JOURNAL OF ENDOUROLOGY Volume 28, Number 12, December 2014 ª Mary Ann Liebert, Inc. Pp. 1414–1417 DOI: 10.1089/end.2014.0215

Predicting an Effective Ureteral Access Sheath Insertion: A Bicenter Prospective Study Yakov Mogilevkin, MD,1 Mario Sofer, MD,2 David Margel, MD,2 Alexander Greenstein, MD,2 and David Lifshitz, MD1


Introduction: The use of a ureteral access sheath (UAS) may provide significant advantages, particularly, in the treatment of a large renal stone burden. However, in some patients, the passage of a UAS up the ureter is impossible. We prospectively evaluated the ability to insert a 14F UAS and analyzed the possible predictors for an effective insertion. Patients and Methods: In a bicenter prospective study, 248 consecutive patients undergoing ureteroscopy and retrograde intrarenal surgery (RIRS) were recruited. In each case, we attempted initially to pass a 14F FlexorCook UAS. If passage was difficult, gradual dilation using semirigid ureteral dilators (Cook Medical) was performed. Patients were categorized into three groups: effective passage, with and without dilation, and failure to pass the UAS. Age, gender, body–mass index (BMI), an indwelling Double-J stent, and a history of previous ureteroscopy or Double-J stent were all analyzed, as possible predictors for an effective UAS insertion. Results: In 22% of the patients, we could not pass a 14F UAS. Of the preoperative parameters that were examined, we found three independent predictors for an effective 14F UAS insertion: age (odds ratio: 1.5 and 95% CI [1.3, 1.9]), previous same-side procedures (odds ratio: 9.7 and 95% CI [8.3, 14.5]), and an indwelling Double-J stent (odds ratio: 21.73 and 95% CI [20, 30]). The gender, BMI, and side of surgery did not predict the success rate. Conclusions: Insertion of a 14F UAS before RIRS may fail in approximately one-fifth of the patients. An indwelling Double-J stent, a history of previous ureteroscopy or Double-J stent, and older age are all significant predictors for an effective 14F UAS insertion. Introduction

lexible ureterorenoscopy, often referred1 to as retrograde intrarenal surgery (RIRS),1 is currently one of the first-line treatment options for renal calculi < 2 cm.2,3 A ureteral access sheath (UAS) is an important adjunct during RIRS. The use of a UAS facilitates reentry into the ureter and, consequently, may decrease operative time and costs and improve stone- free rates. Furthermore, the superior pressure-flow relationships associated with the application of the UAS improves visibility, while maintaining a relatively low pressure in the collecting system.4,5 Commercially available sheaths range in length from 20 to 55 cm and in outer diameter from 9.5F to 18F. While the smaller diameter UAS is more easily inserted, it is limited by the size of the stone fragments that can be removed and is associated with reduced outflow and, therefore, less efficient irrigation.6 The largest UAS would generally require a predilated ureter. Therefore, the midrange UAS with an external diameter of 14F is often chosen as the standard UAS7 and is widely utilized.8–13


1 2

The 14F UAS is larger than the median 3 mm diameter reported for a normal nonstented ureter.14 Therefore, it is not always possible to traverse the ureteral orifice with the UAS. There are no data as to the failure rate to insert a 14F UAS. Failure rates of ureteroscopy due to a difficult impassable ureter range from 8% to 10%.15 However, the failure rate to insert a standard UAS is probably higher because, in most cases of failed ureteroscopy, even the smaller diameter ureteroscopes could not be inserted into the ureter. Various strategies are used to allow the passage of a UAS when performing RIRS. Some authors advocate routine stent placement before RIRS to allow passive ureteral dilation.13 However, although efficient and safe, this strategy entails a two-stage procedure for all patients. Other authors utilize balloon dilatation in cases of difficult ureters.15 Actively dilating the ureter using a balloon dilator or the UAS as a dilator may cause significant ureteral injury. Traxer and Thomas reported the results of a prospective evaluation and classification of ureteral wall injuries from the insertion of a 14F UAS. In a group of 359 patients, low-grade injuries were observed in 311 of the patients (86.6%). Highgrade injuries were noted in 13.4% of the patients.7

Department of Urology, Rabin Medical Center, Petah Tikva, Israel. Department of Urology, Sackler Faculty of Medicine, Tel Aviv Sourasky Medical Center, Tel Aviv University, Tel Aviv, Israel.



When presenting the different treatment options to a patient with a renal stone, the chances of a failed ureteroscopy and the need for a two-stage procedure are an integral part of the discussion. However, limited data is available to help predict which of the patients may have a difficult ureter and in which cases success is most probable. We prospectively evaluated the ability to insert a 14F UAS and analyzed the possible predictors for an effective insertion. Patients and Methods

This prospective study was performed at two academic referral centers. Institutional review board approval was obtained at both study sites. Included in the study were consecutive patients, with ureteral and renal stones, planned for ureteroscopy or RIRS. Excluded were patients with distal ureteral stones or a known distal ureteral stricture. All patients received prophylactic parenteral antibiotics before the procedure. Procedures were performed under spinal or general anesthesia. Patients were placed in the lithotomy position. After cystoscopy and retrograde pyelography, a safety hydrophilic guidewire was positioned in the upper tract in all cases. We routinely calibrated the ureter with an 8F/10F coaxial ureteral dilator (Boston Scientific) in patients without stents.16 For the purpose of the study, we have replaced the 8F/10F coaxial ureteral dilator with the Flexor-Cook 12F/14F UAS. Dilation was performed over the hydrophilic wire to the level of the sacroiliac joint or higher, when RIRS was performed. If initial passage of the UAS was not easily achieved, sequential ureteral dilators were used (Cook Urological). Gradual sequential dilation from 8F to 14F was performed. Caution was taken not to cause trauma to the ureter. We avoided using extra measures, such as replacing the hydrophilic wire with a superstiff wire or using a balloon dilator, when a 14F dilator failed to pass into the ureter despite gradual dilation. Patients were stratified according to the results into three groups: effective passage of 14F UAS without a need for sequential dilation, effective passage of a 14F dilator following sequential dilation, and failure to pass the 14F dilator. Our primary outcome was the effective insertion of the 14F UAS. Patient’s data collected included age, gender, body– mass index (BMI), side treated, presence of an indwelling ureteral stent, and history of a previous ipsilateral ureteroscopy or stent. Statistical analyses

The impact of perioperative variables on the effective insertion of a 14F ureteral dilator was analyzed. Statistical tests were performed using SPSS version 10 and S-PLUS Professional version 1. Multiple univariable binary logistic regression analyses were used to identify potential predictors that were significantly associated with effective insertions. Predictors that obtained significance or showed a trend toward significance ( p < 0.05 or p < 0.1, respectively) were entered into a multivariable logistic regression model, to determine the independent predictors for an effective 14F ureteral dilator insertion. Results

The study group included 248 consecutive patients recruited at both centers. Patient’s data are presented in Table 1.


Table 1. Patient Demographics Patients, n Mean age years ( – SD) Gender, n (%) Men Women Mean BMI (kg/m2) ( – SD) Indications (%) Ureteral stone Renal stone Diagnostic ureteroscopy Mean stone size, mm ( – SD) Side left/right Previous procedures Indwelling Double-J stent (%) Previous same-side ureteroscopy (%) None (%)

248 50 (16) 170 (69) 78 (31) 26 (10) 124 (50) 95 (38) 29 (12) 11.1 (9) 129/119 104 (42) 39 (16) 105 (42)

BMI = body–mass index.

Ureteroscopy and RIRS were performed in 64% and 36% of the patients, respectively. In 42% of the patients a Double-J stent was inserted before surgery, mostly due to acute obstruction, intractable pain, or fever. Previous history (up to 10 years) of a same-side ureteroscopy or a Double-J stent was noted in 16% of the patients. In 144 (58%) patients, a 14F UAS could be passed easily. In 49 (20%) patients, sequential dilation was required. In 55 (22%) patients, the 14F dilator could not be passed despite sequential dilation (Table 2). Of the preoperative parameters that were examined, we have found three independent predictors for an effective 14F UAS insertion: age (odds ratio: 1.5 and 95% CI [1.3, 1.9]), previous same-side procedures (odds ratio: 9.7 and 95% CI [8.3, 14.5]), and an indwelling Double-J stent (odds ratio: 21.73 and 95% CI [20, 30]). Gender, BMI, and side of surgery did not predict the success rate (Table 3). Discussion

Improvements during the past decade in flexible ureteroscope design and digital optics have led to an increasing role of RIRS for renal stones, particularly, for renal calculi < 2 cm.17,18 The use of a UAS may provide significant advantages: simplified and rapid entry and re-entry into the ureter and collecting system, decreased renal pressure that prevents pyelovenous backflow, and enhanced visibility and improved clearance of small stone fragments.19 The UAS is particularly useful for patients with a large stone burden when there is a need to remove multiple fragments following holmium laser lithotripsy. The smaller diameter access sheaths (9.5F internal diameter) allow only small, < 3 mm,

Table 2. Results of Ureteral Calibration and Dilation Effective initial insertion of a 14F ureteral dilator, n (%) Effective insertion of a 14F ureteral dilator following sequential dilation, n (%) Failure to insert a 14F ureteral dilator, n (%)

144 (58) 49 (20) 55 (22)



Table 3. Predictors of Effective 14F Ureteral Access Sheath Insertion Predictor Age, years Previous ureteroscopy/stent (yes/no) Indwelling stent (yes/no)

Odds ratio (95% CI)


1.5 (1.3, 1.9) 9.7 (8.3, 14.5)

< 0.05 < 0.05

21.7 (20, 30)

< 0.05

stone fragments to be removed. Fragments of that size may be difficult to entrap in a basket. Furthermore, fragmentation of a stone to such small pieces can be tedious and may be associated with a risk of injuring the tissue. In addition, not all flexible ureteroscopes can pass through the smaller diameter UAS. Only the Flex-X2 (Storz) and the URV-P6 (Olympus) can pass through a Flexor-Cook of 9.5F/11.5F sheath. For the new digital ureteroscopes a minimum internal diameter of 12F is required, as has been recently reported by Al-Qahtani et al.20 Currently, the 12F inner diameter (14F outer diameter) UAS is often the first choice when performing RIRS in a nondilated ureter. Primary access up the ureter is not always possible with the modern small-diameter ureteroscopes, and more so, for the 14F UAS. When seeking consent for a treatment, the clinician must outline all potential adverse outcomes. The incidence of a failed access into the ureter, and the need for a second procedure following ureteral stent insertion should be considered and discussed with patients, when obtaining preoperative consent, especially for purely elective, nonurgent upper tract cases.21 However, there is paucity of data regarding the failure rate of UAS insertion and the predictors that may help to identify which patient is more likely to have an effective single-stage RIRS following its insertion. To the best of our knowledge, this is the first report specifically focusing on the success rate and the predictors for an effective insertion of a 14F UAS. Overall dilation to 14F was not possible in 22% of the patients. We have found that patients with an indwelling Double-J stent are 21 times more likely to accommodate a 14F UAS. Prestenting was universally associated with an easy and effective insertion of a 14F UAS. More interestingly, patients without an indwelling stent, but with a history of previous ipsilateral ureteroscopy or stent, are also almost 10 times more likely to have an effective 14F UAS insertion in comparison with patients undergoing their first endoscopic procedure. Finally, age was shown to be an independent predictor; older patients were more likely to accommodate the 14F UAS than younger patients. Our findings are in accordance with previous reports in the literature. Shields et al. in a study comparing the two types of a 12F/14F UAS, analyzed factors possibly affecting sheath deployment. UAS deployment failed in 10% of the patients, while balloon dilation was required in an additional 10% to allow the sheath insertion. Only the preexistence of a ureteral stent was significantly associated with an effective UAS deployment. BMI and gender did not correlate with effective insertions.9 Traxer and Thomas prospectively evaluated ureteral injuries secondary to UAS insertion. As the injury is likely related to the degree of force required to insert the UAS, one can deduct, from this study, which patients are expected to have a more accommodating ureter. The authors found that

the most significant predictor of severe ureteral injury was no placement of a Double-J stent before RIRS. Prestenting versus no prestenting decreased the risk of severe injury by sevenfold ( p < 0.0001).7 Likewise, Bin et al. recently reported on the predictive factors for intraoperative balloon dilation in semirigid ureteroscopy (6.5F–8F in diameter) and found that previous stent placement virtually eliminated the need for balloon dilatation. However, age was not shown to correlate with the need for balloon dilatation.22 In the current study, we show that not only the patients with an indwelling stent have a high likelihood for an effective UAS insertion but also patients who in the past underwent ureteroscopy or a Double-J stent insertion. Although not examined in this study, it would seem that the same would apply to patients with previous history of spontaneous stone expulsion. Therefore, we may conclude that once the ureter is dilated passively or actively it tends to stay permissive for future UAS insertion. This study is not without limitations. For the purpose of the study, we chose not to use more aggressive methods such as balloon dilators or stiffer wires, to avoid inadvertent ureteral injury. Therefore, the actual failure rate for a 14F UAS may be lower. An additional limitation is the subjective impression for an impassable ureter by the different surgeons in the two participating centers. Conclusions

Insertion of a 14F UAS before RIRS may fail in up to onefifth of the patients. An indwelling Double-J stent, a history of previous ureteroscopy or Double-J stent, and older age are all significant predictors for an effective 14F UAS insertion. Disclosure Statement

No competing financial interests exist. References

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Address correspondence to: David Lifshitz, MD Department of Urology Rabin Medical Center Petah Tikva 65552 Israel E-mail: [email protected]

Abbreviations Used BMI ¼ body–mass index RIRS ¼ retrograde intrarenal surgery UAS ¼ ureteral access sheath

Predicting an effective ureteral access sheath insertion: a bicenter prospective study.

The use of a ureteral access sheath (UAS) may provide significant advantages, particularly, in the treatment of a large renal stone burden. However, i...
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