Lithotripsy Use Declining?

by Wayne Kuznar

CLEVELAND—A shift away from shock-wave lithotripsy (SWL) and toward flexible ureteroscopy is changing the landscape of stone disease treatment, said Mihir M. Desai, MD, during the Cleveland Clinic's Nephrology Update 2008.
The enthusiasm for SWL at many academic centers in the United States is waning as new-generation compact lithotriptors are less successful at stone fragmentation compared with the earlier Dornier HM3, said Dr. Desai, Director of the Stevan B. Streem Center for Endourology, Glickman Urological and Kidney Institute of the Cleveland Clinic, and associate professor of surgery at the Cleveland Clinic Lerner College of Medicine of Case Western Reserve University. This is because of attempts to reduce SWL's effect on surrounding tissue by reducing the focal zone and the persistence of long-term safety concerns with shock-wave delivery.
The preferred methods for treating renal stones at the Cleveland Clinic, as in many other centers, are now percutaneous nephrolithotomy (PNL) for larger calculi and flexible ureteroscopy for small- to medium-sized renal calculi, he said. “Second and third generation flexible ureteroscopes are smaller, have greater deflection and can reach more areas of the urinary tract,” he said.

SWL safety concerns

SWL may pose certain safety concerns. In a 19-year follow-up of patients undergoing SWL for renal and proximal ureteral stones, Krambeck and colleagues found significantly increased risks of hypertension and diabetes compared with controls, even after adjusting for BMI, Dr. Desai noted.
Limitations of this study included its retrospective nature, the 59% response rate from the original series, the use of a first-generation (Dornier HM3) lithotriptor in all cases, and the lack of a clear causal relationship between SWL and hypertension and diabetes.

Recent research, however, has found an elevation of pancreatic enzymes in patients undergoing SWL, establishing a potential link between it and the development of diabetes, Dr. Desai noted.
Japanese investigators found no such link between SWL of renal stones and hypertension or diabetes. Even though the association of SWL and diabetes currently remains controversial, the potential for diabetes should be factored into counseling of patients when explaining options for the treatment of kidney stones, he said.
A poor response to lithotripsy has been observed with certain stone characteristics. Predictors of a poor response are greater stone density, a greater stone-to-skin distance, and a larger stone volume.

Ureteroscopy advances

Active deflection of scopes and the availability of accessories, such as nitinol baskets and holmium laser, have also enabled the increasing application of flexible ureteroscopy for renal calculi, Dr. Desai added.
One advantage of flexible ureteroscopy is fragmentation of stone under direct visualization. “It doesn't have the unpredictability of shock-wave lithotripsy,” he said.
Other advantages include the ability to reposition fragments into a favorable location, basket removal of some stone burden, and proper identification of parenychmal calcifications.

Recent studies also indicate that flexible ureteroscopy can be performed in patients on active coagulation without hemorrhagic or thromboembolic complications, he said.

 “Multiperc”

Complete removal of staghorn calculi is mandatory, as these stones are associated with high rates of morbidity, mortality, persistent infection, and rapid stone regrowth.

For staghorn calculi, Dr. Desai recommends aggressive PNL, or “multiperc” [multiple percutaneous access]. Multiperc is the philosophy of completely clearing all calculi using multiple tracts and/or sittings, with SWL reserved for the occasional patient in whom percutaneous clearance is either dangerous or unfeasible.

Multiperc offers the capability for complete stone clearance in a single hospitalization with a reduced need for ancillary procedures and re-treatments.

Examining multiperc results over a 13-year period during which 650 kidneys were treated reveals a complete clearance rate of 85%, a need for ancillary procedures 9% of the time, and a 91% final clearance. Thirty-two percent of the cases were managed with a single tract, 36% needed two tracts, and 12.4% required more than three.

The potential impact on renal function has been a concern with multiperc, but percutaneous nephrostomy tracts appear to cause minimal change in renal function, said Dr. Desai. “There is a slight decrease [during] the immediate postoperative period in creatinine clearance and estimated glomerular filtration rate but a marginal improvement in kidney function [as ascertained by CKD class] at one year,” he said. “The overall impact on renal function was positive.”

Kukreja and colleagues in 2003 showed that PNL in patients with preoperative renal insufficiency resulted in normalization of kidney function in one third and an improvement in another 47%. Pre-existing conditions, such as proteinuria and infection, were significant predictors of long-term renal function.

For patients with renal insufficiency, technical modifications, including staging (less than 90 minutes of nephroscopy time), prior nephrostomy drainage, hydration, and antibiotics, may be necessary to preserve renal function.

Multiperc does result in blood loss that was associated with a mean drop in hemoglobin of 1.9% and higher loss with multiple tracts. The procedure-specific transfusion rate is about 11%. Aside from multiple tracts, other factors that affect blood loss during PNL are previous open surgery or PNL, an operative time greater than 90 minutes, intraoperative complications, and diabetes. PNL appears safe in anticoagulated patients, he said.

Medical expulsive therapy

Medical expulsive therapy can be offered as an initial treatment if pain is well-controlled, renal function is adequate, and sepsis is absent, Dr. Desai said. Persistent obstruction, a stone that is not passing, or increasing colic are indications for removal.

“Ninety-five percent of stones pass within the first four weeks; this is the cutoff we generally use when observation stops and treatment is indicated,” he said.

Robotics: The future

An attempt to overcome these limitations has led to the introduction of robotics, said Dr. Desai. Investigators at Cleveland Clinic have worked on a flexible robotic catheter control system to perform flexible ureteroscopy. The robotic catheter system has instinctive control via a joystick. The tip of the sheath can be positioned in space at any time by control of the 3D joystick called the master input device.

After showing its feasibility in animal models, the robotic system was used to perform flexible ureteroscopy in 18 adult humans, 15 of whom had one stone each. On kidney, ureter, bladder radiography, stone clearance was 44% on postoperative day 1, 78% at two weeks, and 89% at three months; an ancillary ureteroscopic stone removal was required in one case.