Characterisation of iatrogenic human ureteral laser injury - results from ex vivo testing with a Ho: YAG laser at commonly used lithotripsy settings

Introduction: Modern endourology relies on Ho: YAG lasers for definitive management of urolithiasis. Current safety data is drawn predominantly from Ho: YAG laser testing in animal tissue. We aim to evaluate and characterise the grades of iatrogenic human ureteral injury due to contact with a Ho: YAG laser at commonly used lithotripsy settings. Methodology: Human ureters were collected from consenting adults at the time of radical nephrectomy. A custom rig was developed to secure a 273micron (µm) laser fibre in contact with the urothelium for periods of 5, 10 and 20 s. Testing settings used included 8 Hz (Hz) and 800millijoules (mJ), 10 Hz/1000 mJ, and 5 Hz/1500 mJ. Grades of ureteric injury were then characterised with histopathology. Results: A total of 31 specimens were tested and the mean specimen thickness was 2.2 mm (range 0.9–3.1 mm). The depth of laser-related injury ranged from urothelium alone to full thickness perforation at all settings depending on the duration of laser contact with tissue and specimen thickness. No full thickness perforation was seen in specimens ≥ 3 mm, even at 20 s of contact duration at 10 Hz/1000 mJ. However, in specimens < 1 mm the level of injury depth ranged from urothelium to full thickness perforation at 5 s of testing. Discussion: Ho: YAG laser causes variable levels of injury, with both superficial and extensive injury noted. The thickness of the ureter may determine the extent of trauma following laser contact. Concerningly, full thickness ureter perforation may occur with commonly used laser settings at short laser contact durations.