Pressure-flow behavior during RIRS irrigation: a controlled ex vivo porcine kidney study of flow-dependent apparent outflow resistance.

PURPOSE: To measure actual irrigation flow and intrarenal pressure (IRP) under different irrigation modes during retrograde intrarenal surgery (RIRS), and to develop a controlled ex vivo empirical pressure-flow model for the tested endoscope-sheath configurations.

METHODS

A controlled ex vivo porcine kidney-ureter model was used, with all measurements taken using a 200 μm holmium laser fiber in the working channel of a 7.5Fr or 6.3Fr flexible ureteroscope and 10/12Fr or 12/14Fr suction access sheaths. Manual syringe, gravity, and automatic pump irrigation were tested across three porcine kidney-ureter units. Each condition was measured in triplicate (technical repeats); condition-level means were used for model fitting and internal assessment.

RESULTS

Actual flow rose with driving pressure and fell with scope deflection. For the ZSR pump, flow increased from 32.0 to 99.8 mL/min (7.5Fr) and from 9.3 to 49.7 mL/min (6.3Fr) across the tested pressures. Pooling pump and syringe data, apparent outflow resistance increased at higher flow, so the non-suction relation was described by [Formula: see text]. Across 20 condition-level means, the complete model gave an RMSE of 1.04 mmHg and R² of 0.994. In a single-operator full-speed syringe test, back-calculated driving pressure was approximately 600 to 770 mmHg.

CONCLUSION

In this controlled ex vivo model, apparent outflow resistance was flow-dependent, and the empirical model described the tested pressure-flow behavior. Forceful syringe flushing should not be routine when controlled pump, water-injection, or adequate gravity irrigation is available. Clinical safety claims require in vivo and clinical validation.