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.