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.