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of fragments and a higher chance of stone recurrence and need for another procedure in a short period of time. You want to get your patient stone-free, and then you want to keep them stone-free. The ureteral access sheath means decreased case time, higher stone-free rates, less urosepsis, lower renal pelvis pressures, as well as other benefits. What's the downside? Splitting the ureter. At UCI, we have come to realize that if you do split a ureter out to periureteral fat, there's a 13% chance that the patient may go on to form a ureteral stricture; in all of these individuals you are going to extend your stent indwell time to two to six weeks. A question arose seven or eight years ago, when I was working with Dr. Kam Kaler, a former fellow, who is now on the faculty at the University of Calgary. We had completed a ureteroscopic case with an access sheath and on the way out noted that the ureter had been split. The question arose: "Ηow much force does it take to split the human ureter?". Nobody knew. So, with that that simple question in mind, we went to the UC Irvine Samueli School of Engineering, got involved with Mike Klopfer and created a student project. He and his students developed an access sheath specific force sensor, that we could put over the guide wire and measure how much force we were putting on the access sheath, while passing it. With that single device, we went to the laboratory and did a series of in vivo studies with the porcine ureter. We learned that, if you're using less than 6 newtons of force, you would
not split a ureter, but if you went over 8 newtons, you started splitting ureters. Well, what's the difference between 6 newtons and 8 newtons of force? It is half a pound. Your ability to distinguish the difference between a pound and a half of force (6N) and two pounds of force (8N), when you're trying to put up a 55 cm long access sheath over a guide wire, is pretty much nonexistent. To show how difficult this was, Mr. Amir Lavasani and other people in our laboratory created a model and showed that a third of urologists actually push at less than 4 newtons, a third push in the 4- just under 8N range, and another third routinely go over 8N. This seems to be quite accurate, because in separate reports by Manoj Monga and Olivier Traxer, ureters were being split when placing a 14 Fr access sheath in 13% to 24% of patients.
Subsequently with this knowledge, we completed a large clinical study in which we instructed our surgeons to use the force sensor and stay at or below 6N of force when placing a ureteral access sheath. What was fascinating was that in doing this our surgeons pass a 16 Fr access sheath in 53% of their patients and there were 0% ureteral tears. Right now, we're in the process of trying to make a very inexpensive disposable force sensor, that you could use in the operating room. Dr. Bruce Gao, who's our current fellow, has helped us create an air- based force sensor, that will indicate to the surgeon when 2, 4, 6 or 8 Newtons is applied to the access sheath. All of this would never have happened without the collaboration with engineering. Endourology would never have happened without collaboration with radiology. Clearly, the ability and willingness to collaborate with other specialties is so important and beneficial. Together we can do things than neither one of us alone can accomplish.
T.S.: You are one of the urologists who established the ESWL for urolithiasis management. Do you believe that in 2024 there is still room for ESWL?
Prof. Ralph V. Clayman: Let’s be perfectly clear, Christian Chaussy and his colleagues in Germany discovered and then perfected shockwave lithotripsy. I had no role whatsoever. The people focused on urolithiasis in the United States who then promoted ESWL were James Lingeman and Don Griffith along with George Drach. I came much later. We got our
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