Fluid management and suction in Endourology

As stone surgery has evolved over the last 50 years from open surgery to minimally invasive options two goals remain central: to improve stone-free status and to reduce the risk of complications. For many years, technological improvements focused on miniaturisation of equipment and improving devices to fragment stones (lasers and lithoclasts). In the last 5 years a new and equally important technological advance has emerged in stone surgery: fluid management with suction. The BJUI has featured many manuscripts on this topic as it has developed. The data from benchtop and clinical studies compel us to shift our perception of fluid outflow with suction to an integrated component of stone treatment across both retrograde intrarenal surgery (RIRS) and mini-percutaneous nephrolithotomy (mPCNL). Controlling irrigation is now synonymous with controlling outcomes and minimising patient morbidity. Studies have established a threshold for infectious risk: pyelovenous backflow increases exponentially above an IRP of 60 mmHg directly leading to bacteraemia and increased sepsis risk 1. With conventional techniques, IRP frequently breaches these limits. Direct in-scope suction (DISS) can reduce the IRP by aspiration of the fluid in the kidney and recreate a pressure gradient between fluid bag and kidney for irrigation to flow into the kidney again. Flexible and navigable suction sheaths (FANS) equilibrate IRP with atmospheric pressure and reduce outflow resistance even without suction. This allows higher irrigation flow rates with lower IRPs. These flow rates can be enhanced with suction (if the system is closed). Studies show that low suction pressures, typically around 50–80 mmHg, are sufficient to balance irrigation inflow and maintain flow equilibrium, thereby keeping IRP within safe, physiological ranges, particularly when using optimal sheath sizes like 11/13 F and 12/14 F 2. This concept has translated into clinical benefit, with a meta-analysis on mPCNL confirming that vacuum-assisted access sheaths (VAAS) significantly reduce postoperative fever and overall minor complications compared to conventional sheaths 3. This indicates that effective pressure control is key to reducing infectious complications. Retrograde intrarenal surgery (FANS vs DISS): in retrograde approaches, suction dramatically enhances SFRs, especially for challenging lower-pole and larger stones, positioning RIRS as a viable alternative to mPCNL in select cases 4. Benchtop analyses now define the distinct roles of the major suction modalities: Factors such as stone size and calibre of the lumen of the ureter determine which approach is most applicable in each patient. The continued success of suction hinges on optimising the balance between device size, flow rate, and manoeuvrability. Research demonstrates that simply decreasing sheath size or increasing scope size significantly impacts the outflow resistance (the annulus space), which in turn dictates the flow rate achievable within safe IRP limits even without applied suction 8. This is the current technical trade-off: while larger aspiration devices (like the 11.9-F synchronous suction CVAC® Calyxo, Inc., Pleasanton, California, USA system) offer powerful evacuation capacity, they may compromise anatomical flexibility and require larger access 5. Conversely, smaller DISS ureteroscopes respect ureteric anatomy but are prone to blockage by fragments larger than 250 μm 6. The ultimate goal must be the development of an ‘integrated suction concept’ 9. This ideal system must combine anatomical size, high-quality vision, integrated energy and fluid management that incorporates simultaneous irrigation, suction, pressure control, and crucially, automatic blockage detection and unblocking mechanisms. Until this device is realised, clinicians must strategically tailor the combination of ureteroscope and access sheath size to the specific stone burden and anatomy, recognising that optimal outcome is achieved by maximising evacuation while enforcing IRP safety thresholds. Fluid management with suction has earned its place as a cornerstone of endourological practice. It enhances safety by mitigating the exponential risk of high IRP-related bacteraemia, and it improves efficacy by boosting SFR and shortening operative time in both PCNL and RIRS. The field now faces the challenge of translating these findings into standardised protocols. By embracing these data and pushing for the integrated, intelligent suction systems of tomorrow, we can confidently move toward the ultimate goal of zero RFs, with minimised procedural risk. Ben Turney has received research grants from Boston Scientific and has acted as a consultant for Boston Scientific, Pusen, EMS, Olympus and Dornier.