Omar M. Aboumarzouk, The Royal Bournemouth and Christchurch Hospitals NHS Trust, Urology Department, Castle Lane East, Bournemouth, BH7 7DW, UK. e-mail: firstname.lastname@example.org
Study Type – Prognosis (systematic review)
Level of Evidence 1a
What's known on the subject? and What does the study add?
Case series on ureteroscopy for obese patients have been published in the literature, but as yet no decisive conclusion has been published because of the small patient numbers included the study cohorts.
This review provides an overview of the literature discussing ureteroscopy for obese patients. In addition, it provides a meta-analysis of the case series and published literature on the topic, which focuses on the safety and efficacy of ureteroscopy for obese patients.
• To look at the role and safety of ureteroscopy for stone management in obese patients.
• We searched MEDLINE, PubMed and the Cochrane Library from January 1990 to June 2011 for results of ureteroscopy and stone treatment in obese patients.
• Inclusion criteria were all English language articles reporting on ureteroscopy in patients with morbid obesity.
• Data on the outcomes and complications was extracted and a meta-analysis of the results conducted.
• Seven studies with 131 patients (136 renal units) were included.
• All the studies included obese patients (mean BMI 42.2) treated with flexible URS for urinary calculi. The mode of fragmentation was pulse dye laser, holmium laser, and combined modality including electrohydraulic lithotripsy and basket retrieval in others.
• The average stone size was (1.37). The stone free rate was 87.5% after completion of treatment with a ranged follow up between 3 months and 3.5 years. The mean operative time was 97.1 minutes (30-275).
• There was an overall 11.4% complication rate, however, none of the patients needed further monitoring and were treated conservatively.
• A sub-group analysis of the stones depending on size found the URS has a higher stone free rate in stones <2 cm in size (P= 0.0003). Furthermore, URS has a higher stone free rate when treating ureteric stones compared to renal stones (P= 0.04).
• Retrograde stone treatment using ureteroscopy is a safe and efficient modality for treating obese patients with urinary tract calculi with an increased efficiency with smaller stones less than 2 cm in size.
Preferred Reporting Items for Systematic Reviews and Meta-Analyses
Nephrolithiasis is a common condition with a lifetime risk in the general population of ≈13% in men and 7% in women. Its peak incidence is in the third to fourth decades of life [1,2]. With obesity now considered a worldwide epidemic, affecting >300 million people, more obese patients are presenting with urinary calculi [3,4]. Numerous studies have shown that obesity increases the risk of nephrolithiasis; specifically, the risk of uric acid and calcium oxalate stones increases in obese people because the defect in ammonia excretion leads to low pH [3–5].
Obesity poses a management dilemma with regard to diagnostic imaging, anaesthetic risk and surgical approach . Normally, stone disease is diagnosed by CT scans and treated with either ESWL, ureteroscopy (URS), or percutaneous nephrolithotripsy (PCNL) but, in the case of an obese patient, excessive weight or girth (abdominal circumference) might prevent their entry through the CT scanner . Furthermore, intubation and high pressure ventilating might be required during surgical procedures which might also be complicated by carbon dioxide retention or difficulty with weaning the patient off of the ventilator after surgery . Obesity also increases the risk of cardiovascular, respiratory, thromboembolic and wound complications after surgery  and, because of the increased distance from the skin to the stone, ESWL might not be successful . With regard to PCNL, the positioning of the patient in the prone position increases the respiratory compromise and impedes venous return . This can leave URS as the only potentially viable treatment method, but treating larger stones requires longer and possibly repeat procedures  and this, in itself, puts the patient at risk of anaesthesia.
To address these issues, we aimed to conduct a systematic review to assess the safety and efficacy of ureteroscopic lithotripsy in obese patients.
SEARCH STRATEGY AND STUDY SELECTION
The systematic review was performed according to the Cochrane reviews guidelines and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines . The search strategy was aimed at finding relevant studies from MEDLINE (1966 to March 2011), EMBASE (1980 to March 2011), the Cochrane Central Register of Controlled Trials: CENTRAL (in The Cochrane Library– Issue 1, 2011), CINAHL (1872 to March 2011), Clinicaltrials.gov, Google Scholar and individual urological journals. The search terms used were ‘ureteroscopy’, ‘obese’, ‘obesity’, ‘endoscopy’, ‘urolithiasis’ and ‘calculi’. Mesh phrases included: (‘Ureteroscopy’[Mesh]) AND ‘Obesity’[Mesh]; ((‘Obesity’[Mesh]) AND ‘Ureteroscopy’[Mesh]) AND ‘Urolithiasis’[Mesh]); and ((‘Obesity’[Mesh])) AND ‘Urolithiasis’[Mesh]). Papers in languages other than English were excluded and the references of searched papers were evaluated for potential inclusion.
Two reviewers (O.A. and B.S.) identified all studies that appeared to fit the inclusion criteria for full review. Each reviewer independently selected studies for inclusion in the review. Disagreement between the two extracting authors was resolved by consensus. If consensus between the two reviewers could not be reached, the third author (M.M.) was deferred to for arbitration.
DATA EXTRACTION AND ANALYSIS
Studies relevant to the ureteroscopic management of obese patients were included. The following variables were extracted from each study: population demographics, period of the study; country of origin of the study; body mass index (BMI); stone size and location; stone-free rates; follow-up; and complications. For complications the Clavien classification for surgical complications was used . The data from each study were grouped into a meta-analysis, on an intention-to-treat basis, to allow a numerical representation of the results.
A sub-group analysis was conducted to determine whether or not the safety and efficacy of URS was affected by stone size. A Mantel–Haenszel chi-squared test was used for calculating the absolute risk difference with 95% CI, to be able to identify the absolute change in risk that was attributed to the intervention .
A quality assessment of harms, using the McHarm scale, was conducted for each included study . We used Review Manager (RevMan 5.0.23) to plot the quality assessment of harms tables.
The literature search yielded 497 studies, of which 486 were excluded owing to non-relevance, based on titles and abstracts (Fig. 1). Eleven studies were then retrieved for further assessment, seven of which were included in the review [11–17]. All the included studies were published between 1998 and 2010. All seven studies were retrospective and all reported on the variables indicated in the ‘data extraction section’ and are shown in Table 1[11–17].
Table 1. Characteristics of the studies included in the review
Patients (renal units)
Sex M : F
Mean age, years
Mean (range) BMI, kg/m2
Mean stone size, cm
Mean stone-free rate, %
Mean (range) operating time, min
Mean weight given rather than BMI. NM, no mention; ND, No differentiation.
Four articles were excluded after reading the full manuscript [3,4,18,19] because none of them looked at URS for stones in obese patients.
CHARACTERISTICS AND META-ANALYSIS OF THE INCLUDED STUDIES
Six of the studies were from the USA, and the remaining studies were from the UK (Table 1). A total of 131 obese patients in 136 renal units were included in the present review and a total of 68 renal stones and 68 ureteric stones were treated. All the patients were treated with flexible URS for urinary stones. The mean (range) age of the present review population was 53.3 (19–67) years. The mean (range) BMI was 42.2 (30.13–65.2) kg/m2. The mean (range) stone size was 1.37 (0.4–7.2) cm.
There was a discrepancy between the studies with regard to investigative method; two of the studies used CT scans [11,17], one used only plain x-rays  and two used either plain x-rays, i.v. urogram, ultrasonography or CT [14,15]. One study used x-rays, CT and ultrasonography .
The majority of the studies used URS with holmium laser to treat the stones [11–15,17], while Nguyen and Belis  used pulsed dye laser. Dash et al.  also used electrohydraulic lithotripsy if the stone was too large for laser treatment. Andreoni et al.  used all three intracorporeal lithotripters: holmium and pulsed dye laser and electrohydraulic lithotripsy.
Only two of the studies mentioned if their patients had stents inserted before surgery. The number of patients who had stent insertions before surgery was not clear in one of these studies , while Dash et al.  mention that 9/18 patients had this procedure. A further two studies reported they routinely stented all their patients after surgery [11,16].
None of the studies reported whether or not preoperative urine analysis was done and only one study reported giving antibiotics prophylactically on induction .
Three of the studies routinely used ureteric access sheaths in their patients [11,15,17]. Dash et al.  state these were not routinely used, but were used in selected patients where access was difficult .
With regard to stone-free rates, 87.5% (119/136) of the patients were stone-free. Three studies defined the stone-free rate as having no residual stones [11,16,17], while a further three studies defined it as having stones <2 mm in size [12,13,15]. Dash et al.  did not define what they meant by stone-free.
The mean (range) operating time was 97.1 (30–275) min and the overall complication rate in the included studies was 11.4%. Most of the complications were Grade II, requiring antibiotics or strong analgesics, with only one Grade III complication, a ureteric perforation (Table 1). There were no Grade IV or V complications.
A sub-group analysis of the studies reporting on stones with a mean size <2 cm was conducted [11–16]. Six studies of 122 patients in 127 renal units were analysed. The mean BMI of these patients was 41.5 kg/m2. The mean (range) stone size was 1.37 (0.4–1.8) cm with a mean stone-free rate of 91.3% (P < 0.001; RD (Risk Difference) [M-H (Mantel-Haenszel), 95% CI]: 0.58 [0.27–0.89]) and an overall complication rate of 9.5%.
A sub-group analysis based on stone location was also conducted, but only five of the studies had data available on stone-free rates according to location [11–14,17]. There were 48 renal stones and 24 ureteric stones, with stone-free rates of 75% and 91.7%, respectively (P= 0.04; RD [M-H, 95% CI]: −0.17 [−0.33–−0.0016]). A further subanalysis was done on the same group, in which stones >2 cm were excluded. This raised the renal stone-free rate to 84.6%.
Only two studies mentioned the number of URS procedures conducted per stone, The study by Bultitude et al.  had a mean of 2.6 procedures while that of Wheat et al.  had a mean of 2.3. Furthermore, only two studies mentioned if additional procedures were done: in the study by Bultitude et al.  two patients required open pyelolithotomy owing to stag horn calculi, while no patients required any further procedures in the study by Best et al. .
METHODOLOGICAL QUALITY ASSESSMENT OF THE INCLUDED STUDIES
The quality of the reported studies was modest to high in standard, although all of the studies were retrospective. All the included studies might be subject to risk of bias as they all recruited patients from databases, which could lead to selection as well as reporting bias; however, the data reported seemed to be complete. All the studies had a clear definition of their objectives with a clear methodological approach to how the patients were recruited and to the conduction of the study. Furthermore, all the studies discussed their findings and compared them with the literature for analysis. The quality assessment of harms indicates that the studies have a low risk of bias concerning reporting the harms that could potentially be caused by the procedure (Figs 2 and 3).
The present review includes all the topics and completes the checklist required by the PRISMA guidelines.
Obesity has always been a challenge to surgeons of all specialties. It is widely recognised that with obesity comes a higher risk of stone formation owing to the increased secretion of calcium, oxalate and uric acid in obese patients . With the increasing prevalence of obesity, more and more urologists will be faced with the dilemma of how to treat these patients. Interestingly, a search of the literature yielded only a few endo-urological papers that discuss the risks when it comes to stone treatment and these were retrospective small patient studies [11–17].
Traditionally, the first-line treatment for small stones was ESWL [12,14], but with obese patients this poses a few issues, the first being the weight restrictions of the operating table [13,17]. The second, a logistic problem, is the shockwave focal length. The skin to stone distance increases because of the girth of obese patients, which leads to difficulties with focusing the shockwave to the stone [3,13,17]. Ultimately, with this reduction in focusing power, stone fragmentation rates are reduced, leading to increasing failure rates or repeat procedures .
A thorough search of the literature found no study that compared the various treatment methods in obese patients (ESWL, URS and PCNL); however, previous studies have shown that stone-free rates after ESWL were significantly better in non-obese patients . Furthermore, de la Rosette et al. , in their review, looked at the outcomes of prone vs supine PCNL and found that, for obese patients, the stone-free rate was slightly higher and operating time was significantly shorter in the prone position. This was in contrast to the non-obese patients where the mean operating time was significantly shorter in the supine position, with similar success in both positions.
Carson et al.  were the first to publish on the endoscopic treatment of obese patients and reported that they successfully treated 44 obese patients by PCNL with few complications. Nonetheless, risks of open surgery in obese patients do exist [11,13,17]. Putting the risk of anaesthesia and surgery itself aside, further issues with the surgical approach include the positioning of the patients and the instruments used [14,15,17]. Numerous studies published their techniques and modified instruments in dealing with these issues, but the results were variable [13–15]. Despite these studies, there are still conflicting data on how best to manage stones in obese patients ; in fact, a few studies reported an increased complication rate, transfusion rate, and secondary procedure rate in obese patients after PCNL .
Advances in endoscopic instruments have led to the development of smaller-diameter scopes with increased flexibility, coupled with a greater angle of deflection of the tip of the scope and improved optics, which in turn has led to the ability to visualize and treat stones in the whole upper urinary system [12,23–25]. Advances in laser technology led to the development of the holmium laser, which provides effective and efficient intracorporeal lithotripsy for even hard stones such as cysteine and calcium oxalate monohydrate stones, and can also be used to ablate upper urinary tract tumours [25,26]. Furthermore, holmium lasers offer haemostatic capabilities during the procedure, which give an additive benefit to patients with bleeding diathesis . All these have led to the increased use of URS in the management of urinary stones. Furthermore, as the scope is passed through the ureter, the patients' size and girth do not affect the procedure itself .
The present review found that the use of URS on obese patients is not only safe but also efficient, with an overall stone-free rate of 87.5%, a minor complication rate (Grade I, II, or III) of 11.4% and a major complication rate (Grade IV) or mortality (Grade V) rate of 0%. Furthermore, the stone-free rate was significantly higher for ureteric stones compared with renal stones (P= 0.04).
When taking into consideration stone size, we found that URS has a significantly higher stone-free rate (91.3%, P < 0.001) as well as a lower complication rate (9.5%) if we only calculate the stones <2 cm in size.
Limitations of the present review include the fact that all the studies included small cohorts and were retrospective; however, there were no missing data, which allowed for an accurate meta-analysis of the results. Another limitation was that we were unable to analyse the stone-free rate according to the stones' location in the ureter, however, we were able to analyse the rate of ureteric stones in general. Furthermore, we were unable to sub-categorize the findings according the types of obesity, i.e. obese, morbidly obese, or super obese.
Future research efforts should be concentrated on higher quality, more rigorous evaluation of URS in obese patients. Studies should be multi-institutional and protocol-driven, and preferably peer-reviewed before the start. Studies should be prospectively evaluated and include a control group of patients who have a normal BMI for comparison, in addition to comparing the different positioning of the patient during the procedure, i.e. supine or prone. These studies should specifically look at how the stones were investigated, patients should, if possible, be randomized to ESWL, PCNL, or URS depending on the size and site of the stone, and the studies should include the operating time, stone-free rate, complication rate and length of follow-up. Furthermore, health economic outcome measures should be analysed. More precise definitions should be used, such as the definition of stone-free, and the complications should be categorized into classifications using a known complication classification system.
In conclusion, URS is a safe and efficient treatment method for obese patients with urinary tract stones, and has an increased efficiency with smaller stones, i.e. those <2 cm. URS also has a high ureteric stone-free rate and a renal stone-free rate similar to other treatment methods and the relatively short duration of the procedure reduces the anaesthetic risks.