Safe pressures for suction ureteric access sheaths: in vitro conversion of pressures to flow

Objective To convert suction pressure settings into practical, size‐specific operating limits for suction ureteric access sheaths (sUAS). Materials and Methods Using an 8.7‐F flexible ureteroscope with a standard 3.9‐F working channel, we measured irrigation inflow at various pressures with no instrument, 270‐μm laser fibre, and 1.9‐F basket. Outflow was measured using 10/12‐, 11/13‐, and 12/14‐F sUAS with suction applied via Neptune 3™ (Stryker, Kalamazoo, MI, USA) at 30‐s intervals and pressures ranging from 50 to 300 mmHg. Inflow and outflow were matched by linear interpolation deriving conservative size‐ and instrument‐specific suction pressure limits for all evaluated sUAS configurations. Results Ureteroscope irrigation inflow ranged from 30 to 130 mL/min as irrigation pressure irrigation increased from 50 cmH 2 0 (gravity) to 300 mmHg. Working channel instruments reduced inflow: mean (± 2 × the standard error of the mean) change of −57.1% (1.6%) for the 1.9‐F basket and −42.1% (2.1%) for the 270‐μm laser fibre vs no instrument. Negative pressure via sUAS generated outflow as slow as 5 mL/min (10/12‐F sUAS, 50 mmHg suction) and as fast as 700 mL/min (12/14‐F sUAS, 300 mmHg suction). Outflow and negative pressure were linearly related ( R 2 0.94–0.99). Increased scope‐to‐sheath ratio (SSR) reduced irrigation outflow. Fully opening the valve significantly reduced outflow by 70.8% on average. The 40‐cm sUAS modestly increased outflow by 13.3% on average compared to 50‐cm sUAS of same diameter. Suction of 50–80 mmHg was ideal for maintaining flow equilibrium with 11/13‐ and 12/14‐F sUAS. The small diameter and high SSR (0.87) of the 10/12‐F sUAS required greater negative pressures (150–300 mmHg) to maintain flow equilibrium. Conclusions Suction pressures as low as 50–80 mmHg are sufficient for majority of sUAS cases. Increasing irrigation inflow with pressure bag systems may counter excessive sUAS outflow; however, introducing instruments can negate this effect.