The Impact of One Week of Pre-stenting on Porcine Ureteral Luminal Circumference

Development and validation of a predictive model for failure of ureteral access sheath placement in patients with ureteral calculi

OBJECTIVE

The Ureteral Access Sheath (UAS) has notable benefits but may fail to traverse the ureter in some cases. Our objective was to develop and validate a dynamic online nomogram for patients with ureteral stones who experienced UAS placement failure during retrograde intrarenal surgery (RIRS).

METHODS

This study is a retrospective cohort analysis using medical records from the Second Hospital of Tianjin Medical University. We reviewed the records of patients with ureteral stones who underwent RIRS in 2022 to identify risk factors associated with UAS placement failure. Lasso combined logistic regression was utilized to identify independent risk factors associated with unsuccessful UAS placement in individuals with ureteral stones. Subsequently, a nomogram model was developed to predict the likelihood of failed UAS placement in this patient cohort. The model's performance was assessed through Receiver Operating Characteristic Curve (ROC) analysis, calibration curve assessment, and Decision Curve Analysis (DCA).

RESULTS

Significant independent risk factors for unsuccessful UAS placement in patients with ureteral stones included age (OR = 0.95, P < 0.001), male gender (OR = 2.15, P = 0.017), body mass index (BMI) (OR = 1.12, P < 0.001), history of stone evacuation (OR = 0.35, P = 0.014), and ureteral stone diameter (OR = 0.23, P < 0.001). A nomogram was constructed based on these variables. Model validation demonstrated an area under the ROC curve of 0.789, indicating good discrimination. The calibration curve exhibited strong agreement, and the decision curve analysis revealed a favorable net clinical benefit for the model.

CONCLUSIONS

Young age, male sex, high BMI, no history of stone evacuation, and small diameter of ureteral stones were independent risk factors for failure of UAS placement in patients with ureteral stones, and the dynamic nomogram established with these 5 factors was clinically effective in predicting the outcome of UAS placement.

The relationship between the force applied and perceived by the surgeon during ureteral access sheath placement: ex-vivo experimental model

PURPOSE

To define a peak force of insertion (PFOI) threshold for ureteral damage during ureteral access sheath (UAS) placement on an experimental ureteral orifice model.

METHODS

A specially designed water tank using 2 laparoscopic 5 mm ports and 2 different size (10 Fr and 8 Fr) sealing cap adaptors (SCA) as ureteral orifices was used to perform the test. A 10-12 Fr UAS was fixed to a load cell and the force of insertion (FOI) was continuously recorded with a digital force gauge.13 experts in the field of endourology who participated performed 3 UAS insertions. The FOI was recorded initially with 10 Fr followed by 8 Fr SCA. On the final insertion, the orifice was obstructed, leaving a 5 cm length to insert the UAS. The experts were asked to "Stop at the point they anticipate ureteral damage, and they would not proceed in real life".

RESULTS

Using 10 Fr SCA the PFOI was 2.12 ± 0.58 Newton (N) (range:1.48-3.48) while 8 Fr SCA showed a PFOI 5.76 ± 0.96 N (range:4.05-7.35). Six of the experts, said they would stop proceeding when they reached above 5.1 N. Three experts had PFOI < 5.1 N and the other 4 stated they would go with PFOIs of 5.88, 6.16, 6.69 and 7.35 N when using SCA of 8 Fr.The highest load they would stop proceeding had a PFOI of 6.09 ± 1.87 N (range: 2.53-10.74).

CONCLUSION

The PFOI threshold for ureteral damage inserting UAS of the experts is variable. Although FOI is a subjective perception, experience suggests that ureteral injury may occur at an average of 6.05 N perceived by surgeons' tactile feedback. In-vivo measurement of UAS PFOI may confirm a threshold.

Mechanical characteristics of the ureter and clinical implications

The ureteric wall is a complex multi-layered structure. The ureter shows variation in passive mechanical properties, histological morphology and insertion forces along the anatomical length. Ureter mechanical properties also vary depending on the direction of tensile testing and the anatomical region tested. Compliance is greatest in the proximal ureter and lower in the distal ureter, which contributes to the role of the ureter as a high-resistance sphincter. Similar to other human tissues, the ureteric wall remodels with age, resulting in changes to the mechanical properties. The passive mechanical properties of the ureter vary between species, and variation in tissue storage and testing methods limits comparison across some studies. Knowledge of the morphological and mechanical properties of the ureteric wall can aid in understanding urine transport and safety thresholds in surgical techniques. Indeed, various factors alter the forces required to insert access sheaths or scopes into the ureter, including sheath diameter, safety wires and medications. Future studies on human ureteric tissue both in vivo and ex vivo are required to understand the mechanical properties of the ureter and how forces influence these properties. Testing of instrument insertion forces in humans with a focus on defining safe upper limits and techniques to reduce trauma are also needed. Last, evaluation of dilatation limits in the mid and proximal ureter and clarification of tensile strength anisotropy in human specimens are necessary.

Ureteral Access Sheaths and Its Use in the Future: A Comprehensive Update Based on a Literature Review

Ureteral access sheaths (UASs) are part of urologist’s armamentarium when performing retrograde intrarenal surgery (RIRS). Recently, the world of RIRS has changed dramatically with the development of three game-changers: thulium fiber laser (TFL), smaller size single use digital flexible ureterosopes and intraoperative intrarenal pressure (IRP) measurement devices. We aimed to clarify the impact of UASs on IRP, complications and SFRs and put its indications in perspective of these three major technological improvements. A systematic review of the literature using the Medline, Scopus and Web of Science databases was performed by two authors and relevant studies were selected according to PRISMA guidelines. Recent studies showed that using a UAS lowers IRP and intrarenal temperature by increasing irrigation outflow during RIRS. Data on the impact of a UAS on SFRs, postoperative pain, risk of infectious complications, risk of ureteral strictures and risk of bladder recurrence of urothelial carcinoma after diagnostic RIRS were inconclusive. Prestenting for at least one week resulted in ureteral enlargement, while the influence of pre-operative administration of alpha-blockers was unclear. Since TFL, smaller single use digital ureteroscopes and devices with integrated pressure-measuring and aspiration technology seemed to increase SFRs and decrease pressure and temperature related complications, indications on the use of a UAS may decrease in the near future.

Identification of the Risk Factors for the Failure of Ureteral Access Sheath Placement

PURPOSE

Insertion of a ureteral access sheath (UAS) may fail in some patients in retrograde intrarenal surgery (RIRS), and this study aimed to seek preoperative risk factors for the failure of 12/14F UAS placement.

METHODS

We retrospectively analyzed 260 consecutive patients who underwent RIRS between May 2020 and March 2022 at our institution. Data on patient and stone characteristics and several computed tomography (CT)-based measurements were collected and compared between the success and failure UAS placement groups.

RESULTS

Twenty-nine (11.2%) patients failed to insert the UAS. Age, gender, height, weight, stone side, stone location, length of history, and computed tomography (CT)-based parameters were not significant differences between the two groups. Univariate logistic regression analyses showed sex (female/male) (odds ratio: 0.287 and 95% CI [0.107, 0.722], p=0.013), length of history 15-31 days (odds ratio: 0.315 and 95% CI [0.102, 0.974], p=0.045), length of history >31 days (odds ratio: 0.202 and 95% CI [0.051, 0.805], p=0.023), and diameter of the ipsilateral common iliac artery (odds ratio: 1.285 and 95% CI [1.018, 1.623], p=0.035) were associated with UAS placement.

CONCLUSION

Our study indicated that males, the short length of history, and the short diameter of the ipsilateral common iliac artery were the risk factors for the failure of UAS placement.