An intraoperative methylene blue test can guide patient selection for totally tubeless percutaneous nephrolithotomy

Introduction and Objective Totally tubeless percutaneous nephrolithotomy (PCNL) has been demonstrated to be feasible and safe, particularly for mini-PCNL. Having an objective test to guide patient selection could improve confidence in this practice and facilitate broader adoption. The purpose of this study was to evaluate the utility of an intraoperative methylene blue test to determine candidacy for totally tubeless PCNL.

Adult patients undergoing PCNL at four institutions were included in this study. Patients with prior reconstructive surgery, chronic pain, or requiring ureteral dilation were excluded. After stone clearance, 10 mL methylene blue (MB) dye was injected into the percutaneous access tract. A positive test (“pass”) was defined as visualization of blue dye in the bladder catheter within two minutes of injection. In some standard PCNL cases, totally tubeless management was simulated by placement of a capped nephrostomy tube. Post-operative complications within 7 days were evaluated as the primary outcome.

The intraoperative MB test was performed in 91 PCNL cases: 60 mini-PCNLs (16 Fr access) and 31 standard PCNLs (24+ Fr access). Mini-PCNL cases were more likely to pass the MB test compared to standard PCNL cases (75% vs 38.7%, p = 0.001). Of the 45 mini-PCNL subjects who passed, 40 were left totally tubeless, resulting in two minor complications (urinary retention, obstructing ureteral stone fragment). In the standard PCNL cohort, 12 passed the MB test. Five were left totally tubeless and 3 simulated totally tubeless management with capped nephrostomy tubes; one subject had a transient postoperative creatinine elevation, and one required uncapping for steinstrasse. There were no other obstructive or infectious complications, and no surgical reintervention was required.

An intraoperative methylene blue test is a simple test with high positive-predictive value to determine candidacy for totally tubeless PCNL in real time for both mini and standard PCNLs. Competing Interest Statement The authors have declared no competing interest. Funding Statement This study was supported by the American Urological Association Research Scholar Award (HY), the Urology Care Foundation (HY), and the National Institutes of Health (NIH) through TL1DK139565 (HY) and U2CDK133488 (HY, MS). Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Ethics committee/IRB of University of California, San Francisco gave ethical approval for this work (IRB# 14-14533); Ethics committee/IRB of University of Colorado gave ethical approval for this work (CO-MIRB# 24-0726); Ethics committee/IRB of University of Michigan gave ethical approval for this work (IRB# HUM00278429) I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Footnotes This version corrects errors in the statistical analysis reported in the original preprint. The results and associated interpretations have been updated accordingly. Data Availability All data produced in the present study are available upon reasonable request to the authors.