Boston scientific Navigator™ HD ureteral access sheath
Data on stone-free rates with the use of ureteral access sheaths is conflicting. L’Esperance et al. compared 173 cases with an access sheath to 83 without and found a significantly higher stone-free rate in the access sheath group, 79% versus 67% . Contrary to the prior study, Berquet et al. retrospectively reviewed 280 ureteroscopy cases, 157 with an access sheath and 123 without. They found no significant difference in postoperative stone-free rate . On multivariate analysis, the only factor predictive of a higher stone-free rate was stone size . A recent meta-analysis including 3099 patients and 3127 procedures found there was no significant difference in stone-free rates between patients in whom an access sheath had been used and patients in whom a sheath had not been used, p = 0.45 . However, as with studies on multiple other topics without endourology , weakness lies in absence of CT scans to determine postoperative stone-free rates.
Some of the main criticisms of ureteral access sheaths, including decreased blood flow to the ureter and tissue inflammation and necrosis, come from studies done in the porcine model. Lallas et al. studied blood flow to the ureter with the use of access sheaths . Blood flow to the porcine ureter was measured with a Doppler ultrasound after the placement of a 10/12 Fr, 12/14 Fr, or 14/16 Fr sheath in the ureter for 70 min. He found there was an initial decrease in ureteral blood flow; however it was followed by a gradual rise toward baseline. Blood flow in the ureters with the 10/12 Fr sheath changed the least with an average nadir blood flow of 75% before compensation to 88.4% of baseline blood flow by the end of the procedure. The 12/14 Fr and 14/16 Fr had nearly identical blood flow nadirs, 34.6% and 34.4%, respectively, but the larger sheath reached the nadir more rapidly and rose toward compensation more slowly . Lallas also looked at the histopathology of the ureters at 3 time points – directly after the procedure, at 48 h, and at 72 h. Overall there were inflammatory changes but no evidence of ischemic necrosis to the deeper muscularis propria layer . Another study looked at the more long-term histopathologic changes in the ureter after the use of a 9.5/11.5 Fr access sheath inserted in the ureter for 30 min and 60 min . Again there were findings of inflammatory changes, more pronounced in the distal than proximal ureter, but by 2 weeks, the changes were minimal. The ureters that had the sheaths inserted for 30 min showed no inflammation at 2 weeks, and the ureters that had the sheaths for 60 min showed minimal inflammation with intact epithelium . Lildal et al. confirmed that COX-2 and TNF-α mRNA are increased in ureteral tissue after the use of a 13/15 Fr access sheath, more so in the distal ureter than proximal ureter . While the expression of these markers is associated with inflammation and is found in urinary obstruction, the clinical significance is unknown. In addition, the study was done without a comparison arm looking to see if just inserting a ureteroscope would have a similar effect.
Endoscopic grading system for ureteral injuries
No ureteral lesion or only mucosal petechiae
Mucosal erosion or mucosal flap without smooth muscle injury
Injury involves mucosa and smooth muscle, but not adventitia
Full-thickness ureteral perforation
Ureteral avulsion with loss of ureteral continuity
As mentioned above, patients who are pre-stented have a lower rate of ureteral injury with the use of an access sheath. Pre-stenting has been found to be predictive of an effective ureteral access sheath insertion , and a preoperative stent is associated with an increased stone-free rate and decreased procedure-related events such as patient phone calls and emergency department visits . When looking at the necessity of leaving a postoperative ureteral stent, the literature is more conflicting. Torricelli et al. compared 51 patients who had a stent placed after ureteroscopy with a ureteral access sheath to 51 patients without a postoperative stent . He found that patients in whom a ureteral stent was not left had a significantly increased amount of postoperative pain and more unplanned encounters than stented patients. However, there was no difference in the number of admissions, overall complication rate, UTI, or hematuria between the two groups. There was also no notable effect of pre-stenting or sheath size . Astroza et al. specifically studied pre-stented patients to see if a postoperative stent is necessary after using a ureteral access sheath . They found no difference in operative time, emergency department visits, UTIs, or reported renal colic, therefore indicating that patients who are pre-stented do not need a postoperative stent, saving the cost of a secondary procedure to remove the stent .
The advantages versus disadvantages to using a larger diameter access sheath are often debated. A larger access sheath allows for larger scopes, increased irrigation, as well as the removal of larger stone fragments. Ureteroscopes are oval, while the access sheaths are circular. Therefore, just because a ureteroscope has a smaller diameter than the diameter of the access sheath, it may not be useable. Overall, access sheaths with a diameter of at least 12 Fr can accommodate most flexible ureteroscopes . While an 11/13 Fr sheath can accept all ureteroscopes, the Olympus digital scope has high resistance and low maneuverability . But is bigger better? Tracy et al. found a 30% more efficient rate of stone treatment and removal when using a 14/16 Fr sheath versus a 12/14 Fr sheath, although the overall stone-free rate did not differ . In addition, the complication rate was not different between the two sheath sizes .
Literature on the use of ureteral access sheaths in the pediatric population is limited, with reported risks of the development of vesicoureteral reflux and ureteral injury. Wang et al. retrospectively reviewed 40 patients under the age of 21 who had ureteroscopy with a ureteral access sheath used . They found an increased rate of intraoperative complications and postoperative stent placement. Patients in whom the sheath was used tended to have a higher stone burden and a history of other stone procedures. Only seven patients (10%) had postoperative imaging, but of those four had notable hydronephrosis. Three out of the four had spontaneous resolution, and none of the patients had a clinically confirmed postoperative ureteral stricture . There was a trend toward a higher stone-free rate with patients without a ureteral access sheath, but again, very few patients had postoperative imaging . Another study looked specifically at pre-stented preschool aged children less than 20 kg and found that the ureteral access sheath was inserted without complication in 93.8% of patients, and none had long-term complications . Therefore, while there is no clear advantage to using an access sheath in the pediatric population, it does appear to be relatively safe with no long-term complications.
The use of ureteral access sheaths is not just limited to the surgical management of stones. Endourologists often diagnose and manage upper tract urothelial carcinoma, when nephroureterectomy is not indicated or desired. One of the limitations in the diagnosis of upper tract urothelial carcinoma is the difficulty of obtaining an adequate biopsy specimen. Theoretically, an access sheath would aid in the diagnosis by allowing a larger lumen to atraumatically remove tissue and easily facilitate multiple passes of the ureteroscope. No clinical trials exist between the endoscopic management of upper tract disease with and without the use of ureteral access sheaths, given the low prevalence of the disease, but Gorin et al. published a study looking at 88 patients with UTUC diagnosed or treated with a ureteral access sheath . He found a high diagnostic yield with concordance between tumor grade of the biopsy and tumor grade of the final specimen after nephroureterectomy in 88.6% of patients .
In our practice we often use a ureteral access sheath during both ureteroscopy and percutaneous nephrolithotomy and decide the diameter of the sheath to use after an estimate of ureteral capacity during semirigid ureteroscopy or retrograde pyelogram . If the patient was pre-stented for any reason, we feel more comfortable using a larger sheath. We feel the sheath aids in visualization of the upper tract and helps with stone removal efficiency . The ureter is inspected while withdrawing the sheath at the conclusion of the case, and any injuries are noted. It is our routine practice to place a postoperative stent and leave it in place for 7–10 days, even if a high-grade ureteral injury is noted. In our patient population, the long-term stricture rate is negligible, even in patients with a high-grade injury from an access sheath.
During ureteroscopy, visualization is of utmost importance. Pressurized irrigation is necessary to maintain adequate distention of the urinary tract and visualization of the lumen . There are multiple irrigation devices commercially available, from gravity pressure bags to foot pumps and various hand-operated devices to automated devices. Ultimately, the best device limits retropulsion but has enough pressure to clear debris and blood to keep visualization optimal. In addition, the optimal device is ergonomic and limits surgeon or assistant fatigue.