Comparison of Shockwave Lithotripsy and Flexible Ureteroscopy for the Treatment of Kidney Stones in Patients with a Solitary Kidney

Abstract

Introduction and Objectives:

To compare the outcomes of these minimally invasive procedures in this patient population.

Patients and Methods:

The database of our institution has been retrospectively reviewed, and medical records of urolithiasis patients with a solitary kidney who underwent flexible ureteroscopy (F-URS) or extracorporeal shock wave lithotripsy (SWL) between January 2009 and December 2012 were examined. Retreatment rates, complications, changes in estimated glomerular filtration rates (eGFRs), chronic kidney disease (CKD) stages, and stone-free rates were compared between the two groups.

Results:

Stones of 48 patients (mean age: 48.8±15.4, range: 14–76) with solitary kidneys were treated with SWL (n=30, 62.5%) or F-URS (n=18, 37.5%). Patient demographics and stone related parameters were similar. The most common stone location was the pelvis in the SWL group (36.6%), whereas it was the pelvis and a calix in the F-URS group (38.8%). Complications and success rates were similar in both groups, however, patients in the SWL group needed more sessions to achieve stone clearance (2.2±0.89 vs 1.06±0.24, p=0.0001). Preoperative and postoperative eGFR and CKD stage changes were also similar.

Conclusion:

Both SWL and F-URS are effective and safe techniques, which can be used for the treatment of stones in patients with solitary kidneys. However, patients treated with SWL need more sessions to achieve stone clearance.

Introduction

Extracorporeal shock wave lithotripsy (SWL), flexible ureteroscopy (F-URS), percutaneous nephrolithotomy (PNL), and the combinations of these treatment modalities are now considered as standard treatment of most upper tract stone diseases.¹ Although higher stone-free rates can be achieved with PNL, this procedure is commonly reserved for larger stones due to its complications such as bleeding and visceral organ injury; thus, SWL and F-URS are commonly preferred due to their minimally invasive nature.¹ However, SWL and F-URS may also result in various complications.^2

–6

Complications encountered in the treatment of a solitary kidney are similar to what occurs when the patient has two normal kidneys, but the potential consequences of injury are much greater. Therefore, physicians should always focus on preserving nephrons and preventing stone-related renal complications to prevent chronic renal failure and the risk of hemodialysis need.

Although the efficacy and safety of SWL and F-URS in patients with solitary kidneys are demonstrated in various studies,^7
–9 the functional outcomes of these two modalities have not been compared. Therefore, the aim of this study is to compare the outcomes of SWL and F-URS in patients with solitary kidneys.

Materials and Methods

Study design

The data of patients who underwent SWL or F-URS in a tertiary referral center between January 2009 and December 2012 were retrospectively reviewed. Patients with either functional (scintigraphically confirmed using dimercaptosuccinic acid renography) or anatomical solitary kidneys were included into the study. Patient demographics and stone-free rates were noted, whereas renal functional parameters were compared before and after the procedures. Renal functions were evaluated with both the estimated glomerular filtration rate (eGFR) formulation¹⁰ and the chronic kidney disease (CKD) classification¹¹ and the patients were staged as follows^10,11:

Stage 1: normal (eGFR>90 mL/minute/1.73 mm²)

Stage 2: mildly decreased (60–89 mL/minute/1.73 mm²)

Stage 3: moderately decreased (30–59 mL/minute/1.73 mm²)

Stage 4: severely decreased (15–29 mL/minute/1.73 mm²)

Stage 5: requiring renal replacement therapy, including dialysis and renal transplant (<15 mL/minute/1.73 mm²)

Preoperative evaluation

Patients' demographic parameters, including age, sex, and body–mass index (BMI), were recorded along with the size and the location of the stones. Preoperative serum creatinine levels were measured and urine cultures were performed. All patients had sterile urine culture before both SWL and F-URS. Imaging studies included noncontrast CT and intravenous urography.

F-URS technique

All of the procedures were performed under general anesthesia. After the placement of two guidewires into the renal pelvis, a ureteral access sheath was placed whenever possible. In cases when it was not possible to engage either the scope or the access sheath into the ureter, ureteral orifice was enlarged with ureteral balloon dilatation. Alternatively, a Double-J catheter might be placed for passive dilation and the procedure was postponed for 10 days. A 7.5F fiberoptic (Storz FLEX-X², Tuttlingen, Germany) or 8.7F digital flexible ureteroscope (DUR-D Gyrus ACMI, Southborough, MA) was used with either 200 or 273 μm laser fibers. The StoneLight^® (American Medical Systems, Inc., Minnetonka, MN) laser generator was used with the laser settings set to 0.8 to 1.0 J energy and 8 to 10 Hz rate. At the end of laser lithotripsy, stone fragments smaller than 2 mm were left for spontaneous passage, whereas bigger fragments were removed with basket catheters. A 4.8F Double-J stent was placed after every F-URS procedure, which was removed at second postoperative weeks.

Kidney, ureter, and bladder radiograph (KUB) was taken on the first postoperative day to check the presence of residual stones and the location of the catheters. Serum creatinine levels were also measured at the same day and eGFR was calculated for each patient. Patients were reevaluated on the third postoperative month with urine analysis, serum creatinine level, and CT scan.

SWL technique

Dornier Compact Sigma (Dornier MedTech GmbH, Wessling, Germany) was used by a single senior urologist for SWL treatment, which was performed under ultrasonography guidance. A Double-J stent was placed in all cases before the sessions. All patients received tramadol hydrochloride 1 mg/kg 30 minutes before the SWL sessions. Patients were checked with KUB and ultrasonography on the 10th postoperative day and SWL treatment was repeated if needed. Patients were considered SWL resistant if stones were either not fragmented or were too large for spontaneous passage after the third session.

Patients were reevaluated on the third month after the last SWL session and urine analysis, serum creatinine measurement, and CT scan were repeated. Patients with marked residual fragments on the third month were referred to auxiliary treatments, whereas the Double-J stent of the stone-free patients was removed.

Statistical analyses

Statistical analyses were performed with the Number Cruncher Statistical System 2007 statistical software package program (NCSS, LLC, Kaysville, UT). In addition to descriptive statistics (mean, standard deviation, median, interquartile range), an independent t-test was used for variables with normal distribution. Moreover, pre- and postoperative values were compared with the matched t-test, chi-square test, Fisher's exact test, and Mc Nemar's test. Statistical significance was set as p<0.05.

Results

Of the 48 patients with solitary kidney stones, 62.5% and 37.5% were treated with SWL and F-URS, respectively. Mean patient age (p=0.320) and male to female ratio (p=0.102) of the groups were similar (Table 1). Patients treated with SWL had a significantly higher BMI (p=0.021). The prevalence of comorbidities and the rate of previously failed stone therapies were not different between the two groups (Table 1).

Table 1.

Comparison of Patient and Stone Characteristics

	SWL (n=30)	F-URS (n=18)	p
Mean patient age (years±SD)	51.7±17.8	47.1±13.8	0.320
	(range: 24–76)	(range: 14–72)
Gender (male/female)	22/8	9/9	0.102
Mean BMI	28.8±5.4	25.5±4.2	0.021
Side (right/left)	18/12	9/9	0.823
Previous treatment	20 (66.6%)	14 (77.7%)	0.412
PNL	12	6
SWL	11	8
F-URS	2	6
DM	8 (26.6%)	8 (44.4%)	0.206
HT	17 (56.6%)	7 (38.8%)	0.233
Stone size (mm±SD)	14.9±3.8	16.0±2.6	0.293
	(range: 7–22)	(range: 12–21)
Stone location			0.877
Caliceal	19	11
Pelvis and UPJ	11	7
Complications			0.454
Colicky pain (Grade 3a)	11	5
Transient hematuria (Grade 1)	3	1
Fever (Grade 1)	1	1

Bold values indicate statistical significance=p<0.05.

BMI=body–mass index, kg/m²; DM=diabetes mellitus; F-URS=flexible ureteroscopy; HT=hypertension; PNL=percutaneous nephrolithotomy; SWL=extracorporeal shock wave lithotripsy; UPJ=ureteropelvic junction.

Preoperative evaluation was performed using a noncontrast CT scan in 83.3% of patients in the SWL group and 100% in the F-URS group (p=0.067). The mean stone size and stone location distribution were also similar in both groups (p=0.293 and p=0.877, respectively, Table 1).

The mean number of shock waves per session was 1997.8±294.6 (range: 800–2800) shocks with 90 shock waves per minute. Low to higher power ramping protocol was used in all patients.

In the F-URS group, operation duration and fluoroscopic screening time were 52.05±17.54 minutes (range: 30–90) and 2.46±1.09 minutes (range: 0.7–4.6), respectively. Access sheath was used in 15 (83.3%) patients and a Double-J stent was placed at the end of all cases.

Colicky pain (Clavien Grade 3a) was the most common complication in both the SWL (36.6%) and the F-URS (27.7%) group (Table 1).

Stone-free rates at the third postoperative month were 73.3% and 66.6% in the SWL and the F-URS groups, respectively (p=0.0623). Salvage F-URS was required for 7 (23.3%) and 1 (5.5%) patients in the SWL and the F-URS groups, respectively. The number of sessions to achieve the stone-free status was significantly lower in the F-URS group compared with the SWL group (1.06±0.24 and 2.2±0.89, p=0.0001).

Preoperative and postoperative eGFR in the F-URS group were significantly lower compared with the SWL group (p=0.011 and p=0.005, respectively) (Table 2). However, eGFR did not significantly change after the procedures in either the SWL group or the F-URS group (p=0.842 and p=0.402, respectively) (Table 2). Preoperative and postoperative CKD classes of the SWL and F-URS groups were also compared (Table 3). Although preoperative CKD classes were different, postoperative CKD class distribution was similar (p=0.018 and p=0.097, respectively).

Table 2.

Comparison of Preoperative and Postoperative Renal Function

	SWL (n=30)	F-URS (n=18)	p^a
Preoperative mean serum Cr (mg/dL)	1.12±0.29	1.38±0.4	0.013
Postoperative mean serum Cr (mg/dL)	1.13±0.37	1.46±0.51	0.014
p ^b	0.784	0.400
Preoperative mean eGFR (mL/minute/1.73 m²)	77.17±23.1	59.67±19.9	0.011
Postoperative mean eGFR (mL/minute/1.73 m²)	78.0±25.7	56.6±20.9	0.005
p ^b	0.842	0.402

Independent t-test.

Matched t-test.

Bold values indicate statistical significance=p<0.05.

Cr=creatinine; eGFR=estimated glomerular filtration rate using Chronic Kidney Disease Epidemiology Collaboration [CKD-EPI] formula; F-URS=flexible ureteroscopy.

Table 3.

Comparison of Preoperative and Postoperative Renal Function

	SWL group (n=30) (%)	F-URS group (n=18) (%)	P^a
Pre-op CKD class
1	9 (30.0)	1 (5.6)	0.018
2	14 (46.7)	6 (33.3)
3	7 (23.3)	11 (61.1)
Post-op CKD class
1	11 (36.7)	1 (5.6)	0.097
2	10 (33.3)	7 (38.9)
3	8 (26.7)	9 (50)
4	1 (3.3)	1 (5.6)
p ^b	0.306	0.564

Chi-square test.

Mc Nemar's test.

Bold values indicate statistical significance=p<0.05.

CKD=chronic kidney disease; Pre-op=preoperative; Post-op=postoperative.

Discussion

Our results demonstrated that both SWL and F-URS can safely be performed in patients with solitary kidneys. The eGFR remained almost stable in both groups when compared to the preoperative values. Complications and stone-free rates were similar in both the SWL and the F-URS groups. The main advantage of the F-URS over SWL seems to be the decreased number of sessions.

As most of the stones in our study group were smaller than 20 mm (range: 7–22 mm), the majority of the patients underwent SWL, which is in accordance with the recommendations of recent guidelines.³ However, despite its noninvasive nature, some major complications, including steinstrasse (4%–7%), sepsis (1%–2.7%), and symptomatic renal hematoma (<1%) may still develop after SWL.^12
–14 Increased long-term risk of diabetes mellitus and hypertension are other concerns related to SWL.^15

–19 In the present study, the overall complication rate after SWL was 50%, most of which were colicky pain (36.6%). None of the patients had any renal or splenic hematoma on the CT scan, which was taken at the end of the third month. One (3.3%) of the patients in the SWL group developed fever and he was treated with antibiotics on an outpatient setting.

F-URS has the advantage of preventing renal parenchyma from direct injury.²⁰ However, the use of high-pressure irrigation fluid may result in deterioration of the renal function.²¹ Besides the most catastrophic complication of pelvic perforation, high intra-pelvic pressures seen during F-URS²² have the theoretical disadvantages of bacterial and endotoxin translocation into the systemic circulation through the pyelovenous and pyelolymphatic backflow.²³ Therefore, the use of access sheaths, which provide maximum flow of irrigation fluid while maintaining a low intrarenal pelvic pressure is recommended.²⁴ Of note, the use of the access sheath may result in ureteral lesion in up to 46.5% patients³ and the access sheath was used during the F-URS procedure in 15 (83.3%) patients with solitary kidneys in this study. On the other hand, we do not really know to what extent increased intraoperative pelvic pressure contributes to complications such as pain and infection during the postoperative period. Finally, inserting a Double-J stent after the procedure may help to ameliorate postoperative outcomes.²⁵ In this study, a Double-J stent was routinely placed in all cases. As a result, fever that responded well only to antipyretics was seen in 1 (5.5%) patient, while 5 (27.7%) patients had colicky pain. Colicky pain was the most common complication in both the SWL (36.6%) and the F-URS (27.7%) group. Our results seem to be higher than the previously reported rates in the literature.^1,25 This relatively higher incidence of colicky pain may be due to the routine placement of ureteral stents after F-URS. The lower pain threshold in our population may also contribute to this phenomenon.

The beneficial effects of PNL on kidney function have been well demonstrated in patients with bilateral kidneys.^26,27 However, data on the functional outcome of this procedure in patients with solitary kidneys are limited and contradictory. The Clinical Research Office of the Endourological Society (CROES) PNL study group reported that PNL in solitary kidneys yields in lower stone-free rates when compared to patients with bilateral kidneys.²⁸ The study also reported increased serum creatinine levels during the immediate postoperative period. This finding resulted in a debate on the long-term safety of PNL for patients with solitary kidneys. However, Akman and colleagues²⁹ showed that kidney function was stable or even improved after PNL in 90.1% of patients with solitary kidneys at the end of the sixth month. Similarly, there are limited data regarding the impact of SWL on the renal functions of patients with solitary kidneys. El-Assmy and colleagues retrospectively analyzed the data of patients with solitary kidneys who underwent SWL monotherapy.⁷ The authors recruited 156 patients, 108 of which had long-term follow-up data (3.8±3.5 years). These authors also demonstrated that the mean eGFR of the patients did not change significantly after SWL therapy (84.6±24.7 and 82.5±26.5, p=0.33). The impact of F-URS on the renal functions of the patients with solitary kidneys is not well established either. Atis and colleagues retrospectively analyzed the effects of F-URS on renal functions in 24 patients with solitary kidneys⁹ and demonstrated that serum creatinine levels did not change significantly at the end of the second postoperative week (1.54±0.55 vs 1.56±0.5 mg/dL, p=0.92). Our results confirmed these findings as both the eGFR and CKD class of our patients remained stable.

With the technological advancements and increased experiences regarding both SWL and F-URS techniques, the efficacy and safety of these procedures in patients with solitary kidneys will be improved in the future. Since there is no clear advantage of one of these modalities over another, surgeons must prefer the treatment option in which they are more experienced.

The present study has several limitations. First, this is a retrospective study analyzing a small population of patients with solitary kidneys who underwent either SWL or F-URS. The mean follow-up duration is also short for both of the procedures and future studies with longer follow-up periods are necessary to confirm our findings.

Conclusion

Both SWL and F-URS are safe and effective procedures that can be used for the treatment of kidney stones in patients with a solitary kidney. However, patients treated with SWL need more sessions to achieve stone clearance.

Footnotes

Acknowledgment

The authors would like to thank Ege Can Serefoglu, MD, for his contributions to the study.

Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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