Patient Data Collection
The methods and procedures for this study were approved by the Ethics Committee of Hirao Hospital (project identification code: 2019-4). The retrospective analyses evaluated data from 1361 patients who underwent URSL at Hirao Hospital from January 2011 to December 2017. There was no history of pre-URSL pyelonephritis, ureteral stone of ileal conduit, or transplant renal stone in 1122 of these patients, leaving 239 patients with a history of pre-URSL obstructive pyelonephritis eligible for this study. All patients underwent urinary drainage by insertion of a ureteral stent or nephrostomy.
The diagnosis of obstructive pyelonephritis was based on computed tomography (CT) and laboratory data, such as bacteriuria and leukocyturia. According to criteria established by the American College of Chest Physicians/Society of Critical Care Medicine Consensus Conference Committee , systemic inflammatory response syndrome (SIRS) was defined by the presence of ≥ 2 of the following features: (1) body temperature lower than 36°C or higher than 38°C (2) heart rate > 90 beats per minute; (3) respiratory rate > 20 breaths per minute or PaCO2 less than 32 mmHg; (4) a white blood cell count higher than 12,000 per mm3 or lower than 4,000 per mm3. In this study, fUTI accompanied with SIRS were defined as sepsis based on an international definition .
Treatment policy of obstructive pyelonephritis
The first line treatment for obstructive pyelonephritis is urinary drainage, which is mainly performed by ureteral stenting. Retrograde placement of a 6 Fr ureteral stent was performed using a flexible cystoscope under transurethral local anesthesia. In case with highly viscosity of the renal pelvic urine, we used a single J stent that can clean the renal pelvis because of a high risk of ureteral stent occlusion. If retrograde placement was not possible, nephrostomy using an 8.3 Fr pigtail stent (Jinro, Boston Scientific, Tokyo, Japan) was performed under ultrasound and fluoroscopy. In most cases, renal pelvic urine cultures were submitted, and empirical antibiotic treatment was administered for at least 14 days. The period between pyelonephritis treatment and URSL was based on the judgment of each physician. The day of antipyresis was defined as the first day of body temperature less than 37°C, which continued for two or more days.
All URSLs were performed under general anesthesia in the lithotomy position. Ureteral stent was removed at the beginning of URSL. A semi-rigid 6.4/7.8 Fr ureteroscope (Olympus, Tokyo, Japan) was inserted into the ureter along with a flexible 0.035 inch guidewire. If there were only distal ureteral stones, they were broken up with a holmium: yttrium-aluminum-garnet laser (VersaPulse; Lumenis, Tel Aviv, Israel) using a semi-rigid ureteroscope and collected with basket forceps. If there were renal stones, a ureteral access sheath (UAS) (Flexor, 12/14 Fr, COOK, Tokyo, Japan; Bi-Flex, 12/14 Fr or 10/12 Fr, ROCAMED, Mclean, VA, USA) was inserted into the proximal ureter along with the guidewire under fluoroscopy. A part of upper ureteral stones were pushed back into the renal pelvis during URSL, and a UAS was inserted to perform intrarenal surgery. The flexible ureteroscope (URF-P5, Olympus) was then inserted through the UAS, and stones were crushed by the same methods of semi-rigid ureteroscopy. Ureteral stents and urethral catheters were placed after all ureteroscopic procedures. If there was no fever after URSL, urethral catheters were removed the day after operation, and ureteral stents were removed 7-14 days after operation outpatiently. Pre-URSL antibiotic prophylaxis was based on the judgment of each physician. Mostly perioperative antibiotics were infused with second or third generation cephems for 3 days from the operation date. Based on the results of preoperative renal pelvic urine culture, the antibiotic was appropriately changed to a sensitive antibiotic. Post-URSL fUTI was defined as a fever of 38°C or higher accompanied by pyuria or bacteriuria within 7 days of surgery.
Analysis of potential risk factors
The parameters investigated as potential risk factors included age, sex, body mass index (BMI), comorbidity (diabetes, hypertension, hyperlipidemia), presence or absence of pre-URSL ureteral stent, stone position at URSL, stone laterality, stone size, Hounsfield unit (HU) value, history of sepsis during obstructive pyelonephritis, renal pelvic urine culture at urinary drainage, period from antipyresis to URSL, pre-URSL ureteral stent placement period, operation time, and presence or absence of UAS at URSL. In addition, the stone components and renal pelvic urinary culture bacterial species at urinary drainage during pre-URSL pyelonephritis were also examined.
Data are shown as bar charts or dot plots and were evaluated using the Student t-test, the Mann-Whitney U test, or the χ2 test, as appropriate. Multivariate analyses were used to identify independent prognostic variables based on logistic analysis (p < 0.05 in the univariate analyses). Multivariate analyses were performed using StatMate (version 5.0; Tokyo, Japan) and other data were analyzed using PRISM software (version 7.00; San Diego, CA, USA). A p value < 0.05 was considered statistically significant.