Discussion:
The indications of FURS in the management of urolithiasis has expanded
considerably in recent years thanks to the development related to
technology in terms of miniaturisation and durability of flexible
ureterorenoscope. Therefore, publications on the use of FURS for kidney
stones larger than 20 mm have began to be published in the
literature6-8. Due to being a minimal invasive method,
the choice of the FURS has been increased in the treatment of large
renal stones6-8. Despite reports on the safety of this
operation, severe infective complications, such as sepsis, may occur in
FURS9. For that reason, we believe that the factors
affecting infection should be analyzed in all aspects.
In the literature infective complication rates following FURS change
between 1.7% and 18.8% 4 and it was found as 4.7%
in consistence with the literature in the present study. Factors that
affect infective complications following FURS were investigated by
various studies5-10. OT is one of the important
factors associated with infective events4. However, in
the treatment of kidney stones larger than 20 mm with FURS, studies that
reported the most appropriate operation time to avoid infective
complications and evaluated the effect of UAS use on these complications
are limited.
According to our results in terms of the OT, it could not established
the statistical difference concerning age, BMI, density, localisation of
the stones and stone free rates between the group lasting less than 60
minutes and the group lasting longer than 60 minutes. In this way, two
homogeneous groups were consisted, and therefore we could more
accurately analyzed the effect of operation time on infective events
following FURS (Table 1). As expected, the stone size and area were
larger statistically in the group lasting longer 60 min than in the
group lasting less than 60 min ( p<0.05, Table 1). Increased
stone size has the strongest impact on OT11. The OT
was prolong proportionally with the burden of stone in the present
study. According to Sorokin’s et al, localisation of stone is another
related factor with OT and it was reported that lower pole stones
increase the OT11. However, contrary to that study,
Jacquemet et al. stated the OT did not differ between lower pole stones
and stones in locations other than lower pole12.
Whereas, according to our results, the stones localised in the renal
pelvis caused longer operation time. The main reason for this situation
may be due to the migration of some fragments to different calyx during
stone fragmentation and the time lost during the search for these
fragments in calyxes of kidney. When the groups formed according to the
OT were compared in terms of infection rates, the infection rates were
found to be significantly lower in the group lasting less than 60
minutes [ 1(0.3%) and 27 (9.2%) for the groups lasting lesser than
60 min and longer than 60 min, respectively, p<0.05, Table
1]. According to the Jung’s et al study, with the use of forced
irrigation during ureteroscopy, intrarenal pressure increases above 300
mmHg13. And it was established that according to the
results obtained from some animal and human studies, when intrarenal
pressure rises above 30 mmHg, some defense mechanisms which depend on
the intrarenal pressure including pyelo-tubular, pyelo-venous,
pyelo-sineous and pyelo-lymphatic backflow come into
play14-17. These mechanisms have the potential to
decrease kidney function as well as they may be related to infectious
and hemorrhagic process13. According to our results,
the OT is related to the infectious process. These defense mechanisms,
which initially tried to balance intrarenal pressure with the
compensatory mechanism, create an effect that worsens the situation in
terms of infectious, inflammatory and hemorrhagic processes as the
operation time is prolonged.
When we analysed our data according to the presence of infection, while
there was no statistical difference in terms of age, sex, stone size,
surface area and location parameters. We also evaluated the probable
factors that affecting infective complications following FURS in this
current study. The infection rates were primarily affected by the OT
(Table 2). In the same group, the OT was longer statistically in the
infection group ( 94.1±14.2 and 67.9±23.1 for the groups with and
without infection, respectively, p<0.05, Table 2). In fact,
this result has been confirmed in our precede analysis according to the
OT by determining the rate of infection statistically significant higher
in the group whose operation time lasts longer than 60 minutes ( Table
1).
A logistic regression analysis was performed in order to determine
independent risk factors affecting post-operative urinary infective
process. In our analysis, the only independent factor affecting the
occurrence of infection in the FURS was the OT (Table 4). In addition to
this analysis, in terms of operation time, we applied the ROC analysis
to determine a cut-off value that facilitates the postoperative risk of
infection and, the cut-off value of OT for the infective process was
found as 87.5 min with 89.3% sensitivity and 70% specificity (Table
5). The area under curve (AUC) for OT time was 0.82 ( 95% CI 0.77-0.88;
p=0.000) (Fig.1). According to this result, in cases the operation time
exceeds 87.5 minutes, a closer follow-up of patients may be recommended
in order not to get worse in terms of infection risk. The earlier
diagnosis means the more effective treatment in case of infection. This
approach may be more important for patients who are at risk in terms of
undergoing anesthesia for the other session. However, if there is no
problem for the patient to receive anesthesia for the second time, the
operation can be terminated by leaving a second session when the
operation time is close to 87.5 minutes by making a decision with the
patient before the operation.
According to our results, the only difference between the groups that
formed in terms of UAS usage was the longer OT in the UAS using group.
(79.3±24.4 and 66.7±22.4, for the groups which used and unused the UAS,
respectively, p <0.05,Table 3). This time difference depends
on the wasted time because of the extraction of the fragmented parts of
the stone and refocusing to the stone in the kidney. In addition, it was
a striking finding that the infection rate in the group which the UAS
used is not statistically different than the unused group. According to
analysis of this kind of group, although the infection rate in the group
which used the UAS was a bit higher than in the group which unused, this
difference is not significant statistically ( Table 3). But, we
associated this difference with the length of the OT in the group which
used the UAS.
According to the literature, entrance of the bacteria or bacterial
endotoxins into the bloodstream because of the intrarenal backflow due
to elevated intrarenal pressure could be the reason of infective events
following FURS4. Based on this knowledge, the
reduction of the intrarenal pressure constitutes a protection from risk
for bacterial dissemination during stone
fragmentation18. Although it has been reported that
the usage of the UAS reduced the intrarenal pressure in some
literature19, Berardinelli has shown that the absence
of UAS does not increase the risk of post-operative infection rate in
accordance with our results10. In fact, the reduction
of intrarenal pressure due to UAS usage may constitutes a protection for
infective events. According to this theory, we were expecting lower
infection rates in UAS using group. However, increased risk of infection
due to long-term operation seems to had got ahead of the protective
effect of UAS, as shown in table 3. The fact that OT was independently
risk factor in our regression analysis also supports this finding.
In addition, the usage of UAS seems as a two-edged sword; on the one
hand it reduces the intrarenal pressure which might be related with
infective complications, on the other hand it might increase tension
related lesions on the ureter wall9. Thus, Osther et
al had recommended using UAS in case of the indication rather than
routinely9. Since the long-term effects of UAS usage
on the ureter wall are uncertain, we do not prefer to use UAS during
FURS routinely, especially for long-term operations. The protective
effect of using the UAS in terms of the infection risk appears to
decrease as the operation time increases. In the lights of these
findings we believe that FURS without using UAS could be perform without
an increased risk in terms of infective complications.