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

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.