In this study, we compared the effect of preoperative ureteral stent on the infection status and surgical outcomes of patients undergoing flexible ureteroscopy interventions.
According to our analysis, there were no significant difference in each demographic data item between the two groups, this comparison could rule out the interference of demographic differences on the results of the study. Longer duration of the ureteroscopic procedure resulted increased incidence of postoperative complications (10), so we strictly control the operation time below 90 minutes. We found that there was no significant difference in the operative time between the two groups of patients.
It was generally believed that urine culture results can reflect the patient's urinary tract infections. For patients with positive urine culture results, clinicians should apply a full range of sensitive antibiotics based on drug susceptibility results (11).
Among the patients enrolled in our study, the positive rate of urine culture in the stent group was higher than that in the non-stent group (p=0.013). This result suggested that the urinary infection in the stent group was more severe than the non-stent group.
Interestingly, however, some researchers believed that the results of urine culture did not accurately reflect the bacterial colonization of the ureteral stent and a negative culture did not rule out a colonized stent (12,13), which further strengthened the connection between ureteral stent and urinary tract infections. In the research reported by Kehinde, E. O, of the 104 patients with positive stent cultures, in 62 patients (60%), urine culture was sterile (14).
Another test that can visually reflect the urinary tract infection in patients was urinary leukocyte count (ULC). In the patient population of this study, patients in the stent group received routine oral antibiotics after placement of the ureteral stent, yet their ULC at admission was higher than the non-stent group. It was unclear whether the cause of this phenomenon was that oral empiric antibiotics were ineffective or that the infection in the stent group was still heavier than the non-stent group after oral antibiotics did take effect.
Furthermore, even though receiving longer intravenous antibiotic treatment before surgery, and the ULC had a certain degree of decline in both group, the ULC of the stent group was still significantly higher than that of the non-stent group. The comparison of these two indicators prompted that the antibiotic dosage and duration of use in the stent group were much higher than those in the non-stent group. However, the treatment effect of antibiotic therapy on urinary tract infection associated with ureteral stent was not satisfactory.
Albumin was considered as a negative acute phase protein and nutritional marker. Earlier researchers have reported that preoperative hypoalbuminemia/malnutrition was one of the unfavorable factors leading to postoperative complications, including infection-related complications (15,16). Gong J, et al. pointed out that there might be a correlation between albumin and inflammatory response, because they found a correlation between postoperative serum albumin levels and postoperative CRP levels, and lower albumin levels suggested a more severe inflammatory response (17). For patients in the stent group, their ALB levels at admission and ALB levels within 1 hour after surgery were both significantly lower than those in the non-stent group. This result indirectly demonstrated that patients in the stent group had a greater infection status preoperatively and postoperatively than the non-stent group and had a higher risk of postoperative infection complications.
At the initial stage of severe infection, a decrease in WBC levels was a characteristic feature (18,19). It was well known that WBC reduction (WBC＜4.0*109/L) was included in the diagnostic criteria of SIRS and sepsis, since the decline in blood leukocyte levels was closely related to infection. Although there was no statistically significant difference, the WBC level at admission was still lower in the stent group (6.71±1.81*109/L vs 6.96±1.92*109/L). The WBC difference in the two groups after surgery was very obvious. Compared with the preoperative level, the WBC level in 1 hour after surgery of the stent group decreased (6.71±1.81*109/L to 6.39±1.92*109/L), while this indicator in non-stent group increased (6.96±1.81*109/L to 7.23±1.92*109/L). This significant difference further suggested that preoperative ureteral stents could aggravate perioperative urinary tract infections in patients.
Current mainstream theory considered that the mechanism leading to ureteral stent-associated infection was bacterial colonization and the formation of biofilm. Bacteria were capable of interacting and adhering to the stent surface, besides, they could express adhesins that could help form the biofilm (20). Thereafter, once the biofilm was formed, the phenotype and behavior of bacteria would change a lot, which caused the process of treating chronic bacterial infection was fraught with difficulties (21).
The total days of hospital stays and days from admission to surgery of the stent group were significantly prolonged due to the use of intravenous antibiotics for a longer period of time prior to surgery. Correspondingly, this would increase the financial burden and mental stress of the patient in a single hospitalization. However, considering the passive dilation of the ureteral stent could increase the ureterorenoscopy access success rates, preoperative stenting might reduce the total cost for ureterorenoscopy. (22)
In the final outcome comparison, although the incidence of postoperative urosepsis was higher in the stent group than in the non-stent group, this difference was not statistically significant. The main cause of this phenomenon might be the longer-term intravenous antibiotic use and the use of oral antibiotics during the stent retention for the stent group. Another important reason was that the passive expansion effect of the ureteral stent could reduce the pressure of the renal pelvis during surgery, and high renal pelvic pressure was an considerable factor leading to postoperative infection (23). Although preoperative stents did not significantly increase the probability of postoperative urosepsis, further research on how to reduce stent-related urinary tract infections was still imminent, as it related to the quality of life of patients carrying stent.
There were still some shortcomings in this research. In the first place, this study was a single-center retrospective study with a relatively small sample size. Besides, we did not pay attention to the impact of the duration of carrying the stent and the length of surgery and on the occurrence of postoperative urosepsis. Finally, large-scale prospective studies and basic research were needed to confirm our findings.