The primary goal of this retrospective study was to develop and internally evaluate a nomogram to predict the occurrence of SIRS in patients after PCNL. This is the first clinical retrospective research of a group of patients who had undergone PCNL in which the related risk variables can be collected in the first preoperative phase, allowing for an early assessment of the risk of postoperative urosepsis and prompt intervention and treatment.
The safety and effectiveness of PCNL have improved in recent years as a result of the development of minimally invasive technology; however, postoperative infection remains a prominent concern. According to previous research, the incidence of infectious complications after PCNL surgery ranges from 2.8–32.1%[9]. Septic shock can occur if a surgical infection is not discovered in time and no active anti-infective treatment is available. Indeed, fatality rates for severe sepsis and septic shock vary amongst medical centers in different locations and nations, with reported outcomes ranging from 22–76% based on available epidemiological data [10]. The surviving sepsis campaign guideline 2021 recommends SIRS, NEWS, or MEWS as a single screening tool for sepsis or septic shock [quality of evidence: moderate] [11]. In our study, a screening tool as SIRS criteria was used for the early detection of postoperative urosepsis.
The incidence of SIRS after PCNL has been reported in recent studies (23.4% [12], 25.5% [13], and 22% [14]). In our study, a 44% incidence rate was found regardless of careful preoperative preparation, possibly because most patients with SIRS recover without sequelae. Kumar et al. demonstrated the importance of time as a prognostic factor: initiating empirical antibiotic therapy within an hour of the diagnosis of sepsis was associated with 80% survival. For each hour of delayed antibiotic use, the survival rate decreased by an average of 7.6% (79.9% for 1–2 hours, 42.0% for 5–6 hours, and 25.4% for 9–12 hours) [13]. Therefore, the early identification and treatment of SIRS before the patient develops urosepsis have important clinical significance, which is also the aim of this study.
In our study, the overall incidence of SIRS was 44% (41.6% had staghorn stones) compared with another study in which the incidence of SIRS was 23.4% (approximately 16.7% had staghorn stones) [12]. The incidence is relatively high, and it is currently believed that the reason for the increased incidence of postoperative SIRS caused by staghorn stone (OR, 2.87; 95% CI, 1.73–4.77, p < 0.001) may be related to the following mechanisms: the percutaneous removal of urinary calculi has a significant risk for inducing bacteria or bacterial toxins to the systemic circulation, clinically significant bacteriemia, and the consequence of immune reactions, such as the development of SIRS or clinical sepsis. Another factor is that staghorn calculi are caused by infections with large renal stones that occupy most or all of the renal collecting system. These stones have been so named because these branched stones look like the antlers of a deer or stag on imaging. Most staghorn stones are composed of struvite, which is caused when, during an infection, bacteria split urea and provide conditions for stone formation [16]. Bacteria may play a role in stone formation by causing damage to the mucosal layer of the urinary tract, which leads to an increase in bacterial colonization and crystal adhesion [17]. Staghorn stones can also be caused by a long-term or recurrent infection with urease-producing bacteria, and they can be accompanied by or exacerbated by urinary obstruction or stasis [18]. Staghorn stones, on the other hand, may always be difficult to treat with PCNL surgery. Staghorn stones also have a complicated morphology, with many calyces. As a result, lithotripsy stone removal during surgery may take longer, and the risk of multiple tracts increases. Rivera used multivariate analysis to find that the presence of staghorn stones alone was independently linked with an elevated risk of postoperative infection problems (OR, 3.14; p = 0.02) after PCNL surgery [19]. Patients having PCNL had similar outcomes in similar studies.
In this study, positive preoperative midstream urine culture results were found to be an independent risk factor for predicting SIRS after PCNL in patients using multivariate analysis (OR, 2.89; 95% CI, 16.63–5.13; p = 0.017). Current investigations, however, have proven that preoperative midstream urine culture findings have a sensitivity of just 50% for predicting postoperative SIRS when compared to pelvic urine and stone cultures, and that it cannot predict the likelihood of postoperative SIRS [20]. However, specimens for pelvic urine and stone cultures must be taken during surgery, and the wait time for results after surgery is longer. As a result, timely intervention in cases of postoperative infection is impossible, limiting the clinical use of pelvic urine and stone cultures. More research has revealed that the importance of a preoperative midstream urine culture cannot be overstated. Indeed, Gutierrez looked at 865 PCNL patients and discovered that a positive preoperative midstream urine culture (OR, 2.12; p 0.05) was an independent risk factor for fever after surgery [21]. Similarly, Uchida et al. found that obstructive pyelonephritis, positive preoperative bladder urine culture findings, and female sex were all linked to postoperative SIRS in a multivariate analysis of 496 patients receiving ureteroscopic laser lithotripsy [22]. Our findings are consistent with prior research, which found that positive preoperative midstream urine culture results are related with an increased risk of SIRS after surgery. This result can also be acquired before to surgery, which is useful for predicting infection risk and preventing infection after PCNL.
In the multivariate regression analysis of our trial, positive preoperative WBC, positive urine nitrite, and the Guy's stone score were not independent risk factors for SIRS following PCNL. Preoperative WBC and urine nitrite levels, on the other hand, may help predict urinary tract infection and the requirement for treatment. Preoperative WBC (WBC > 1x1010/L) (p = 0.027) was linked with intraoperative and postoperative urosepsis in patients with calculous pyonephrosis, according to Liang et al. in a retrospective review of 287 patients who had had stone surgery. In addition, individuals with urine nitrite had a 3.697-fold higher postoperative risk of urosepsis than those without urine nitrite (p = 0.010), according to the same study. After PCNL surgery, residual stones may contain bacteria and endotoxins, increasing the risk of infection [23].
We added the following three risk factors related with the development of SIRS after PCNL based on the findings of the multivariable analyses: positive preoperative urine culture (p = 0.017), positive preoperative urine WBC (p = 0.028), and stones size 3 cm (p 0.001). Because these three factors may be linked, we created a nomogram based on the relative risk of each component, which is useful for quick clinical reference and application. The area under the curve of this nomogram was found to be 0.702 after internal testing using the ROC curve, indicating fair accuracy. Because the three risk indicators described above can be collected during the preoperative period, the danger of SIRS in high-risk patients must be thoroughly evaluated when surgery is planned. The use of this tool not only aids clinical decision-making and prompt intervention for patients with potentially serious infections, but it also provides a digital basis for surgical prognosis and facilitates preoperative communication with patients about surgical options and risks, which is critical for the perioperative management of the PCNL population. This study has some limitations. First, this is a retrospective cohort study, and there are some confounding factors in postoperative SIRS, such as fever due to atelectasis or inflammatory processes, that cannot be excluded, which might indicate selection bias. Second, there are some missing data in some factors, possibly resulting in non-significant results related to the prediction model, which made the results quite different from previous studies. Despite these limitations, to our knowledge, this study is the first to use a nomogram in patients who had urosepsis secondary to PCNL surgery.