DISCUSSION
The use of a UAS during RIRS, despite having several advantages over RIRS without a UAS, also which remains a controversial tool in endourology owing to an increased risk of ureteral injury. Normal ureteral lumen is narrower than any UAS on the market [12]. Insertion of a UAS dilates the ureteral wall, and thus has the risk of producing ureteral injury (variable degree mucosal erosions, mucosal and submucosal edema and hematoma) additionally placement of reinforced UAS may produce partial or even complete transection [13]. Another concern about UAS is effect on ureteral blood flow. Lallas et al. [9] investigated the possible acute ischemic effects of varying diameters UAS using a swine model. Blood flow to that segment of ureter was measured via laser doppler flowmetry and UAS remained in the ureter for 70 minutes. Authors demonstrated minimal decreases in ureteral blood flow with use of a 10/12-F (avarage; 12%), compared with an up to 64.5% decrease with use of larger UAS. Reached the nadir blood flow averaging 20.0 to 30.0 minutes. They concluded that despite its apparent safety with regard to acute ischemic changes, one should continue to proceed with caution when selecting the appropriate-size sheath, as chronic effects remain in question. Although the reperfusion that occurs after UAS removal might expose the ureteral wall to free radicals and subsequent tissue damage [7].Another study examined the expression of the acute inflammation cytokines cyclooxygenase-2 and tumour necrosis factor alpha in ureteral tissue and demonstrated a significant 6.5-fold and 8-fold upregulation of cyclooxygenase-2 and tumour necrosis factor alpha after 2 minutes of UAS deployment, respectively [14].
At first, Traxer and Thomas [7] prospectively evaluated the incidence and severity of UAS related ureteral wall injury and they generated classification system in 2013. Their study included 359 consecutive patients who underwent RIRS for kidney stone disease and 12/14-F diameter UAS was used to allow passage of the digital ureterorenoscop. The study population was divided into 2 groups, including low grade injuries (grade 0 or 1) and high grade injuries (grades 2 to 4), which involved the ureteral smooth muscle layers. Low grade injuries were found in 86.6% patients, grade 2 injuries observed in 10.1% patients and grade 3 injuries in 3.3%. The authors did not report grade 4 injury. The incidence of postoperative complications was 7%. In a recent study conducted by Loftus et al. [13]95 patients were randomized to two same size (12/14-F) different brand of UAS and they were analyzed incidence of UAS related ureteral injury. The authors used same classification system as we used [7] and they aimed to validate this 5-point classification system. End of study they found grade 1, 2, 3 and 4 injuries in 47.8%, 13.4%, 10.4% and 0.0% of patients, respectively. The authors concluded that ureteral trauma can be easily assessed using a standardized 5-point scale with good inter-rater reliability and high grade injury may be prevented by avoiding pushing against resistance when placing a sheath and using surgeon digression to switch to a smaller diameter sheath when sheath placement time is prolonged. In our series, grade 1 injury rate of 40.9% is also similar to results with two studies as mentioned above. Unlike the other two studies, we did not observe grade 2 and higher injuries. This is presumably related to our use of a smaller size of UAS. Because pushing against large size UAS into the narrow ureter during placement, possibly cause high grade ureteral trauma. Another reason may be mismatch in UAS and ureteral tone. Using the larger UAS may require more force during insertion and a higher force would mean a higher risk of ureteral injury. Koo et al. [15] found that high grade ureteral injury did not occur in cases in which the UAS force of insertion was <600 G (600 G=5.88 N).
We know that ureteric strictures can develop even after seemingly uncomplicated or complicated endoscopic treatment of urolithiasis. [16,17] Also decreased blood flow related to usage of UAS theoretically increase the risk of ureteral stricture. The literature also supports limiting the time of ureteroscopic procedures to avoid complications, as complications and stricture risk increase when operative time is prolonged. Loftus et al. [13]claimed that knowing the rates of ureteral stricture correlated with ureteral injury grade would help determine to what degree these injuries have clinical significance. Delvecchio et al.[8] retrospectively evaluated 62 patients undergoing 71 ureteroscopic procedures with the aid of the UAS and with complete follow-up longer than 3 months. Authors found only one stricture (1.4%) in left ureteropelvic junction . But this patient had undergone multiple endoscopic surgeries because of recurrent struvite calculi.
In a recent study, Huang JS et al. [18] shared their data on ureteral stenosis, in which they evaluated the results of RIRS performed for kidney stones of 2 cm and larger. The authors reported that Over a period of 6-month follow-up, no ureteric stricture was identified. Unlike our study, Huang et al. used 13 / 15F ureteral access sheaths during the operation and the follow-up times were shorter than our study. In another recent study, Sarı S et al. [19] evaluated the efficacy and safety of RIRS in 1489 patients with using UAS. The authors reported that they detected ureteral stenosis in 3 patients. In this study, 2 different size UAS (9.5/11.5 F or 11/13 F) were used and the patients were evaluated retrospectively. The major difference of our study is that it has a prospective design and we used UAS with the smallest diameter in all patients.
In the present study, we prospectively evaluated 154 consecutive RIRS procedures with adjunctive use of an UAS after 1-year follow-up and we did not detect any ureteral stricture. In spite of the fact that grade 2 or higher ureteral lesions may cause ureteral stricture because we do not detect high grade injury in our cohort. We speculate that, using larger diameter UAS may lead to more frequent ureteral injury, more ureteral ischemia, and hence more ureteral stricture. Using the smallest diameter UAS has high protection in terms of all these parameters.
There are a few limitation of our study. First of all, as we are aware that the number of patients in our study is low. We think that our study can shed light on higher volume studies. Latter; the study is of cohort design. Comparative studies can provide further contribution and information. In addition, there may be a relationship between stone types and ureteral stricture. Studies to be conducted on this subject may contribute more to the development of ureteral stenosis. Another limitation of our study is the lack of stone analysis data.
In conclusion, the results of our series indicate that the 9.5/11.5-F UAS is safe for routine use to facilitate flexible ureteroscopy and no cause complication on long term period. However, awareness of the potential ureteral wall injury and ischemic effects with the use of unnecessarily large UAS for long periods in patients at risk of injury should be considered.
Acknowledgement: None
Funding Sources: None
Statement of Ethics: This study was approved by the local institutional ethical board (ANEAH-E-1762)
Disclosure Statement: The authors have no direct or indirect commercial financial support associated with the publishing of this article.
Research involving Human Participants and/or Animals: The study was performed in accordance with the most recent version of the Declaration of Helsinki.
İnformed consent: The approval of the local ethics committee was obtained and written informed consent was obtained from all the patients.
Conflicts of Interest : The authors declare that there is no conflict of interest.