Original Research
Prophylactic Use of Negative Pressure Wound Therapy After Cesarean Delivery Nelson C. Echebiri, MD, MBA, M. Maya McDoom, PhD, MPH, Meaghan M. Aalto, MD, Jessie Fauntleroy, MD, Nagammai Nagappan, MD, and Vanessa M. Barnabei, MD, PhD OBJECTIVE: To evaluate the economic benefit of prophylactic negative pressure wound therapy on a closed laparotomy incision after cesarean delivery in comparison with standard postoperative dressing. METHODS: We designed a decision-analytic model from a third-party payer’s perspective to determine the cost– benefit of prophylactic application of negative pressure wound therapy compared with standard postoperative dressing on a closed laparotomy incision after cesarean delivery. Our primary outcome measure was the expected value of the cost per strategy. Baseline probabilities and cost assumptions were derived from published literature. We conducted sensitivity analyses using both deterministic and probabilistic models. Cost estimates reflect 2014 U.S. dollars. RESULTS: Under our baseline parameters, standard postoperative dressing was the preferred strategy. Standard postoperative dressing and prophylactic negative pressure wound therapy cost $547 and $804 per strategy, respectively. Sensitivity analyses showed that prophylactic negative pressure wound therapy can be cost-beneficial if it is priced below $192; standard postoperative dressing is the preferred strategy among patients with surgical site infection rate of 14% or less. If surgical site infection rates are greater than 14%, prophylactic negative pressure wound therapy could be cost-beneficial depending on See related editorial on page 297.
From the Department of Obstetrics and Gynecology, University at Buffalo, Buffalo, New York; Social Science Research Center, Mississippi State University, Starkville, Mississippi; and the Department of Global Health and Population, Harvard School of Public Health, Boston, Massachusetts. The authors thank James A. Shelton, MS, for his help in the analysis, comments, suggestions, and statistical advice. Corresponding author: Nelson C. Echebiri, MD, MBA, University at Buffalo, Department of Obstetrics–Gynecology, 219 Bryant Street, Buffalo, NY 14221; e-mail: [email protected]. Financial Disclosure The authors did not report any potential conflicts of interest. © 2015 by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. All rights reserved. ISSN: 0029-7844/15
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the degree of reduction in surgical site infections. At a surgical site infection rate of 30%, the rate must be reduced by 15% for negative pressure wound therapy to become the preferred strategy. Monte Carlo simulation of 1,000 patients in 1 million trials showed that standard postoperative dressing was the preferred cost-beneficial strategy with a frequency of 85%. CONCLUSION: Our cost–benefit analysis provides economic evidence suggesting that negative pressure wound therapy should not be used on closed laparotomy incisions of patients with low risk of postcesarean delivery surgical site infections. However, among patients with a high risk of surgical site infections, prophylactic negative pressure wound therapy is potentially cost-beneficial. (Obstet Gynecol 2015;125:299–307) DOI: 10.1097/AOG.0000000000000634
M
ore than 1 million cesarean deliveries are performed annually in the United States (32.8% of births in 2012).1,2 The rate of surgical site infection after cesarean delivery is between 3 and 18%3–7 and may be as high as 30% in patients with body mass indexes (BMIs, calculated as weight (kg)/[height (m)]2) of 50 or higher.3,8 These infections add substantial costs to health care attributable to maternal readmissions, reoperations, additional antibiotic therapy, and home health services.9,10 As a result of the morbidity, mortality, and costs associated with surgical site infection, the Centers for Disease Control and Prevention developed guidelines for preventing infections including: appropriate selection and timing of prophylactic antibiotics, optimizing preoperative skin hygiene, and surgical skin preparation.4,11 Although negative pressure wound therapy is not part of the current guidelines, it has emerged as an accepted technique in contemporary wound healing.12 The benefits of negative pressure wound therapy12–15 are widely recognized. Negative pressure wound therapy is now routinely used to facilitate closure of open
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abdominal wounds,16 open fractures,17 skin graft sites,18 and surgical wounds expected to heal by primary intention.12,13,19 At our institution, there is an increasing trend toward the prophylactic application of negative pressure wound therapy to a closed incision after cesarean delivery to reduce the incidence of surgical site infection after cesarean delivery. At a cost of approximately $500 per device, evidence regarding the cost–benefit of adopting this technology in routine clinical practice is needed. Currently, there are no published economic analyses of prophylactic negative pressure wound therapy devices on a closed laparotomy incision after cesarean delivery. Therefore, we designed a decision-analytic model to estimate whether the use of prophylactic negative pressure wound therapy after a cesarean delivery is costbeneficial.
MATERIALS AND METHODS We designed a cost–benefit analysis decision tree model using techniques described by Plevritis,20 Detsky et al,21 Naglie et al,22 and Krahn et al.23 The decision tree diagram and all computations were performed using a commercially available decisionanalysis software: TreeAge Pro Suite Software Inc (Fig. 1). The model was framed from the third-party payer’s perspective. The model was structured as a decision tree starting with theoretical cohorts of patients entering the model, as shown in Figure 1. Each cohort will undergo nonemergent cesarean delivery, then receive one of two postoperative incision management strategies: 1) application of negative pressure wound therapy after closure of skin incision or 2) application of a standard postoperative dressing only. Patients will then undergo a cascade of events and health interventions in the presence of surgical site infection. The model assumes that standard clinical guidelines11 regarding preoperative and postoperative measures to avoid or reduce surgical site infection were followed. The primary outcome measure was the expected value of the cost per strategy. To perform this cost–benefit analysis, we obtained and evaluated data from numerous sources. We conducted literature searches in PubMed and Google search engines for the following terms: negative pressure wound therapy after cesarean delivery; Prevena; surgical site infection after cesarean delivery; effectiveness of negative pressure wound therapy on closed skin incisions; cost of surgical site infection after cesarean delivery; cost of home health services; and diagnosis-related group (DRG) codes. We also reviewed the reference lists from retrieved articles. The broad literature search ensured that no single
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source or type of publication provided the majority of the data elements. When available, we used published randomized controlled trials, Cochrane reviews, and meta-analyses to derive probability estimates. Baseline assumptions and variables used for the analysis represent best available estimates from the literature and are summarized with their references in Table 1. The ranges noted in Table 1 were also used to derive the mean for the baseline analysis when published baseline values were unavailable. This study was approved by the University at Buffalo institutional review board under the determination of “does not involve human subjects” because we only used a collection of publicly available and deidentified data sources. The reported incidence of surgical site infection after cesarean delivery varies widely from 3 to 18%3–7 and maybe as high as 30% in patients with BMIs of 50 or higher.8 As a result of this wide variation, we used a mean of 17% and a range of 3–30% as the risk of surgical site infection after cesarean delivery in patients without prophylactic negative pressure wound therapy. Paul et al13 reported the incidence of surgical site infection after ventral hernia repair in 25.8% of patients with standard wound dressing compared with 20.4% of patients with closed incision negative pressure wound therapy, whereas Blackham et al15 reported fewer total surgical site infections in 16.0% of patients with negative pressure wound therapy compared with 35.5% of patients with standard wound dressing after a closed laparotomy incision. However, a recent Cochrane review concluded that the evidence for the effectiveness of negative pressure wound therapy on surgical wounds expected to heal by primary intention remains unclear.12 Therefore, based on these data,12,13,15 we extrapolated that the incidence of surgical site infection after cesarean delivery in patients with prophylactic negative pressure wound therapy ranged from 1 to 20% with an average baseline risk of 11%. For sensitivity analysis we increased the risk of surgical site infection after cesarean delivery with or without prophylactic negative pressure wound therapy to 100%. The standard postoperative dressing and the negative pressure wound therapy branches of the tree have similar nodes and events with the exception of wound complications from negative pressure wound therapy. Based on published data, the incidence of wound complications from negative pressure wound therapy is very low.24–27 To account for this risk, patients in the prophylactic negative pressure wound therapy branch of the tree have a 3–20% risk of skin blisters.24–27 We assumed that 5–10% of these complications would require additional skin care at the time
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Complications from prophylactic negative pressure wound therapy
Prophylactic negative pressure wound therapy
Complications from prophylactic negative pressure wound therapy requiring skin care Complications from prophylactic negative pressure wound therapy. Self-limiting. No additional skin care Surgical site infection despite prophylactic negative pressure wound therapy
No complications from prophylactic negative pressure wound therapy Management of closed laparotomy incision following cesarean delivery
No surgical site infection due to prophylactic negative pressure wound therapy
Hospatilization for inpatient management Surgical site infection without prophylactic negative pressure wound therapy
Outpatient management
No prophylactic negative pressure wound therapy No surgical site infection
Fig. 1. Abbreviated decision tree of prophylactic negative pressure wound therapy compared with standard postoperative dressing. Echebiri. Prophylactic Negative Pressure Wound Therapy. Obstet Gynecol 2015.
of device removal.27 After passing through the node for wound complications from negative pressure wound therapy, patients in the prophylactic branch continued through different chance nodes with probabilities of specific events including risk of surgical site infection after cesarean delivery despite use of negative pressure wound therapy, outpatient management, or readmission for inpatient management. Patients who failed outpatient management were readmitted for inpatient management. Those that were readmitted will have a 2% risk of reoperation.28 Because the risk of reoperation secondary to surgical site infection after cesarean delivery is very low, we assumed a range from 2 to 5%28 for sensitivity analysis. The final event in both the prophylactic and standard postoperative dressing branches was the need for home health services. Literature reports that 47–62% of patients with surgical site infection will require home health services.29 To balance the tree, we assumed that
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0–1% of patients without surgical site infection will require home health services. We defined the benefit as the costs saved by avoiding surgical site infection after cesarean delivery. We defined direct costs as: 1) the fee paid to the manufacturer for providing the negative pressure wound therapy device at the authors’ institution, 2) third-party payer reimbursement for rehospitalization and reoperation, and 3) direct costs of outpatient management. Indirect costs of surgical site infection are difficult to quantify and were not included in this analysis. Our literature review showed that estimated cost of treating surgical site infection varies widely depending on the geographical location, the type of surgery performed, and the depth of the infection.30 Kirkland et al9 reported in the 1990s that the total excess hospitalization and direct costs attributable to surgical site infection was $5,038 per case. To our knowledge based on an extensive literature search, the only available
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Table 1. Probability and Cost Variables Variable Probability of complications from NPWT Probability of skin irritation from NPWT requiring additional care Probability of SSI after cesarean delivery without NPWT Probability of SSI after cesarean delivery with NPWT Probability of rehospitalization from SSI after cesarean delivery Probability of outpatient management of SSI after cesarean delivery Probability of successful outpatient management of SSI after cesarean delivery Probability of reoperation from SSI after cesarean delivery Probability of successful inpatient management of SSI after cesarean delivery without reoperation Probability of home health needed for patients without SSI after cesarean delivery Probability of home health needed for SSI after cesarean delivery Hospital cost of SSI readmission without operation (DRG 863) Hospital cost of SSI readmission with operating (DRG 858) Cost of outpatient management of SSI after cesarean delivery Cost of home health for SSI after cesarean delivery Cost of ALLEVYN nonadhesive Cost of NPWT
Value
Range
Distribution*
Sensitive
Reference
0.12 0.08
0.03–0.20 0.05–0.10
Beta Beta
No No
24–27 27
0.17
0.03–0.30
Beta
Yes
3–8
0.11
0.01–0.20
Beta
Yes
Assumption
0.09
0.07–0.11
Beta
Yes
5,28,36,41,42
0.91
0.89–0.93
Beta
Yes
5,28,36,41,42
0.92
0.90–0.93
Beta
Yes
28,41
0.02
0.02–0.05
Beta
No
28
0.98
0.95–0.98
Beta
No
28
0.01
0.0–0.01
Beta
No
Assumption
0.5
0.47–0.62
Beta
Yes
29
$5,605
$2,220–10,000
Gamma
Yes
7,9,10,31
$7,467
$2,220–20,000
Gamma
Yes
27,31
$1,766
$533–3,000
Gamma
Yes
29
$1,375 $10 $450
$917–$1,834 $3–$50 $200–$500
Gamma Normal Normal
Yes No Yes
27,29,32 43 Authors’ institution
NPWT, negative pressure wound therapy; SSI, surgical site infection; DRG, diagnosis-related group. * A statistical function that describes all the possible values and likelihoods that a random variable can take within a given range.
estimate of attributable hospital cost of surgical site infection after cesarean delivery was published in 2008 by Olsen et al,10 reporting the average cost of $2,852 ($2,006–4,378). After adjusting the 2008 estimates for inflation and also considering Medicare reimbursement for specific DRG 863 and 858, we extrapolated that the cost of hospital admission for surgical site infection after cesarean delivery without reoperation ranges from $2,220 to $10,000,7,9,31 and the cost of hospital admission for surgical site infection after cesarean delivery with reoperation ranges from $2,220 to $20,000.27,31 For sensitivity analysis, we increased the range for both the cost of readmission with and without operation to $50,000. We used the DRG estimates for readmission and reoperation for our baseline analysis. According to the Centers for Medicare & Medicaid Services report, the average cost of a home visit by a nurse in 2013 was $131.32 Based on experience at our institution, we estimated that a nursing visit for surgical site infection after cesarean
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delivery can range from 7 to 14 days ($917–1,834). Given this range, we used the average, $1,375, for baseline analysis and increased the range to $50,000 for sensitivity analysis. Perencevich et al29 reported in 1998 that the average cost of outpatient visits for surgical site infection was $365 ($533 in 2014), and the average cost of outpatient management of surgical site infection was $809 ($1,182 in 2014). Adjusting for inflation, we estimated that the cost of outpatient management for surgical site infection after cesarean delivery can range from $533 to $3,000; we used the average $1,766 for our baseline analysis and also increased the range to $50,000 for sensitivity analysis. All costs were in 2014 U.S. dollars. Annual discounting was not necessary because the time horizon was within 1 year. Sensitivity analyses were conducted to evaluate the uncertainty of the results. We varied probability and cost parameters to take into account potential clinical scenarios that might deviate from our baseline estimates. One-way deterministic sensitivity analysis,
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depicted by a tornado diagram, provided a bar chart of the main variables of influence that had the greatest effect on the expected values. Once we identified the influential variables from the tornado diagram, we performed additional univariate sensitivity analyses by comparing the rate of surgical site infection without negative pressure wound therapy with the three most influential variables while keeping the noninfluential variables fixed at baseline values. Finally, we performed a probabilistic sensitivity analysis with Monte Carlo simulation to assess the robustness of our findings by simultaneously varying all parameters. In this simulation, we sent a cohort of 1,000 patients through the decision analysis model 1,000 times for a total of 1 million trials. Different variable distributions were used for the simulation: b distribution for probabilities, normal distribution for DRG costs, and gamma distribution for other costs based on estimates. We calculated all distributions using the range for each variable as shown in Table 1.
RESULTS Our baseline analysis in Figure 1 showed that standard postoperative dressing was the preferred costbeneficial strategy in managing closed laparotomy incisions after a cesarean delivery. Based on the baseline probability variables and cost estimates, standard postoperative dressing will result in a cost of $547 per strategy, whereas the use of prophylactic negative pressure wound therapy will cost $804. Sensitivity analyses were performed over several assumptions and parameters used in the baseline analysis. The univariate sensitivity analyses showed that the variables that elicit the most influence on the model are the probability of surgical site infection after cesarean delivery without negative pressure wound therapy, cost of outpatient management, the cost of surgical site infection readmission without re-operation, and the cost of negative pressure wound therapy. Analyses of each of the aforementioned influential variables showed that standard postoperative dressing was the preferred strategy when 1) the cost of readmission without reoperation was less than $32,472 (figure not shown), 2) the cost of outpatient management was less than $6,476 (figure not shown), or 3) the cost of negative pressure wound therapy was more than $192 as shown in Figure 2. Among patients with a surgical site infection after cesarean delivery rate of 14% or less, standard postoperative dressing was the preferred cost-beneficial strategy. However, for patients with an infection rate greater than 14%, the use of prophylactic negative pressure wound therapy became the preferred cost-beneficial strategy as shown in
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Figure 3. At a surgical site infection rate of 30%, the rate must be reduced by 15% for negative pressure wound therapy to become the preferred strategy. Appendices 1–3 (available online at http://links. lww.com/AOG/A599) show the sensitivity analyses of surgical site infection without negative pressure wound therapy to the three most influential variables while keeping the noninfluential variables fixed at baseline values. As shown in Appendix 1, (http://links.lww.com/AOG/ A599), standard postoperative dressing is the preferred strategy irrespective of the readmission cost at a surgical site infection rate of 0.16 or less. If the surgical site infection rate is between 0.16 and 0.27, standard postoperative dressing or prophylactic negative pressure wound therapy is preferred depending on the cost of readmission. However, at a surgical site infection rate above 0.28, negative pressure wound therapy is preferred. Appendix 2 (http://links.lww.com/AOG/A599) shows that, if the surgical site infection rate is 0.12 or less, standard postoperative dressing is the preferred strategy. If the surgical site infection rate is between 0.12 and 0.30, standard postoperative dressing or prophylactic negative pressure wound therapy is preferred depending on the cost of outpatient management. If the surgical site infection rate is above 0.30, prophylactic negative pressure wound therapy is preferred. Appendix 3 (http://links. lww.com/AOG/A599) shows that, if the surgical site infection rate is 0.14 or less, standard postoperative dressing is the preferred strategy. If the surgical site infection rate is between 0.14 and 0.26, standard postoperative dressing or prophylactic negative pressure wound therapy is preferred depending on the cost of the negative pressure wound therapy device. However, prophylactic application of negative pressure wound therapy is the preferred strategy irrespective of its cost if the surgical site infection rate is above 0.26. Monte Carlo probabilistic sensitivity analysis showed that in 1 million trials, standard postoperative dressing was selected as the optimal strategy with a frequency of 85%, whereas prophylactic negative pressure wound therapy was selected as the optimal strategy with a frequency of 15% (Appendix 4, available online at http://links.lww.com/AOG/A599). The simulation also showed that standard postoperative dressing had an average cost of $543 and a minimum of $89 and a maximum cost of $1,864 per strategy, whereas the application of prophylactic negative pressure wound therapy had an average cost of $807, a minimum of $464, and a maximum cost of $1,878 per strategy. The Monte Carlo probability distributions for the expected cost per strategy are shown in Appendices 5 and 6 (available online at http://links.lww.com/AOG/A599).
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Expected value ($)
$192.80 –420 –440 –460 –480 –500 –520 –540 –560 –580 –600 –620 –640
No prophylactic negative pressure wound therapy Prophylactic negative pressure wound therapy
–660 –680 –700 –720 –740 –760 –780 –800 –820 –840 –860
Fig. 2. Sensitivity analysis of the cost of negative pressure wound therapy. Standard postoperative dressing (blue); prophylactic negative pressure wound therapy (red); the dashed line represents the cost threshold at which negative pressure wound therapy becomes cost-beneficial. 100
200 300 400 Cost of negative pressure wound therapy ($)
DISCUSSION We found that prophylactic negative pressure wound therapy on closed laparotomy incisions after cesarean delivery is not cost-beneficial in patients with low risk
500
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of postoperative infection. Additionally, our model also suggests that the device is not cost-beneficial at its current price in cohorts with a postcesarean surgical site infection rate of 14% or less.12 However, negative
1.00 0.96
No prophylactic negative pressure wound therapy
0.91
Prophylactic negative pressure wound therapy
0.86 0.81 Probability of surgical site infection with negative pressure wound therapy
0.76 0.71 0.66 0.61 0.56 0.51 0.46 0.41 0.36 0.31 0.26 0.21 0.16 0.11 0.06 0.01
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00
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1.
93 0. 88 0. 83 0. 78 0. 73 0. 68 0. 63 0. 58 0. 53 0. 48 0. 43 0. 38 0.
13
33 0. 28 0. 23 0. 18
0.
0.
03
08
0.
0.
Probability of surgical site infection without negative pressure wound therapy
Fig. 3. Probability of surgical site infection with and without negative pressure wound therapy. Standard postoperative dressing (blue); prophylactic negative pressure wound therapy (red). Shaded area is where a particular strategy is preferable. Echebiri. Prophylactic Negative Pressure Wound Therapy. Obstet Gynecol 2015.
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pressure wound therapy could be potentially costbeneficial in cohorts with infection rates greater than 14% such as morbidly obese patients (BMI higher than 45).33 The cost-savings among this population could be sizeable because more than one half of pregnant women in the United States are overweight or obese, and 8% of reproductive-aged women are morbidly obese.34 Our findings corroborate those of Lewis and colleagues.27 They conducted a cost–benefit analysis examining the economic benefit of prophylactic negative pressure wound therapy compared with routine incision care after closed laparotomy incision for gynecologic malignancy. Their study showed that in obese and morbidly obese cohorts with a high risk of infection, negative pressure wound therapy could be beneficial. Besides obesity, patients with other risk factors for surgical site infection after cesarean delivery such as susceptibility of the host to infection, chorioamnionitis, American Society of Anesthesiologists score 3 or greater, and diabetes35,36 may also benefit from the device. The model was sensitive to the cost of outpatient management, the cost of surgical site infection readmission without reoperation, and the cost of negative pressure wound therapy. By varying these cost inputs to their logical extremes, we demonstrated potential cost savings from negative pressure wound therapy as the cost of surgical site infection after cesarean delivery continued to increase. The only available estimate of attributable hospital cost of surgical site infection after cesarean delivery was published in 2008 by Olsen et al.10 Interestingly, threshold analysis revealed that if the baseline parameters were held constant, the negative pressure wound therapy device needed to be priced below $192 to be cost-beneficial. As this technology continues to evolve and the number of commercialized negative pressure wound therapy devices saturate the market, manufacturers will be challenged to create inexpensive devices for consumers. The results from this analysis were also sensitive to probability of surgical site infection after cesarean delivery without negative pressure wound therapy. The potential economic benefit from negative pressure wound therapy is dependent on its effectiveness in reducing infection. We acknowledge that there are several limitations of our study. First, decision-analytic models are not complete representations of real life, but a simplification of the most important components37; therefore, no model—including ours—can account for every possible outcome regarding surgical site infection after cesarean delivery.38 Second, decision-analytic models
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have uncertainties that are dependent on the data used in the formulation of the model, which are applicable to our model.39 Third, like any cost–benefit analysis, reasonable assumptions and rough cost estimates without precision were made. In the prophylactic branch with skin blisters from the device, we assumed that 5–10% of these complications would require additional skin care at the time of device removal. We could have overestimated this complication, resulting in a bias against negative pressure wound therapy. We estimated the cost of outpatient management of surgical site infection after cesarean delivery based on the publication by Perencevich et al in 1998.29 We could have underestimated the cost of outpatient wound management40, thereby allowing a bias against the cost savings from prophylactic negative pressure wound therapy. We also assumed, based on experience at our institution, that home nursing visits for surgical site infection after cesarean delivery can range from 7 to 14 days. The number of nursing visits might be higher because it is not unusual for home visits to continue up to 60 days after complications of laparotomy incisions. Despite these limitations, this is currently the only cost–benefit analysis model to compare the economic effect of adopting prophylactic negative pressure wound therapy on a closed laparotomy incision after cesarean delivery. A search of MEDLINE (English language; 1990–2014; search terms: “negative pressure wound therapy,” “surgical site infection after cesarean delivery,” “cesarean delivery,” “economic analysis,” and “cost–benefit”) revealed no other cases. The strengths of this decision-analytic model is in its design, timeliness, and usefulness. We used the best data currently available. Nevertheless, these parameters carry inherent uncertainty. We addressed these uncertainties by both deterministic and probabilistic sensitivity analyses. With more than 1 million cesarean deliveries performed each year in the United States,1 current evidence suggests that prophylactic negative pressure wound therapy on closed laparotomy incisions after cesarean delivery is unlikely beneficial among lowrisk populations. The potential savings from prophylactic negative pressure wound therapy can only be derived if the unit price is lower than the current market price or if the device is used in cohorts who have higher baseline risk of infection. We believe that our analysis provides useful and timely economic evidence for those interested in formulating guidelines for the use of prophylactic negative pressure wound therapy in the obstetric population. However, additional studies, including randomized controlled trials,
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are necessary to establish the effectiveness of negative pressure wound therapy on incisions intended to heal by primary intention. REFERENCES 1. Martin JA, Hamilton BE, Ventura SJ, Osterman MJ, Mathews T. Births: final data for 2011. Natl Vital Stat Rep 2013;62:1–69, 72. 2. American College of Obstetricians and Gynecologists (College), Society for Maternal-Fetal Medicine, Caughey AB, Cahill AG, Guise JM, Rouse DJ. Safe prevention of the primary cesarean delivery. Am J Obstet Gynecol 2014;210:179–93. 3. Witter FR, Lawson P, Ferrell J. Decreasing cesarean section surgical site infection: an ongoing comprehensive quality improvement program. Am J Infect Control 2014;42:429–31. 4. Corcoran S, Jackson V, Coulter-Smith S, Loughrey J, McKenna P, Cafferkey M. Surgical site infection after cesarean section: implementing 3 changes to improve the quality of patient care. Am J Infect Control 2013;41:1258–63. 5. Mackeen AD, Khalifeh A, Fleisher J, Vogell A, Han C, Sendecki J, et al. Suture compared with staple skin closure after cesarean delivery: a randomized controlled trial. Obstet Gynecol 2014;123:1169–75.
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9. Kirkland KB, Briggs JP, Trivette SL, Wilkinson WE, Sexton DJ. The impact of surgical-site infections in the 1990s: attributable mortality, excess length of hospitalization, and extra costs. Infect Control Hosp Epidemiol 1999;20:725–30. 10. Olsen MA, Butler AM, Willers DM, Gross GA, Fraser VJ. Comparison of costs of surgical site infection and endometritis after cesarean delivery using claims and medical record data. Infect Control Hosp Epidemiol 2010;31:872–5. 11. Mangram AJ, Horan TC, Pearson ML, Silver LC, Jarvis WR. Guideline for Prevention of Surgical Site Infection, 1999. Centers for Disease Control and Prevention (CDC) Hospital Infection Control Practices Advisory Committee. Am J Infect Control 1999;27:97–132. 12. Webster J, Scuffham P, Sherriff KL, Stankiewicz M, Chaboyer WP. Negative pressure wound therapy for skin grafts and surgical wounds healing by primary intention. The Cochrane Database of Systematic Reviews 2012, Issue 4. Art. No.: CD009261. DOI: 10.1002/14651858.CD009261.pub2. 13. Pauli EM, Krpata DM, Novitsky YW, Rosen MJ. Negative pressure therapy for high-risk abdominal wall reconstruction incisions. Surg Infect (Larchmt) 2013;14:270–4.
26. Webb LX, Schmidt U. Wound management with vacuum therapy [in German]. Unfallchirurg 2001;104:918–26. 27. Lewis LS, Convery PA, Bolac CS, Valea FA, Lowery WJ, Havrilesky LJ. Cost of care using prophylactic negative pressure wound vacuum on closed laparotomy incisions. Gynecol Oncol 2014;132:684–9. 28. Cardoso Del Monte MC, Pinto Neto AM. Postdischarge surveillance following cesarean section: the incidence of surgical site infection and associated factors. Am J Infect Control 2010; 38:467–72. 29. Perencevich EN, Sands KE, Cosgrove SE, Guadagnoli E, Meara E, Platt R. Health and economic impact of surgical site infections diagnosed after hospital discharge. Emerg Infect Dis 2003;9:196–203. 30. Urban JA. Cost analysis of surgical site infections. Surg Infect (Larchmt) 2006;7(suppl 1):S19–22. 31. Find-A-Code. Diagnosis related group. 2014. Available at: http://www.findacode.com/drg/. Retrieved August 8, 2014.
14. Karlakki S, Brem M, Giannini S, Khanduja V, Stannard J, Martin R. Negative pressure wound therapy for management of the surgical incision in orthopaedic surgery: A review of evidence and mechanisms for an emerging indication. Bone Joint Res 2013;2:276–84.
32. Morefield B, Christian TJ, Goldberg H. Analyses in support of rebasing & updating the Medicare home health payment rates— CY 2014. 2014:19. Available at: http://www.cms.gov/Medicare/ Medicare-Fee-for-Service-Payment/HomeHealthPPS/Downloads/ Analyses-in-Support-of-Rebasing-and-Updating-the-MedicareHome-Health-Payment-Rates-Technical-Report.pdf. Retrieved August 16, 2014.
15. Blackham AU, Farrah JP, McCoy TP, Schmidt BS, Shen P. Prevention of surgical site infections in high-risk patients with
33. Stamilio DM, Scifres CM. Extreme obesity and postcesarean maternal complications. Obstet Gynecol 2014;124:227–32.
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34. Obesity in pregnancy. Committee Opinion No. 549. American College of Obstetricians and Gynecologists. Obstet Gynecol 2013;121:213–7. 35. Tran TS, Jamulitrat S, Chongsuvivatwong V, Geater A. Risk factors for postcesarean surgical site infection. Obstet Gynecol 2000;95:367–71. 36. Wloch C, Wilson J, Lamagni T, Harrington P, Charlett A, Sheridan E. Risk factors for surgical site infection following caesarean section in England: results from a multicentre cohort study. BJOG 2012;119:1324–33. 37. Detsky AS, Naglie G, Krahn MD, Naimark D, Redelmeier DA. Primer on medical decision analysis: Part 1—Getting started. Med Decis Making 1997;17:123–5. 38. Singh A, Bartsch SM, Muder RR, Lee BY. An economic model: value of antimicrobial-coated sutures to society, hospitals, and third-party payers in preventing abdominal surgical site infections. Infect Control Hosp Epidemiol 2014;35:1013–20.
39. Goel V. Decision analysis: applications and limitations. The Health Services Research Group. CMAJ 1992;147:413–7. 40. Fife CE, Carter MJ, Walker D, Thomson B. Wound care outcomes, associated cost among patients treated in US outpatient wound centers: data from the US wound registry. Wounds 2012;24:10–7. 41. Mitt P, Lang K, Peri A, Maimets M. Surgical-site infections following cesarean section in an Estonian university hospital: postdischarge surveillance and analysis of risk factors. Infect Control Hosp Epidemiol 2005;26:449–54. 42. Kamat AA, Brancazio L, Gibson M. Wound infection in gynecologic surgery. Infect Dis Obstet Gynecol 2000;8:230–4. 43. Smith & Nephew. Non-adhesive hydrocellular polyurethane dressing. Available at: http://www.smith-nephew.com/professional/ products/advanced-wound-management/allevyn/allevyn-nonadhesive/. Retrieved August 1, 2014.
Maintenance of Certification Articles Maintenance of Certification is a program of the American Board of Obstetrics and Gynecology (ABOG; http://www.abog.org). All articles from the reading lists for the current year will be listed on the Obstetrics & Gynecology web site at the beginning of January, May, and August. To access the lists, go to www.greenjournal.org and click on the “ABOG MOC II” tab. Links to content are provided, as well as an indication of the article’s status (ie, available by subscription only or open access).
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Prophylactic Use of Negative Pressure Wound Therapy After Cesarean Delivery Nelson C. Echebiri, MD, MBA, M. Maya McDoom, PhD, MPH, Meaghan M. Aalto, MD, Jessie Fauntleroy, MD, Nagammai Nagappan, MD, and Vanessa M. Barnabei, MD, PhD OBJECTIVE: To evaluate the economic benefit of prophylactic negative pressure wound therapy on a closed laparotomy incision after cesarean delivery in comparison with standard postoperative dressing. METHODS: We designed a decision-analytic model from a third-party payer’s perspective to determine the cost– benefit of prophylactic application of negative pressure wound therapy compared with standard postoperative dressing on a closed laparotomy incision after cesarean delivery. Our primary outcome measure was the expected value of the cost per strategy. Baseline probabilities and cost assumptions were derived from published literature. We conducted sensitivity analyses using both deterministic and probabilistic models. Cost estimates reflect 2014 U.S. dollars. RESULTS: Under our baseline parameters, standard postoperative dressing was the preferred strategy. Standard postoperative dressing and prophylactic negative pressure wound therapy cost $547 and $804 per strategy, respectively. Sensitivity analyses showed that prophylactic negative pressure wound therapy can be cost-beneficial if it is priced below $192; standard postoperative dressing is the preferred strategy among patients with surgical site infection rate of 14% or less. If surgical site infection rates are greater than 14%, prophylactic negative pressure wound therapy could be cost-beneficial depending on See related editorial on page 297.
From the Department of Obstetrics and Gynecology, University at Buffalo, Buffalo, New York; Social Science Research Center, Mississippi State University, Starkville, Mississippi; and the Department of Global Health and Population, Harvard School of Public Health, Boston, Massachusetts. The authors thank James A. Shelton, MS, for his help in the analysis, comments, suggestions, and statistical advice. Corresponding author: Nelson C. Echebiri, MD, MBA, University at Buffalo, Department of Obstetrics–Gynecology, 219 Bryant Street, Buffalo, NY 14221; e-mail: [email protected]. Financial Disclosure The authors did not report any potential conflicts of interest. © 2015 by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. All rights reserved. ISSN: 0029-7844/15
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the degree of reduction in surgical site infections. At a surgical site infection rate of 30%, the rate must be reduced by 15% for negative pressure wound therapy to become the preferred strategy. Monte Carlo simulation of 1,000 patients in 1 million trials showed that standard postoperative dressing was the preferred cost-beneficial strategy with a frequency of 85%. CONCLUSION: Our cost–benefit analysis provides economic evidence suggesting that negative pressure wound therapy should not be used on closed laparotomy incisions of patients with low risk of postcesarean delivery surgical site infections. However, among patients with a high risk of surgical site infections, prophylactic negative pressure wound therapy is potentially cost-beneficial. (Obstet Gynecol 2015;125:299–307) DOI: 10.1097/AOG.0000000000000634
M
ore than 1 million cesarean deliveries are performed annually in the United States (32.8% of births in 2012).1,2 The rate of surgical site infection after cesarean delivery is between 3 and 18%3–7 and may be as high as 30% in patients with body mass indexes (BMIs, calculated as weight (kg)/[height (m)]2) of 50 or higher.3,8 These infections add substantial costs to health care attributable to maternal readmissions, reoperations, additional antibiotic therapy, and home health services.9,10 As a result of the morbidity, mortality, and costs associated with surgical site infection, the Centers for Disease Control and Prevention developed guidelines for preventing infections including: appropriate selection and timing of prophylactic antibiotics, optimizing preoperative skin hygiene, and surgical skin preparation.4,11 Although negative pressure wound therapy is not part of the current guidelines, it has emerged as an accepted technique in contemporary wound healing.12 The benefits of negative pressure wound therapy12–15 are widely recognized. Negative pressure wound therapy is now routinely used to facilitate closure of open
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abdominal wounds,16 open fractures,17 skin graft sites,18 and surgical wounds expected to heal by primary intention.12,13,19 At our institution, there is an increasing trend toward the prophylactic application of negative pressure wound therapy to a closed incision after cesarean delivery to reduce the incidence of surgical site infection after cesarean delivery. At a cost of approximately $500 per device, evidence regarding the cost–benefit of adopting this technology in routine clinical practice is needed. Currently, there are no published economic analyses of prophylactic negative pressure wound therapy devices on a closed laparotomy incision after cesarean delivery. Therefore, we designed a decision-analytic model to estimate whether the use of prophylactic negative pressure wound therapy after a cesarean delivery is costbeneficial.
MATERIALS AND METHODS We designed a cost–benefit analysis decision tree model using techniques described by Plevritis,20 Detsky et al,21 Naglie et al,22 and Krahn et al.23 The decision tree diagram and all computations were performed using a commercially available decisionanalysis software: TreeAge Pro Suite Software Inc (Fig. 1). The model was framed from the third-party payer’s perspective. The model was structured as a decision tree starting with theoretical cohorts of patients entering the model, as shown in Figure 1. Each cohort will undergo nonemergent cesarean delivery, then receive one of two postoperative incision management strategies: 1) application of negative pressure wound therapy after closure of skin incision or 2) application of a standard postoperative dressing only. Patients will then undergo a cascade of events and health interventions in the presence of surgical site infection. The model assumes that standard clinical guidelines11 regarding preoperative and postoperative measures to avoid or reduce surgical site infection were followed. The primary outcome measure was the expected value of the cost per strategy. To perform this cost–benefit analysis, we obtained and evaluated data from numerous sources. We conducted literature searches in PubMed and Google search engines for the following terms: negative pressure wound therapy after cesarean delivery; Prevena; surgical site infection after cesarean delivery; effectiveness of negative pressure wound therapy on closed skin incisions; cost of surgical site infection after cesarean delivery; cost of home health services; and diagnosis-related group (DRG) codes. We also reviewed the reference lists from retrieved articles. The broad literature search ensured that no single
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source or type of publication provided the majority of the data elements. When available, we used published randomized controlled trials, Cochrane reviews, and meta-analyses to derive probability estimates. Baseline assumptions and variables used for the analysis represent best available estimates from the literature and are summarized with their references in Table 1. The ranges noted in Table 1 were also used to derive the mean for the baseline analysis when published baseline values were unavailable. This study was approved by the University at Buffalo institutional review board under the determination of “does not involve human subjects” because we only used a collection of publicly available and deidentified data sources. The reported incidence of surgical site infection after cesarean delivery varies widely from 3 to 18%3–7 and maybe as high as 30% in patients with BMIs of 50 or higher.8 As a result of this wide variation, we used a mean of 17% and a range of 3–30% as the risk of surgical site infection after cesarean delivery in patients without prophylactic negative pressure wound therapy. Paul et al13 reported the incidence of surgical site infection after ventral hernia repair in 25.8% of patients with standard wound dressing compared with 20.4% of patients with closed incision negative pressure wound therapy, whereas Blackham et al15 reported fewer total surgical site infections in 16.0% of patients with negative pressure wound therapy compared with 35.5% of patients with standard wound dressing after a closed laparotomy incision. However, a recent Cochrane review concluded that the evidence for the effectiveness of negative pressure wound therapy on surgical wounds expected to heal by primary intention remains unclear.12 Therefore, based on these data,12,13,15 we extrapolated that the incidence of surgical site infection after cesarean delivery in patients with prophylactic negative pressure wound therapy ranged from 1 to 20% with an average baseline risk of 11%. For sensitivity analysis we increased the risk of surgical site infection after cesarean delivery with or without prophylactic negative pressure wound therapy to 100%. The standard postoperative dressing and the negative pressure wound therapy branches of the tree have similar nodes and events with the exception of wound complications from negative pressure wound therapy. Based on published data, the incidence of wound complications from negative pressure wound therapy is very low.24–27 To account for this risk, patients in the prophylactic negative pressure wound therapy branch of the tree have a 3–20% risk of skin blisters.24–27 We assumed that 5–10% of these complications would require additional skin care at the time
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Complications from prophylactic negative pressure wound therapy
Prophylactic negative pressure wound therapy
Complications from prophylactic negative pressure wound therapy requiring skin care Complications from prophylactic negative pressure wound therapy. Self-limiting. No additional skin care Surgical site infection despite prophylactic negative pressure wound therapy
No complications from prophylactic negative pressure wound therapy Management of closed laparotomy incision following cesarean delivery
No surgical site infection due to prophylactic negative pressure wound therapy
Hospatilization for inpatient management Surgical site infection without prophylactic negative pressure wound therapy
Outpatient management
No prophylactic negative pressure wound therapy No surgical site infection
Fig. 1. Abbreviated decision tree of prophylactic negative pressure wound therapy compared with standard postoperative dressing. Echebiri. Prophylactic Negative Pressure Wound Therapy. Obstet Gynecol 2015.
of device removal.27 After passing through the node for wound complications from negative pressure wound therapy, patients in the prophylactic branch continued through different chance nodes with probabilities of specific events including risk of surgical site infection after cesarean delivery despite use of negative pressure wound therapy, outpatient management, or readmission for inpatient management. Patients who failed outpatient management were readmitted for inpatient management. Those that were readmitted will have a 2% risk of reoperation.28 Because the risk of reoperation secondary to surgical site infection after cesarean delivery is very low, we assumed a range from 2 to 5%28 for sensitivity analysis. The final event in both the prophylactic and standard postoperative dressing branches was the need for home health services. Literature reports that 47–62% of patients with surgical site infection will require home health services.29 To balance the tree, we assumed that
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0–1% of patients without surgical site infection will require home health services. We defined the benefit as the costs saved by avoiding surgical site infection after cesarean delivery. We defined direct costs as: 1) the fee paid to the manufacturer for providing the negative pressure wound therapy device at the authors’ institution, 2) third-party payer reimbursement for rehospitalization and reoperation, and 3) direct costs of outpatient management. Indirect costs of surgical site infection are difficult to quantify and were not included in this analysis. Our literature review showed that estimated cost of treating surgical site infection varies widely depending on the geographical location, the type of surgery performed, and the depth of the infection.30 Kirkland et al9 reported in the 1990s that the total excess hospitalization and direct costs attributable to surgical site infection was $5,038 per case. To our knowledge based on an extensive literature search, the only available
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Table 1. Probability and Cost Variables Variable Probability of complications from NPWT Probability of skin irritation from NPWT requiring additional care Probability of SSI after cesarean delivery without NPWT Probability of SSI after cesarean delivery with NPWT Probability of rehospitalization from SSI after cesarean delivery Probability of outpatient management of SSI after cesarean delivery Probability of successful outpatient management of SSI after cesarean delivery Probability of reoperation from SSI after cesarean delivery Probability of successful inpatient management of SSI after cesarean delivery without reoperation Probability of home health needed for patients without SSI after cesarean delivery Probability of home health needed for SSI after cesarean delivery Hospital cost of SSI readmission without operation (DRG 863) Hospital cost of SSI readmission with operating (DRG 858) Cost of outpatient management of SSI after cesarean delivery Cost of home health for SSI after cesarean delivery Cost of ALLEVYN nonadhesive Cost of NPWT
Value
Range
Distribution*
Sensitive
Reference
0.12 0.08
0.03–0.20 0.05–0.10
Beta Beta
No No
24–27 27
0.17
0.03–0.30
Beta
Yes
3–8
0.11
0.01–0.20
Beta
Yes
Assumption
0.09
0.07–0.11
Beta
Yes
5,28,36,41,42
0.91
0.89–0.93
Beta
Yes
5,28,36,41,42
0.92
0.90–0.93
Beta
Yes
28,41
0.02
0.02–0.05
Beta
No
28
0.98
0.95–0.98
Beta
No
28
0.01
0.0–0.01
Beta
No
Assumption
0.5
0.47–0.62
Beta
Yes
29
$5,605
$2,220–10,000
Gamma
Yes
7,9,10,31
$7,467
$2,220–20,000
Gamma
Yes
27,31
$1,766
$533–3,000
Gamma
Yes
29
$1,375 $10 $450
$917–$1,834 $3–$50 $200–$500
Gamma Normal Normal
Yes No Yes
27,29,32 43 Authors’ institution
NPWT, negative pressure wound therapy; SSI, surgical site infection; DRG, diagnosis-related group. * A statistical function that describes all the possible values and likelihoods that a random variable can take within a given range.
estimate of attributable hospital cost of surgical site infection after cesarean delivery was published in 2008 by Olsen et al,10 reporting the average cost of $2,852 ($2,006–4,378). After adjusting the 2008 estimates for inflation and also considering Medicare reimbursement for specific DRG 863 and 858, we extrapolated that the cost of hospital admission for surgical site infection after cesarean delivery without reoperation ranges from $2,220 to $10,000,7,9,31 and the cost of hospital admission for surgical site infection after cesarean delivery with reoperation ranges from $2,220 to $20,000.27,31 For sensitivity analysis, we increased the range for both the cost of readmission with and without operation to $50,000. We used the DRG estimates for readmission and reoperation for our baseline analysis. According to the Centers for Medicare & Medicaid Services report, the average cost of a home visit by a nurse in 2013 was $131.32 Based on experience at our institution, we estimated that a nursing visit for surgical site infection after cesarean
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delivery can range from 7 to 14 days ($917–1,834). Given this range, we used the average, $1,375, for baseline analysis and increased the range to $50,000 for sensitivity analysis. Perencevich et al29 reported in 1998 that the average cost of outpatient visits for surgical site infection was $365 ($533 in 2014), and the average cost of outpatient management of surgical site infection was $809 ($1,182 in 2014). Adjusting for inflation, we estimated that the cost of outpatient management for surgical site infection after cesarean delivery can range from $533 to $3,000; we used the average $1,766 for our baseline analysis and also increased the range to $50,000 for sensitivity analysis. All costs were in 2014 U.S. dollars. Annual discounting was not necessary because the time horizon was within 1 year. Sensitivity analyses were conducted to evaluate the uncertainty of the results. We varied probability and cost parameters to take into account potential clinical scenarios that might deviate from our baseline estimates. One-way deterministic sensitivity analysis,
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depicted by a tornado diagram, provided a bar chart of the main variables of influence that had the greatest effect on the expected values. Once we identified the influential variables from the tornado diagram, we performed additional univariate sensitivity analyses by comparing the rate of surgical site infection without negative pressure wound therapy with the three most influential variables while keeping the noninfluential variables fixed at baseline values. Finally, we performed a probabilistic sensitivity analysis with Monte Carlo simulation to assess the robustness of our findings by simultaneously varying all parameters. In this simulation, we sent a cohort of 1,000 patients through the decision analysis model 1,000 times for a total of 1 million trials. Different variable distributions were used for the simulation: b distribution for probabilities, normal distribution for DRG costs, and gamma distribution for other costs based on estimates. We calculated all distributions using the range for each variable as shown in Table 1.
RESULTS Our baseline analysis in Figure 1 showed that standard postoperative dressing was the preferred costbeneficial strategy in managing closed laparotomy incisions after a cesarean delivery. Based on the baseline probability variables and cost estimates, standard postoperative dressing will result in a cost of $547 per strategy, whereas the use of prophylactic negative pressure wound therapy will cost $804. Sensitivity analyses were performed over several assumptions and parameters used in the baseline analysis. The univariate sensitivity analyses showed that the variables that elicit the most influence on the model are the probability of surgical site infection after cesarean delivery without negative pressure wound therapy, cost of outpatient management, the cost of surgical site infection readmission without re-operation, and the cost of negative pressure wound therapy. Analyses of each of the aforementioned influential variables showed that standard postoperative dressing was the preferred strategy when 1) the cost of readmission without reoperation was less than $32,472 (figure not shown), 2) the cost of outpatient management was less than $6,476 (figure not shown), or 3) the cost of negative pressure wound therapy was more than $192 as shown in Figure 2. Among patients with a surgical site infection after cesarean delivery rate of 14% or less, standard postoperative dressing was the preferred cost-beneficial strategy. However, for patients with an infection rate greater than 14%, the use of prophylactic negative pressure wound therapy became the preferred cost-beneficial strategy as shown in
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Figure 3. At a surgical site infection rate of 30%, the rate must be reduced by 15% for negative pressure wound therapy to become the preferred strategy. Appendices 1–3 (available online at http://links. lww.com/AOG/A599) show the sensitivity analyses of surgical site infection without negative pressure wound therapy to the three most influential variables while keeping the noninfluential variables fixed at baseline values. As shown in Appendix 1, (http://links.lww.com/AOG/ A599), standard postoperative dressing is the preferred strategy irrespective of the readmission cost at a surgical site infection rate of 0.16 or less. If the surgical site infection rate is between 0.16 and 0.27, standard postoperative dressing or prophylactic negative pressure wound therapy is preferred depending on the cost of readmission. However, at a surgical site infection rate above 0.28, negative pressure wound therapy is preferred. Appendix 2 (http://links.lww.com/AOG/A599) shows that, if the surgical site infection rate is 0.12 or less, standard postoperative dressing is the preferred strategy. If the surgical site infection rate is between 0.12 and 0.30, standard postoperative dressing or prophylactic negative pressure wound therapy is preferred depending on the cost of outpatient management. If the surgical site infection rate is above 0.30, prophylactic negative pressure wound therapy is preferred. Appendix 3 (http://links. lww.com/AOG/A599) shows that, if the surgical site infection rate is 0.14 or less, standard postoperative dressing is the preferred strategy. If the surgical site infection rate is between 0.14 and 0.26, standard postoperative dressing or prophylactic negative pressure wound therapy is preferred depending on the cost of the negative pressure wound therapy device. However, prophylactic application of negative pressure wound therapy is the preferred strategy irrespective of its cost if the surgical site infection rate is above 0.26. Monte Carlo probabilistic sensitivity analysis showed that in 1 million trials, standard postoperative dressing was selected as the optimal strategy with a frequency of 85%, whereas prophylactic negative pressure wound therapy was selected as the optimal strategy with a frequency of 15% (Appendix 4, available online at http://links.lww.com/AOG/A599). The simulation also showed that standard postoperative dressing had an average cost of $543 and a minimum of $89 and a maximum cost of $1,864 per strategy, whereas the application of prophylactic negative pressure wound therapy had an average cost of $807, a minimum of $464, and a maximum cost of $1,878 per strategy. The Monte Carlo probability distributions for the expected cost per strategy are shown in Appendices 5 and 6 (available online at http://links.lww.com/AOG/A599).
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Expected value ($)
$192.80 –420 –440 –460 –480 –500 –520 –540 –560 –580 –600 –620 –640
No prophylactic negative pressure wound therapy Prophylactic negative pressure wound therapy
–660 –680 –700 –720 –740 –760 –780 –800 –820 –840 –860
Fig. 2. Sensitivity analysis of the cost of negative pressure wound therapy. Standard postoperative dressing (blue); prophylactic negative pressure wound therapy (red); the dashed line represents the cost threshold at which negative pressure wound therapy becomes cost-beneficial. 100
200 300 400 Cost of negative pressure wound therapy ($)
DISCUSSION We found that prophylactic negative pressure wound therapy on closed laparotomy incisions after cesarean delivery is not cost-beneficial in patients with low risk
500
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of postoperative infection. Additionally, our model also suggests that the device is not cost-beneficial at its current price in cohorts with a postcesarean surgical site infection rate of 14% or less.12 However, negative
1.00 0.96
No prophylactic negative pressure wound therapy
0.91
Prophylactic negative pressure wound therapy
0.86 0.81 Probability of surgical site infection with negative pressure wound therapy
0.76 0.71 0.66 0.61 0.56 0.51 0.46 0.41 0.36 0.31 0.26 0.21 0.16 0.11 0.06 0.01
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00
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1.
93 0. 88 0. 83 0. 78 0. 73 0. 68 0. 63 0. 58 0. 53 0. 48 0. 43 0. 38 0.
13
33 0. 28 0. 23 0. 18
0.
0.
03
08
0.
0.
Probability of surgical site infection without negative pressure wound therapy
Fig. 3. Probability of surgical site infection with and without negative pressure wound therapy. Standard postoperative dressing (blue); prophylactic negative pressure wound therapy (red). Shaded area is where a particular strategy is preferable. Echebiri. Prophylactic Negative Pressure Wound Therapy. Obstet Gynecol 2015.
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pressure wound therapy could be potentially costbeneficial in cohorts with infection rates greater than 14% such as morbidly obese patients (BMI higher than 45).33 The cost-savings among this population could be sizeable because more than one half of pregnant women in the United States are overweight or obese, and 8% of reproductive-aged women are morbidly obese.34 Our findings corroborate those of Lewis and colleagues.27 They conducted a cost–benefit analysis examining the economic benefit of prophylactic negative pressure wound therapy compared with routine incision care after closed laparotomy incision for gynecologic malignancy. Their study showed that in obese and morbidly obese cohorts with a high risk of infection, negative pressure wound therapy could be beneficial. Besides obesity, patients with other risk factors for surgical site infection after cesarean delivery such as susceptibility of the host to infection, chorioamnionitis, American Society of Anesthesiologists score 3 or greater, and diabetes35,36 may also benefit from the device. The model was sensitive to the cost of outpatient management, the cost of surgical site infection readmission without reoperation, and the cost of negative pressure wound therapy. By varying these cost inputs to their logical extremes, we demonstrated potential cost savings from negative pressure wound therapy as the cost of surgical site infection after cesarean delivery continued to increase. The only available estimate of attributable hospital cost of surgical site infection after cesarean delivery was published in 2008 by Olsen et al.10 Interestingly, threshold analysis revealed that if the baseline parameters were held constant, the negative pressure wound therapy device needed to be priced below $192 to be cost-beneficial. As this technology continues to evolve and the number of commercialized negative pressure wound therapy devices saturate the market, manufacturers will be challenged to create inexpensive devices for consumers. The results from this analysis were also sensitive to probability of surgical site infection after cesarean delivery without negative pressure wound therapy. The potential economic benefit from negative pressure wound therapy is dependent on its effectiveness in reducing infection. We acknowledge that there are several limitations of our study. First, decision-analytic models are not complete representations of real life, but a simplification of the most important components37; therefore, no model—including ours—can account for every possible outcome regarding surgical site infection after cesarean delivery.38 Second, decision-analytic models
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have uncertainties that are dependent on the data used in the formulation of the model, which are applicable to our model.39 Third, like any cost–benefit analysis, reasonable assumptions and rough cost estimates without precision were made. In the prophylactic branch with skin blisters from the device, we assumed that 5–10% of these complications would require additional skin care at the time of device removal. We could have overestimated this complication, resulting in a bias against negative pressure wound therapy. We estimated the cost of outpatient management of surgical site infection after cesarean delivery based on the publication by Perencevich et al in 1998.29 We could have underestimated the cost of outpatient wound management40, thereby allowing a bias against the cost savings from prophylactic negative pressure wound therapy. We also assumed, based on experience at our institution, that home nursing visits for surgical site infection after cesarean delivery can range from 7 to 14 days. The number of nursing visits might be higher because it is not unusual for home visits to continue up to 60 days after complications of laparotomy incisions. Despite these limitations, this is currently the only cost–benefit analysis model to compare the economic effect of adopting prophylactic negative pressure wound therapy on a closed laparotomy incision after cesarean delivery. A search of MEDLINE (English language; 1990–2014; search terms: “negative pressure wound therapy,” “surgical site infection after cesarean delivery,” “cesarean delivery,” “economic analysis,” and “cost–benefit”) revealed no other cases. The strengths of this decision-analytic model is in its design, timeliness, and usefulness. We used the best data currently available. Nevertheless, these parameters carry inherent uncertainty. We addressed these uncertainties by both deterministic and probabilistic sensitivity analyses. With more than 1 million cesarean deliveries performed each year in the United States,1 current evidence suggests that prophylactic negative pressure wound therapy on closed laparotomy incisions after cesarean delivery is unlikely beneficial among lowrisk populations. The potential savings from prophylactic negative pressure wound therapy can only be derived if the unit price is lower than the current market price or if the device is used in cohorts who have higher baseline risk of infection. We believe that our analysis provides useful and timely economic evidence for those interested in formulating guidelines for the use of prophylactic negative pressure wound therapy in the obstetric population. However, additional studies, including randomized controlled trials,
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