Modified scope reduces luminal pressure by 40%

June 1, 2008

By simply placing grooves at the 3 o'clock and 9 o'clock positions down part of the length of a semi-rigid ureteroscope, urologists were able to decrease luminal pressures by nearly 40% in an in vitro model.

By simply placing grooves at the 3 o'clock and 9 o'clock positions down part of the length of a semi-rigid ureteroscope, Dr. DiTrolio and colleagues were able to decrease luminal pressures by nearly 40% in an in vitro model. Presumably, the grooves will allow irrigation fluid to drain more easily out of the ureter and improve visibility, Dr. DiTrolio reported at the European Association of Urology annual congress here.

"With the standard ureteroscope, the fluid is trapped in the ureter and renal pelvis, and much of it is reabsorbed by the patient," said Dr. DiTrolio, clinical professor of surgery at the University of Medicine and Dentistry of New Jersey in Roseland.

That's exactly what happened under lab conditions.

Working with representatives from the New Jersey Institute of Technology, Dr. DiTrolio's group made two 10F artificial ureters from silicone. A standard 6.9F semi-rigid scope served as the control, while the modified scope featured the bilateral back-flow grooves. The 2F grooves began at the dilated 13F section of the scope's shaft from 10 to 25 cm.

Both scopes had 50 cc syringes attached to them, as well as a perfusion pump, which was set to 20 cc/hour and connected to the bridge of each scope. One scope was placed into each artificial ureter at distances of 12.3 and 16 cm, and the ureter was obstructed 5.3 cm distal to the tip of the scope.

"We had used this modified scope and felt that it was working better than the normal scope, but we wanted to prove it," Dr. DiTrolio said. "There's no way you could prove a difference in vivo. Even if you took the same person and put one scope up the ureter once and another scope a minute later, you've already dilated the ureter, so it's impossible to get an accurate reading."

Less fluid, pressure

At the 12.3-cm mark, the modified ureteroscope required 33% less fluid than the regular scope to reach the leak point on three consecutive readings. At 16 cm, the difference was 38%. Over the length of the groove, Dr. DiTrolio noted, up to 50% less pressure was required.

In light of these findings, Olympus America, Inc. (Orangeburg, NY), which provided both ureteroscopes for the trial, announced that it would begin production of the modified scope later this year, said Dr. DiTrolio, who serves as an unpaid consultant for the company.

"I suppose what I find most amazing is that in 100 years of performing cystoscopy, no one had thought of putting a groove on the side of the scope to let the water flow back around the side," he added.

"You have a hypothesis in your head as to what will happen [in the in vivo model], but you're not sure. Everything was done three times, and it was remarkable how consistent it was."

The authors noted in the conclusion of their study that "utilization of dead space within a ureteroscope can enhance its performance and reduce intrarenal pressure without compromising the efficiency and structural integrity of the instrument."