Urolithiasis is among the most frequently encountered urological conditions. Between 1994 and 2010, the global prevalence of urinary stone disease increased from 5.2% to 8.8% (1). Depending on the size, location, and shape, upper urinary tract stones that cannot be removed on their own (≥6 mm) require different interventions such as percutaneous nephrolithotomy (PCNL), rigid ureteroscopy (rURS), flexible ureteroscopy (fURS), and extracorporeal shock wave lithotripsy (ESWL) (2, 3).

One of the most serious conditions of postoperative infection is systemic inflammatory response syndrome (SIRS). SIRS, if not diagnosed in time, can rapidly progress to septic shock with a relatively high mortality rate. Thus, well prediction and timely treatment of SIRS are important for a better outcome (4). Relevant studies have shown that a preoperative positive urine culture is a major risk factor for postoperative infection, and treatment should be based on the results of the urine culture such as upper urinary tract drainage (5). However, for patients with positive urine culture who require surgery, the factors influencing the postoperative incidence of SIRS are still unclear.

In our study, we analyzed the key information of patients with positive urine culture includes preoperative history, preoperative laboratory examinations, operation time, operation methods, intraoperative findings, postoperative vital signs, and postoperative laboratory examinations. We found out two risk factors, one protective factor, and two predictors of SIRS after upper urinary tract stone surgery of the patients with urine culture-positive stones, which provided new insights in the prevention and prediction of SIRS after infection stone lithotripsy.

SIRS, which lacks a specific treatment regimen, marks the early stage of urosepsis and often persists throughout its progression, posing significant risks to both morbidity and mortality (3). Similar to previous studies, our data also identified several factors associated with SIRS after lithotripsy for infectious urinary stones. These include risk factors such as preoperative WBC in urinalysis, protective factors such as preoperative upper urinary tract drainage, and predictive factors such as CRP and PCT in the postoperative complete blood count (5–7). In addition, relevant studies have shown that people with positive preoperative nitrites on are more likely to develop septic shock (8). However, since positive leukocytes in the urinalysis were included in the multivariate logistic regression analysis, positive nitrites, which correlate with positive leukocytes, were excluded to maintain variable independence.

Interestingly, to date, no literature has suggested an association between postoperative hemoglobin drop and SIRS, which our multivariate logistic regression analysis identified. The result may be attributed to intraoperative vascular wall injury, which subsequently leads to the entry of infectious bacteria attached to stone particles into the bloodstream. However, this also awaits a clearer causality and needs more detailed evidence, as sometimes severe infections can also lead to a hemoglobin drop. We further analyzed the potentially influential factors for the decrease in postoperative hemoglobin and found no significant differences among the three surgical approaches. However, the surgical duration showed a weak correlation with the decrease in postoperative hemoglobin. This suggests that while the correlation between these two variables is not strong, an underlying association might exist that requires a larger sample size and more precise data for accurate measurement. Regarding PCNL, we found no statistically significant difference in the impact of nephrostomy sheath size on hemoglobin drop. Besides, whether or not using EMS had no significant effect on hemoglobin drop, but the use of EMS could effectively shorten the operative time. This may be due to the higher energy level of EMS, which accelerate the surgery but not causing more injury of kidney (9).

Although our data found a slightly higher incidence of SIRS after PCNL and fURS than rURS, the difference was not statistically significant. And the coverage of PCNL and fURS, which mainly target renal stones and some upper ureteral stones, does not overlap with that of rURS. The factors most closely associated with the occurrence of SIRS were preoperative positive urine WBC and postoperative hemoglobin drop. Besides, the preoperative placement of a double J-stent or nephrostomy tube could reduce the incidence of SIRS. Perhaps in the case of patients with infectious stones, whose urinalysis suggests a large number of leukocytes and CT suggests severe obstruction, drainage should be performed in advance in all patients. And more attention should be paid to minimize vascular wall injury to reduce the possibility of SIRS. In addition, the patient's CRP and PCT should be monitored in the postoperative period, which are good predictors of SIRS. Combining preoperative and intraoperative conditions, if they are abnormally elevated in the 12 h after the surgery or even earlier, it is necessary to choose sensitive antibiotics in a timely manner to prevent septic shock. Furthermore, for larger stones requiring longer surgical duration, the use of EMS can effectively shorten the operative time and improve the stone clearance rate (9, 10). And the 22Fr nephrostomy sheath that is suitable for EMS wouldn't cause an extra hemoglobin drop.

However, our study does have some limitations. Our sample size is still relatively small and lacks more precise data. The number of people who developed SIRS after all three surgical procedures was small, especially after rURS, and the number of people who developed SIRS after rURS was less than 10. Therefore, performing multivariate regression analysis of the risk factors for SIRS in the subgroups of the different surgical procedures would result in statistical error. Additionally, there are certain influential factors that we were unable to consider, such as the surgeon's experience, intrarenal pressure, stone location, severity of hydronephrosis, and duration of obstruction.

In a nutshell, our study has identified several factors associated with SIRS following lithotripsy for infectious urinary stones. Preoperative positive WBC in urinalysis and postoperative hemoglobin drop were found to be significantly associated with SIRS. Preoperative upper urinary tract drainage appears to mitigate the risk of SIRS. Monitoring postoperative CRP and PCT levels can help predict the occurrence of SIRS. Future studies with larger cohorts and comprehensive data collection are needed to validate these results and explore other potential influencing factors. Overall, our findings suggest strategies for reducing the risk of SIRS and improving outcomes in patients undergoing lithotripsy for infectious urinary stones.