Comparison of the Effectiveness of Two Prophylactic Single-Use Negative Pressure Wound Therapy Devices in Reducing Surgical Site Complications After Cesarean Delivery: Insights From a Large US Claims Database

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The rate of cesarean delivery use in the United States increased by 55.1% between 1996 and 2021, from 20.7% to 32.1%.^1,2 SSI, one of the most common SSCs, has an incidence of 5.3% to 9.6% in cesarean delivery and is associated with increased rates of maternal morbidity and mortality compared with patients without an SSI.^3-7 Wound dehiscence, seroma, and hematoma are also common SSCs of cesarean delivery, with surgical wound dehiscence representing one of the most common causes of maternal morbidity.^8,9 SSCs also negatively affect postnatal recovery and maternal well-being.¹⁰ The financial implications of SSCs are substantial. In the United States, SSIs are associated with hospital costs exceeding $900 million annually due to additional hospital days,¹¹ and attributable costs after cesarean delivery have been reported to be $2852 per patient.¹²

Data continue to emerge regarding the effectiveness of sNPWT in reducing the risk of SSC in at-risk patients after a cesarean delivery.^9,13-17 However, existing evidence on the effectiveness of a −80 mm Hg device (PICO; Smith & Nephew Medical Ltd) and a −125 mm Hg device (Prevena; 3M) in preventing SSIs vs standard of care is conflicting.^9,18 To date, no RWE studies have directly compared the 2 devices with distinct modes of action. Up to 85% of exudate evaporates through a 4-layer absorbent dressing in the −80 mm Hg device; in comparison, exudate passes via a foam filler and collects into a canister in the −125 mm Hg device.^19-21 

The present study used RWE to compare both the effectiveness of 2 commonly used sNPWT devices, the −80 mm Hg device and the −125 mm Hg device, in
preventing SSCs, and their effect on health care resource use after cesarean delivery in the United States.

Data source

Patient data were obtained from the US-based PINC AI Healthcare Database (Premier Inc; hereafter “claims database) from January 2017 through June 2022. The data in this claims database are primarily obtained from community and teaching hospitals and health care systems that are geographically diverse, nonprofit, and nongovernmental in rural and urban areas, representing approximately 25% of inpatient admissions in the United States.^22,23 No additional data cleaning processes were carried out before the eligibility criteria were applied. This study was exempt from institutional review board approval because all patient records were de-identified, and all data complied with the Health Insurance Portability and Accountability Act. 

Patient selection

Eligibility criteria were applied to the entire claims database population (Table S1). Patients who were 18 years or older and who had an inpatient encounter in which the −80 mm Hg or the −125 mm Hg device was used were identified using a pattern matching algorithm that searched the hospital charge description variable in the billing tables. The search terms used to identify the devices from the billing tables are listed in Table S1. The cesarean delivery surgical procedure category was selected based on the Agency for Healthcare Research and Quality CCS tool, which organizes the ICD-10-PCS codes into categories. Cesarean delivery codes used to identify the cohort were 10D00Z0 (Extraction of Products of Conception, High, Open Approach), 10D00Z1 (Extraction of Products of Conception, Low, Open Approach), and 10D00Z2 (Extraction of Products of Conception, Extraperitoneal, Open Approach). Patients were excluded if they had been treated with both the −80 mm Hg and the −125 mm Hg device and if open wounds were present, or if an SSC diagnosis was present on admission as identified by ICD-10-CM codes (Table 2). Additional exclusion criteria included multiple surgical encounters in which the −80 mm Hg device or the −125 mm Hg device was used, additional surgery within 30 days, insufficient follow-up of less than 30 days, and cases in which cost of encounter could not be determined.

Patient demographics and matching

Patients were matched between the −80 mm Hg device and the −125 mm Hg device using 1-to-1 propensity score matching to control for selection bias. A greedy matching method where k equals 1 was implemented using patient characteristics and comorbidities at the index encounter (Table S3). Comorbidities were defined by ICD-10-CM diagnosis codes (Table S4). Standardized differences were calculated for the variables included in the propensity score model to examine the ​
effectiveness of propensity score matching. Balance between the groups was achieved when the absolute values of the standardized differences of the matching variables were no greater than 0.1. Dummy dichotomous variables were created to allow inclusion in the matching procedure. 

End points

End points were defined by ICD-10-CM diagnosis codes (Table S2). The SSC clinical end points measured were incidence of overall SSI (referring to both superficial and deep SSI, in line with US Centers for Disease Control and Prevention criteria), superficial SSI, dehiscence, seroma, and hematoma, all at 30 days postsurgery, and incidence of deep SSI at 90 days postsurgery.²⁴ Incidence was defined as the percentage of all cases with the end point. The health care resource use end points included LOS, cost at index encounter, and cost at 30 days and 90 days post​surgery. The device index admission costs were calculated based on the patient’s encounter in which the device was used, including documented cesarean delivery ICD-10-PCS procedure codes within the same encounter up to the discharge date. The 30-day and 90-day costs represent the average total billed expenses incurred within 30 or 90 days following the index encounter. These costs were identified through claims for services provided in the inpatient setting, outpatient setting, and emergency department. Due to the nonnormal distribution of the cost data, a generalized linear model was selected to assess statistical significance between the device costs.

Statistical analyses

The SSC incidence by group and the unadjusted OR were calculated for each end point. An adjusted OR and P value were then calculated by controlling for covariates, such as age, diabetes, obesity, hypertension, and smoking status, using a logistic regression model (Table S3). For index encounter LOS, the mean LOS for each group was reported, and because all cases were hospital inpatients and the LOS cannot be zero, a regression model using the truncated negative binomial distribution was used to give an adjusted difference in mean LOS between groups and P value. The mean cost at the index encounter, as well as at 30 days and 90 days postsurgery, was reported for each group. A generalized linear model with  log-link and gamma distribution provided an adjusted percentage difference between groups and P value. No power calculations were performed. All analyses were conducted using SAS (version 9.4; SAS Institute Incorporated).

Matching and patient characteristics

Before exclusion criteria were applied,
173 134 cases were identified using the  claims database. After exclusions, there were 27 856 cases for the −80 mm Hg device and 29 325 cases for the −125 mm Hg device, for a total of 57 181 cases (Table S5). When the “C-SECTION” CCS label was applied, there were 11 747 patients treated with the −80 mm Hg device and 5396 patients treated with the −125 mm Hg device. One-to-one matching resulted in 2 cohorts with 5332 cases in each group (Table 1). 

SSCs

The unadjusted incidence was lower with the −80 mm Hg device compared with the −125 mm Hg device for the following end points at 30 days postsurgery unless otherwise specified: overall SSI (0.6% vs 1.0%), superficial SSI (0.2% vs 0.4%), dehiscence (1.0% vs 1.7%), seroma (< 0.1% vs 0.2%), and deep SSI (< 0.1% vs 0.1%; 90 days postsurgery) (Table 2). The unadjusted incidence of hematoma at 30 days was equal for both devices, at 0.2% (Table 2). After adjusting for covariates, the OR for overall SSI, superficial SSI, dehiscence, and seroma at 30 days was significantly lower when the −80 mm Hg device was used compared with the −125 mm Hg device (P ≤ .05) (Table 2). In contrast, no statistically significant differences were identified for hematoma (at 30 days) and deep SSI (at 90 days). 

Health care resource utilization

The unadjusted mean index admission cost was lower for the −80 mm Hg device ($10 612.89) compared with the −125 mm Hg device ($11,102.51) (Table 3). After adjusting for covariates, the adjusted mean index admission cost was significantly lower for the −80 mm Hg device compared with the −125 mm Hg device (−3.8%; P < .001) (Table 4). Additionally, the unadjusted mean total cost was lower for the −80 mm Hg device at 30 days ($9318.45) and 90 days ($9472.12) vs the −125 mm Hg device at 30 days ($9979.98) and 90 days ($10 200.34) (Table 3). When adjusted for covariates, the adjusted mean total costs at both 30 days and 90 days were significantly lower for the −80 mm Hg device compared with the −125 mm Hg device (30 days: −6.1%, P < .001; 90 days: −6.6%, P < .001) (Table 4). Unadjusted mean index encounter LOS was lower for the −80 mm Hg device compared with the −125 mm Hg device (3.39 days and 3.47 days, respectively). After adjusting for covariates, the adjusted mean index encounter LOS was 2.4% lower for the −80 mm Hg device compared with the −125 mm Hg device, although this difference was not statistically significant (P = .101) (Table 5).

This study provides the first direct comparison of the 2 most used sNPWT devices, the −80 mm Hg and the −125 mm Hg. Most of the available data support using sNPWT as an effective treatment modality to decrease the risk of SSI compared with standard dressings.^14-17 However, some studies have reported mixed or equivocal results, indicating that further research is necessary to fully elucidate the efficacy of the intervention under specific conditions or in certain patient populations.^25,26 Additionally, conflicting results exist regarding the effectiveness of different sNPWT devices.^9,18 For example, Goldman and Costa⁹ found a significant reduction in the odds of developing overall and superficial SSIs compared with standard of care with the −80 mm Hg but not the −125 mm Hg device. In the present study, the −80 mm Hg device did not demonstrate significantly lower odds of developing a hematoma at 30 days or deep SSI at 90 days. Similarly, Goldman and Costa⁹ found no improvement for hematoma or deep SSI. However, they found that the −80 mm Hg device was not associated with a lower risk of developing dehiscence or seroma,⁹ which contrasts with the findings of the present study. The present study uses a real-world study design, whereas randomized controlled trials were included in the meta-analyses in Goldman and Costa,⁹ which could explain this difference. 

The present study suggests that the −80 mm Hg device may be associated with improved clinical outcomes after cesarean delivery compared with the −125 mm Hg device. This may lead to decreased patient burden, including reduced anxiety, pain, morbidity, and mortality.^3,27-29 Differences in the devices’ modes of action have previously been flagged as a potential reason for differing clinical outcomes.⁹ The −45 mm Hg pressure difference between the devices could affect clinical outcomes due to its effect on skin adhesion, skin vascularization, and fluid removal from the subcutaneous layer.³⁰ Additionally, the high moisture vapor transmission of the top film layer in the −80 mm Hg device, compared with the −125 mm Hg device, may lead to variations in wound moisture between the 2 devices, which could explain the observed clinical outcomes.^19-21 

This study demonstrated that the −80 mm Hg device was associated with a significantly lower financial burden than the −125 mm Hg device. This may be partially explained by the price difference between the devices; the unit price of the −80 mm Hg device is lower than that of the −125 mm Hg device.³¹ Considering the unadjusted costs at 90 days postsurgery associated with both devices, using the −80 mm Hg device could lead to cost savings of $728 220 per 1000 patients, demonstrating the potential for short-term cost savings. The present study indicates that the −80 mm Hg device improves clinical outcomes compared with the −125 mm Hg device; thus, use of the former device after cesarean delivery could ultimately lead to financial and resource savings for health care systems due to lower postdischarge care costs.²⁹ However, a cost-effectiveness study is warranted to address the question of value for money, that is, whether the observed reductions in SSC with a −80 mm Hg device translate into a cost-effective finding compared with a −125 mm Hg device. 

The present study has limitations. Using a real-world nationwide database allowed for a direct comparison of robustly matched cohorts while maintaining a large sample size that is representative of and generalizable to the broader population. However, the study is bound by the limitations of hospital billing databases, such as improper or incomplete coding and missing data. In the inclusion criteria, prevention of SSCs was defined as billing of the product on the same day as surgery; however, the dressing could have been used for other purposes. In the real-world setting, the protocols used for the 2 devices may also differ between hospitals and health care providers. These care differences cannot be captured in a real-world database study. Additionally, adverse outcomes related to the 2 devices, such as possible blistering, could not be captured in this dataset. This is particularly important because research on the −125 mm Hg device found blistering to be a notable adverse outcome.²⁵ Finally, data for outcomes outside of the hospital setting following discharge were not included in the claims database, meaning that any potential effects of the devices after discharge have yet to be captured. 

This large, nationwide US-based study demonstrated that of the 2 commonly used sNPWT devices, the −80 mm Hg device was associated with a lower likelihood of developing overall SSI, superficial SSI, dehiscence, and seroma following cesarean delivery compared with the −125 mm Hg device, as well as a lower financial and health care resource burden. A nonsignificant trend in reduced LOS and deep SSI in favor of the −80 mm Hg device and no difference in hematoma was observed. Further studies are required to confirm these findings. However, the differences in the devices’ modes of action may explain the difference in clinical outcomes observed in this study.