Risk factors for fUTI after URSL have been reported as the presence of pre-URSL pyuria, a history of pre-URSL pyelonephritis, pre-URSL ureteral stent placement, and operation duration of 90 minutes or more [5, 8–10]. Youssef et al. reported that URSL in patients with a history of pre-URSL pyelonephritis with sepsis resulted in an increase in complications, including post-URSL fUTI, prolonged hospital stays, and prolonged post-URSL antibiotic administration [6]. A ureteral stent is often used for urinary drainage in stone-associated pyelonephritis, but there are no studies examining the relationship between the ureteral stenting period and post-URSL fUTI.
In this study, a risk factor for the development of fUTI following treatment of obstructive pyelonephritis and URSL was identified as > 21 days of ureteral stenting (Fig. 1a). Pre-stenting can improve the passive dilation of the ureter and increase the stone-free rate during URSL [11, 12]. It has been reported that bacteriuria and bacterial colonization of the stent occurs over time after stent placement [13]. Bacterial colonization of the stent was not observed within 2 weeks but was observed in 23.5–33% of patients after less than 4 weeks, 33.3–50% after 4–6 weeks, and 71.4% after more than 6 weeks [14]. Therefore, the optimal timing of URSL appears to be 7–21 days following stent placement .
An increased duration of operation was correlated with higher the risk of fUTI. Some studies have indicated that the risk of fUTI increases after an operation > 90 minutes [5, 10], but in this study the risk increased after operations of 75 minutes (Fig. 2). The reason for this may be that URSL performed after pyelonephritis poses a higher risk of bacterial exposure, so shorter operation times would reduce the incidence of fUTI. Furthermore, this study also showed that post-URSL SIRS complications increased with an operation time of > 90 minutes. These results indicate that the optimal duration of URSL after pyelonephritis should be 75 minutes or less, and operations longer than 90 minutes should be avoided in order to prevent severe fUTI.
Regarding the stone position, renal stones were considered to increase the intrapelvic pressure during URSL and cause fUTI regardless of the use of UAS [15]. However, in this study, there was no significant difference in the incidence of fUTI depending on the diameters of the access sheath. The reason for the high fUTI in patients with renal stones is considered to be that they are older than patients with ureteral stones, have many comorbidities such as DM, and have a large stone size and a long operation time, as shown in Table 2.
It has been previously reported that administration of prophylactic antibiotics reduced the rate of post-URSL bacteriuria, but the post-URSL fUTI incidence rate was not significantly different to the control group [16]. In a recent systematic review, it was reported that prophylactic antibiotics showed a certain effect [17]. In this study, no effect of prophylactic antibiotics on fUTI onset was observed, with similar results seen in selective cases of pre-URSL pyelonephritis with SIRS. However, the criteria for prophylactic antibiotic administration were not constant in this study, It is considered that prophylactic antibiotics should be more aggressively administered in the future to prevent the fUTI development, especially in patients with ureteral stent for > 21 days and renal stones with large stones. The Infectious Diseases Society of America guidelines state that replacing long-term indwelling catheters immediately before surgery is more effective than administering antibiotics [18]. Therefore, when URSL is performed on a patient with a ureteral stent that has been indwelling for > 21 days, it is recommended that the stent be replaced before URSL. However, the replacement procedure itself is mildly invasive, and there is a slight risk of fUTI, so indication needs to be considered.
This study has limitations, which must be considered. First, our retrospective analysis of data is from a single institution and of a small sample size, which are associated with a high risk of selection bias. Second, the types and duration of antibiotics administered during pyelonephritis and the prophylactic antibiotics before URSL were dependent on each attending physician and were not standardized. However, these factors would not increase the risk of post-URSL fUTI and were considered to have little effect on the results of the study.