Characterizing the flow-pressure relationship for flexible and navigable suction ureteral access sheaths in...

To characterize the relationship between irrigation flow and intrarenal pressure (IRP), and determine the maximum irrigation flow rate for maintaining IRP below threshold of 30 mmHg during retrograde intrarenal surgery (RIRS) with the flexible navigable suction ureteral access sheath (FANS). Fresh ex vivo porcine kidney model were used to establish a manometric system for measuring IRP. IRP was measured through needle tubes punctured into the upper and lower calyces. Flexible ureteroscopes (F-URS) and FANS with varying scope-to-sheath ratios were used to simulate RIRS. The FANS was connected to a vacuum suction device with a suction pressure set at 0.02 MPa (150 mmHg). IRPs were recorded at different irrigation flow rates under no-suction, vent-open, and vent-close conditions, while adjusting the positions of the F-URS and sheath within the kidney. At a scope-to-sheath ratio of 0.716, IRPs exceeded the safe threshold of 30 mmHg at irrigation flow rates of 150 and 250 ml/min under no-suction and vent-open conditions. However, at a flow rate of 300 ml/min, IRPs remained below the safe threshold under vent-closed conditions. At a scope-to-sheath ratio of 0.75, IRPs exceeded 30 mmHg at irrigation flow rates of 150, 250, and 300 ml/min under no-suction, vent-open, and vent-close conditions, respectively. The maximum irrigation flow rate to maintain IRP below the 30 mmHg threshold for the FANS during RIRS increased with the application of negative pressure. Furthermore, under the same negative pressure conditions, the maximum irrigation flow rates decreased as the scope-to-sheath ratio increased.