Assessment of Patient and Surgical Variables Including Residency Training Level on Adverse Events After Ureteroscopy for Ureteral Stones: A Multivariate Analysis

Introduction

Urinary stones are a very common condition with a prevalence that has nearly doubled in the past 15 years and now affects close to 10% to 15% of individuals in the United States. ¹ Some stones are observed with a period of medical expulsive therapy, whereas others necessitate urologic intervention to facilitate removal. Reasons for intervention include large stone size, infection, uncontrolled symptoms, or failure of medical therapy. Ureteroscopy (URS) is increasingly selected as first-line therapy for renal and ureteral calculi, and it has proved to have higher success rates than extracorporeal shock wave lithotripsy. ² Despite the widespread use of URS, past research reports a wide range of post-operative complications from 3.5% to up to 30%. ^3,4 These complications can result in emergency department (ED) visits, hospital admissions, or returns to the operating room (OR). A high rate of complications comes at a hefty price, with each episode of unplanned care costing our healthcare system an average of $23,436 and resulting in decreased patient satisfaction. ⁵ Therefore, ascertaining what factors result in increased complications can have a great impact on not only individual patient care but also our healthcare system.

Several studies have attempted to characterize the post-operative complications and readmission rates relative to technical difficulty of the procedure such as stone size, composition, and location but no standard conclusions have been made. ^{5 –7} Studies have indicated that high-volume centers report a lower complication rate after stone surgery, implying that experience with the procedure may play a role. ⁵ One analysis by Netsch and colleagues suggested that fellowship training in Endourology did not affect complication rate and that, with standardized training protocols, residents performing surgery did not have increased complication rates compared with that of board-certified urologists. ³

Regarding resident experience, research has shown that the fluoroscopy time during URS is increased with first year urology residents when compared with second year residents. This suggests that resident level of training does have some effect on the procedure. ³ However, no specific studies have been performed that examine the resident's level of training on the rate of complications with URS. In this retrospective study, we review our experience with URS for ureteral stones and create a model to predict what factors, including resident level of experience, impact the rate of post-operative complications in specific relation to ureteral stones.

Materials and Methods

After IRB approval was obtained, the University of Missouri–Columbia retrospectively reviewed all ureteroscopies performed at our institution between 2009 and 2013 (CPT code 52353 and 52352). We identified all cases of patients who underwent URS for ureteral stones only. These patients were identified by review of the pre-operative imaging and the operative report. URS was performed with a 4.7F semirigid and/or a 6.8F flexible ureteroscope depending on the location of the stone and surgeon preference. Resident house staff performed all procedures with one of eight full-time attending physicians present. Two of these staff physicians had completed an endourology fellowship. Although the exact degree of staff physician involvement was variable from case to case, our institution's practice is for the supervising physician to act as a surgical assistant for the resident. The staff assists with endoscopic accessories such as wires and baskets, but will take over the ureteroscope only if necessary.

Patients with renal stones or ureteral and renal stones were excluded in an attempt to create a more uniform cohort of patients who had planned single-stage procedures for mostly sub-centimeter stones. The holmium:YAG laser (200 or 270 μm) was used when the stone was unable to be safely retrieved by using the tipless nitinol basket. Stone dusting was not routinely part of our practice at the time of the study. Pre- and post-operative stenting and follow-up imaging were also left to the discretion of the operating attending physician.

A retrospective analysis of the data was then performed. We identified the resident who performed the procedure and their level of training (post-graduate year [PGY] 1 through PGY5/6). PGY5 and PGY6 years were combined as our residency program transitioned from a 6- to a 5-year training program during this period. The electronic medical record was reviewed for patient demographics (age, race, sex, body mass index [BMI], history of stones), stone characteristics (size, location), and operative techniques (pre- and post-operative stenting, use of laser, use of ureteral access sheath, and total stone clearance).

All deviations from the normal post-operative course were identified. This included unplanned visits to the ED or urology clinic, readmissions, or returns to the operating room within 30 days of the original procedure.

Simple descriptive statistics were initially used to identify significant variables that affected the likelihood of adverse events. A p value of <0.05 was considered statistically significant. Logistic regression was then performed by using statistical analysis software to create a predictive model of adverse events.

Results

A total of 1120 elective ureteroscopies were performed between 2009 and 2013 by seven different surgeons at the University of Missouri Hospital. Of these, there were 417 cases of URS for ureteral-only stones. These cases were included in the study. The average age of all patients was 42. Forty-six percent of patients were women, and most (93%) were Caucasian. About half (45.6%) of the patients were experiencing their first stone episode, and the average stone was 6.9 mm. The average patient BMI was 30.4 kg/m².

The stone was identified as proximal (32.6%), mid-ureteral (23%), or distal (46%). Thirty percent of patients had preoperative stenting before definitive URS, and 80% had an indwelling stent with or without a string attached post-operatively. A ureteral access sheath was used in half of the procedures, and the laser was used in 79.6% of all cases. At the conclusion of the procedure, 92.6% of patients were considered clinically cleared of stones. Full descriptive statistics can be reviewed in Table 1.

We identified 53 (12.7%) of patients who had an unexpected post-operative course. Of all the ureteroscopies performed, 29 (6.9%) had a return to the ED, 25 (6%) required readmission, and 12 (2.88%) required unplanned repeat operative intervention under anesthesia. The most common return to the OR was for repeat URS for additional stone burden, followed by stent placement for pain or obstruction. Two cases required interventional radiology—one for percutaneous nephrostomy and one for drainage of a perirenal abscess (Table 2).

There were no significant differences in the groups with and without adverse post-operative events in regards to patient age, sex, race, stone size, BMI, history of previous stones, stone location (proximal, mid, or distal ureter), or use of a sheath. Twenty-two percent of patients who had adverse events were stented before URS vs 31% who did not have an adverse event. This approached but did not reach statistical significance (p = 0.16).

Patients who had adverse events post-operatively were more likely to have residual stone remaining after URS than those who did not have adverse events (p = 0.0009). This was defined as intraoperative assessment of complete clearance vs fragmenting into “clinically insignificant fragments.” Post-operative imaging was not performed routinely enough within 30 days to assess stone-free status radiographically.

PGY2 and PGY3 residents performed the majority of all ureteroscopies (40% and 31.9%). No resident year had statistically significant different rates of adverse events except for PGY5 residents, who were less likely to have any complication (p = 0.04). However, a very small overall number of ureteroscopies were performed by PGY5/6 residents (Table 3).

The first logistic regression model created a predictive model of adverse events with residency year, stone clearance, stone location, and stone size (mm) as predictor variables. While controlling for all other noted variables, only lack of stone clearance had an odds ratio significant for increasing the likelihood of an adverse event (Table 4).

A second logistic regression model was performed to determine the odds ratio of an adverse event, with stone clearance and residency PGY as predictor variables. Chief residents (PGY5/6) were used as the reference group. In this model, while controlling for stone clearance, no residency year showed higher odds of adverse outcomes (Table 5).

Finally, a third logistic regression model was performed with the outcome variable as adverse events and the predictor variables as residency year (grouped as PGY1–3 and PGY4–5/6), stone clearance, and stone size. Again, while controlling for all other variables, only lack of stone clearance was significant for increasing the likelihood of an adverse event (Table 6).

Discussion

At our institution, the first and second year urology residents (PGY2 and PGY3) perform the vast majority of ureteroscopies, and therefore the majority of complications were in this group. However, while controlling for many other variables, they did not appear to have more adverse events than either more junior or more senior residents. It may be argued that more junior residents have closer supervision and attending physicians may be more attentive and quick to intervene. Although more senior residents may have more training, he or she may have less supervision and be more aggressive. Despite this, it appears that thorough stone removal is the most important factor in preventing post-operative adverse outcomes. Use of pre- and post-operative stenting or a ureteral sheath does not appear to impact 30-day adverse outcomes.

When shock-wave lithotripsy is used, stones are broken into presumed “passable fragments.” The patient then will clear the stone on his or her own with a small risk of Steinstrasse. From these data, it appears that using the similar logic of fragmenting stones into “passable fragments” may not be the safest technique for the patient. This is consistent with other studies showing that patients with residual fragments had more urinary tract infections than patients without residual fragments. ² With this study in mind, clearing the patient of all visible stones appears the most important variable in preventing an adverse outcome.

There are some inherent limitations in this study. Our study focused on a single academic institution in the Midwest and the patient population may not be generalizable to the entire United States. As a retrospective study, it is possible that not all post-operative adverse events were captured as some patients presumably presented to local outside hospitals. Although most patients who presented to the ED or clinic with adverse events were re-imaged, there was no standard post-operative plan for imaging all patients, so it is unclear how many uncomplicated cases were truly stone free other than operative reporting. However, immediate (<30 days) post-operative imaging is not currently part of the American Urologic Association Guidelines as a standard of care for all patients who undergo stone surgery. The utility of subjecting all of these patients to an X-ray, ultrasound, or CT scan within 30 days of surgery is not known. Determination of “stone free rate” based on ureteroscopic visualization may be more broadly generalizable in a real-world setting.

Continuing to expand this database and follow outcomes will help improve models to predict adverse events in patients undergoing this common urologic procedure. With the increasing prevalence of stone dusting, it would be prudent to investigate the rates of adverse events in dusted patients vs “cleared” patients vs those who were left with “passable fragments.” In addition, prospective studies identifying the degree of supervision, advisement, and assistance by attending surgeons to different post-graduate levels may improve our ability to identify the impact that supervision has on post-operative outcomes. Identifying these factors will become more and more crucial in delivering good patient care in the era of the Affordable Care Act and the possibility of Medicare/Medicaid reimbursement adjustments based on surgical outcomes and unplanned care.

Conclusion

URS continues to be the gold standard for extraction of ureteral stones; however, some patients continue to have unplanned post-operative courses. Resident level of training does not appear to influence the rate of unplanned outcomes for URS but complete clearance of stones does. Identifying potential predictors and modifiable factors for unplanned adverse events after URS will be even more important in the evolving health policy and reimbursement programs. The increased use of dusting settings for URS may change these outcomes and should be further investigated.