Study population. This retrospective study was performed in line with STROCSS guidelines. After obtaining an institutional ethics approval (#2019186), we retrospectively reviewed patients with IC/BPS who underwent hydrodistension in our hospital during January 2010 and May 2021. The diagnosis of IC/BPS was made by the same senior urologist according to the National Institute of Diabetes, Digestive and Kidney Diseases guidelines. A stepwise procedure of elimination of disorders with similar symptoms was performed. Generally, urinalysis and urine culture were performed to exclude UTI and some specific infections, ultrasound and imaging were conducted to exclude malformation, carcinoma and urinary stones, and urodynamic studies were performed to assess functional disorders. Patients who met the inclusion and exclusion criteria were considered eligible for the study. Medical records were reviewed to extract baseline information, including age, body mass index (BMI), duration, antithrombotic use and classification, symptom assessment, and perioperative parameters. Patients were then contacted and volunteered to undergo a follow-up.

Antithrombotic therapy. Antithrombotic drugs in the current study included anticoagulation (heparin, warfarin, as well as rivaroxaban) and antiplatelet drugs (aspirin, clopidogrel). The study aimed to investigate if perioperative bleeding complications were more common in patients on antithrombotic therapy. The algorithm of managing antithrombotic use is based on clinical practice. After a cardiologic and anesthetic consultation, patients taking aspirin remained on therapy throughout the procedure and after the procedure. Clopidogrel was held 5 days before hydrodistension and was restarted 24 hours postoperatively. Both low molecular weight heparin (LMWH) and rivaroxaban were discontinued 1 day before surgery and were restarted one day postoperatively. Warfarin was held 5 days before hydrodistension and was restarted 12 hours postoperatively, keeping an international normalized ratio (INR) 2-3.

Bladder hydrodistension. All patients signed informed consents. Patients' basic conditions were carefully evaluated and managed before surgery. The hydrodistension was in a day-surgery setting in our institute and was performed by the same urologist or under his supervision. Broad spectrum antibiotics were given 30 minutes preoperatively. After general anesthesia, Hunner lesions were identified by cystoscopy with the bladder slightly filled with saline. Then, the bladder was distended with normal saline at the pressure of 70 cmH2O for 2 minutes. Under this circumstance, a waterfall bleeding sign from Hunner lesion or glomerulations in submucosa might be visualized. Subsequently, biopsy was performed to exclude carcinomas in situ. At last, a 16 Fr three-way catheter was inserted with continuous saline irrigation. The time to remove catheters and the time to discharge after voiding tests were decided by the treating physician. Intravesical instillation of hyaluronic acid was performed as a follow-up treatment for all patients according to the instructions. Telemedicine-based follow-ups were performed at 3 months after surgery. Perioperative parameters, including operation time, hospital stays, catheterization time, and hematological results (hemoglobin, platelet count, and coagulated parameters) were recorded.

Outcomes. Primary outcomes were complications that were defined by Clavien-Dindo classification of surgical complications. The complications were recoded within 3 months after surgery. Then, the mean frequency of voids per day, number of night urination, O'Leary-Sant Interstitial Cystitis Symptom index (ICSI), O'Leary-Sant Interstitial Cystitis Problem Index (ICPI), and 10-point visual analog scale (VAS) 3 months postoperatively were analyzed to evaluate the improvement of symptoms.

Data analysis. SPSS software (version 25) and GraphPad Prism software (version 8.0) were applied to perform all statistical analyses. Continuous variables are presented as the means ± standard deviation or medians (range), and differences between groups were tested using the Student's t test or the Mann-Whitney U test, respectively. The changes of pre- and postoperative continuous variables were tested by the paired t test. Categorical parameters were reported as the numbers (percentage), and the chi-square test with and without Yates' correction was applied where appropriate. Subsequently, odd ratio (OR) and 95% confidence interval of each adverse event after antithrombotic use were calculated. A p value of \< 0.05 was considered statistically significant.