Predicting failed access in unstented ureteroscopy

The risk of failed access (FA) in unstented ureteroscopy ranges from 7.7 to 16%, with young females and those with prior ipsilateral stone surgery, narrow ureteral anatomy, and proximal ureteral stone location carrying higher risk. We aim to determine the rate of failed access at our institution and analyze demographic, clinical, and operative variables associated with FA. We conducted a review of all unstented ureteroscopy procedures at our institution between January 2018 and June 2022. Ureteroscopy for stone, stricture, and neoplasm were included. The primary endpoint was rate of FA, when the unstented ureter failed to accommodate the ureteroscope distal to the target lesion. Demographic, clinical, and operative variables were analyzed to determine if there was an association with FA. Of the 562 ureteroscopies cases reviewed, 221 unstented ureteroscopies fit our inclusion criteria. FA occurred in 34 (15.4%). Previous stone passage (p = 0.039) and distal ureteral location (p = 0.042) were associated with successful access (SA). Proximal ureteral location was associated with FA (p = 0.008). These variables remained statistically significant when analyzed with multivariable logistic regression. There was no association with other demographic, clinical and operative variables. FA occurred at a rate of 15.4% at our institution. Previous stone passage and distal ureteral location were associated with SA, while proximal ureteral location was associated with FA. Prospective studies are needed to better determine predictors of FA.


Introduction
Ureteroscopy is the most commonly performed therapeutic intervention for ureteral and renal calculi not amenable to spontaneous passage [1].It is also the primary apparatus used in diagnosing (and often treating) ureteral stricture disease and upper tract neoplasia.Advances in technology over the last 2 decades have yielded smaller and more dexterous ureteroscopes.As a result, stone-free rates and diagnostic accuracy have improved.
Placing a ureteral stent prior to ureteroscopy (prestenting; PS) allows for passive dilation of the ureter, making it more amenable for staged ureteroscopic access.Several studies have shown that PS is associated with higher calculus-free rates [2][3][4].Despite this, the American Urological Association (AUA) and Endourology Society guidelines do not recommend routine PS because of the potential for increased patient morbidity and cost [1].
Ureteroscopy without a previously placed ureteral stent is commonly performed.In these procedures, there is a risk of failed access when the surgeon is unable to advance the ureteroscope to the level of the calculus, tumor, or stricture.This precludes definitive calculus removal, stricture dilation, or tumor diagnosis at that time, and a stent is usually left in place with plans to perform a staged intervention.Estimates of the risk of failed access (FA) in unstented ureteroscopy range between 7.7 and 16%, with young female gender, prior ipsilateral stone surgery, narrow ureteral anatomy, and proximal ureteral location all risk factors [5][6][7][8].The aims of our study are to determine the failure rate of unstented ureteroscopy at our institution and to identify demographic, clinical, and operative variables associated with failed access.

Materials and methods
We conducted an IRB-approved, retrospective review of every consecutive unstented ureteroscopy procedure at our institution between January 1, 2018 and June 30, 2022.These included ureteroscopy for stone, stricture, or neoplasm.Exclusion criteria were active pregnancy, age < 18 years, ectopic ureters, non-native bladders and urethrae, and previous history of ipsilateral ureteral repair.
The primary endpoint was rate of FA when the unstented ureter failed to accommodate the ureteroscope distal to the target lesion.Demographic, clinical, and operative variables were compared between failed and successful access (SA) groups.These included age, sex, race, body mass index (BMI), American Society of Anesthesiologists (ASA) score, tobacco use, alpha-adrenergic blocker use, positive urine culture, previous stone passage, previous intervention(s) for ureteral or renal stones, stone size, laterality, location, use of stiff wire, and use of semi-rigid ureteroscope.Location was characterized as renal, proximal ureter (ureteral origin to the sacroiliac joint), mid ureter (overlying the sacroiliac joint), and distal ureter (below sacroiliac joint into the bladder).Time from diagnosis to procedure was measured in days and was only applied to ureteral calculi.
Our study includes seven different attending surgeons.When encountering difficulty with access, different strategies were employed by the surgeons at their discretion.These included using a ureteral access sheath, ureteral dilation with dilators or a semi-rigid ureteroscope, and downsizing to a fiberoptic ureteroscope.There was no standardized algorithm.Ureteroscopes used included Olympus ® URF-V3 or URF-V2 with an 8.4 Fr outer diameter, Olympus URF-P6R fiberoptic ureteroscope with a 7.95 Fr outer diameter, and Gyrus-ACMI MR-6LA semirigid ureteroscope with a 6.9 Fr outer diameter.Stiff wires used were Cook 0.35 Amplatz wires.
Statistical analysis was performed using SPSS statistical software version 27.Ratio variables were analyzed using a two-tailed t test for independent groups using the unequal variance assumptions.The independent variable was access success or failure.To determine if there was an association between the success variable and other nominal variables, a Chi-square test of independence was performed.Multivariable logistic regression was performed only for variables statistically significant on univariate analysis.An alpha value of 0.05 was considered significant.

Results
A total of 562 consecutive ureteroscopies were performed at our institution between January 1, 2018 and June 30, 2022.Of these, 242 cases were previously unstented (43%).After our inclusion and exclusion criteria were applied, our study cohort was comprised of 221 unstented ureteroscopies performed on 206 patients.Eight of these were concomitant bilateral ureteroscopies, and 7 ureteroscopies were performed on the same patients on two separate occasions.
SA was achieved in 187 (84.6%), with FA in 34 (15.4%).There were no demographic differences between the SA and FA groups (Table 1).Analysis of clinical and operative variables are displayed in Tables 2, 3, and 4. Previous stone passage associated with higher success rate (p = 0.039).There was a rejection of the null hypothesis in the location of the targeted lesion (p = 0.031), with a higher failure rate of the proximal ureteral location (26.9%) and lower failure rate of the distal ureteral location (6.1%) when compared to the other locations.In a separate analysis of each individual location versus the others (Table 4), proximal ureteral location (p = 0.008) was associated with failed access, and distal location (p = 0.042) was associated with SA.These variables remained statistically significant on multivariable logistic regression (Table 5).[8].The authors also found that longer time from first diagnosis to ureteroscopy was associated with failure [8].
In our study, the FA rate was 15.4%.This falls within the previously described FA range, albeit on the higher end.One of the seven surgeons in our study was Endourology Society Fellowship-trained, though all were very experienced in ureteroscopy.Urology residents ranging from post-graduate years 2 through 5 assisted in every procedure and were usually the primary surgeons, with the attending urologist present as a teaching assistant.It is certainly possible that this influenced our success rate.There was no standard algorithm for when a surgeon encountered a "difficult" ureter.Ancillary maneuvers were left to the discretion of the surgeon.These included access sheath placement, ureteral dilation, or switch to semi-rigid ureteroscope or fiberoptic ureteroscope.After each FA, a ureteral stent was placed, and the patient returned to the operating room for a stented ureteroscopy in a staged fashion.
We identified previous stone passage as a variable associated with SA (p = 0.039).This was not found in the above studies.We hypothesize that a patient's previous ability to spontaneously pass stones may indicate a certain degree of ureteral accommodation and compliance.We also found that proximal ureteral location of disease had the highest failure rate (26.9%) of any of the other locations, and distal ureteral  [7].They lastly suggested that surgeons may be less aggressive in the proximal ureter.Fuller et al. also hypothesized that a narrow proximal ureter where a stone arrests may suggest a smaller caliber ureter [8].At our institution, PS is offered to all patients planning to undergo ureteroscopy.We have the ability and infrastructure to place ureteral stents in the clinic setting without general anesthesia.Providing patients with accurate estimates of the risk of FA and risk stratification based on the above data will aid in their decision-making.This data can be applied to all patients considering unstented ureteroscopy, regardless of institution, as it can help with counseling and setting expectations.
Our study is unique from the previously described studies.We included ureteroscopy not only for urinary stone disease but also for diagnosis of ureteral stricture disease or neoplasm.This makes our data more generalizable to ureteroscopy for multiple purposes.We also analyzed operative variables such as use of stiff wire and semi-rigid ureteroscopes.There are several limitations to our study, primarily its retrospective design.Data were pulled from progress notes and operative notes, which may be misprinted or misinterpreted.No standardized surgical algorithm was followed when a difficult ureter was encountered.Several ancillary maneuvers could have been employed or no ancillary maneuvers could have been employed, as this was left to the surgeon's discretion.Our surgeons included one fellowship-trained Endourologist, while the others were either fellowship-trained in other subspecialties or not fellowshiptrained.From our standpoint, this makes our data more generalizable to other urologists with different types of training and practices.

Conclusions
Our FA rate in unstented ureteroscopy is 15.4%, which falls within previously described ranges.Previous stone passage and distal ureteral location was associated with SA, while proximal ureteral location is associated with FA.These data are useful when counseling patients during the informed consent discussion.It can also help with decision making, particularly in patients considering PS before ureteroscopy.Prospective studies are needed to better establish factors associated with FA.

Table 1
[6]ociation between demographic variables and SAPrior to their intervention, patients should be counseled that FA is an important risk of unstented ureteroscopy.There are gaps in in the literature identifying the rate of access failure and variables associated with failure.Cetti et al. described a failure rate of 8.4% in their study of 119 patients[5], while Viers et al. cited a failure rate of 16%[6].The authors found that prior ipsilateral stone intervention and stent placement were associated with a lower failure rate, while FA was asso- [7]ted with a narrower ureteropelvic junction on computed tomography urogram[6].In their study of 535 patients, Fuller et al. cited a failure rate of 7.7% with younger median age in females and proximal ureteral stone location associated with access failure[7].Most recently in March of 2021, Lavoie et al. descried a failure rate of 8%, with proximal ureteral stone location being associated with a higher failure rate

Table 2
Association between binary clinical and operative variables and SA

Table 3
Comparison of access success and failure in polytomous clinical and operative variables

Table 4
Analysis comparing individual lesion locations