Ureterorenoscopy with Holmium-Yttrium-Aluminum-Garnet Fragmentation Is a Safe and Efficient Technique for Stone Treatment in Patients with a Body Mass Index Superior to 30 kg/m 2

Abstract

Purpose:

The aim of the study was to analyze results and morbidity after flexible ureterorenoscopy in patients with a body mass index (BMI) >30 kg/m² and to compare with results obtained in a large cohort of nonobese patients.

Patients and Methods:

We conducted a retrospective study including all flexible ureterorenoscopy performed for stone retrieval in our institution between January 2004 and December 2008. During the study period, 224 procedures were performed, of which 18 had to be excluded because of missing BMI data. Thus, a total of 206 procedures were included in the final analysis (34 in 29 obese patients, 172 in 149 nonobese patients). Characteristics of the patients (age, BMI, previous treatment), stones (nature, location, number), and procedures (operating time, morbidity, outcome) were analyzed. Success was defined as clear imaging (completely stone free) on renal tomography and ultrasonography at 1, 3, and 6 months follow-up.

Results:

Mean BMI was 34±0.6 kg/m² in obese patients (OP) and 24±0.2 kg/m² in nonobese patients (NOP). Mean stone size, location, and composition were not significantly different between groups. Operative time was also similar in OP and NOP (102.5±6.1 min vs 103±3.4 min, P=NS). The rate of minor complications (fever, hematuria, flank pain) was similar in OP (11.8%) and NOP (11.4%). No major complication necessitating prolonged hospital stay or new surgical procedure was observed. The overall stone-free rate was not significantly different between OP (79.4%) and NOP (70%).

Conclusion:

Flexible ureterorenoscopy is an appropriate treatment for use in obese patients and achieves excellent stone-free rates with low morbidity.

Introduction

O besity is a chronic disease whose prevalence has dramatically increased around the world during the past decade.¹ Obesity is significantly associated with comorbid disease, mortality rates, and overall healthcare costs. Morover, obese patients (OP) are recognized to be at higher risk for general postoperative complications, such as deep venous thrombosis and pulmonary embolism.² In parallel to the increasing prevalence of obesity, we have observed an increasing prevalence of urolithiasis. Obesity is associated with lithogenic factors such as insulin resistance, high sodium intake, hypercalciuria, urinary pH related to metabolic syndrome which increase the risk of stone formation.³ It has been shown that almost all OP present with at least one urinary lithogenic factor, while 80% have three or more risk factors.⁴

Stone management may necessitate urologic procedures to fragment and remove the calculi. Current guidelines for stone management of the upper urinary tract (renal and proximal ureter) propose extracorporeal shockwave lithotripsy (SWL), percutaneous nephrolithotomy (PCNL), and optional ureterorenoscopy (URS).^5,6 Obesity renders these procedures hazardous and less efficient, however. The thickness of the abdominal wall may alter stone location and fragmentation after SWL and may increase the technical difficulty of the percutaneous puncture for PCNL. In parallel to these technical difficulties, OP are at risk of anesthetic complications because of associated comorbidities, such as diabetes or hypertension.

Endoscopic treatment with flexible URS and in situ fragmentation with holmium:yttrium-aluminum-garnet (YAG) laser is a minimally invasive technique that is associated with a high stone-free rate and low morbidity for the management of upper urinary tract calculi in the general population. Indeed, URS is now considered as a valuable option in the management of upper urinary tract stones according to the 2011 guidelines of the European Association of Urology.⁷

The feasability of URS in OP has been reported in various small series^8
–10 with high stone-free rates and acceptable morbidity. Nevertheless, to the best of our knowledge, the morbidity and efficacy of URS in obese patients has never been compared with a large cohort of nonobese patients (NOP).

The objectives of our study were to report our experience in a large cohort of patients undergoing URS and to evaluate the efficacy and safety of flexible URS with holmium:YAG laser fragmentation for the management of kidney and ureteral stones in OP, and to compare these results with those obtained in a large cohort of NOP.

Patients and Methods

We conducted a large retrospective study of all URS procedures for upper urinary tract calculi performed in our institution between January 2004 and December 2009. During this period, 224 procedures were performed. Data for the calculation of body mass index (BMI) were not available for 18 procedures, and these cases were excluded from the study. Data from 206 procedures were thus included in the final analysis (34 procedures in 29 OP, and 172 procedures in 149 NOP). Recorded data included demographics for each patient (age, BMI, previous treatment), stone characteristics (nature, location, size), and procedural characteristics (operative time, surgical and anesthesiologic complications according to the Clavien-Dindo classification of surgical complications,¹¹ outcome).

Obesity was defined as a BMI ≥30 kg/m², according to the World Health Organization.¹² Follow-up was standardized and included simple radiography coupled with ultrasonography or renal CT scan at 1, 3, and 6 months. We chose to define success according to stringent criteria—namely, a completely stone-free status at all follow-up visits (1, 3, and 6 mos). Presence of residual fragments (RF) was considered as a failure, regardless of the size of the RF. Thirty-four procedures were performed in OP (first procedure in 29, second in 4, and third in 1) and 172 in NOP (first procedure in 149, second in 21, and third in 2).

URS treatment was performed by several experienced operators (EC, GG, SB, HB, FK) following a single standardized protocol. When preoperative urine culture was positive, the patient was treated with antibiotics for 2 to 7 days before the procedure. All procedures were performed under general anesthesia with orotracheal intubation. Patients were installed in the URS position; ie, with the leg on the treated side in semiextension to straighten the ureter. The video column was placed on the side to be treated.

The procedure began with rigid cystoscopy to explore the bladder and insertion of a stiff guidewire up to the kidney. Ureteral dilation and access sheath were used when necessary. The access sheath (mainly 12F–14F) was inserted under fluoroscopic guidance. The position of the access sheath depended on the location of the stone; ie, it was placed in contact with the calculi in case of ureteral location, or under the ureteropelvic junction for stones located in the kidney. The flexible ureterorenoscope was then advanced over the guidewire or inside the access sheath into the ureter or kidney. An irrigation pressurizing system was routinely used to allow optimum irrigation flow through the ureterorenoscope.

All the calices were inspected, and stones were identified. Small stones (<5 mm) were grasped and removed en bloc without destruction. Larger calculi were fragmented with a holmium:YAG laser (272 or 365 μm fibers). Once the fragmentation was completed, as many fragments as possible were extracted with a nitinol stone basket. After stone removal, a double pigtail indwelling ureteral stent (7F) was placed, depending on the operative time, the local conditions, the presence of residual fragments, and at the surgeon's discretion.

Statistical analysis was performed using Prism software (GraphPad, San Diego, CA) and XLstat software (Addinsoft, Brooklyn, NY). Categorical variables were analyzed using the chi-square test or the Fisher exact test where applicable. Continuous variables were analyzed parametrically using the Student t test. For univariate analysis, a P value<0.05 was considered statistically significant.

Results

Thirty-four procedures were performed in OP and 172 in NOP. The characteristics of the patients and the stones are presented in Table 1. Mean BMI was significantly higher in OP compared with NOP (34±0.6 vs 24±0.2 kg/m², respectively, P<0.0001). Age and sex at the time of surgery did not differ between groups. A history of urolithiasis was present in 49% of NOP and 56% of OP (P=0.49). No difference in stone characteristics was observed between the two groups in terms of size, location (ureteral and renal, lower, middle, upper collecting system), or chemical composition. On average, 1.25 procedures per patient were performed in OP and 1.12/patient in NOP.

Table 1.

Characteristics of Patients and Stones

	Nonobese patients (172 procedures)	Obese patients (34 procedures)
Patient characteristics
Age (years)	48.2±1.2	53.5±1.9	P=0.06
Sex (male)	64%	47%	P=0.06
BMI (kg/m²)	24±0.2	34±0.6	P<0.0001
History of urolithiasis	49%	56%	P=0.49
Previous stone treatment	34%	44%	P=0.3
SWL failure	13.9%	20.6%	P=0.32
Stone characteristics
Stone size (mm)	9.35±0.4	8.38±0.8	P=0.32
Stone location
Ureteral	19.2%	11.8%	P=0.45
Renal
Renal pelvis	15.1%	17.6%	P=0.71
Lower pole	40%	47%	P=0.45
Upper pole	8%	9%	P=0.89
Middle calix	9%	6%	P=0.57
Multiple Locations	8.4%	8.6%	P=0.9
Stone composition
Calcium oxalate	51%	61%	P=0.27
Phosphate	7.6%	5.6%	P=0.72
Uric acid	4.6%	2.9%
Calcium phosphate	11.1%	11.7%	P=0.91

BMI=body mass index ; SWL=shockwave lithotripsy.

The procedural characteristics are described in Table 2. The mean operative time was 103.1±3.4 minutes vs 102.5±6.2 minutes in NOP and OP, respectively (P=0.94). Ureteral dilation was necessary in 19.9±3% in NOP vs 23.5±7% in OP (P=0.63). Access sheath was widely used to allow optimal irrigation flow (54.9±3% vs 58.8±8% in NOP and OP respectively, P=0.68). Stones were extracted whole where possible (17.4±2% in NOP vs 18.2±7%, P=0.91). Lower pole stones were displaced to a more favorable location before fragmentation in 20.9±3% in NOP and 30.3±8%, P=0.23.

Table 2.

Procedural Characteristics and Outcomes of Ureterorenoscopy in Obese and Nonobese Patients

	Nonobese patients (172 procedures)	Obese patients (34 procedures)
Procedural characteristics
Operative time (min)	103.1±3.4	102.5±6.2	P=0.94
Ureteral dilation	19.9±3 %	23.5±7 %	P=0.63
Access sheath	54.9±4 %	58.8±8 %	P=0.68
Extracted whole	17.4±3 %	18.2±7 %	P=0.91
Stone relocation	20.9±3 %	30.3±8 %	P=0.23
Postoperative drainage	91.2±2 %	94.1±4 %	P=0.58
Results
Stone-free rate after one procedure	69.9±3%	79.4±7 %	P=0.23
Stone-free patients	85.2%	86.2 %	P=0.89
Mean length of stay (d)	3.9±0.12	3.7±0.17	P=0.58
Complications
Overall	11.6±2 %	11.8±5 %	P=0.98
Hematuria	1.1±0.8%	0%
Flank pain	1.7±1 %	5.9±4 %	P=0.15
Sepsis	8.7±2 %	5.8±4 %	P=0.58
Severity of complications
Clavien Dindo grade I	25%	50%
Clavien Dindo grade II	75%	50%
Clavien Dindo grade III	0	0

The stone-free rate after one URS procedure was not significantly different between groups (69.9% vs 79.4%, P=0.23 in NOP and OP, respectively). The overall rate of patients without residual fragments (after one or multiple procedures) was similar in both groups (85.2% in NOP and 86.2% in OP, P=0.89).

The average length of hospital stay was similar in both groups (3.9±0.12 vs 3.7±0.17 days in the NOP and OP groups respectively, p=0.58). The rate of complications was similar in both groups, as was the severity of complications. Complications such as persistent flank pain, sepsis, or hematuria, were reported in 11.6±2% in NOP and in 11.8±5% in OP (P=0.98). Details of complications are summarized Table 2. We noted only Clavien-Dindo grade I or II complications in both groups (Table 2). No complications necessitating surgical intervention (Clavien-Dindo grade III) were observed. No anesthetic complications occurred during the endoscopic procedures or in the 2 days after surgery in either group.

Discussion

Our study showed that flexible URS with holmium:YAG laser fragmentation of kidney and ureteral stones is safe and effective in OP. The increasing incidence of obesity in Europe and the United States will likely be associated with an increased need for surgical management of urinary stones. Obesity and overweight increase the risk of urinary stones through the metabolic syndrome, which can lead to insulin resistance, hyperoxaluria, and hypercalcemia.¹³

There are two specific issues in OP with urinary stones. The first is the management of the cardiovascular, respiratory, and metabolic comorbidities that dramatically increase perioperative morbidity. The second is the technical challenge of stone surgery in these OP. Currently, SWL and PCNL are the recommended techniques for upper urinary tract stone removal, but URS with holmium:YAG stone fragmentation is now a validated alternative.^5,6 The choice of treatment is guided mainly by the size of the calculi (more or less than 20 mm) and their location. The indications for flexible URS coupled with holmium:YAG laser are constantly being widened, and URS is now a good alternative for complex cases (eg, failure of previous treatments and anatomic features, associated comorbidity).¹⁴

SWL is a noninvasive procedure that is associated with a high success rate for small renal and ureteral stones. In obese patients, however, SWL presents specific challenges. The equipment, especially the operating table, is limited in the weight it can support. Furthermore, the depth between the skin and the kidney renders the stone harder to visualize by plain radiography and ultrasonography, thus making it difficult to focus the shockwaves accurately.¹⁵ This skin-to-stone distance associated with the thickness of the tissues can also be responsible for attenuation of the shockwaves, and consequently suboptimal fragmentation of the calculi.^16,17 These factors likely contribute to the poor results reported with SWL in OP. A recent French study analyzed the results of SWL in OP and reported that complete success was obtained in only 56.7%, with a mean of 1.67 procedures per patient.¹⁸ In an older study, a success rate of about 70% with two procedures per patients was reported.¹⁹ In our study, the complete success rate was 86.2% in OP, with only 1.25 procedures per patient.

PCNL yields very good results in terms of stone-free rates in NOP for renal calculi >2 cm. Pearle and associates²⁰ compared results from PCNL in OP and NOP and achieved a stone-free rate of 88.3%, with complications and transfusion in 14% and 8.8%, respectively. Outcome and morbidity of PCNL were not linked to BMI and were comparable in unselected patients, but necessitated a modification of the standard procedure and a specific, longer instrument.^16,20 The classic prone decubitus position in OP can induce ventilatory troubles, and some authors have proposed the use of the Valdivia procedure (PCNL in the lateralized supine decubitus position).²¹ Conflicting data, however, regarding morbidity of PCNL in OP have been reported.²² Faerber and colleagues²² reported a higher rate of complications (37% vs 16%) and a longer hospitalization time (4.4 vs 3.5 days) in OP.

In light of these difficulties, flexible URS coupled with holmium:YAG laser seems to be an attractive option to manage renal and proximal ureteral calculi in OP. This mini-invasive technique presents low morbidity and yields results similar to those obtained with SWL in the general population.²³ Different studies assessing the feasibility and effectiveness of flexible URS in OP have reported a success rate between 70 and 83%, with very low morbidity.^8
–10 Our study confirms these results in terms of efficacy and morbidity, which were similar between OP and NOP. Our definition of a successful procedure (ie, complete absence of RF) was stricter than others (some authors defined success by the absence of RF >4 mm), but we observed a stone-free rate of 76% in OP after one procedure and 86% after multiple procedures. As in NOP, stone size is an important predictive factor affecting the results of flexible URS.^14,24 In our population of OP, 11 presented with a stone >1 cm, and 9 needed multiple procedures to achieve a completely stone-free result. It is therefore possible to manage large calculi (with an accepted maximum size of 30 mm) with multiple sessions of flexible URS without increasing the rate of complications.^10,25

An important point, in our view, is the very low morbidity of URS in OP. In our study, we compared the morbidity observed with URS in OP and with that observed in a large cohort of NOP. We observed similar results, with a complication rate of about 10%. Moreover, all complications were Clavien-Dindo grade I or II. Most of the complications were postoperative fever ncessitating short-term antibiotics (Clavien-Dindo grade II). No specific complications were observed in OP. Our findings show that URS in OP is safe and efficient, with outcomes comparable to those achieved in NOP. Our study reinforces the idea that URS can be used as first-line therapy in OP, as it is now mentioned in current French guidelines.²⁶

Conclusion

Our study strongly demonstrates that URS with holmium:YAG laser fragmentation is a viable option for the management of renal and proximal ureter calculi in OP. URS is a safe and efficient treatment strategy with outcomes and morbidity comparable to those observed in NOP. These results favor the use of flexible URS as a first-line treatment option in these patients.

Footnotes

Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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