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Percutaneous Nephrolithotomy With X-Ray Free Technique in Morbidlyobese Patients: Outcomes and Skills From A Large High-Volume Stone Management Center

TL;DR: The feasibility and safety of complete ultrasound (US)-guided percutaneous nephrolithotomy (PNL) in morbidly obese patients was technically feasible and safe and the stone-free rate and complication rate were acceptable and comparable with those in non-obese patients.
Abstract: Objectives This study was performed to investigate the feasibility and safety of complete ultrasound (US)-guided percutaneous nephrolithotomy (PNL) in morbidly obese patients and to introduce the US skills used in a high-volume stone management center. Methods We retrospectively reviewed consecutive patients with a body mass index (BMI) of ≥ 40 kg/m2 who underwent X-ray-free PNL for treatment of upper urinary tract stones from October 2013 to March 2020. The patients’ demographic information and intraoperative and postoperative parameters were collected and analyzed. Surgical complications were recorded and classified according to the modified Clavien classification system. Results In total, 52 patients were included. Their mean BMI was 45.5 kg/m2 (range, 40.3–61.6 kg/m2), and their mean age was 46 years (range, 28–58 years). The mean stone burden was 2.8 cm (range, 2.1–8.8 cm). Thirty-nine patients underwent surgery in the prone position, and the remaining 13 underwent surgery in the lateral position. All procedures were completed successfully with no major intraoperative complications. The mean operative duration was 68 min (range, 38–97 min). The mean time required for establishment of each access was 6.6 min (range, 3.5–14.7 min). No blood transfusion or embolization was needed for any patient. The initial stone-free rate was 80.8% (42/52 patients). Five patients required second-look PNL. Two patients underwent flexible ureteroscopic lithotripsy. The final stone-free rate was 90.4% (47/52 patients). Conclusions Complete US-guided PNL was technically feasible and safe in morbidly obese patients. The stone-free rate and complication rate were acceptable and comparable with those in non-obese patients.

Summary (1 min read)

Jump to: [Introduction][Materials And Methods][Results][Discussion] and [Conclusion]

Introduction

  • A high BMI is associated with multiple chronic diseases and is a dependent risk factor for urolithiasis.
  • Stone formation is closely linked to metabolic syndrome.
  • US is sometimes used to reduce radiation exposure in some Western countries, while X-ray-free techniques for PNL have been widespread in China for > 10 years.
  • The prevalence of obesity has been increasing worldwide, including in China, during the past several years.
  • This study was performed to investigate the feasibility and safety of total US-guided PNL in morbidly obese patients and highlight the di culties and problems that can be encountered and effectively resolved.

Materials And Methods

  • The medical records of 59 obese patients who underwent PNL from October 2013 to March 2020 were retrospectively reviewed.
  • A retrograde 5-Fr ureteric catheter was rst inserted into the renal pelvis with the patient in the lithotomy position, and a 16-Fr Foley bladder catheter was placed.
  • The transducer was xed and the needle was inserted in front of it when the calyx was con rmed.
  • Successful US-guided access was de ned as arrival at the target calyx with the ability to perform fragmenting procedures.
  • The number of access tracts, time required to establish each access, operative duration, postoperative hospital stay, related complications, stone composition analysis, and auxiliary therapy were recorded.

Results

  • Thirty-two patients were diagnosed with urinary tract infection by urinalysis, and Escherichia coli and Proteus mirabilis were the most common bacteria grown from urine culture.
  • Sixty-three tracts were established during the rst-stage surgery (single in 42 patients, double in 9 patients, and triple in 1 patient), and the mean time required for each access establishment was 6.6 min (range, 3.5-14.7 min).

Discussion

  • Obesity has been linked to many metabolic disorders, such as type 2 diabetes mellitus, hypertension, and urolithiasis.
  • 7 found that exible ureteroscopy for small stones could achieve a comparable stone-free rate between obese and non-obese patients.
  • Such as in pediatric patients, patients with a solitary kidney, and even patients with spinal deformity, its use in morbidly obese patients has rarely been reported.
  • Anesthetic challenges can arise in the prone position.
  • The third 30-degree angle corresponds to the second one; after the needle enters the skin vertically, the needle handle is moved from the vertical to the head side (puncture from the front of the transducer) or tail side (puncture from the back of the transducer), and the tilt angle is about 30 degrees.

Conclusion

  • Total US-guided PNL was feasible and safe in this population of morbidly obese patients.
  • The authors recommend that this procedure be carried out after completion of the learning curve because of the risk of technical problems.

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Page 1/15
Percutaneous Nephrolithotomy With X-Ray Free
Technique in Morbidlyobese Patients: Outcomes
and Skills From A Large High-Volume Stone
Management Center
Bo Xiao
Beijing Tsinghua Chang Gung Hospital
Xue Zeng
Beijing Tsinghua Chang Gung Hospital
Chaoyue Ji
Beijing Tsinghua Chang Gung Hospital
Gang Zhang
Beijing Tsinghua Chang Gung Hospital
Weiguo Hu
Beijing Tsinghua Chang Gung Hospital
Song Jin
Beijing Tsinghua Chang Gung Hospital
Boxing Su
Beijing Tsinghua Chang Gung Hospital
Yuzhe Tang
Beijing Tsinghua Chang Gung Hospital
Jianxing Li ( lijianxing2015@163.com )
Beijing Tsinghua Chang Gung Hospital
Research Article
Keywords: ultrasound guidance, percutaneous nephrolithotomy, morbidly obese, stone, safety
Posted Date: September 7th, 2021
DOI: https://doi.org/10.21203/rs.3.rs-753573/v1
License: This work is licensed under a Creative Commons Attribution 4.0 International License. 
Read Full License

Page 2/15
Abstract
Objectives
This study was performed to investigate the feasibility and safety of complete ultrasound (US)-guided
percutaneous nephrolithotomy (PNL) in morbidly obese patients and to introduce the US skills used in a
high-volume stone management center.
Methods
We retrospectively reviewed consecutive patients with a body mass index (BMI) of  40 kg/m
2
who
underwent X-ray-free PNL for treatment of upper urinary tract stones from October 2013 to March 2020.
The patients’ demographic information and intraoperative and postoperative parameters were collected
and analyzed. Surgical complications were recorded and classied according to the modied Clavien
classication system.
Results
In total, 52 patients were included. Their mean BMI was 45.5 kg/m
2
(range, 40.3–61.6 kg/m
2
), and their
mean age was 46 years (range, 28–58 years). The mean stone burden was 2.8 cm (range, 2.1–8.8 cm).
Thirty-nine patients underwent surgery in the prone position, and the remaining 13 underwent surgery in
the lateral position. All procedures were completed successfully with no major intraoperative
complications. The mean operative duration was 68 min (range, 38–97 min). The mean time required for
establishment of each access was 6.6 min (range, 3.5–14.7 min). No blood transfusion or embolization
was needed for any patient. The initial stone-free rate was 80.8% (42/52 patients). Five patients required
second-look PNL. Two patients underwent exible ureteroscopic lithotripsy. The nal stone-free rate was
90.4% (47/52 patients).
Conclusions
Complete US-guided PNL was technically feasible and safe in morbidly obese patients. The stone-free
rate and complication rate were acceptable and comparable with those in non-obese patients.
Introduction
Morbid obesity is dened as a body mass index (BMI) of  40 kg/m
2
according to the World Health
Organization. A high BMI is associated with multiple chronic diseases and is a dependent risk factor for
urolithiasis.
1
Although the exact association between obesity and nephrolithiasis is unclear, stone
formation is closely linked to metabolic syndrome.
2
Alterations in urinary citrate, electrolytes, oxalate, uric

Page 3/15
acid, and urinary pH may also contribute to stone formation. Some studies have shown that a high BMI
might be correlated with increased stone size, which indicates that stones in these patients might be
much more dicult to manage than in patients of normal weight.
3
Percutaneous nephrolithotomy (PNL) is the rst-line treatment for complex and staghorn stones.
Performing PNL in morbidly obese patients is challenging because of the potent risks and higher
morbidity rate.
4
Previous studies have conrmed the safety and feasibility of PNL under uoroscopy.
However, the eciency of total ultrasound (US) guidance in morbidly obese patients has not been proven;
the traditional view is that obesity is a risk factor for more dicult US-guided access to the renal
collecting system. US is sometimes used to reduce radiation exposure in some Western countries, while
X-ray-free techniques for PNL have been widespread in China for > 10 years. Most urologists in China use
US as the only method for PNL guidance. Although China has a relatively low proportion of morbidly
obese patients, the prevalence of obesity has been increasing worldwide, including in China, during the
past several years. This study was performed to investigate the feasibility and safety of total US-guided
PNL in morbidly obese patients and highlight the diculties and problems that can be encountered and
effectively resolved.
Materials And Methods
The medical records of 59 obese patients who underwent PNL from October 2013 to March 2020 were
retrospectively reviewed. Seven patients were excluded because of incomplete data. All procedures were
performed by one experienced urologist. The preoperative demographic data reviewed were age, sex, BMI,
stone size (maximum length on computed tomography [CT]), and operative position. The stone size was
determined by a preoperative CT scan.
All procedures were performed under general anesthesia. The prone position was preferred, but the lateral
position was selected for patients who could not tolerate the prone position[Fig.1].. A retrograde 5-Fr
ureteric catheter was rst inserted into the renal pelvis with the patient in the lithotomy position, and a 16-
Fr Foley bladder catheter was placed. The distal end of the ureteric catheter was connected to a saline
bag for gravity infusion to create articial hydronephrosis. The patient was then placed in a suitable
position with appropriate padding of pressure points. A 3.5-MHz convex abdominal US transducer
(Esaote, Genoa, Italy) was used to detect the kidneys and surrounding organs. Percutaneous access was
established using a 15-cm-long 18-gauge needle (Urotech, Bad Aibling, Germany). The ideal target calyx
was determined totally by US. The transducer was xed and the needle was inserted in front of it when
the calyx was conrmed. The needle tract could be visualized on the screen. The tract was dilated with
either Alken coaxial telescopic dilators (Richard Wolf GmbH, Knittlingen, Germany) or a high-pressure
balloon dilator (X Force® N30 balloon dilator; Bard Urological, Covington, GA, USA) to standard 24 Fr.
Nephroscopy was performed using an 18-Fr rigid nephroscope. Successful US-guided access was dened
as arrival at the target calyx with the ability to perform fragmenting procedures. Stones were
disintegrated and suctioned with a combined ultrasonic/pneumatic lithotripter (Swiss LithoClast; EMS
Electro Medical Systems, Nyon, Switzerland). Additional accesses were established if needed. US was

Page 4/15
then used to recheck the collecting system and conrm whether residual stones were left. A 6-Fr
indwelling ureteral stent was routinely placed in an antegrade manner and kept in place for 2 to 4 weeks
after surgery. A 14-Fr nephrostomy tube was routinely placed at the end of surgery and removed 3 to 4
days later if no complications occurred.
The stone-free status was evaluated 2 to 3 days after surgery with a kidney, ureter, and bladder (KUB)
radiograph or non-enhanced CT scan[Supplementary Fig.1]. The number of access tracts, time required
to establish each access, operative duration, postoperative hospital stay, related complications, stone
composition analysis, and auxiliary therapy were recorded. Estimated blood loss was evaluated 24 hours
postoperatively. The modied Clavien classication system was used to grade the perioperative
complications. A stone-free status was dened as the presence of clinically insignicant (4-mm)
residual stone fragments on the postoperative KUB radiograph or CT scan.
Results
In total, 52 patients (32 men, 20 women) were included in our study. Their mean age was 46 years (range,
28–58 years), and their mean BMI was 45.5 ± 5.2 kg/m
2
(range, 40.3–61.6 kg/m
2
). The mean stone
burden was 2.8 cm (range, 2.1–8.8 cm). Thirty-two patients were diagnosed with urinary tract infection by
urinalysis, and
Escherichia coli
and
Proteus mirabilis
were the most common bacteria grown from urine
culture. All patients with urinary tract infections underwent antibiotic therapy before surgery. Thirty-nine
patients underwent surgery in the prone position and 13 underwent surgery in the lateral position
according to their anesthetic requirement or preoperative CT image. Percutaneous access was
successfully established in all patients, and uoroscopy was not needed to assist the guidance. The
mean operative duration was 68 min (range, 38–97 min). Sixty-three tracts were established during the
rst-stage surgery (single in 42 patients, double in 9 patients, and triple in 1 patient), and the mean time
required for each access establishment was 6.6 min (range, 3.5–14.7 min). Six tracts were lost during the
primary procedure, requiring re-puncture; all occurred in the course of the second or third tract
establishment. Twenty-ve patients (48%) had an upper pole tract to the preferred calyx. No severe
complications occurred during the procedures. The mean hemoglobin drop 24 hours postoperatively was
1.6 g/dl (range, 0.5–3.7 g/dl). The mean postoperative hospital stay was 6.7 days (range, 4–10 days).
The complication rate using the modied Clavien classication system was 25%, including grade I
complications in 10 patients (fever in 6, pain in 4) and grade II complications in 3 patients (transient
bleeding in 2, subcapsular hematoma in 1). No septic shock or embolization occurred. The initial stone-
free rate was 80.8% (42/52 patients) after the rst-stage surgery (40 with CT scan, 12 with KUB
radiograph). Five patients required second-look PNL (four additional tracts): two patients underwent
exible ureteroscopic lithotripsy to remove the residual stones after a 7-day interval, and three patients
with residual stone fragments were observed with medical expulsive therapy. The nal stone-free rate
was 90.4% (47/52 patients) when the ureteral stent was removed (Table1).

Page 5/15
Table 1
Preoperative, intraoperative and postoperative variables in patients
Gender, n (%)
Male
Female
32 (61.5)
20 (38.5)
BMI (kg/m
2
), mean ± SD
45.5 ± 5.2
Age (y), mean (range) 46 (28–58)
Stone size (cm), mean ± SD 2.8 ± 1.2
UTI, n (%) 32 (61.5)
Surgical position, n (%)
Lateral
Prone
13 (25)
39 (75)
Operative time (min), mean (range) 68 (38–97)
Access number, n (%)
Single
Double
Triple
42 (80.8)
9 (17.3)
1 (1.9)
Each access establishment time (min), mean (range) 6.6 (3.5–14.7)
Primary access, n (%)
Upper pole tract
Middle calyx tract
Lower pole tract
25 (48)
15 (29)
12 (23)
Hemoglobin loss (g/dl), mean (range) 1.6 (0.5–3.7)
Postoperative hospital stay (d), mean (range) 6.7 (4–10)
Perioperative complications, n (%)
Grade I
Grade II
Grade III
10 (28.8)
3 (5.8)
0

References
More filters
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26 Jan 2005-JAMA
TL;DR: Obesity and weight gain increase the risk of kidney stone formation, and the magnitude of the increased risk may be greater in women than in men.
Abstract: ContextLarger body size may result in increased urinary excretion of calcium, oxalate, and uric acid, thereby increasing the risk for calcium-containing kidney stones. It is unclear if obesity increases the risk of stone formation, and it is not known if weight gain influences risk.ObjectiveTo determine if weight, weight gain, body mass index (BMI), and waist circumference are associated with kidney stone formation.Design, Setting, and ParticipantsA prospective study of 3 large cohorts: the Health Professionals Follow-up Study (N = 45 988 men; age range at baseline, 40-75 years), the Nurses’ Health Study I (N = 93 758 older women; age range at baseline, 34-59 years), and the Nurses’ Health Study II (N = 101 877 younger women; age range at baseline, 27-44 years).Main Outcome MeasuresIncidence of symptomatic kidney stones.ResultsWe documented 4827 incident kidney stones over a combined 46 years of follow-up. After adjusting for age, dietary factors, fluid intake, and thiazide use, the relative risk (RR) for stone formation in men weighing more than 220 lb (100.0 kg) vs men less than 150 lb (68.2 kg) was 1.44 (95% confidence interval [CI], 1.11-1.86; P = .002 for trend). In older and younger women, RRs for these weight categories were 1.89 (95% CI, 1.52-2.36; P<.001 for trend) and 1.92 (95% CI, 1.59-2.31; P<.001 for trend), respectively. The RR in men who gained more than 35 lb (15.9 kg) since age 21 years vs men whose weight did not change was 1.39 (95% CI, 1.14-1.70; P = .001 for trend). Corresponding RRs for the same categories of weight gain since age 18 years in older and younger women were 1.70 (95% CI, 1.40-2.05; P<.001 for trend) and 1.82 (95% CI, 1.50-2.21; P<.001 for trend). Body mass index was associated with the risk of kidney stone formation: the RR for men with a BMI of 30 or greater vs those with a BMI of 21 to 22.9 was 1.33 (95% CI, 1.08-1.63; P<.001 for trend). Corresponding RRs for the same categories of BMI in older and younger women were 1.90 (95% CI, 1.61-2.25; P<.001 for trend) and 2.09 (95% CI, 1.77-2.48; P<.001 for trend). Waist circumference was also positively associated with risk in men (P = .002 for trend) and in older and younger women (P<.001 for trend for both).ConclusionsObesity and weight gain increase the risk of kidney stone formation. The magnitude of the increased risk may be greater in women than in men.

977 citations


"Percutaneous Nephrolithotomy With X..." refers background in this paper

  • ...A high BMI is associated with multiple chronic diseases and is a dependent risk factor for urolithiasis [1]....

    [...]

Journal ArticleDOI
TL;DR: It is proposed that UA nephrolithiasis may be added to the conditions that potentially are associated with insulin resistance, and it is suggested that patients with UA stones, especially if overweight, should be screened for the presence of type 2 diabetes or components of the metabolic syndrome.
Abstract: An increased prevalence of nephrolithiasis has been reported in patients with diabetes. Because insulin resistance, characteristic of the metabolic syndrome and type 2 diabetes, results in lower urine pH through impaired kidney ammoniagenesis and because a low urine pH is the main factor of uric acid (UA) stone formation, it was hypothesized that type 2 diabetes should favor the formation of UA stones. Therefore, the distribution of the main stone components was analyzed in a series of 2464 calculi from 272 (11%) patients with type 2 diabetes and 2192 without type 2 diabetes. The proportion of UA stones was 35.7% in patients with type 2 diabetes and 11.3% in patients without type 2 diabetes (P < 0.0001). Reciprocally, the proportion of patients with type 2 diabetes was significantly higher among UA than among calcium stone formers (27.8 versus 6.9%; P < 0.0001). Stepwise regression analysis identified type 2 diabetes as the strongest factor that was independently associated with the risk for UA stones (odds ratio 6.9; 95% confidence interval 5.5 to 8.8). The proper influence of type 2 diabetes was the most apparent in women and in patients in the lowest age and body mass index classes. In conclusion, in view of the strong association between type 2 diabetes and UA stone formation, it is proposed that UA nephrolithiasis may be added to the conditions that potentially are associated with insulin resistance. Accordingly, it is suggested that patients with UA stones, especially if overweight, should be screened for the presence of type 2 diabetes or components of the metabolic syndrome.

260 citations


"Percutaneous Nephrolithotomy With X..." refers background in this paper

  • ...Although the exact association between obesity and nephrolithiasis is unclear, stone formation is closely linked to metabolic syndrome [2]....

    [...]

Journal ArticleDOI
01 Nov 2005-Urology
TL;DR: The skin-to-stone distance (SSD), body mass index (BMI), and Hounsfield unit (HU) density can be used as independent predictors of stone-free (SF) status after shock wave lithotripsy (SWL) of lower pole kidney stones to predict the outcome after SWL.

248 citations


"Percutaneous Nephrolithotomy With X..." refers background in this paper

  • ...The efficiency of shock wave lithotripsy may be influenced by the increased skin-to-stone distance [6]....

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Journal ArticleDOI
TL;DR: PNL in obese and morbidly obese patients yields a stone-free rate that is comparable to that achieved in nonobese patients, and the complication rate and length of hospital stay are also similar.

112 citations


Additional excerpts

  • ...A previous study indicated that the lower pole calyx is the preferred calyx under fluoroscopy [9]; however, we usually choose the upper calyx because the upper pole of the kidney is closer to the back and the lower pole is much closer to the ventral side in the sagittal view....

    [...]

  • ...[9] reported major complications in 6....

    [...]

Journal ArticleDOI
TL;DR: Percutaneous nephrolithotomy may be done safely in obese patients, although with a longer operative time, an inferior stone-free rate and a higher re-intervention rate.

99 citations


"Percutaneous Nephrolithotomy With X..." refers background in this paper

  • ...Performing PNL in morbidly obese patients is challenging because of the potent risks and higher morbidity rate [4]....

    [...]

Frequently Asked Questions (1)
Q1. What contributions have the authors mentioned in the paper "Percutaneous nephrolithotomy with x-ray free technique in morbidlyobese patients: outcomes and skills from a large high-volume stone management center" ?

Bo Xiao Beijing Tsinghua Chang Gung Hospital Xue Zeng and Xue Xue this paper, Xue Xue and Xue Xiong.