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Original Articles

Cost-effectiveness of Routine Postoperative Retrograde Voiding Trials Following Pelvic Surgeries

Wang, Rui MD; Soeteman, Djøra I. PhD; Hacker, Michele R. ScD; Lefevre, Roger MD

Author Information
Female Pelvic Medicine & Reconstructive Surgery: May 2020 - Volume 26 - Issue 5 - p 306-313
doi: 10.1097/SPV.0000000000000577
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Abstract

Postoperative voiding dysfunction is the difficulty in emptying one's bladder during the postoperative period. Undetected, it has the potential to create functional sequelae that may chronically affect patients' quality of life. Prolonged overdistention of the bladder can lead to temporary or permanent damage to the detrusor muscle, with incidences of prolonged postoperative voiding dysfunction ranging between 2% and 4%.1–3 Such patients may eventually develop a chronically dysfunctional bladder, which requires long-term care that would add to our continuously increasing health care costs.2,4,5

Retrograde voiding trials involve backfilling the bladder and, within a short period thereafter, comparing the volume voided to the total amount instilled. The procedure can at times involve the use of a bladder scanner to help measure the postvoid residual volume. Voiding trials are routinely performed following anti-incontinence procedures and are increasingly becoming part of the postoperative care for pelvic surgeries.4,6,7 They can help increase the detection of transient postoperative voiding dysfunction when compared with the traditional practice of monitoring for spontaneous voiding. However, evidence indicates that the risk of postoperative voiding dysfunction varies from 2% to 43%, depending on the type of pelvic procedure,2,4,8–12 and there is still no consensus on the routine use of voiding trials following pelvic surgeries.

The objective of this study was to compare the cost-effectiveness, in terms of cost per quality-adjusted life-year (QALY) and cost per case of chronic voiding dysfunction avoided, of retrograde voiding trials with expectant management in the evaluation of postoperative voiding dysfunction. We also investigated the factors that affect the cost-effectiveness of these strategies.

MATERIALS AND METHODS

Model Overview

We developed a disease simulation model that integrated empirical data from the published literature to estimate the impact of postoperative retrograde voiding trials on clinical and cost-effectiveness outcomes (Fig. 1). The model was constructed using SilverDecisions.13 The input parameters of the model and assumptions are discussed below and listed in Table 1.

FIGURE 1
FIGURE 1:
Decision tree analyzing cost-effectiveness of postoperative retrograde voiding trials versus expectant management.
TABLE 1
TABLE 1:
Input Parameters Including Costs, Utilities, and Probabilities for Decision Tree

Women entered the model after having undergone pelvic surgery and received either expectant management (“no voiding trial” branch in Fig. 1) or routine postoperative voiding trials (“voiding trial” branch in Fig. 1). For those in the expectant management group, no voiding trial is performed postoperatively, and some patients developed postoperative voiding dysfunction, depending on the expected incidences for voiding dysfunction based on surgery type and patient population. In these cases, patients sought care in clinical settings such as the emergency department (ED), urgent care, or the doctor's office.16,17 Because of lack of estimates from literature, we gathered expert opinions from a group of Female Pelvic Medicine and Reconstructive Surgery fellowship–trained urogynecologists at an academic medical center and estimated that 60% of those with postoperative voiding dysfunction would present to the ED, 30% would present to urgent care, and 10% would present to the doctor's office. In each of these settings, patients would usually have a urinary catheter placed or learn self-catheterization. Following acute treatments, patients would have either persistent chronic urinary dysfunction or resolution of their symptoms. We assumed that patients who presented to the ED, on average, had more symptomatic acute urinary retention and a higher risk of developing chronic sequelae compared with those presenting to urgent care or the office. We assigned a 4% incidence of chronic voiding dysfunction to patients presenting to the ED (designated as “severe voiding dysfunction” in Fig. 1) based on prospective studies that showed the baseline incidence of chronic voiding dysfunction to be 2% to 4%.1,14,15 We assumed this incidence was 3% for the group presenting to urgent care (designated as “moderate voiding dysfunction” in Fig. 1) and 2% for the group presenting to the doctor's office (designated as “mild voiding dysfunction” in Fig. 1).

For those in the routine postoperative retrograde voiding trial group, we assumed a sensitivity to detect postoperative voiding dysfunction lasting at least 7 days of 94.4% and a specificity of 58.1% based on results from a randomized controlled trial.6 Among patient who initially failed their postoperative retrograde voiding trials, both the true positives and false positives would undergo temporary treatment with an indwelling urinary catheter. After this treatment, the false-positive results would all return to their normal voiding function, whereas the baseline level of 2% of the true-positive results would go on to develop chronic urinary dysfunction. Among the patients who initially passed their postoperative voiding trial (“Test- [passed]” branch in Fig. 1), 97.6% would not have voiding dysfunction (“true negative” branch in Fig. 1), and 2.4% would have undetected postoperative voiding dysfunction (“false negative” branch in Fig. 1). Among the latter, we again assumed that 60% would present to the ED (“severe voiding dysfunction”), 30% would present to urgent care (“moderate voiding dysfunction”), and 10% would present to the doctor's office (“mild voiding dysfunction”). These patients also would undergo temporary treatment with a urinary catheter or intermittent self-catheterization, followed by the development of chronic voiding dysfunction in 2% to 4% of cases based on the location of presentation.

We investigated the impact of the incidence of postoperative voiding dysfunction on the cost-effectiveness results. For each incidence between 2% and 60%, we calculated the incremental cost-effectiveness ratio (ICER) comparing postoperative retrograde voiding trials to expectant management for spontaneous voiding. To demonstrate our results with clinically relevant examples, we then chose 10% as the incidence of postoperative voiding dysfunction following a simple hysterectomy7,23 and 20% as the incidence of postoperative voiding dysfunction following a midurethral sling.2,24 Using the midurethral sling as an example, for the strategy of no routine postoperative retrograde voiding trial, this meant that 20% of the patients would develop postoperative voiding dysfunction, whereas 80% would void well and not need further intervention.

We calculated costs and health benefits over a 1-week time horizon. However, given that the lifetime costs might be substantial in the rare cases when a patient developed chronic urinary dysfunction, we also reported the results using a lifetime time horizon. We assumed 25 years as the average time from surgery to death.25 For the lifetime analysis, both QALYs and costs were discounted at a rate of 3% annually. We assumed that the incidence, sensitivity, and specificity do not vary significantly in the long term as postoperative voiding dysfunction occurred shortly after surgery.

Costs

We estimated costs from the health care system's perspective, with all costs in 2016 US dollars. The calculations included direct medical costs (ie, primary treatment costs and costs of health care utilization after discharge). The costs parameters we used are listed in Table 1 and were based on public national databases from the Fair Health Consumer and Healthcare Bluebook.18,19 We did not include indirect costs because of the unavailability of data on productivity losses and transportation costs. For each strategy, we calculated the expected costs by taking a weighted average of the costs incurred through each pathway in the tree and the proportion of the cohort of women who followed that pathway.

Health Benefits

We measured health benefits in terms of QALYs and number of cases of chronic voiding dysfunction avoided. We calculated QALYs based on health state utilities, ranging from 0 to 1, with 0 representing a health state equivalent to death and 1 representing perfect health. To reflect the diminished quality of life in women with chronic urinary retention, we assigned a utility of 0.87 to this health state based on a study of 2200 patients (Table 1).20,22 Women living without chronic urinary retention were assigned a utility of 0.965 to reflect the baseline health state.20,21 We calculated the expected number of QALYs for each strategy by taking a weighted average of the utility of each pathway in the tree and the proportion of the cohort of women who followed that pathway. To estimate the number of cases of chronic voiding dysfunction avoided, we assigned 0 to health states that resulted in chronic voiding dysfunction and 1 to health states that did not result in chronic voiding dysfunction.

Cost-effectiveness Analysis

We used the expected values of costs, number of cases of chronic voiding dysfunction avoided, and QALYs for each strategy to calculate the ICER, defined as the additional cost divided by the additional health benefit associated with one strategy compared with the next-less-costly strategy. We expressed the outcomes as cost per QALY and cost per case of chronic voiding dysfunction avoided. The most cost-effective strategy was identified by comparing the ICER against the threshold value of $100,000/QALY, which reflects the decision maker's willingness to pay (WTP) for an additional unit of effect (QALY). Strategies below a specific WTP threshold generally represent good value for money; the most cost-effective strategy is the strategy with the highest ICER below the WTP threshold, representing the option that yielded the highest level of benefit for an acceptable cost. Willingness-to-pay values of $50,000/QALY to 150,000/QALY are recommended for cost-effectiveness analyses conducted in the United States.26 Therefore, we extended our analyses to investigate the cost-effectiveness of routine retrograde voiding trials across a range of different WTP thresholds.

To report on the impact of uncertainty in the model input parameter on the cost-effectiveness results, we conducted 1- and 2-way sensitivity analyses. We varied the cost of retrograde voiding trials and examined this effect across a range of postoperative voiding dysfunction incidences. We also varied the incidence of ED visits, while dividing the remaining probability equally between urgent care and office visits.

This study was based solely on deidentified published data; thus, it did not meet the definition of human subjects research and did not require institutional review board approval.

RESULTS

Cost-effectiveness Analysis

The lifetime analysis showed that when we varied the incidence of postoperative voiding dysfunction between 2% and 60% (Fig. 2) the strategy of routine retrograde voiding trials was the most cost-effective strategy when the voiding dysfunction incidence exceeded 12.2% (assuming a WTP threshold of $100,000/QALY). When the incidence exceeded 31.1%, retrograde voiding trials were the dominant strategy (ie, less costly and more effective).

FIGURE 2
FIGURE 2:
Incremental cost-effectiveness ratio given a range of incidence of postoperative voiding dysfunction with willingness-to-pay (WTP) thresholds of $100,000/QALY. The dotted line is at WTP of $100,000/QALY. The switch point at which there was a change in the optimal option from expectant management to routine voiding trials was located at an incidence of 12.2%. The point at which voiding trials became a dominant strategy was located at an incidence of 31.1%.

Given a WTP threshold of $50,000/QALY, routine retrograde voiding trials were considered the most cost-effective option when the incidence of postoperative voiding dysfunction exceeded 17.5%. Given a WTP of $150,000/QALY, routine retrograde voiding trials were considered the most cost-effective strategy when the incidence of postoperative voiding dysfunction exceeded 9.34%.

Table 2 shows the mean 1-week and lifetime costs and health outcomes and cost-effectiveness results for simple hysterectomies (estimated at approximately 10% incidence of postoperative voiding dysfunction) and midurethral sling procedures (estimated at approximately 20% incidence of postoperative voiding dysfunction). The costs of routine retrograde voiding trials are substantially higher compared with expectant management, whereas the differences in health benefits are small. The differences in costs between the 2 strategies become less pronounced when the incidence of postoperative voiding dysfunction increases.

TABLE 2
TABLE 2:
Clinical Examples Showing 1-Week and Lifetime Costs, Health Benefits, and Cost-effectiveness Results

The cost-effectiveness results demonstrate that for simple hysterectomies with a 10% incidence of postoperative voiding dysfunction retrograde voiding trials were associated with an ICER of $138,419,396/QALY over a 1-week period and $135,335/QALY over a lifetime time horizon. For midurethral sling procedures with a 20% incidence of postoperative voiding dysfunction, retrograde voiding trials were associated with an ICER of $45,573,175/QALY over a 1-week period and $35,558/QALY over a lifetime time horizon.

With respect to cases of chronic voiding dysfunction avoided, for simple hysterectomies with a 10% incidence of postoperative voiding dysfunction, it costs $230,069 to avoid 1 case of chronic voiding dysfunction by performing routine postoperative retrograde voiding trials over a lifetime time horizon and $252,876 over a 1-week time horizon. For midurethral sling procedures with a 20% incidence of postoperative voiding dysfunction, it costs $60,449 to avoid 1 case of chronic voiding dysfunction by performing routine postoperative retrograde voiding trials over a lifetime time horizon and $83,256 over a 1-week time horizon.

Sensitivity Analyses

Figure 3 shows the results of the 1-way sensitivity analyses with a 10% incidence of postoperative voiding dysfunction. The input parameters are ranked by their impact on the ICER comparing routine retrograde voiding trials and expectant management. We centered the lower and upper bound ranges on the base case ICER of $135,335/QALY. The input parameters with the most impact were the incidence of presentation to the ED for acute urinary retention and the incidence of chronic urinary retention following acute retention care in the ED. Figure 4 shows the 1-way sensitivity analyses with a 20% incidence of postoperative voiding dysfunction. In this case, we centered the lower and upper bound ranges for each input parameter on the ICER of $35,558/QALY. The same 2 input parameters affected the cost-effectiveness results the most, but fewer input parameters changed the optimal strategy as compared with Figure 3.

FIGURE 3
FIGURE 3:
One-way sensitivity analysis with base case of 10% incidence of postoperative voiding dysfunction and ICER of $135,335/QALY.1 For each input parameter, we list the threshold at which the optimal strategy changes from expectant management to routine voiding trials (ie, resulting ICER is <$100,000/QALY). The value “N/A” denotes input parameters that do not change the optimal strategy.
FIGURE 4
FIGURE 4:
One-way sensitivity analysis with base case of 20% incidence of postoperative voiding dysfunction and ICER of $35,558/QALY.1 For each input parameter, we list the threshold at which the optimal strategy changes from expectant management to routine voiding trials (ie, resulting ICER is <$100,000/QALY). The value “N/A” indicates that altering these parameters did not result in the ICER crossing the $100,000/QALY threshold.

We conducted 2-way sensitivity analyses to assess the impact of varying the incidence of ED visits for acute urinary retention and the incidence of postoperative voiding dysfunction on the cost-effectiveness results. As shown in Figure 5, the incidence of postoperative voiding dysfunction for which the ICER was below the WTP threshold of $100,000/QALY decreased as the incidence of ED visits for acute urinary retention increased. We also performed a 2-way sensitivity analysis to assess the impact of varying the cost of retrograde voiding trials and the incidence of postoperative voiding dysfunction on the cost-effectiveness results. As shown in Figure 6, the incidence of postoperative voiding dysfunction for which the ICER was below the WTP threshold of $100,000/QALY increased as the cost of retrograde voiding trials increased.

FIGURE 5
FIGURE 5:
Sensitivity analysis of the incidence of ED visits for urinary retention and prevalence of postoperative voiding dysfunction above which routine voiding trials remain cost-effective at an ICER threshold of $100,000/QALY.
FIGURE 6
FIGURE 6:
Sensitivity analysis of the cost of a voiding trial and prevalence of postoperative voiding dysfunction above which routine voiding trials remain cost-effective at an ICER threshold of $100,000/QALY.

COMMENT

Using a disease simulation model that incorporated relevant clinical events in the management of postoperative voiding dysfunction, we compared the cost-effectiveness of routine retrograde voiding trials versus expectant management over a 1-week and lifetime time horizon. Our findings showed that performing postoperative retrograde voiding trials following pelvic procedures with an expected postoperative voiding dysfunction risk higher than 12.2% can be considered a cost-effective intervention assuming a WTP for health of $100,000/QALY. For example, for a simple hysterectomy with an incidence of voiding dysfunction approximately 10%, the ICER was $135,335/QALY over a lifetime horizon, indicating that expectant management can be considered the most cost-effective choice. On the other hand, for a midurethral sling procedure with approximately 20% incidence of voiding dysfunction, retrograde voiding trials would be the most cost-effective strategy given that the ICER was $35,558/QALY over a lifetime horizon, which is lower than the WTP for health. With respect to the clinical outcome measure, for a simple hysterectomy with a 10% incidence of postoperative voiding dysfunction, the cost per case of chronic voiding dysfunction avoided was $230,069. For a midurethral sling procedure with a 20% incidence, the cost per case of chronic voiding dysfunction avoided was substantially less ($60,449). Sensitivity analysis showed that the WTP for health, the incidence of presentation to the ED for acute urinary retention, and the incidence of chronic urinary retention following acute retention care in the ED had the greatest impact on the cost-effectiveness of routine retrograde voiding trials.

If a gynecologic surgeon could reasonably estimate the expected postoperative risk of voiding dysfunction for a particular patient group, the findings of this study would enable the surgeon to determine if postoperative voiding trials are a cost-effective intervention given the society's currently accepted WTP for each additional QALY.

The major strength of this study was the use of decision-analytic modeling, which provided a framework for informed decision making under conditions of uncertainty. For the vast majority of probabilities, costs, and utilities used in our model, we based the numbers on published national data. This enables generalizability of our results. Our sensitivity analyses allowed us to vary uncertain parameters over a broad range of values and investigate factors that might have a significant influence on the cost-effectiveness results.

This study used population-level data to inform the input parameters of the model, and the results can therefore inform treatment decision making on a population level. The results should be used only as a guide in decision making for individual patient care. That process should also account for other factors, such as medical history, comorbidities, and patient preferences. Inherent to the nature of modeling, we were limited by the availability of data and the accuracy of our assumptions. There were limited data on the incidence of presentation to EDs, urgent care, or physicians' offices, as well as the incidences of chronic urinary retention following acute retention care in these facilities. In particular, our estimate for the utility of living with chronic voiding dysfunction was extrapolated from data on male patients because of unavailability of such data for women. Hence, we have used sensitivity analyses across reasonable ranges of values for these and other input parameters and have presented our results in the context of these sensitivity analyses. We used placement of an indwelling catheter as the main treatment for postoperative retention and recognize that some practitioners might opt for teaching intermittent self-catheterization. In future analyses, this variation could be incorporated into the model and explored further. We also recognize that voiding trials may not prevent the sequelae of chronic voiding dysfunction. Finally, we presented a simplified version of the myriad of possible management options, potential outcomes, and other issues that may arise during the postoperative period related to voiding dysfunction. We recognize that there was a tradeoff between allowing enough complexity to accurately model the real-world situation in a decision tree and having enough simplicity to make the model transparent. Future research on the probabilities and costs, such as the frequency of patients presenting to the ED, urgent care, or clinic with acute urinary retention, will help decrease the uncertainty in model input parameters and thus the uncertainty in the study findings. We also plan to expand our model to other types of voiding trials such as spontaneous trials of void in the future, as well as use our decision tree structure to evaluate other postoperative interventions.

Despite these limitations, we can conclude that retrograde voiding trials following pelvic surgery can be considered cost-effective screening compared with expectant management when the incidence of voiding dysfunction exceeds 12.2%. These results are sensitive to the WTP for health, the incidence of presentation to the ED for acute urinary retention, and the incidence of chronic urinary retention following acute retention care in the ED.

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Keywords:

cost-effectiveness; gynecological surgery; pelvic surgery; postoperative voiding trial; voiding dysfunction

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