Retrograde Intrarenal Surgery (RIRS) and Intrarenal Pressures

Retrograde intrarenal surgery (RIRS) is one of the main Renal stone removal treatments and has been gaining popularity among urologists for the last years. To achieve better visibility during the procedure, irrigation flow (IF) and irrigation pressures (IPs) must be increased. Normal IRPs range from zero to a few H2O cm. Nevertheless, consequent intraoperative increments in intrarenal pressures (IRPs) are able to deteriorate any procedure. And yet only a few endourologists remain cognizant and are aware of normal and pathological IRP values. Furthermore, the impact of increased ISPs in preoperative complications and the ways to prevent them by controlling IRPs remain unknown.

Complications directly related to increased IRPs are:

- Backflow and fluid absorption: pyelo-venous backflow may occur at pressure range of 13.6-27.2 H2O cm. Preexisting factors such as low urine flow, ischemic damage, and vesicoureteral reflux lower the critical pressure for backflow. A serious complication of pyelovenous backflow is excessive irrigation fluid absorption, it may result in fluid overload, electrolyte imbalance and cardiovascular instability.

- Infectious complications: increased IRP constitutes a major predisposing factor for postoperative fever and sepsis. SIRS occurs in 8.1% of cases after RIRS.

- Kidney damage: IPs higher than 204 cm H2O have been demonstrated to cause significant pathological changes in the kidneys resulting in calyces urothelium denudation, submucosal edema formation, congestion, and pericalyceal vasculitis. Forniceal rupture with pyelovenous backflow has been associated with perirenal pseudocysts, retroperitoneal edema, fibrolipomatosis, perinephritic abscess, and perirenal hemorrhage.

Tools and strategies to maintain decrees values of IRPs during surgery are the use of:

- Ureteral access sheaths (UAS): in flexible ureteroscopy. 10/12F UAS is the new standard UAS with low friction rates.

- Automated irrigation/suction pump system.

- Small size ureteroscopes.

- Intraluminal pharmacological treatment with isoproterenol.

To conclude, IRPs lower than 30 H2Ocm should be maintained during endourological procedures to avoid complications and deleterious effects on the renal units.