally poorer parameters in obese patients when compared with their normal weight counterparts.⁹ Anast and colleagues²⁴ reviewed 189 patients treated with transperitoneal laparoscopic nephrectomies and showed increased EBL, OR time, and transfusion requirements but comparable complications rates in obese patients.

The current literature available on laparoscopic renal surgery in obese patients and their findings are detailed in Table 6. Three studies comparing hand-assisted laparoscopic renal surgery (HALRS) in obese patients showed varying influences of BMI on perioperative outcomes. Parker and coworkers²⁵ showed no significant differences in clinical parameters, although obesity was found to be a predictor for postoperative complications in their regression model. Gabr and associates²⁶ revealed that BMI was associated with a greater EBL and increased conversion to open surgery in standard laparoscopic surgery, although not in HALRS. Hedican and colleagues²⁷ provided an early report of HALRS in obese patients demonstrating comparable outcomes to that in the current literature, but this study did not have a nonobese patient population for comparative outcomes.

Table 6.

Contemporary Series of Laparoscopic Renal Surgery in Obese Patients

Studies of laparoscopic surgery in obese patients (BMI >30)
						Postop complications (n)
						M=major
Author et al	Sample size (n=obese)	Surgery	OR time (mean)	EBL (mean)	LOS (mean)	m=minor	Significant findings
Reynolds^{31 a} (2014)	184 (113)	LPN/RAPN	218	150	3	28.3% Mm	No association between increased BMI and adverse perioperative or pathologic outcomes
Kiziloz³² (2013)	270 (108)	RAPN	200	295.6	3.4	6.6% Mm5.6% M0.4% m	Increased BMI associated with greater EBL, LOS, and OR time
Isac^{33 a} (2012)	250 (103)	RAPN	185.44	213.59	3.3	36.9% Mm4.9% M22.3% m	Higher ASA, greater median EBL, larger tumor size in morbidly obese (BMI ≥40)
Eaton³⁴(2011)	118 (48)	LPN	213.65	290.8	3.8	10.4% M20.8% m	Greater EBL in morbidly obese (BMI >35)
Naeem³⁵ (2011)	97 (49)	RAPN	265	150	2	8.3% Mm	Greater median EBL in obese group
Parker^{25 a} (2008)	150 (55)	HALRN	171	100	3	42% Mm	Obese more likely to experience complications
Romero³⁶ (2008)	112 (56)	LPN	195	392	3.2	17.9%	Greater EBL in obese
Feder³⁰ (2008)	45 (17)	LRN	157	161	3.5	18% Mm	Obese with less complications than nonobese, better outcomes with lap (LOS, EBL, OR time)^c
Colombo¹⁴ (2007)	378 (140)	LPN	204	310	2.8	13% Mm	No significant differences^b
Gong¹⁵ (2007)	239 (94)	LRS	210/201/233 (Grade1–3)	157/197/270 (Grade1–3)	2.3/2.6/3.6 (Grade1–3)	22%/33%/23% (Grade1–3)	No significant differences^b
Fugita (2004)	101 (32)	LRN	242	257	3.8	3.1% M	No significant differences^b
Hedican²⁷ (2004)	30 (30)	HALRS	262	217	4.1	23%m	No major complications
Anast²⁴ (2004)	189 (59)	LRS	280	230	3.0	8.5% M13.6% m	Increased EBL, OR time, transfusion in obese for LPN, LRN
Gabr²⁶ (2008)	350 (167)	HALRN/LRN	209/211 (Grade 1+2, 3)	393/490 (Grade 1+2, 3)	2.5/3.1 (Grade 1+2, 3)	30%/12% m/M	BMI associated with increased EBL only
Kuo³⁷ (2000)	40 (12)	LDN	310	182	2.1	0%	No significant differences

BMI=body mass index; OR=operating room; EBL=estimated blood loss; LOS=length of stay; LPN=laparoscopic partial nephrectomy; RAPN=robot-assisted partial nephrectomy; ASA=American Society of Anesthesiologists; HALRN=hand-assisted laparoscopic renal nephrectomy; HALRS=hand-assisted laparoscopic renal surgery; LDN=laparoscopic donor surgery.

Median values reported.

Laparoscopic vs laparoscopic.

The largest series to date to examine laparoscopic renal surgery in obese patients compared outcomes of 378 patients undergoing LPN of whom 140 had a BMI >30kg/m². There was no significant difference in EBL, LOS, OR time, clamp time, or complications between patients, but LPN with retroperitoneal access (n=45), demonstrated a statistically significant shorter operative time compared with a transperitoneal approach, and reduced LOS in obese patients.¹⁴ Renal functional outcomes have not been dutifully evaluated in previous series, and in our study, there was no significant change in absolute serum creatinine level at 6 months; although obese patients were observed to have a lesser percent change in eGFR postoperatively, it is most definitely related to the use of the Cockcroft-Gault equation to estimate EGR, which takes into consideration weight in contrast to the Modification of Diet in Renal Disease and Chronic Kidney Disease Epidemiology Collaboration calculations that incorporate race.

A systematic review and meta-analysis by Aboumarzouk and coworkers²⁸ looked at four studies with a total of 659 patients of which 256 were obese and 403 nonobese. Studies were limited to those that strictly compared LPN between obese and nonobese patients, and excluded any involving robot- or hand-assistance. No difference was identified in operative duration, warm ischemic time, EBL, LOS, total complications, intraoperative complications, or postoperative complications. Significantly more Clavien grade III complications occurred in the obese group; however, the absolute incidence was low in both the obese and nonobese groups.

Postoperative complications have been hard to gauge among current studies addressing obese patients because of a lack of standardized criteria. In our study, we retrospectively gathered data regarding postoperative outcomes that demonstrated an overall complication rate of 15.4% using the modified Clavien classification of surgical complications.²⁹ Interestingly Feder and colleagues³⁰ did show less postoperative complications and transfusion rate in obese patients. In contrast, our series demonstrated an increased number of complications among obese patients, although when stratified by complication type, only bleeding necessitating angioembolization was associated with increasing BMI (P=0.033). The etiology of this difference is unclear and may potentially be because of a more challenging renorrhaphy/intracorporeal suturing related to body habitus, although renorrhaphy technique was identical in all patients. Despite the established concerns of anesthetic and surgical risks in obese patients, we were unable to detect a significant difference in cardiovascular, respiratory, thromboembolic, or infectious events between the groups.

Limitations

The main limitations of our study are its retrospective nature and its inherent disadvantages that can introduce selection bias. The number of complications, specifically Clavien IV complications, may be underestimated because intensive care treatment was not recorded routinely. In addition, creatinine-based estimations of renal function can demonstrate variability associated with muscle mass (especially in obese patients), hydration status, and nutritional status. Unfortunately, the inconsistent availability of race data precluded the use of alternate calculations of eGFR. Finally, the results of our study represent a single surgeon series with significant experience with laparoscopic surgery, and results may not be readily generalized to routine clinical practice.

Conclusion

As data regarding laparoscopic surgery in the obese accumulate, the trend will be for outcomes to equilibrate for all groups. Our study suggests that even among the morbidly obese (obese Class II–III), perioperative outcomes are not significantly different and hence supporting minimally invasive surgery as the optimal intervention for renal surgery, rather than a relative contraindication in the ever-growing clinically obese population.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

Abbreviations Used

References

Flegal

, Carroll

, Kit

, Ogden

. Prevalence of obesity and trends in the distribution of body mass index among US adults, 1999–2010. JAMA, 2012; 307:491–497.

Yuan

, Castelao

, Gago-Dominguez

, et al. Hypertension, obesity and their medications in relation to renal cell carcinoma. Br J Cancer, 1998; 77:1508–1513.

Bergstrom

, Hsieh

, Lindblad

, et al. Obesity and renal cell cancer—A quantitative review. Br J Cancer, 2001; 85:984–990.

Chow

, Gridley

, Fraumeni

Jr , Järvholm

. Obesity, hypertension, and the risk of kidney cancer in men. N Engl J Med, 2000; 343:1305–1311.

Kurzer

, Leveilee

, Bird

. Obesity as a risk factor for complications during laparoscopic surgery for renal cancer: Multivariate analysis. J Endourol, 2006; 20:794–799.

Jackson

, Sidawy

, Amdur

, Macsata

. Obesity is an independent risk factor for death and cardiac complications after carotid endarterectomy. J Am Coll Surg, 2012; 214:148–155.

Masoomi

, Nguyen

, Dolich

, et al. Comparison of laparoscopic versus open appendectomy for acute nonperforated and perforated appendicitis in the obese population. Am J Surg, 2011; 202:733–739.

George

, Srinivasan

, Cho

, et al. Surgical site infection rates following laparoscopic urological procedures. J Urol, 2011; 185:1289–1293.

Mendoza

, Newman

, Albala

, et al. Laparoscopic complications in markedly obese urologic patients (a multi-institutional review). Urology, 1996; 48:562–567.

10.

Forrest

, Rehder

, Cahalan

, Goldsmith

. Multicenter study of general anesthesia. III. Predictors of severe perioperative adverse outcomes. Anesthesiology, 1992; 76:3–15.

11.

Nguyen

, Wolfe

. The physiologic effects of pneumoperitoneum in the morbidly obese. Ann Surg, 2005; 241:219–226.

12.

Choban

, Flancbaum

. The impact of obesity on surgical outcomes: A review. J Am Coll Surg, 1997; 185:593–603.

13.

Anaya

, Dellinger

. The obese surgical patient: A susceptible host for infection. Surg Infect, 2006; 7:473–480.

14.

Colombo

Jr , Haber

, Aron

, et al. Laparoscopic partial nephrectomy in obese patients. Urology, 2007; 69:44–48.

15.

Gong

, Orvieto

, Lyon

, et al. Analysis of impact of body mass index on outcomes of laparoscopic renal surgery. Urology, 2007; 69:38–43.

16.

George

, Herati

, Srinivasan

, et al. Perioperative outcomes of off-clamp vs. complete hilar control laparoscopic partial nephrectomy. BJU Int, 2013; 111:E235–E241.

17.

Salami

, George

, Rais-Bahrami

, et al. Off-clamp laparoscopic partial nephrectomy for hilar tumors: Oncologic and renal functional outcomes. J Endourol, 2014; 28:191–195.

18.

George

, Herati

, Rais-Bahrami

, et al. Laparoscopic partial nephrectomy for hilar tumors: Oncologic and renal functional outcomes. Urology, 2014; 83:1111–1115.

19.

Rais-Bahrami

, George

, Herati

, et al. Off-clamp versus complete hilar control laparoscopic partial nephrectomy: Comparison by clinical stage. BJU Int, 2012; 109:1376–1381.

20.

Fugita

, Chan

, Roberts

, et al. Laparoscopic radical nephrectomy in obese patients: Outcomes and technical considerations. Urology, 2004; 63:247–252.

21.

Dindo

, Muller

, Weber

, Clavien

. Obesity in general elective surgery. Lancet, 2003; 362:2032–2035.

22.

Kuczmarski

, Carroll

, Flegal

, et al. Varying body mass index cutoff points to describe overweight prevalence among US adults: NHANES III (1988 to 1994). Obes Res, 1997; 5:542–548.

23.

Bensalah

, Raman

, Bagrodia

, et al. Does obesity impact the costs of partial and radical nephrectomy?. J Urol, 2008; 179:1714–1718.

24.

Anast

, Stoller

, Meng

, et al. Differences in complications and outcomes for obese patients undergoing laparoscopic radical, partial, or simple nephrectomy. J Urol, 2004; 172:2287–2291.

25.

Parker

, Lewis

, Heckman

, et al. Evaluation of the impact of body mass index on outcome among renal mass patients treated with hand-assisted laparoscopic radical nephrectomy. J Endourol, 2008; 22:301–306.

26.

Gabr

, ElSayed

, Gdor

, Roberts

, Wolf

Jr . Obesity and morbid obesity are associated with greater conversion rate to open surgery for standard but not hand assisted laparoscopic radical nephrectomy. J Urol, 2008; 180:2357–2362.

27.

Hedican

, Moon

, Lowry

, Nakada

. Hand-assisted laparoscopic renal surgery in the morbidly and profoundly obese. J Endourol, 2004; 18:241–244.

28.

Aboumarzouk

, Stein

, Haber

, et al. Laparoscopic partial nephrectomy in obese patients: A systematic review and meta-analysis. BJU Int, 2012; 110:1244–1250.

29.

Dindo

, Demartines

, Clavien

. Classification of surgical complications: A new proposal in a cohort of 6336 patients and results of a survey. Ann Surg, 2004; 240:205–213.

30.

Feder

, Patel

, Melman

, et al. Comparison of open and laparoscopic nephrectomy in obese and nonobese patients: Outcomes stratified by body mass index. J Urol, 2008; 180:79–83.

31.

Reynolds

, Hannon

, Lehman

, et al. An obese body habitus does not preclude a minimally invasive partial nephrectomy. Can J Urol, 2014; 21:7145–7149.

32.

Kiziloz

, Dorin

, Finnegan

, et al. The impact of body mass index on perioperative outcomes in robot-assisted laparoscopic partial nephrectomy. J Endourol, 2013; 27:1000–1007.

33.

Isac

, Autorino

, Hillyer

, et al. The impact of body mass index on surgical outcomes of robotic partial nephrectomy. BJU Int, 2012; 110: 997–1002.

34.

Eaton

, Thirumavalaven

, Katz

, et al. Effect of body mass index on perioperative outcomes for laparoscopic partial nephrectomy. J Endourol, 2011; 25:1447–1450.

35.

Naeem

, Petros

, Sukumar

, et al. Robot-assisted partial nephrectomy in obese patients. J Endourol, 2011; 25:101–105.

36.

Romero

, Rais-Bahrami

, Muntener

, et al. Laparoscopic partial nephrectomy in obese and non-obese patients: Comparison with open surgery. Urology, 2008; 71:806–809.

37.

Kuo

, Plotkin

, Stevens

, Cribbs

, Johnson

. Outcomes of laparoscopic donor nephrectomy in obese patients. Transplantation, 2000; 69(1):180–182.