Intrarenal pressures during flexible ureteroscopy: an insight into safer endourology

Automatic irrigation system with a fiber-optic pressure sensor regulating intrapelvic pressure for flexible ureteroscopy

Increased intrapelvic pressure (IPP) due to irrigation during flexible ureteroscopy (f-URS) can pose a risk of postoperative severe urinary tract infection associated with pyelovenous backflow. An automatic regulation system for maintaining safe IPP levels could enable surgeons to perform f-URS safely without postoperative complications. This study aimed to assess the measurement accuracy of an ultra-miniature fiber-optic pressure sensor incorporated into a small-caliper ureteroscope for assessing IPP and to develop an automatic irrigation system linked to this sensor. A porcine kidney was used for the ex vivo experiment. The nephrostomy catheter, connected to the conventional pressure transducer, was placed on the renal pelvis to evaluate the actual IPP (a-IPP). For measuring IPP using the fiber-optic pressure sensor (fo-IPP) built into the f-URS, a diaphragm pressure sensor of Φ250 μm was used. To establish an irrigation system, the optimal proportional-integral-derivative (PID) controller was explored to accurately adjust the irrigation pump flow rate. A high correlation between a-IPP and fo-IPP was confirmed across irrigation pressure values of 60-180 mbar (all, r ≥ 0.7, p < 0.001). When performing bolus irrigation, although fo-IPP showed relatively a higher peak value than a-IPP, the response time of fo-IPP was equivalent to that of a-IPP. After PID parameter optimization, our automatic irrigation system based on fo-IPP smoothly and accurately regulated the intended IPP set in the 5-20 mmHg range without overshooting. We successfully developed and demonstrated an automatic irrigation system regulating IPP based on the PID controller for f-URS, utilizing a fiber-optic pressure sensor. Further research, including in vivo studies, will be needed to assess clinical feasibility.