Statistical analysis
All statistical tests were performed using SPSS Statistics version 24 (IBM, Armonk, NY, USA) software. The sample mean was used to determine the average of collected data as quantitative variables met the normal distribution; otherwise, the sample median was used. A chi-square test was performed for nominal variables in the groups. A Student’s t-test was applied to make group comparison when the normality assumption was satisfied for both groups. If the normality assumptions were not satisfied for either group or both groups, the equivalent nonparametric Mann-Whitney U test was applied.
Binomial logistic regression was then performed analysing the statistically significant univariate factors. Predictors that obtained significance for surgical success were entered into a multivariable logistic regression model to determine the independent predictors.
RESULTS
The study consisted of 422 consecutive patients (113 in Group 1; 289 in Group 2) that meet the criteria for inclusion. Of these, 179 (42%) were females and 243 (58%) were males, with a mean age of 48.8 ± 14 (14–80) years. Patients’ demographics, baseline stone status and characteristics and operative outcomes are presented in Table 1.
Group 1 (sURS group) and group 2 (non-sURS group) patients’ comparisons are also listed in Table 2. There was no statistically significant difference between the two groups in terms of stone and patient characteristics. However, the mean operation time was significantly longer in the sURS group (87.1±37min vs 67.3±27 min,p<0.0001 ). Fluoroscopy times were similar between the groups (p=0.53 ). UAS was unable to be placed in four (3.0%) patients in the sURS group and 25 (8.7%) patients in non-sURS group (p=0.03 ). In the non-sURS group a fURS was unable to be inserted through a working guidewire in two patients whose UASs were unable to be placed as well. The JJ stent was placed and reoperation was planned in these patients. While the surgical success was 94.7% in the sURS group, it was 84.1% in the non-sURS group, and this was statistically significant (p=0.002 ). The intraoperative complication rate was lower in the sURS group than in the non-sURS group (1 (0.8%) vs 14 (4.8%), p=0.04 ). In the sURS group, the stone could not be properly visualized in one (0.7%) patient due to intraoperative bleeding. The complications observed in the non-sURS group included eight (2%) mucosal injuries requiring stent insertion, two (0.6%) postoperative prolonged haematuria, two (0.6%) collecting system perforations requiring JJ stent placement, one (0.3%) inability to reach stone and one (0.3%) converted to percutaneous nephrolitomy in the same session. Although postoperative complications were lower in the sURS group compared to the non-sURS group, this was not statistically significant (5 (3.8%) vs 23 (8.0%), p=0.10 , respectively). The postoperative complications for the sURS group were: fever requiring antibiotic (n=2, 1.5%), renal colic requiring analgesic (n=2, 1.5%), gross haematuria not requiring transfusion (n=1, 0.7%); for the non-sURS group: fever requiring antibiotic (n=7, 2.4%), renal colic requiring analgesic (n=10, 3.4%), gross haematuria not requiring transfusion (n=5, 1.7%) and urosepsis (n=1, 0.3%).
The results of univariate analysis of the factors affecting surgical success are presented in Table 3. Although the surgical success was determined to be significantly affected by the optical dilatation through sURS, it was not significant in multivariate analysis (in univariate analysis: p=0.002 , in multivariate analysis:p=0.179 ). We have found two independent factors predicting surgical success in multivariate analysis. These were stone number (p<0.0001, odds ratio: 2.28 and 95% CI [1.48-3.49]) and failed UAS placement (p=0.035, odds ratio: 3.49 and 95% CI [1.04- 11.14]) (Hosmer-Lemeshow test:p=0.378 ).
DISCUSSION
This study is the first research investigating the impact of optical dilatation with sURS on the operative outcomes of RIRS. Our study has revealed two important issues regarding the use of sURS in patients undergoing RIRS. First, when using sURS, UAS is more easily placed into the ureter, and the surgical success rate increases. However, it is not an independent predictor of surgical success. Second, intraoperative complication rates are found to be low.
One of the most essential components of RIRS surgery is the placement of UAS. The use of UAS makes a positive contribution to the operative visibility, stone-free rate, and operation time without increasing the complication rates [ 1,3,4,11]. Furthermore, it is stated in several reports that the utilization of a UAS may have a positive impact on complication rates [8,12]. However, the insertion of a UAS can sometimes be challenging. The authors recommend various strategies to address this problem. Passive ureteral dilatation made with routine stent placement can be safe and efficient, but this method carries the risks of secondary anaesthesia, an operation, and eventually higher costs [1,11]. In addition, stent-related symptoms may be seen, such as prolonged haematuria, flank pain, dysuria and urgency, and patients are usually not willing to accept presenting when they hear about these side-effects [4]. Placement of UAS following active dilatation with a balloon or a coaxial dilator is not routinely recommended because of the risk of significant ureteral injury [1,5]. In the EAU guidelines for approximately 10 years it has been advised that sURS before RIRS can be helpful for optical dilatation. The direct visualization of the whole ureter by semirigid ureteroscopy just before the UAS placement is not only to provide optical dilatation but also allow to evaluation of any additional stones, strictures, or tumours in the ureter [11]. Moreover, it can also help with evaluation of ureteral compliance and diameter [5].
Due to a difficult impassable ureter, the failure rates of primary access of UAS range from 6% to 22% in the literature [1,5,13]. Success rates increase when the appropriate diameter is determined with sURS and when a thinner UAS is used in cases where it is needed [5]. However, the preferred UAS must be narrow enough not to damage the ureter, but wide enough to clean the stone and provide intrarenal circulation. The most reliable method to determine appropriate UAS diameter is to evaluate with sURS. Lima et al. recommend a routine sURS for passive ureteric dilatation and selection of the correct UAS size [8]. In our study, in accordance with the literature the UAS failure rates are 8.7% in the non-sURS group and 3.0% in the sURS group. Diameters of sURS used in the study are 8 or 9.5 fr in circumference at the distal tip and 12 fr in circumference at the proximal tip. We think that the mechanism of cascading diameter increase dilates the intramural ureter, the narrowest and least elastic part of the ureter, without damage shown in Figure 1.
Despite all these advantages of UAS, there are some drawbacks. One of these is deterioration of ureteral blood flow. Lallas et al. show transient decreased ureteral blood flow secondary to the use of a UAS in animal models [14]. However, they stated that the compensatory mechanisms of the ureteral wall restored the blood flow of the ureter wall and the integrity of the ureter was preserved. The authors concluded that the use of a UAS with RIRS might be safe; however, care must be taken in selecting an appropriate size of sheath and the duration of surgery should not be prolonged because of the risk of stricture development. In our study, the duration of the operation was found to be significantly higher in the sURS group than in the non-sURS group (the difference between means: 20 min, p<0.0001 ). The extended duration of the operation is thought to have been spent on sURS, but unfortunately the duration of UAS placement has not been measured.
Another drawback associated with UAS is the risk of ureteral injury during entry. Traxer and Thomas prospectively evaluated ureteral injuries secondary to insertion of a 14F UAS [15]. The authors reported that ureteral wall injuries occurred in 46.5% of the patients, and that the most significant predictor of severe ureteral injury was the absence of stenting before RIRS. However, in another prospective study on 2239 patients treated with fURS, Traxer et al. found that UAS usage did not increase the risk of ureteral wall damage, and postoperative infectious complications were reduced [16]. In a retrospective study in which 4500 RIRS procedures were evaluated, intraoperative incidents occurred during 5.2% of the procedures, and overall complications occurred in 18.9% [12]. The authors reported that in 4.8% of the cases in which a ureteral access sheath was used they encountered grade 2 and 3 ureteral wall lesions. In our study, while one (0.7%) intraoperative complication (inability to reach stone) was observed in the sURS group, 14 (4.8%) intraoperative complications were observed in the non-sURS groups and the majority of these complications were mucosal injury (57%). We suppose that optical dilatation with sURS and selection of the correct UAS size reduce the intraoperative complications. Although the rates of postoperative complications in the sURS group were lower, there was no statistical difference between sURS and non-sURS groups.
In many studies, factors that predict stone-free and surgical success have been investigated. In some studies stone size, presence of lower pole calculi, surgical experience, presence of hydronephrosis, and UAS use are significant predictors of RIRS outcome, while others have only found the number of stones and the number of sites [17-19]. Especially thanks to the advances in the field of lasers, stone access is the most important factor that makes treatment possible. In our series, the mobile lower pole stones were repositioned into the upper or middle calyx. This method may have reduced the impact of localization on the stone-free rate. In our study, UAS usage and the presence of multiple stones were found as independent predictors for surgical success. The failed surgery rates have increased 2.28 times as the number of stones increases, and have increased 3.49 times when the UAS cannot be placed. It is expected that the use of sURS before RIRS increases surgical success by increasing the rate of UAS placement and reducing the rate of intraoperative complications. Finally, we found that the surgical success rate was higher in the sURS group (p=0.002). However, our study found that sURS had no independent effects on the surgical success of RIRS.
CONCLUSION
As a result, the optical dilatation with sURS, which is also recommended in EAU guidelines, makes a positive contribution to surgical success, facilitating UAS placement and leading to a low complication rate. Although it requires longer surgery time, we recommend this method, with acceptable fluoroscopy time, in patients with no previous history of passive dilatation using a JJ stent. However, further randomized prospective studies are needed.