Abstract
Ureteral access sheaths (UASs) were designed to facilitate the endoscopic approach and navigation through the upper urinary tract when performing flexible ureteroscopy. The concept and rationale behind its configuration are to ensure easy and repeatable ureteroscopic passage without needing to navigate the narrower ureteral segments, particularly the intramural ureter and the area adjacent to the iliac vessels. In addition, UASs eliminate part of the friction between the ureteroscope and the ureteral wall, allow continuous drainage that decreases intraluminal pressure, diminish kinking forces on the instrument and potential damage related to repetitive over-the-wire ureteroscope insertions, and permit removal of calculi or excised tissue in cases of upper tract tumors. This device has undergone a revolutionary refinement from its first rudimentary design described by Takayasu and Aso 1 in 1974 followed by the peel-away concept reported by Rich et al. 2 in 1987. The contemporary UAS is a two-part device composed of an external sheath and an inner tapered obturator, each with a hydrophilic coating. It comes in various diameters and lengths to fit all anatomical and clinical requirements. It is manufactured by several companies, among them Cook, Boston Scientific, Rocamed, Colopast, Olympus, Applied Medicals, and Terumo. Its advantages allow for widespread utilization, and they represent the end products of a paradoxical endourologic history. In the 11–13FR ureteroscopes era, when ureteroscopy was in its infancy, surgeons concerned by the high rates of ureteral injuries and of strictures that reached up to 10% demanded that the diameters of the instruments be reduced. The manufacturers responded with a 50% reduction in diameter, downsizing instruments to 6.5FR at the tip. Then, the endourologists called for a quick, easy, and smooth access to the upper tract, and the manufacturers promptly responded in the form of the UAS. As a result, we are currently using miniscopes but through large accesses, and we are back to the 11–16FR outer diameter (OD). Surprisingly, this return to wide tubes is associated with an only 1% stricture rate. Is that thanks to the hydrophilic coating with smooth insertion and no friction between the ureteroscope and the ureteral wall when using a UAS, or the result of surgical expertise gained with performing large series of procedures? Who knows? I believe that both of them can share the credit. The answer to the question of which is the best UAS is considerably trickier.
In this issue, Loftus et al. (pp—) compared the ability of access of two leading products, Cook Flexor (CF) and Boston Scientific Navigator HD (NHD), both 12/14FR. Although they found comparable results of a crossover experiment in the first trial, namely, trying the other product when one of them failed to access, the NHD was able to get access in 43% of the failed CF cases, whereas none of the failed NHD cases could be accessed by the CF. In addition, NHD was subjectively rated by the surgeons as being easier to place. Taking all of these results into consideration, the NHD clearly performed better than the CF. Achieving a p-value of <0.05, however, is not a statistical must to assess trends. It is possible, that with a larger series of patients, this widely, sometimes arbitrarily chosen p-value could have been reached and changed the conclusions.
As for the subjective assessment of the ease of placement, although biased, this parameter is of fundamental importance to all of us in active practice. I personally carry out procedures in an operating room used by six other experienced surgeons who perform 300–500 ureteroscopies yearly, all of them Endourological Society fellowship-trained by leading international figures. Their AUS preferences are so varied that the operating room ensures the availability of four different brands of AUS to keep them all happy.
Patel and Monga and others analyzed physical and mechanical properties of some AUS in the laboratory and, as could be expected, they found different performances in terms of tip perforation force, sheath edge deformation, dilator extraction forces, tip bending, stiffness, kinking, insertion forces, lubricity, and radio-opacity. These objective assessments did not necessarily influence the AUS choice of most of the surgeons, thus explaining the multitude of AUS brands on the market, all of them effectively used in vast numbers of clinical settings. Subjectivity wins over objectivity—it is all in what we feel in our hands.
Another interesting aspect presented in Loftus et al.'s article could be considered a kind of validation of Traxers's classification for AUS-induced ureteral injuries. Familiarity with those sequelae is important, but given that most of these injuries are treatable by merely inserting a stent, with rare long-term consequences and still within the 1% stricture rate, its clinical significance is debatable. In this context, it is possible that avoiding Amplatz Superstiff wires for AUS insertion will result in fewer ureteral injuries at the price of a higher rate of primary access failure. This interesting issue might be worth further analysis in a prospective randomized trial.
Finally, we cannot escape traditions and the pull of subjectivity. For example, the term OD used earlier and widely in our profession is inappropriate. We use it in the context of diameter mentioning in practice a circumference unit, the FR, which needs to be calculated by dividing with π to derive the size of the diameter. We can propose changing the term to outer dimension (still keeping OD) or outer circumference, but it is easier to continue the not-so-accurate customary way, which has been understood by everybody for decades. I conclude by repeating my professional mantra: our endourologic aim is to leave the patient stone free, in one session, after a short hospital stay, and with no complications. Achieve that with whatever means you feel comfortable.