In China, a large number of PCNL procedures are completed every year. With the advancement of imaging equipment and endourological instrumentation, the efficacy and safety of PCNL have been substantially improved. However, postoperative SIRS remains a challenging complication, which can prolong hospital stay and require additional antibiotic treatment. In our study, incidence rate of SIRS (17.2%) after PCNL was similar to the previous reports (9.8 to 37%). Probably, most patients with SIRS recover without sequelae after treatment, but some doctors ignore the underlying risks. Unfortunately, a small part of SIRS patients could progress to catastrophic severe sepsis. A recent series identified an international cohort of > 5,000 patients who underwent PCNL and found that only two died of sepsis [7]. In this study, 3 out of 303 patients developed into severe sepsis, who were admitted to an intensive care unit and rescued successfully.

The pathophysiology of post-PCNL SIRS is multifactorial, including infection, proinflammatory cytokines, ischemia-reperfusion injury, and response to the injury of kidney [8]. Though the exact mechanism of SIRS after PCNL is still obscure, two reasons cannot be neglected. One reason is that the stones as a foreign body contribute to the escape of bacterial eradication by antibiotics and immune system [4]. The other reason is that the minimally invasive nature of PCNL has the potential to create high intrarenal pressure, triggering the backflow of contaminated fluids into the systemic circulation, which may include bacteria, endotoxins and the inflammatory mediators, etc. Several investigators have correlated intrapelvic pressure with postoperative SIRS [9]. The intraoperative intrapelvic pressure was mainly affected by the type of endoscope, the size of access tract and endoscope, irrigation fluid pressure, and flow rate of irrigation. Especially, many Chinese institutions preferred the 18–20 F access tract compared with 24–26 F access tract in America and Europe. In our study, all the procedures were performed with 18 F access tract using an 8/9.8 F rigid ureteroscope by an irrigation pump setting the irrigation fluid pressure at 110 mmHg and the flow rate of irrigation at 0.4 L/min. We aimed to explore the risk factors for post-PCNL SIRS under controlled intrapelvic pressure.

Many investigators have examined the risk factors that increase the likelihood of post-PCNL SIRS. The risk factors for SIRS after PCNL differ among the studies. Gonzalez-Ramirez et al. identified staghorn stones, body mass index < 18.5 kg/m2, bleeding, and prolonged surgical time were associated with postoperative fever in a study of 280 cases [10]. Several studies suggested that female sex, DM, positive renal pelvic urine culture, operative time, stone size, stone culture, blood transfusion, residual stones, and hydronephrosis were the risk factors facilitating the development of SIRS after PCNL [1, 11, 12]. In the current study, the stone size, operative time, history of DM, the value of glycosylated hemoglobin, history of ipsilateral surgery, preoperative urine culture, staghorn calculi, pelvic urine culture, stone culture, number of tracts, blood transfusion, and residual stones were found to have a significant correlation with post-PCNL SIRS. However, only the stone size, preoperative urine culture, pelvic urine culture, number of tracts, and blood transfusion were identified to be the independent risk factors for post-PCNL SIRS. This is probably attributed to the close relationship between risk factors.

Positive preoperative urine culture has been found to be a risk factor for postoperative fever and confirmed by several studies [12, 13]. A recent study demonstrated that the rate of postoperative SIRS in patients with positive preoperative urine culture was nearly twice that of with a sterile urine culture [14]. In this study, positive preoperative urine culture was demonstrated as an independent risk factor for SIRS after PCNL, which is consistent with previous studies. However, preoperative urine culture often fails to grow stone-colonizing bacteria, and the discordance was reported to reach 25% [15]. In the current study, 5 cases were found that the type of bacteria in preoperative urine culture was different from that of stone culture. Therefore, some researchers suggested that positive pelvic urine and stone culture may be better predictors of post-PCNL sepsis than preoperative urine culture [16]. In this cohort of patients, 29 patients (9.6%) had a positive pelvic urine culture or stone culture but a negative preoperative urine culture. In the current study, we found that positive pelvic urine culture (OR = 13.523, 95%CI = 3.756–48.687) may be a stronger predictor than preoperative urine culture (OR = 3.743, 95%CI = 1.333–10.458).

Higher stone burden prolongs the operative time and increases propensity of bleeding while the intraoperative bleeding hampers vision resulting in lengthening the operative time, making it a vicious cycle. Moreover, staghorn stones may require multiple tracts and increase the probability of residual stones. In this study, stone size was an independent risk factor of post-PCNL SIRS, although the operative time and staghorn stones were significantly associated with postoperative SIRS but not an independent risk factor, which was comparative to findings of previous studies [17, 18].

Blood transfusion is a common treatment method for hemorrhage. However, many studies have confirmed that blood transfusion leads to immunosuppression through various pathways, such as the release of inflammatory factors, the inhibition of immune cells, and the production of transplant antibodies [19, 20]. Allogenic blood transfusion within the first 24 h after trauma was also considered an independent predictor of increased SIRS and mortality risk [21]. Similar to many previous studies [22,23,24], our research also found that blood transfusion was a strong independent risk factor for SIRS after PCNL. The requirement of blood transfusion for PCNL often occurs in patients with intraoperative bleeding, which indicates a higher volume of fluid absorption and pyelosinus backflow [25]. Sometimes, a new tract is needed for a better operative field, which leads to an increased risk of bleeding or transfusion. It has been reported that a higher rate of blood transfusion in patients was observed when multiple access tracts were used [26]. Not all renal punctures result in the successful establishment of working tracts. Unsuccessful punctures may elevate the risk of hemorrhage and other complications [27]. Furthermore, Tan et al. reported that puncture through the lower renal calyx is associated with a higher risk of significant postoperative hemorrhage, indicating that the risk of severe bleeding following PCNL varies by puncture site [28]. The number and site of renal punctures should also be considered in future analysis. In summary, the relationship between blood transfusions and SIRS calls for further research and careful clinical decision-making.

Moreover, we used the Spearman correlation analysis to analyze the correlation among various clinical variables in total and different subgroups. Our study found that the correlation pattern of variables in total and different subgroups was different, suggesting that the correlation between variables may vary with gender, disease status or other conditions. Further elucidating the causes of these heterogeneities may help us to better understand the mechanism of post-PCNL SIRS and improve disease management.

This study has several limitations, including the small number of cases, single-center design, and retrospective nature, potentially introducing selection bias. Given the limited sample size and low positivity rate for certain bacterial species, we were unable to assess the impact of different bacterial species on the risk of post-PCNL SIRS. Utilizing various imaging modalities to estimate stone size may introduce bias in the measurement process. Many important factors, such as stone composition, preoperative and postoperative antibiotics, are required to be further investigated regarding their correlation with SIRS. The cause-and-effect relationship between the risk factors and post-PCNL SIRS also needs to be confirmed by a prospective and randomized study. Our results provide the warnings that contribute to the occurrence of SIRS after PCNL.