STONE DISEASE

Characterization of intrapelvic pressure during ureteropyeloscopy with ureteral access sheaths
Rehman J, Monga M, Landman J, Lee DI, Felfela T, Conradie MC, Srinivas R, Sundaram CP, Clayman RV
Department of Surgery, Division of Urologic Surgery, Washington University School of Medicine, St. Louis, Missouri, USA
Urology 2003; 61: 713-8

• Objectives: To evaluate the impact of the ureteral access sheath on intrarenal pressures during flexible ureteroscopy in light of the recent resurgence in their use. As such, using human cadaveric kidneys, we studied changes in intrarenal pressure in response to continuous irrigation at different pressures with and without access sheaths of various sizes and lengths.
• Methods: This study was performed using seven cadaveric kidneys. In three kidneys the study was done in situ with a 7.5F flexible ureteroscope (URS) passed by itself and then passed through a 10/12F sheath (35 and 55 cm in length), whereas, in four kidneys, due to narrowing of the intramural ureter, the study was done ex vivo using the unsheathed URS and then passing the 7.5F flexible URS via the 10/12F, 12/14F, and 14/16F sheaths (all 35 cm in length). A 10F Cope loop pyelostomy was placed to measure intrapelvic renal pressure. Three sets of 3-minute readings (i.e., flow and intrarenal pressure) were taken with the tip of the URS at the distal ureter, middle ureter, and renal pelvis (just above the ureteropelvic junction); the entire process was done at three different irrigant pressure settings: 50, 100, and 200 cm H(2)O. Irrigant flow and intrarenal pressures were measured at all three settings using the URS passed without a sheath and then with the URS passed through the various sheaths positioned at the distal ureter, middle ureter, and renal pelvis.
• Results: With all of the sheaths, intrapelvic pressure remained low (less than 30 cm H(2)O), and there was a 35% to 80% increase in irrigant flow versus the control unsheathed URS. With the sheath in place, the majority of the irrigant drained alongside the URS and out the sheath. Flow and pressure with the 12/14F sheath were equivalent to the 14/16F sheath.
• Conclusions: The 12/14F access sheath provides for maximum flow of irrigant while maintaining a low intrarenal pelvic pressure. Even with an irrigation pressure of 200 cm H(2)O, renal pelvic pressure remained below 20 cm H(2)O.
  
• Editorial Comment
  Ureteral access sheaths have long been available to facilitate access to the ureter and collecting system. However, a cumbersome design and the potential for ureteral perforation prevented the sheath from achieving widespread use. Resurgence in interest in the access sheath occurred with advances in design that improved ease and safety of placement and reduced the tendency of the sheath to buckle. Although the ureteral access sheath has been used primarily to facilitate multiple entries and exits from the ureter and it has been proven advantageous in this regard from the standpoint of operative time and cost, Rehman and colleagues have shown that use of the access sheath is advantageous for physiologic reasons as well. Using a variety of sizes of access sheaths and irrigation pressures in a cadaveric model, these investigators demonstrated that renal pelvic pressure could be kept below 30 cm H2O and irrigation flow could be improved by 35-80% compared to ureteroscopy without a sheath.
  With an increase in the complexity of ureteroscopic procedures has come an increase in operative time. Furthermore, the treatment of larger stones and potentially infected stones has led to an increase in the potential for urinary extravasation and sepsis. The findings of this study suggest that use of a ureteral access sheath, particularly during lengthy ureteroscopic procedures for large renal or ureteral calculi may reduce intrarenal pressure, thereby reducing the likelihood of pyelovenous or pyelolymphatic backflow, as well as the chance of forniceal rupture, extravasation and sepsis, and also improve endoscopic visibility through increased irrigation flow. Particularly when treating a potentially infected stone, maintenance of as low an intrarenal pressure as possible is imperative in order to prevent sepsis. Consequently, use of an access sheath, even when there is no intention of frequent entries and exits from the ureter, may increase the safety of long ureteroscopic procedures.

Dr. Margaret S. Pearle
Associate Professor of Urology
University of Texas Southwestern Med Ctr
Dallas, Texas, USA