- Email: [email protected]
Urolithiasis in pregnancy: a cost-effectiveness analysis of ureteroscopic management vs ureteral stenting
Accepted Manuscript Urolithiasis in Pregnancy: A Cost-Effectiveness Analysis of Ureteroscopic Management Versus Ureteral Stenting Kevin Wymer, BA, Mr, Beth A. Plunkett, MD, MPH, Sangtae Park, MD, MPH PII:
S0002-9378(15)00774-7
DOI:
10.1016/j.ajog.2015.07.024
Reference:
YMOB 10538
To appear in:
American Journal of Obstetrics and Gynecology
Received Date: 17 March 2015 Revised Date:
24 May 2015
Accepted Date: 18 July 2015
Please cite this article as: Wymer K, Plunkett BA, Park S, Urolithiasis in Pregnancy: A CostEffectiveness Analysis of Ureteroscopic Management Versus Ureteral Stenting, American Journal of Obstetrics and Gynecology (2015), doi: 10.1016/j.ajog.2015.07.024. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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UROLITHIASIS IN PREGNANCY: A COST-EFFECTIVENESS ANALYSIS OF URETEROSCOPIC MANAGEMENT VERSUS URETERAL STENTING Kevin WYMER, BA (Mr)1, Beth A. PLUNKETT, MD, MPH2, Sangtae PARK, MD, MPH3
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University of Chicago, Pritzker School of Medicine
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NorthShore University HealthSystem, Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology NorthShore University HealthSystem, Division of Urology, Department of Surgery
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Conflicts of Interest: The authors report no conflict of interest
Corresponding Author: Sangtae Park, MD, MPH NorthShore University HealthSystem,
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Source of Funding: No financial support was provided for this project
Department of Surgery, Division of Urology
Evanston, IL 60201
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1000 Central Ave. Ste 720
Email: [email protected]
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Fax: 847-503-3500
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Office: 847-503-3000
Abstract Word Count: 250 Main Text Word Count: 2,544 1
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Condensation: Antepartum ureteroscopy is less costly and more effective relative to serial stent placement and is most beneficial for women diagnosed early during pregnancy.
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Short Title: Cost-effectiveness of ureteroscopy during pregnancy
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ABSTRACT Objectives: To determine the cost-effectiveness of serial stenting versus ureteroscopy (URS) for
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treatment of urolithiasis during pregnancy as a function of gestational age (GA) at diagnosis. Study Design: We built decision analytic models for a hypothetical cohort of pregnant women diagnosed with symptomatic ureteral calculi and compared serial stenting to URS. We assumed
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ureteral stent replacement every four weeks during pregnancy, intravenous sedation for stent placement, and spinal anesthetic for URS. Outcomes were derived from the literature and included
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stent infection, migration, spontaneous stone passage, ureteral injury, failed URS, postoperative urinary tract infection, sepsis, and anesthetic complications. Four separate analyses were run based on the GA at diagnosis of urolithiasis. Using direct costs and quality-adjusted life years (QALYs), we reported the incremental costs and effectiveness of each strategy based on GA at stone
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diagnosis and calculated the net monetary benefit (NMB). We performed one-way and MonteCarlo sensitivity analyses to assess the strength of the model. Results: URS was less costly and more effective for urolithiasis irrespective of GA at diagnosis.
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The incremental cost of URS increased from -$74,469 to -$7,631 and the incremental effectiveness decreased from 0.49 to 0.05 QALYs for a stone diagnosed at 12 and 36 weeks GA,
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respectively. The NMB of URS progressively decreased for stones diagnosed later in pregnancy. The model was robust to all variables. Conclusion: Ureteroscopy is less costly and more effective relative to serial stenting for urolithiasis regardless of the GA at diagnosis. Ureteroscopy is most beneficial for women diagnosed early during pregnancy.
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Keywords: Cost-effectiveness; urolithiasis; pregnancy; ureteroscopy
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Introduction Genitourinary complications are the leading cause of non-obstetric hospital admissions
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during pregnancy, with kidney stones affecting an estimated 1 in 244 to 1 in 2000 pregnancies.1-3 Many anatomic and physiologic changes that accompany pregnancy are associated with an increased risk of stone formation. These include mechanical obstruction of the ureters,
progesterone-induced reduction in ureteral peristalsis, and increased filtration rates of stone
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promoters such as sodium, calcium, and uric acid.1 In addition, pregnant patients may be at
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increased risk of stone-related complications, such as pyelonephritis or obstetric complications including preterm labor and preterm delivery.1,4–7
As in the general population, analgesia and monitoring for spontaneous passage is often the most appropriate initial treatment for acute renal colic in the pregnant patient. However, recent studies have found that as low as 47% of pregnant patients with confirmed urolithiasis are
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able to pass stones spontaneously.8 If conservative management is unsuccessful, or if there are absolute indications for intervention (e.g. intractable pain, vomiting, fever, etc.), active
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management is warranted. Traditionally, antepartum ureteral stent insertion has been the most commonly used method to temporarily alleviate urinary tract obstruction in pregnant women,
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allowing pregnancy to continue to term without more invasive treatment methods such as ureteroscopy (URS).9–11 Because of changes in urine composition that occur during pregnancy, there is an increased rate of stent encrustation, necessitating stent replacements every 4-6 weeks.2 Antepartum stent placement has two advantages: it allows for immediate relief of the obstruction and subsequently leads to passive dilation of the ureter, potentially facilitating successful URS post-partum.12–15 However, stenting is not entirely benign. Indwelling ureteral stents can become infected, migrate, or cause significant pain.16–20 The pain associated with indwelling stents is 5
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often so severe that many patients report higher total pain scores than those with acute renal colic, and 80% of patients with a stent report a significantly reduced quality of life.21
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In contrast, immediate URS, as is performed in the non-pregnant patient, eliminates the need for antepartum serial ureteral stent placement and provides a definitive surgical treatment. However, there remains controversy regarding the use of URS during pregnancy. URS requires a higher level of anesthesia and increased procedure time relative to ureteral stent placement, and
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carries a risk of ureteral perforation or injury. Additionally, without pre-operative stenting,
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antepartum URS may be less successful relative to postpartum URS following serial stenting.12– In response to these concerns, several studies have demonstrated that URS is highly effective
in pregnancy and can be performed under spinal anesthesia with minimal reported risks to the mother and fetus.22–24 Multiple small studies have also shown no significant differences in complications following URS in pregnant women compared to non-pregnant women.23,25,26
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Additionally, the American Urological Association treatment guidelines now recognize URS as a treatment option to be considered for pregnant patients with urolithiasis.27
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It remains unclear whether antepartum serial stenting or URS is superior for treatment of stones during pregnancy, and how the gestational age (GA) at diagnosis affects the risks and
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benefits of each treatment modality. Because URS is more successful after stent placement,12–15 we hypothesized that stenting later in pregnancy may be the preferred approach while URS earlier in pregnancy may prove to be more beneficial. The objective of this study was to determine the cost-effectiveness of serial stenting versus URS for treatment of urolithiasis in pregnant women as a function of gestational age at diagnosis. Materials and Methods
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To compare patient outcomes resulting from ureteral stent placement versus URS, we developed a decision analytic model for a hypothetical cohort of women presenting with a symptomatic ureteral stone during pregnancy (Figure 1). We conducted the analysis from a
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payer’s perspective and measured effectiveness as quality adjusted life years (QALYs.) QALYs were calculated using life expectancy and utility values, which are defined as numerical judgments of the desirability of specific outcomes.28 We calculated incremental costs,
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incremental effectiveness, incremental cost-effectiveness ratio (ICER), as well as net monetary benefit (NMB). Incremental costs are defined as the difference in the mean cost between the two
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strategies. Similarly, incremental effectiveness is the difference in the mean effectiveness (i.e. QALYs) between the two strategies. We calculated the ICER as the incremental cost divided by the incremental effectiveness and compared this value to a willingness to pay (WTP) threshold of $50,000 per QALY to determine whether URS was cost-effective compared to ureteral stenting.
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Although there is no consensus on a WTP threshold, $50,000 was chosen because it is frequently used in cost effectiveness healthcare analyses originating in the United States.29 We also assessed the cost-effectiveness of URS using NMB, defined as the WTP x incremental effectiveness –
stent placement.
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incremental cost. If the NMB of URS was greater than zero, URS was cost-effective compared to
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To develop the model, we used TreeAge Pro (TreeAge Software, Inc. Williamstown,
MA, 2013). We assumed that patients undergoing stent placement received intravenous sedation, stents were changed every four weeks during pregnancy, and there were no changes in symptoms over the duration of the stent. In addition, we assumed that if stent migration occurred, the stent was replaced, and if ureteral injury occurred during URS, serial stents were placed every four weeks for the remainder of the pregnancy. If the URS procedure failed (i.e. stone recurrence or
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persistence), we assumed that a stent would be placed for 2 weeks, followed by a second attempt at the URS procedure. All pregnancies were assumed to result in delivery at 40 weeks GA. We also assumed patients undergoing URS received spinal anesthesia. We based this assumption on
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findings supporting the safety and efficacy of spinal anesthesia for URS.22,30 Additionally,
regional anesthesia during pregnancy remains the preferred alternative as the implications for general anesthesia for long-term neurodevelopment of the fetus remains unclear.31–33
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We set the gestational age of stone diagnosis at four different time points: 12 weeks, 20 weeks, 32 weeks, and 36 weeks. We conducted separate analyses for each diagnostic time point.
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To calculate stent costs and disutility at the varying time points of diagnosis, we multiplied the cost and disutility of stent placement by the number of stents needed to reach delivery, assuming stent replacement every four weeks.
We obtained all modeling probabilities from the literature (Table 1). If multiple estimates
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were available in the literature, we calculated a mean estimate by weighting the individual estimates based on sample size. We included this weighted average as the parameter value in the base case analysis.
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For stent placement outcomes, we included infection, stent migration, and spontaneous stone passage. We based stent complications on elective stent placement and defined infection by
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the presence of fever and bacteruria.34–36 As stent placement is primarily a temporizing procedure, we included the cost of postpartum treatment within the model for patients who underwent antepartum serial stenting. We assumed that all stented patients underwent an abdominal CT scan to assess for persistent stone following delivery. If spontaneous stone passage occurred following serial stent placement during pregnancy, the patient underwent no further treatment. If no spontaneous stone passage occurred, the patient underwent URS 2 weeks
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postpartum. A higher URS stone-free rate was included for postpartum URS relative to antepartum URS based on the documented improved success of URS following preoperative stenting.12–15
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For URS outcomes, we included temporary postoperative stent placement (for 1 week duration following URS), UTI, sepsis, URS failure without preoperative stent placement, URS failure with preoperative stent placement, and ureteral injury. When available, we included
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complication rates specific to pregnant patients. However, we also incorporated studies including non-pregnant patients due to the equivalent complication rates found between pregnant and non-
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pregnant patients following URS.23,25,26 With regard to anesthesia complications, we included post-dural-puncture headache and aseptic meningitis following spinal anesthesia. We did not include complications of intravenous anesthesia as these complications tend to be rare and transient, likely having an insignificant effect on the outcome of the model.37
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The model included hospital, urologist, and anesthesiologist costs, and the cost of intraoperative fetal monitoring with fetal non-stress test (NST) during URS or stent placement (Table 2). We based urologist costs on the Current Procedural Terminology from the American
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Medical Association.38 We calculated anesthesiologist costs using the Centers for Medicaid and Medicare Services anesthesia charge formula,39 and derived costs for UTI, stent infection, CT
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scan, and postdural headache from the literature. More specifically, we calculated postdural headache costs using the mean cost per patient, including the average costs and use of intravenous caffeine, blood patch, and hospital stay.40 Infection costs included both the cost of treatment and laboratory diagnosis.41 We obtained costs for inpatient procedures and diagnoses (i.e. sepsis, meningitis) from the 2012 Hospital Cost and Utilization Project (HCUPnet), a nationwide inpatient database that reports the national average costs for specific diagnoses and
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procedures.42 For outpatient procedures (URS and stent placement), we used cost data from the NorthShore University HealthSystem financial department. To convert all costs to 2014 dollars,
all future costs and utility values at a 3% annual rate.
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we used the medical care component of the Consumer Price Index.43 Additionally, we discounted
We obtained all utility values from the literature (Table 3). To calculate QALYs, we combined the utility values, tolls, and the estimated life expectancy. We defined a full life
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expectancy as 56.8 years in the model based on the life expectancy of a 25 year-old woman (average age of first pregnancy).44,45 If a patient had multiple complications, we used the
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complication with the lowest utility value at any given time point to calculate the corresponding QALYs.
To test the robustness of the study findings, we performed sensitivity analyses. We conducted one-way sensitivity analyses on all variables and defined the ranges of the
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probabilities by the lowest and highest values reported in the literature. If only one estimate was available in the literature, the sensitivity analysis range was defined as the 95% confidence interval, calculated using the binomial Clopper-Pearson exact method (Table 1).46,47 We varied
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all costs and disutility values from 50-150% of the base-case value and varied the annual discount rate of all costs and QALYs from 0-7% (Tables 2,3). In addition, we used Monte-Carlo
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simulation to conduct probabilistic sensitivity analysis with 10,000 trials run for each model. Beta distributions were used for probabilities and gamma distributions for costs.48 This study was exempt from IRB approval. Results
The results of the base-case analyses are summarized in Figure 2 (A, B). URS was less costly and more effective relative to stent placement for a stone diagnosed at 12, 20, 32, or 36
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weeks GA. In addition, we found a progression of increasing incremental cost and decreasing incremental effectiveness of URS with later GA at stone diagnosis. The incremental cost of URS increased from -$74,469 for a stone diagnosed at 12 weeks GA to -$7,631 for a stone diagnosed
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at 36 weeks GA and the incremental effectiveness decreased from 0.488 to 0.049 QALYs across those same time points.
Net-benefit analysis showed a positive NMB of URS for all gestational ages and an
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overall trend of a decreasing NMB of URS with later GA at diagnosis (Figure 3). The NMB of URS decreased from $98,864 for a stone diagnosed at 12 weeks GA to $10,082 for a stone
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diagnosed at 36 weeks GA.
Based on the results of the one-way sensitivity analyses, the model is very robust towards URS. Irrespective of the GA at stone diagnosis, the model was not sensitive to any variables. Probabilistic analyses using Monte Carlo simulations showed that, corresponding to a WTP of
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$50,000/QALY, URS was preferred 99.04%, 95.56%, 86.77%, and 80.05% of the time for a stone diagnosed at a GA of 12, 20, 32, or 36 weeks respectively. Comment
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Our study demonstrates that URS is dominant (less costly and more effective) relative to stent placement for the treatment of urolithiasis in pregnancy regardless of the GA at stone
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diagnosis. The difference between URS and stent placement, as measured by incremental cost, incremental effectiveness, and net monetary benefit, becomes increasingly greater with an earlier GA at stone diagnosis, suggesting a larger benefit of URS for women who are diagnosed earlier during pregnancy. This trend appears to be driven largely by the cost of stent placement and was further supported by the results of the sensitivity analyses, notably the increasing preference of the Monte-Carlo simulations towards URS with earlier stone diagnoses. Definitive antepartum
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URS was found to be less costly and more effective relative to serial stenting even late in pregnancy when the length of ureteral stent placement was relatively short. In addition, antepartum URS was dominant despite the increased stone-free rate of postpartum URS
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following preoperative, antepartum stent placement.
By examining the cost-effectiveness of stone treatment during pregnancy as a function of GA at diagnosis, our study expands upon prior literature supporting the use of URS for stone
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treatment during pregnancy.2,9,23,25,49 Prior studies have found URS in the pregnant patient to be relatively safe and associated with the same low complication rates as in the general population,
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but have not analyzed cost-effectiveness or directly compared URS to serial stenting.23,25,26 In addition, the costs and outcomes associated with serial stenting vary greatly depending on the GA at stone diagnosis. By analyzing the model according to GA at diagnosis, the results of the current study highlight the changing cost-effectiveness ratio with varying length of ureteral
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stenting. These data could potentially be used to help guide patients’ and physicians’ decisions regarding URS based on a woman’s specific point in pregnancy. Limitations of this study should be noted. As with all decision analytic models, our model
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did not incorporate all possible outcomes, and thus findings from our analyses are only applicable to the clinical scenarios assumed for our models. In addition, decision analytic models
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can be limited by the characteristics of the literature from which the modeling parameters were derived. Because this analysis was conducted from a payer’s perspective, it was limited by the exclusion of indirect costs. The study was also limited by the absence of obstetric complications in the model. However, data comparing women undergoing URS to all women with symptomatic urolithiasis show no difference in obstetric complication rates, including preterm delivery. 9 Based on these data, the treatment of urolithiasis during pregnancy, whether with serial stenting
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or URS, does not have any effect on obstetric complication rates and thus would not have altered the outcomes of the model. In addition, type of anesthesia has not been found to lead to a significant difference in obstetric complication rates.33,50,51
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Despite these limitations, our study has many notable strengths. To the best of our
knowledge, it is the first to compare the cost-effectiveness of interventions for kidney stones during pregnancy, and offers further granularity and clinical application by examining treatment
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at multiple gestational ages. In addition, we employed thorough sensitivity analyses, including Monte-Carlo simulation, which provides strong support for the robustness of our outcomes. The
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model itself is comprehensive in its assessment of stent and URS related complications, and thus provides a reasonable proxy for clinical outcomes.
In conclusion, when considering the treatment of symptomatic urolithiasis during pregnancy, URS is a cost-effective option for stones diagnosed at any gestational age.
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Furthermore, URS is most beneficial for women diagnosed with urolithiasis earlier during their pregnancy. Such findings support and expand on prior work, highlighting the prominent role that
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URS should play in the treatment of urolithiasis during pregnancy.
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51. Ní Mhuireachtaigh R, O’Gorman DA. Anesthesia in pregnant patients for nonobstetric surgery. J Clin Anesth. 2006 Feb;18(1):60–6.
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52. Ngai H-Y, Salih HQ, Albeer A, Aghaways I, Buchholz N. Double-J ureteric stenting in pregnancy: A single-centre experience from Iraq. Arab J Urol. 2013 Jun;11(2):148–51. 53. Breau RH, Norman RW. Optimal prevention and management of proximal ureteral stent migration and remigration. J Urol. 2001 Sep;166(3):890–3. 54. Slaton JW, Kropp KA. Proximal Ureteral Stent Migration: An Avoidable Complication? J Urol. 1996 Jan;155(1):58–61. 55. Jones BJ, Ryan PC, Lyons O, Grainger R, McDermott TE, Butler MR. Use of the double pigtail stent in stone retrieval following unsuccessful ureteroscopy. Br J Urol. 1990 Sep;66(3):254–6.
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56. Laing KA, Lam TBL, McClinton S, Cohen NP, Traxer O, Somani BK. Outcomes of ureteroscopy for stone disease in pregnancy: results from a systematic review of the literature. Urol Int. 2012;89(4):380–6.
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57. Rana AM, Aquil S, Khawaja AM. Semirigid ureteroscopy and pneumatic lithotripsy as definitive management of obstructive ureteral calculi during pregnancy. Urology. 2009 May;73(5):964–7. 58. Goldberg H, Holland R, Tal R, Lask DM, Livne PM, Lifshitz DA. The Impact of Retrograde Intrarenal Surgery for Asymptomatic Renal Stones in Patients Undergoing Ureteroscopy for a Symptomatic Ureteral Stone. J Endourol. 2013 Aug;27(8):970–3.
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59. Perez Castro E, Osther PJS, Jinga V, Razvi H, Stravodimos KG, Parikh K, et al. Differences in Ureteroscopic Stone Treatment and Outcomes for Distal, Mid-, Proximal, or Multiple Ureteral Locations: The Clinical Research Office of the Endourological Society Ureteroscopy Global Study. Eur Urol [Internet]. [cited 2014 May 12]; Available from: http://www.sciencedirect.com/science/article/pii/S0302283814000232 60. Christman MS, Kalmus A, Casale P. Morbidity and Efficacy of Ureteroscopic Stone Treatment in Patients with Neurogenic Bladder. J Urol. 2013 Oct;190(4, Supplement):1479–83.
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61. De La Rosette J, Denstedt JD, Geavlete PA, Keeley F, Matsuda T, Pearle MS, et al. The Clinical Research Office of the Endourological Society Ureteroscopy Global Study: Indications, Complications, and Outcomes in 11885 Patients. J Endourol Endourol Soc. 2013 Oct 22; 62. Se Yun Kwon, Bum Soo Kim, Hyun Tae Kim, Yoon Kyu Park. Efficacy of Percutaneous Nephrostomy During Flexible Ureteroscopy for Renal Stone Management. Korean J Urol. 2013 Oct;54(10):689–92.
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63. Preminger GM, Tiselius H-G, Assimos DG, Alken P, Colin Buck A, Gallucci M, et al. 2007 Guideline for the Management of Ureteral Calculi. Eur Urol. 2007 Dec;52(6):1610–31.
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64. Atar M, Bozkurt Y, Soylemez H, Penbegul N, Sancaktutar AA, Bodakci MN, et al. Use of renal resistive index and semi-rigid ureteroscopy for managing symptomatic persistent hydronephrosis during pregnancy. Int J Surg. 2012;10(10):629–33. 65. Parker BD, Frederick RW, Reilly TP, Lowry PS, Bird ET. Efficiency and cost of treating proximal ureteral stones: Shock wave lithotripsy versus ureteroscopy plus holmium:yttrium-aluminum-garnet laser. Urology. 2004 Dec;64(6):1102–6. 66. Harmon WJ, Sershon PD, Blute ML, Patterson DE, Segura JW. Ureteroscopy: Current Practice and Long-Term Complications. J Urol. 1997 Jan;157(1):28–32. 67. Khalil M. Management of impacted proximal ureteral stone: Extracorporeal shock wave lithotripsy versus ureteroscopy with holmium: YAG laser lithotripsy. Urol Ann. 2013 Apr;5(2):88–92. 18
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68. Horlocker TT, McGregor DG, Matsushige DK, Schroeder DR, Besse JA. A retrospective review of 4767 consecutive spinal anesthetics: central nervous system complications. Perioperative Outcomes Group. Anesth Analg. 1997 Mar;84(3):578–84.
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69. Horlocker TT, McGregor DG, Matsushige DK, Chantigian RC, Schroeder DR, Besse JA. Neurologic complications of 603 consecutive continuous spinal anesthetics using macrocatheter and microcatheter techniques. Perioperative Outcomes Group. Anesth Analg. 1997 May;84(5):1063–70. 70. Vallejo MC, Mandell GL, Sabo DP, Ramanathan S. Postdural Puncture Headache: A Randomized Comparison of Five Spinal Needles in Obstetric Patients: Anesth Analg. 2000 Oct;91(4):916–20.
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71. Wolf JS Jr, Carroll PR, Stoller ML. Cost-effectiveness v patient preference in the choice of treatment for distal ureteral calculi: a literature-based decision analysis. J Endourol Endourol Soc. 1995 Jun;9(3):243–8. 72. Pearle MS, Lingeman JE, Leveillee R, Kuo R, Preminger GM, Nadler RB, et al. Prospective, randomized trial comparing shock wave lithotripsy and urteroscopy for lower pole caliceal calculi 1 cm or less. J Urol. 2005 Jun;173(6):2005–9. 73. Tengs TO, Wallace A. One thousand health-related quality-of-life estimates. Med Care. 2000 Jun;38(6):583–637.
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74. Selai C, Rosser R. Eliciting EuroQol descriptive data and utility scale values from inpatients. A feasibility study. PharmacoEconomics. 1995 Aug;8(2):147–58. 75. Taie K, Jasemi M, Khazaeli D, Fatholahi A. Prevalence and management of complications of ureteroscopy: a seven-year experience with introduction of a new maneuver to prevent ureteral avulsion. Urol J. 2012;9(1):356–60.
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76. Van Roijen L, Essink-Bot ML, Koopmanschap MA, Michel BC, Rutten FF. Societal perspective on the burden of migraine in The Netherlands. PharmacoEconomics. 1995 Feb;7(2):170–9.
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77. Tohmo H, Vuorinen E, Muuronen A. Prolonged impairment in activities of daily living due to postdural puncture headache after diagnostic lumbar puncture. Anaesthesia. 1998 Mar;53(3):299–302. 78. Sackett DL, Torrance GW. The utility of different health states as perceived by the general public. J Chronic Dis. 1978;31(11):697–704. 79. Davis KL, Misurski D, Miller JM, Bell TJ, Bapat B. Cost of acute hospitalization and postdischarge follow-up care for meningococcal disease in the US. Hum Vaccin. 2011 Jan 1;7(1):96–101.
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Table 1. Model parameters- clinical events and probabilities Variable
Baseline (%)
Range (%)
References
Infection
9.86
6.00-12.30
35,36
Migration
2.38
1.20-10.00
Spontaneous Stone
10.00
2.10-26.50
56.70
42.90-72.90
12,13,26,49,56–60
0.00-15.35
12,14,15,26,56,60,61
0.00-17.60
12–15
1.14
0.60-5.20
13,25,49,56,59–66
1.69
0.86-6.70
12,25,49,56,59,61,63–
Temporary Stent Failure of URS without
3.04
preoperative stent
preoperative stent
Ureteral Injuryb
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UTI
0.00
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Failure of URS with
55
67
0.51
0.30-2.30
49,59–61,63,65
Postdural Headache
2.20
1.30-9.60
68,69
Aseptic Meningitis
0.17
0.00-0.90
69
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Sepsis
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URS Complications Post-procedure
16,34,35,52–54
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Passage
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Stent Complications
URS Anesthesia Complicationsc
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a
A lower URS failure rate was used for patients who underwent postpartum URS following
antepartum serial stenting. b
Ureteral Injury included perforation, avulsion, and stricture.
Complications from stent anesthesia were not included due to the relatively low occurrence and
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transient nature of intravenous anesthesia complications.
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c
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Table 2. Model parameters-costsa Variable
Baseline ($)
Range ($)
Stent
10,422
5,211-15,633
URS
13,403
6,702-20,105
CT Scan
383
192-575
Fetal NST
624
312-936
References
Urologist Stent
177
URS
474
Outcome
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237-711
38
77
39-116
39
207
103-310
39
1,573
786-2,359
41
UTI
1,573
786-2,359
41
Ureteral Injurye
13,621
6,810-20,431
42
Sepsis
14,401
7,200-21,601
42
Postdural Headache
1,712
856-2,568
70
Aseptic Meningitis
14,490
7,245-21,735
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Stent Infectiond
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b
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URS
b
89-266
Anesthesiologistc Stent
b
65
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Provider
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Hospital Costs
All costs were converted to 2013 dollars using the CPI.43 22
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b
Based on data from the NorthShore University HealthSystem financial department
c
For anesthesiologist costs, the Medicare formula of “Charge = (base units + time units +
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modifier units) x conversion factor” was used. For URS, the charge calculation was done using 2 base units, 4 time units, and 2 modifier units. For ureter stent placement, the charge calculation was done using 2 base units, 1 time unit, and 0 modifier units.
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Ureteral Injury included perforation, avulsion, and stricture.
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e
The cost of stent infection was estimated using the cost of UTI.
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d
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Table 3. Model parameters- utility and QALY values Variable
Utility
Range
Time Interval
References
Stent
0.76
0.64-0.88
Varieda
URS
0.90
0.85-0.95
7.9 days
Stent Infectionb
0.64
0.46-0.82
7 daysc
73,74
UTIb
0.64
0.46-0.82
7 daysc
73,74
Ureteral Injury
0.60
0.40-0.80
30 days
71,75
Sepsisb
0.64
0.46-0.82
7 daysc
73,74
Postdural
0.77
0.81-0.94
6 days
76,77
0.65
0.48-0.83
8.5 days
78,79
Aseptic Meningitis
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71,72
Time interval used to calculate stent utility based on the length stent(s) placement
b
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a
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Headache
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Outcome
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Procedure
c
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Stent infection, UTI, and Sepsis utility values estimated using utility for “acutely ill” patients
Time interval for stent infection, UTI, and Sepsis assumed to be 7 days
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Figure 1. Simplified Model Tree Diagram. The decision analytic tree depicted demonstrates complications and outcomes associated with serial stenting and URS. The model begins on the
nodes) and terminal nodes (triangle nodes)
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left with the decision node (square nodes) and then consists of multiple chance nodes (circle
Figure 2. Incremental cost and incremental effectiveness of ureteroscopy by GA at stone diagnosis. A, incremental cost of URS = cost of URS – cost of serial stent placement. B,
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Incremental effectiveness of URS = effectiveness of URS – effectiveness of serial stent
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placement.
Figure 3. Net monetary benefit of ureteroscopy by GA at stone diagnosis. Net monetary benefit of URS = (willingness to pay [$50,000/QALY] x incremental effectiveness – incremental
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cost).
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S0002-9378(15)00774-7
DOI:
10.1016/j.ajog.2015.07.024
Reference:
YMOB 10538
To appear in:
American Journal of Obstetrics and Gynecology
Received Date: 17 March 2015 Revised Date:
24 May 2015
Accepted Date: 18 July 2015
Please cite this article as: Wymer K, Plunkett BA, Park S, Urolithiasis in Pregnancy: A CostEffectiveness Analysis of Ureteroscopic Management Versus Ureteral Stenting, American Journal of Obstetrics and Gynecology (2015), doi: 10.1016/j.ajog.2015.07.024. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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UROLITHIASIS IN PREGNANCY: A COST-EFFECTIVENESS ANALYSIS OF URETEROSCOPIC MANAGEMENT VERSUS URETERAL STENTING Kevin WYMER, BA (Mr)1, Beth A. PLUNKETT, MD, MPH2, Sangtae PARK, MD, MPH3
2
University of Chicago, Pritzker School of Medicine
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1
NorthShore University HealthSystem, Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology NorthShore University HealthSystem, Division of Urology, Department of Surgery
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3
Conflicts of Interest: The authors report no conflict of interest
Corresponding Author: Sangtae Park, MD, MPH NorthShore University HealthSystem,
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Source of Funding: No financial support was provided for this project
Department of Surgery, Division of Urology
Evanston, IL 60201
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1000 Central Ave. Ste 720
Email: [email protected]
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Fax: 847-503-3500
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Office: 847-503-3000
Abstract Word Count: 250 Main Text Word Count: 2,544 1
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Condensation: Antepartum ureteroscopy is less costly and more effective relative to serial stent placement and is most beneficial for women diagnosed early during pregnancy.
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Short Title: Cost-effectiveness of ureteroscopy during pregnancy
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ABSTRACT Objectives: To determine the cost-effectiveness of serial stenting versus ureteroscopy (URS) for
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treatment of urolithiasis during pregnancy as a function of gestational age (GA) at diagnosis. Study Design: We built decision analytic models for a hypothetical cohort of pregnant women diagnosed with symptomatic ureteral calculi and compared serial stenting to URS. We assumed
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ureteral stent replacement every four weeks during pregnancy, intravenous sedation for stent placement, and spinal anesthetic for URS. Outcomes were derived from the literature and included
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stent infection, migration, spontaneous stone passage, ureteral injury, failed URS, postoperative urinary tract infection, sepsis, and anesthetic complications. Four separate analyses were run based on the GA at diagnosis of urolithiasis. Using direct costs and quality-adjusted life years (QALYs), we reported the incremental costs and effectiveness of each strategy based on GA at stone
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diagnosis and calculated the net monetary benefit (NMB). We performed one-way and MonteCarlo sensitivity analyses to assess the strength of the model. Results: URS was less costly and more effective for urolithiasis irrespective of GA at diagnosis.
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The incremental cost of URS increased from -$74,469 to -$7,631 and the incremental effectiveness decreased from 0.49 to 0.05 QALYs for a stone diagnosed at 12 and 36 weeks GA,
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respectively. The NMB of URS progressively decreased for stones diagnosed later in pregnancy. The model was robust to all variables. Conclusion: Ureteroscopy is less costly and more effective relative to serial stenting for urolithiasis regardless of the GA at diagnosis. Ureteroscopy is most beneficial for women diagnosed early during pregnancy.
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Keywords: Cost-effectiveness; urolithiasis; pregnancy; ureteroscopy
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Introduction Genitourinary complications are the leading cause of non-obstetric hospital admissions
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during pregnancy, with kidney stones affecting an estimated 1 in 244 to 1 in 2000 pregnancies.1-3 Many anatomic and physiologic changes that accompany pregnancy are associated with an increased risk of stone formation. These include mechanical obstruction of the ureters,
progesterone-induced reduction in ureteral peristalsis, and increased filtration rates of stone
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promoters such as sodium, calcium, and uric acid.1 In addition, pregnant patients may be at
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increased risk of stone-related complications, such as pyelonephritis or obstetric complications including preterm labor and preterm delivery.1,4–7
As in the general population, analgesia and monitoring for spontaneous passage is often the most appropriate initial treatment for acute renal colic in the pregnant patient. However, recent studies have found that as low as 47% of pregnant patients with confirmed urolithiasis are
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able to pass stones spontaneously.8 If conservative management is unsuccessful, or if there are absolute indications for intervention (e.g. intractable pain, vomiting, fever, etc.), active
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management is warranted. Traditionally, antepartum ureteral stent insertion has been the most commonly used method to temporarily alleviate urinary tract obstruction in pregnant women,
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allowing pregnancy to continue to term without more invasive treatment methods such as ureteroscopy (URS).9–11 Because of changes in urine composition that occur during pregnancy, there is an increased rate of stent encrustation, necessitating stent replacements every 4-6 weeks.2 Antepartum stent placement has two advantages: it allows for immediate relief of the obstruction and subsequently leads to passive dilation of the ureter, potentially facilitating successful URS post-partum.12–15 However, stenting is not entirely benign. Indwelling ureteral stents can become infected, migrate, or cause significant pain.16–20 The pain associated with indwelling stents is 5
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often so severe that many patients report higher total pain scores than those with acute renal colic, and 80% of patients with a stent report a significantly reduced quality of life.21
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In contrast, immediate URS, as is performed in the non-pregnant patient, eliminates the need for antepartum serial ureteral stent placement and provides a definitive surgical treatment. However, there remains controversy regarding the use of URS during pregnancy. URS requires a higher level of anesthesia and increased procedure time relative to ureteral stent placement, and
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carries a risk of ureteral perforation or injury. Additionally, without pre-operative stenting,
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antepartum URS may be less successful relative to postpartum URS following serial stenting.12– In response to these concerns, several studies have demonstrated that URS is highly effective
in pregnancy and can be performed under spinal anesthesia with minimal reported risks to the mother and fetus.22–24 Multiple small studies have also shown no significant differences in complications following URS in pregnant women compared to non-pregnant women.23,25,26
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Additionally, the American Urological Association treatment guidelines now recognize URS as a treatment option to be considered for pregnant patients with urolithiasis.27
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It remains unclear whether antepartum serial stenting or URS is superior for treatment of stones during pregnancy, and how the gestational age (GA) at diagnosis affects the risks and
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benefits of each treatment modality. Because URS is more successful after stent placement,12–15 we hypothesized that stenting later in pregnancy may be the preferred approach while URS earlier in pregnancy may prove to be more beneficial. The objective of this study was to determine the cost-effectiveness of serial stenting versus URS for treatment of urolithiasis in pregnant women as a function of gestational age at diagnosis. Materials and Methods
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To compare patient outcomes resulting from ureteral stent placement versus URS, we developed a decision analytic model for a hypothetical cohort of women presenting with a symptomatic ureteral stone during pregnancy (Figure 1). We conducted the analysis from a
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payer’s perspective and measured effectiveness as quality adjusted life years (QALYs.) QALYs were calculated using life expectancy and utility values, which are defined as numerical judgments of the desirability of specific outcomes.28 We calculated incremental costs,
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incremental effectiveness, incremental cost-effectiveness ratio (ICER), as well as net monetary benefit (NMB). Incremental costs are defined as the difference in the mean cost between the two
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strategies. Similarly, incremental effectiveness is the difference in the mean effectiveness (i.e. QALYs) between the two strategies. We calculated the ICER as the incremental cost divided by the incremental effectiveness and compared this value to a willingness to pay (WTP) threshold of $50,000 per QALY to determine whether URS was cost-effective compared to ureteral stenting.
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Although there is no consensus on a WTP threshold, $50,000 was chosen because it is frequently used in cost effectiveness healthcare analyses originating in the United States.29 We also assessed the cost-effectiveness of URS using NMB, defined as the WTP x incremental effectiveness –
stent placement.
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incremental cost. If the NMB of URS was greater than zero, URS was cost-effective compared to
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To develop the model, we used TreeAge Pro (TreeAge Software, Inc. Williamstown,
MA, 2013). We assumed that patients undergoing stent placement received intravenous sedation, stents were changed every four weeks during pregnancy, and there were no changes in symptoms over the duration of the stent. In addition, we assumed that if stent migration occurred, the stent was replaced, and if ureteral injury occurred during URS, serial stents were placed every four weeks for the remainder of the pregnancy. If the URS procedure failed (i.e. stone recurrence or
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persistence), we assumed that a stent would be placed for 2 weeks, followed by a second attempt at the URS procedure. All pregnancies were assumed to result in delivery at 40 weeks GA. We also assumed patients undergoing URS received spinal anesthesia. We based this assumption on
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findings supporting the safety and efficacy of spinal anesthesia for URS.22,30 Additionally,
regional anesthesia during pregnancy remains the preferred alternative as the implications for general anesthesia for long-term neurodevelopment of the fetus remains unclear.31–33
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We set the gestational age of stone diagnosis at four different time points: 12 weeks, 20 weeks, 32 weeks, and 36 weeks. We conducted separate analyses for each diagnostic time point.
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To calculate stent costs and disutility at the varying time points of diagnosis, we multiplied the cost and disutility of stent placement by the number of stents needed to reach delivery, assuming stent replacement every four weeks.
We obtained all modeling probabilities from the literature (Table 1). If multiple estimates
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were available in the literature, we calculated a mean estimate by weighting the individual estimates based on sample size. We included this weighted average as the parameter value in the base case analysis.
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For stent placement outcomes, we included infection, stent migration, and spontaneous stone passage. We based stent complications on elective stent placement and defined infection by
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the presence of fever and bacteruria.34–36 As stent placement is primarily a temporizing procedure, we included the cost of postpartum treatment within the model for patients who underwent antepartum serial stenting. We assumed that all stented patients underwent an abdominal CT scan to assess for persistent stone following delivery. If spontaneous stone passage occurred following serial stent placement during pregnancy, the patient underwent no further treatment. If no spontaneous stone passage occurred, the patient underwent URS 2 weeks
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postpartum. A higher URS stone-free rate was included for postpartum URS relative to antepartum URS based on the documented improved success of URS following preoperative stenting.12–15
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For URS outcomes, we included temporary postoperative stent placement (for 1 week duration following URS), UTI, sepsis, URS failure without preoperative stent placement, URS failure with preoperative stent placement, and ureteral injury. When available, we included
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complication rates specific to pregnant patients. However, we also incorporated studies including non-pregnant patients due to the equivalent complication rates found between pregnant and non-
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pregnant patients following URS.23,25,26 With regard to anesthesia complications, we included post-dural-puncture headache and aseptic meningitis following spinal anesthesia. We did not include complications of intravenous anesthesia as these complications tend to be rare and transient, likely having an insignificant effect on the outcome of the model.37
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The model included hospital, urologist, and anesthesiologist costs, and the cost of intraoperative fetal monitoring with fetal non-stress test (NST) during URS or stent placement (Table 2). We based urologist costs on the Current Procedural Terminology from the American
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Medical Association.38 We calculated anesthesiologist costs using the Centers for Medicaid and Medicare Services anesthesia charge formula,39 and derived costs for UTI, stent infection, CT
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scan, and postdural headache from the literature. More specifically, we calculated postdural headache costs using the mean cost per patient, including the average costs and use of intravenous caffeine, blood patch, and hospital stay.40 Infection costs included both the cost of treatment and laboratory diagnosis.41 We obtained costs for inpatient procedures and diagnoses (i.e. sepsis, meningitis) from the 2012 Hospital Cost and Utilization Project (HCUPnet), a nationwide inpatient database that reports the national average costs for specific diagnoses and
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procedures.42 For outpatient procedures (URS and stent placement), we used cost data from the NorthShore University HealthSystem financial department. To convert all costs to 2014 dollars,
all future costs and utility values at a 3% annual rate.
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we used the medical care component of the Consumer Price Index.43 Additionally, we discounted
We obtained all utility values from the literature (Table 3). To calculate QALYs, we combined the utility values, tolls, and the estimated life expectancy. We defined a full life
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expectancy as 56.8 years in the model based on the life expectancy of a 25 year-old woman (average age of first pregnancy).44,45 If a patient had multiple complications, we used the
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complication with the lowest utility value at any given time point to calculate the corresponding QALYs.
To test the robustness of the study findings, we performed sensitivity analyses. We conducted one-way sensitivity analyses on all variables and defined the ranges of the
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probabilities by the lowest and highest values reported in the literature. If only one estimate was available in the literature, the sensitivity analysis range was defined as the 95% confidence interval, calculated using the binomial Clopper-Pearson exact method (Table 1).46,47 We varied
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all costs and disutility values from 50-150% of the base-case value and varied the annual discount rate of all costs and QALYs from 0-7% (Tables 2,3). In addition, we used Monte-Carlo
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simulation to conduct probabilistic sensitivity analysis with 10,000 trials run for each model. Beta distributions were used for probabilities and gamma distributions for costs.48 This study was exempt from IRB approval. Results
The results of the base-case analyses are summarized in Figure 2 (A, B). URS was less costly and more effective relative to stent placement for a stone diagnosed at 12, 20, 32, or 36
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weeks GA. In addition, we found a progression of increasing incremental cost and decreasing incremental effectiveness of URS with later GA at stone diagnosis. The incremental cost of URS increased from -$74,469 for a stone diagnosed at 12 weeks GA to -$7,631 for a stone diagnosed
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at 36 weeks GA and the incremental effectiveness decreased from 0.488 to 0.049 QALYs across those same time points.
Net-benefit analysis showed a positive NMB of URS for all gestational ages and an
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overall trend of a decreasing NMB of URS with later GA at diagnosis (Figure 3). The NMB of URS decreased from $98,864 for a stone diagnosed at 12 weeks GA to $10,082 for a stone
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diagnosed at 36 weeks GA.
Based on the results of the one-way sensitivity analyses, the model is very robust towards URS. Irrespective of the GA at stone diagnosis, the model was not sensitive to any variables. Probabilistic analyses using Monte Carlo simulations showed that, corresponding to a WTP of
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$50,000/QALY, URS was preferred 99.04%, 95.56%, 86.77%, and 80.05% of the time for a stone diagnosed at a GA of 12, 20, 32, or 36 weeks respectively. Comment
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Our study demonstrates that URS is dominant (less costly and more effective) relative to stent placement for the treatment of urolithiasis in pregnancy regardless of the GA at stone
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diagnosis. The difference between URS and stent placement, as measured by incremental cost, incremental effectiveness, and net monetary benefit, becomes increasingly greater with an earlier GA at stone diagnosis, suggesting a larger benefit of URS for women who are diagnosed earlier during pregnancy. This trend appears to be driven largely by the cost of stent placement and was further supported by the results of the sensitivity analyses, notably the increasing preference of the Monte-Carlo simulations towards URS with earlier stone diagnoses. Definitive antepartum
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URS was found to be less costly and more effective relative to serial stenting even late in pregnancy when the length of ureteral stent placement was relatively short. In addition, antepartum URS was dominant despite the increased stone-free rate of postpartum URS
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following preoperative, antepartum stent placement.
By examining the cost-effectiveness of stone treatment during pregnancy as a function of GA at diagnosis, our study expands upon prior literature supporting the use of URS for stone
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treatment during pregnancy.2,9,23,25,49 Prior studies have found URS in the pregnant patient to be relatively safe and associated with the same low complication rates as in the general population,
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but have not analyzed cost-effectiveness or directly compared URS to serial stenting.23,25,26 In addition, the costs and outcomes associated with serial stenting vary greatly depending on the GA at stone diagnosis. By analyzing the model according to GA at diagnosis, the results of the current study highlight the changing cost-effectiveness ratio with varying length of ureteral
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stenting. These data could potentially be used to help guide patients’ and physicians’ decisions regarding URS based on a woman’s specific point in pregnancy. Limitations of this study should be noted. As with all decision analytic models, our model
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did not incorporate all possible outcomes, and thus findings from our analyses are only applicable to the clinical scenarios assumed for our models. In addition, decision analytic models
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can be limited by the characteristics of the literature from which the modeling parameters were derived. Because this analysis was conducted from a payer’s perspective, it was limited by the exclusion of indirect costs. The study was also limited by the absence of obstetric complications in the model. However, data comparing women undergoing URS to all women with symptomatic urolithiasis show no difference in obstetric complication rates, including preterm delivery. 9 Based on these data, the treatment of urolithiasis during pregnancy, whether with serial stenting
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or URS, does not have any effect on obstetric complication rates and thus would not have altered the outcomes of the model. In addition, type of anesthesia has not been found to lead to a significant difference in obstetric complication rates.33,50,51
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Despite these limitations, our study has many notable strengths. To the best of our
knowledge, it is the first to compare the cost-effectiveness of interventions for kidney stones during pregnancy, and offers further granularity and clinical application by examining treatment
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at multiple gestational ages. In addition, we employed thorough sensitivity analyses, including Monte-Carlo simulation, which provides strong support for the robustness of our outcomes. The
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model itself is comprehensive in its assessment of stent and URS related complications, and thus provides a reasonable proxy for clinical outcomes.
In conclusion, when considering the treatment of symptomatic urolithiasis during pregnancy, URS is a cost-effective option for stones diagnosed at any gestational age.
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Furthermore, URS is most beneficial for women diagnosed with urolithiasis earlier during their pregnancy. Such findings support and expand on prior work, highlighting the prominent role that
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URS should play in the treatment of urolithiasis during pregnancy.
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50. Mazze RI, Kallén B. Reproductive outcome after anesthesia and operation during pregnancy: A Registry study of 5405 cases. Am J Obstet Gynecol. 1989 Nov;161(5):1178– 85.
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51. Ní Mhuireachtaigh R, O’Gorman DA. Anesthesia in pregnant patients for nonobstetric surgery. J Clin Anesth. 2006 Feb;18(1):60–6.
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52. Ngai H-Y, Salih HQ, Albeer A, Aghaways I, Buchholz N. Double-J ureteric stenting in pregnancy: A single-centre experience from Iraq. Arab J Urol. 2013 Jun;11(2):148–51. 53. Breau RH, Norman RW. Optimal prevention and management of proximal ureteral stent migration and remigration. J Urol. 2001 Sep;166(3):890–3. 54. Slaton JW, Kropp KA. Proximal Ureteral Stent Migration: An Avoidable Complication? J Urol. 1996 Jan;155(1):58–61. 55. Jones BJ, Ryan PC, Lyons O, Grainger R, McDermott TE, Butler MR. Use of the double pigtail stent in stone retrieval following unsuccessful ureteroscopy. Br J Urol. 1990 Sep;66(3):254–6.
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56. Laing KA, Lam TBL, McClinton S, Cohen NP, Traxer O, Somani BK. Outcomes of ureteroscopy for stone disease in pregnancy: results from a systematic review of the literature. Urol Int. 2012;89(4):380–6.
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61. De La Rosette J, Denstedt JD, Geavlete PA, Keeley F, Matsuda T, Pearle MS, et al. The Clinical Research Office of the Endourological Society Ureteroscopy Global Study: Indications, Complications, and Outcomes in 11885 Patients. J Endourol Endourol Soc. 2013 Oct 22; 62. Se Yun Kwon, Bum Soo Kim, Hyun Tae Kim, Yoon Kyu Park. Efficacy of Percutaneous Nephrostomy During Flexible Ureteroscopy for Renal Stone Management. Korean J Urol. 2013 Oct;54(10):689–92.
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64. Atar M, Bozkurt Y, Soylemez H, Penbegul N, Sancaktutar AA, Bodakci MN, et al. Use of renal resistive index and semi-rigid ureteroscopy for managing symptomatic persistent hydronephrosis during pregnancy. Int J Surg. 2012;10(10):629–33. 65. Parker BD, Frederick RW, Reilly TP, Lowry PS, Bird ET. Efficiency and cost of treating proximal ureteral stones: Shock wave lithotripsy versus ureteroscopy plus holmium:yttrium-aluminum-garnet laser. Urology. 2004 Dec;64(6):1102–6. 66. Harmon WJ, Sershon PD, Blute ML, Patterson DE, Segura JW. Ureteroscopy: Current Practice and Long-Term Complications. J Urol. 1997 Jan;157(1):28–32. 67. Khalil M. Management of impacted proximal ureteral stone: Extracorporeal shock wave lithotripsy versus ureteroscopy with holmium: YAG laser lithotripsy. Urol Ann. 2013 Apr;5(2):88–92. 18
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68. Horlocker TT, McGregor DG, Matsushige DK, Schroeder DR, Besse JA. A retrospective review of 4767 consecutive spinal anesthetics: central nervous system complications. Perioperative Outcomes Group. Anesth Analg. 1997 Mar;84(3):578–84.
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Table 1. Model parameters- clinical events and probabilities Variable
Baseline (%)
Range (%)
References
Infection
9.86
6.00-12.30
35,36
Migration
2.38
1.20-10.00
Spontaneous Stone
10.00
2.10-26.50
56.70
42.90-72.90
12,13,26,49,56–60
0.00-15.35
12,14,15,26,56,60,61
0.00-17.60
12–15
1.14
0.60-5.20
13,25,49,56,59–66
1.69
0.86-6.70
12,25,49,56,59,61,63–
Temporary Stent Failure of URS without
3.04
preoperative stent
preoperative stent
Ureteral Injuryb
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UTI
0.00
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Failure of URS with
55
67
0.51
0.30-2.30
49,59–61,63,65
Postdural Headache
2.20
1.30-9.60
68,69
Aseptic Meningitis
0.17
0.00-0.90
69
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Sepsis
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URS Complications Post-procedure
16,34,35,52–54
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Passage
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Stent Complications
URS Anesthesia Complicationsc
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a
A lower URS failure rate was used for patients who underwent postpartum URS following
antepartum serial stenting. b
Ureteral Injury included perforation, avulsion, and stricture.
Complications from stent anesthesia were not included due to the relatively low occurrence and
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transient nature of intravenous anesthesia complications.
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c
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Table 2. Model parameters-costsa Variable
Baseline ($)
Range ($)
Stent
10,422
5,211-15,633
URS
13,403
6,702-20,105
CT Scan
383
192-575
Fetal NST
624
312-936
References
Urologist Stent
177
URS
474
Outcome
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237-711
38
77
39-116
39
207
103-310
39
1,573
786-2,359
41
UTI
1,573
786-2,359
41
Ureteral Injurye
13,621
6,810-20,431
42
Sepsis
14,401
7,200-21,601
42
Postdural Headache
1,712
856-2,568
70
Aseptic Meningitis
14,490
7,245-21,735
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Stent Infectiond
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b
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b
89-266
Anesthesiologistc Stent
b
65
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Hospital Costs
All costs were converted to 2013 dollars using the CPI.43 22
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b
Based on data from the NorthShore University HealthSystem financial department
c
For anesthesiologist costs, the Medicare formula of “Charge = (base units + time units +
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modifier units) x conversion factor” was used. For URS, the charge calculation was done using 2 base units, 4 time units, and 2 modifier units. For ureter stent placement, the charge calculation was done using 2 base units, 1 time unit, and 0 modifier units.
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Ureteral Injury included perforation, avulsion, and stricture.
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e
The cost of stent infection was estimated using the cost of UTI.
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Table 3. Model parameters- utility and QALY values Variable
Utility
Range
Time Interval
References
Stent
0.76
0.64-0.88
Varieda
URS
0.90
0.85-0.95
7.9 days
Stent Infectionb
0.64
0.46-0.82
7 daysc
73,74
UTIb
0.64
0.46-0.82
7 daysc
73,74
Ureteral Injury
0.60
0.40-0.80
30 days
71,75
Sepsisb
0.64
0.46-0.82
7 daysc
73,74
Postdural
0.77
0.81-0.94
6 days
76,77
0.65
0.48-0.83
8.5 days
78,79
Aseptic Meningitis
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71,72
Time interval used to calculate stent utility based on the length stent(s) placement
b
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Headache
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Outcome
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Procedure
c
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Stent infection, UTI, and Sepsis utility values estimated using utility for “acutely ill” patients
Time interval for stent infection, UTI, and Sepsis assumed to be 7 days
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Figure 1. Simplified Model Tree Diagram. The decision analytic tree depicted demonstrates complications and outcomes associated with serial stenting and URS. The model begins on the
nodes) and terminal nodes (triangle nodes)
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left with the decision node (square nodes) and then consists of multiple chance nodes (circle
Figure 2. Incremental cost and incremental effectiveness of ureteroscopy by GA at stone diagnosis. A, incremental cost of URS = cost of URS – cost of serial stent placement. B,
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Incremental effectiveness of URS = effectiveness of URS – effectiveness of serial stent
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placement.
Figure 3. Net monetary benefit of ureteroscopy by GA at stone diagnosis. Net monetary benefit of URS = (willingness to pay [$50,000/QALY] x incremental effectiveness – incremental
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cost).
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