Managing incisional wounds with Prevena VAC therapy in lower-extremity vascular surgery: A comparative study

Abstract

Background

Vascular surgical site infections have been reported with an overall incidence of 5–10% for patients undergoing arterial interventions and as high as 10–20% for lower-limb bypass grafting procedures. Given that vascular surgery patients are known to be at a higher risk of postoperative wound infections and other complications, our objective was to evaluate a potential method to reduce such complications. This study compares the rate of wound healing complications between incisional negative pressure wound therapy (NPWT) and conventional dressings in vascular surgery patients with infra-inguinal incisions. The primary endpoint is complete closure of the wound at the 2-week follow-up appointment. Secondary endpoints include frequency infections requiring antibiotics, need for wound revision, and wound dehiscence.

Methods

A prospective cohort study with retrospective control group was performed following infra-inguinal vascular surgeries for peripheral arterial disease at the Mount Carmel Health System. The patients included in this study were those who underwent a lower-extremity vascular procedure with primary closure of an incision distal to the groin between January 2014 and July 2018. Patients that had received an infra-inguinal incision with primary closure were included. Patients in the experimental group who had a Prevena Wound VAC were compared with a retrospectively obtained control arm treated with conventional dressings. Data regarding wound healing and complications, specifically infections and wound dehiscence, were obtained.

Results

A total of 201 patients were recruited in our study: 64 in the Prevena group and 137 in the control group. There was a significant reduction in the number of open wounds in the Prevena group compared to the control group at the 2-week follow-up (10.9% Prevena vs 33.6% control; p = .0005). When evaluated in aggregate, there was a statistically significant reduction in the number of patients who succumbed to any complication in the Prevena arm compared with traditional dressings (13 (20.3%) Prevena vs 72 (52.6%) control; p < .0001).

Conclusion

The results of our study suggest there should be a significant consideration for the use of NPWT as a prophylactic measure to reduce the risk of wound complications of primarily closed infra-inguinal incisions in vascular surgery patients following common vascular procedures. Its use is particularly effective for patients at enhanced risk of infection, especially those with poor vascularization from BMI, smoking, and diabetes. This leads to decreased trends in antibiotic use, ED visits, readmissions, and surgical revisions, which translates to decreased utilization of hospital resources and economic burden.

Keywords

Prevena vascular surgery wound vac lower-extremity wounds lower-extremity vascular

Introduction

Wound healing can be a difficult process to facilitate in the setting of diabetes, obesity, and peripheral artery disease (PAD). Vascular surgical site infections have been reported with an overall incidence of 5–10% for patients undergoing arterial interventions and as high as 10–20% for lower-limb bypass grafting procedures.¹ Complications associated with infection include poor wound healing, failure of arterial bypass, and occasional progression to amputation. Wound healing statistics associated with amputations are also staggering with primary healing of below-knee amputations reported in the range of 30%–92% and re-amputation rates of 4%–30%.²

While good surgical technique is critical to the success of any operation, postoperative wound care also significantly impacts the patient’s overall recovery. There is no current consensus on the ideal dressing following peripheral arterial intervention or amputations. Within the past two decades, the utilization of negative pressure wound therapy (NPWT) has increased. Its use was traditionally described to facilitate wound healing in large open wounds by increasing perfusion, distributing load stress, promoting angiogenesis, and decreasing edema.³ The use of NPWT on closed surgical wounds has also increased dramatically, specifically in the fields of orthopedics and cardiothoracic surgery. Animal models have revealed that closed wounds treated with NPWT demonstrated denser collagen deposition, significantly increased tensile strength, better perfusion, and increased angiogenesis.⁴ Commercially available incisional NPWT systems have recommendations for use limited to patients with risk factors for wound complications such as diabetes, obesity, and poor vascularization.

NPWT has demonstrated improvement in the management of open wounds following partial diabetic foot amputations with an increase in the number of wounds successfully managed and an increased rate of healing with NPWT.³ Anecdotal experience with NPWT in below-knee amputations has been advocated as an adjunct to stump closure via secondary intention.⁵ Incisional NPWT has also been shown to decrease wound dehiscence and infection rates in patients following open reduction and internal fixation of below-knee injuries.⁶

Given that vascular surgery patients are known to be at a higher risk of postoperative wound infections and other complications, our objective was to evaluate a potential method to reduce such complications. This study compares the rate of wound healing complications between incisional NPWT and conventional dressings in vascular surgery patients with infra-inguinal incisions. Patients in the experimental group had a Prevena Wound VAC placed immediately after a lower-extremity vascular procedure with a primarily closed incision distal to the groin. The control arm of this study was obtained through retrospective chart review and included similar patients treated with conventional dressings. The primary endpoint is complete closure of the wound at the 2-week follow-up appointment. Secondary endpoints include frequency of clinically relevant infections, need for wound revision, and wound dehiscence.

Methods

Study subjects

A prospective cohort study with a retrospective control group was performed following patients of two vascular surgeons at the Mount Carmel Health System. The patients included in this study were those undergoing a lower-extremity vascular procedure with an incision distal to the groin between January 2014 and July 2018. Procedures within this study included femoral-popliteal artery bypass, femoral-tibial arterial bypass, embolectomy, thrombectomy, debridement and wound closure, above-knee amputation, below-knee amputation, and foot/toe amputations, as well as other common vascular procedures of the lower extremity. The prospective cohort involved consecutive patients in the Prevena group and was recruited between December of 2016 and July of 2018. Only primarily closed incisions were included in this study.

For the patients in the experimental group, a Prevena Wound VAC dressing was placed following primary skin closure and covered the entirety of the wound. The VAC was set at −125 mmHg and remained in place until removal on postoperative day 7 when the portable battery pack failed. There was no outside funding provided by 3M for the Prevena VAC device. The patients were then seen at their usual postoperative follow-up appointment at 2 weeks following surgery to assess for primary closure, need for surgical revision, and clinically relevant infection. Wound revision included wound debridement, drainage of abscesses or fluid collections, and re-approximation of wound edges. Clinically relevant wound infections were defined as infections warranting the use of antibiotic therapy. Dry wounds were left open to air. Open wounds or those with continued drainage were managed in a conventional fashion with gauze and Kerlix. Wounds were reevaluated in 6–8 weeks.

Patients in the control group were obtained through retrospective chart review by starting with the most recent control patient’s procedure and working backwards consecutively until the desired sample size was achieved. All patients who had undergone intervention for lower-extremity arterial disease were evaluated. Patients that had received an infra-inguinal incision with primary closure were included. Data regarding wound healing and complications, specifically infections and wound dehiscence, were obtained.

At the 2-week follow-up appointments, primary and secondary endpoints were evaluated for this study. The primary endpoint was wound closure at the time of the patient’s first follow-up appointment. Non-closure was defined as a wound that obviously dehisced at the level of the skin as well as wounds with a level of drainage that precluded the removal of sutures or staples. The secondary endpoints were the frequency of surgical site infections that necessitated the use of antibiotics, the frequency of patients returning to the hospital for wound complications, and the need for return to the operating room for surgical revision.

Data sources

The data were collected through review of physician and nursing documentation within the patient’s EMR for both the Prevena group and the control group. Given the prospective nature of the study, confirmation of these encounters with the patient at the time of their first postoperative follow-up was also performed. The study protocol was approved by our institution’s Institutional Review Board.

Statistical analysis

Sample size

Because the Prevena device had been available to the vascular surgeons for <1 year at the time the study was planned, the sample size was calculated based on needing two control patients for every Prevena patient. Under the assumption that the rate of wound remaining open at the 2-week follow-up visit would be 25% in the control group and 10% in the Prevena group, the study would have 80% power to detect this difference in open wound rates with 64 patients in the Prevena group and 128 patients in the control group. The type 1 error rate was 5%.

Statistical analysis

Fisher’s exact test was used to compare the Prevena and control groups in terms of the primary and secondary outcomes. The study groups were also compared with respect to their demographic, clinical, and procedure characteristics using Fisher’s exact test for dichotomous variables and the Wilcoxon rank sum test for numerical variables. Multiple logistic regression compared the study groups on the primary outcome while controlling for other factors which had unequal distributions across the control and Prevena groups. SAS version 9.4 (Cary, North Carolina) was used for statistical analysis.

Results

A total of 201 patients were recruited in our study: 64 in the Prevena group and 137 in the control group. Patients were excluded if they had a sensitivity or allergy to silver due to the silver impregnated foam used as part of the Prevena Wound VAC. All 64 patients that were recruited for the prospective arm involving the Prevena VAC completed the study. Table 1 lists the patient demographics, clinical characteristics, and type of procedures. Patient demographics were not significantly different except for smoking status and procedure type. The Prevena group had significantly more patients with a smoking history than the control group (89.1% Prevena vs 71.5% control; p = .0154). In addition, the Prevena group had more bypass procedures, especially femoral-popliteal (48.4% Prevena vs 31.4% control), rather than below the knee, foot, and toe amputations, which were more prevalent in the control group (p = .0371).

Table 1.

Demographic and clinical characteristics of Prevena and control groups.

Factor	Prevena (n = 64) n (%) or mean (SD)	Control (n = 137) n (%) or mean (SD)	p-Value
Age	65.1 (11.9)	66.0 (10.5)	0.5862
BMI	26.7 (6.9)	28.1 (7.1)	0.1065
Coronary artery disease	28 (43.8%)	75 (54.7%)	0.1734
History of CABG	11 (17.2%)	30 (21.9%)	0.5733
Stent placement	14 (21.9%)	36 (26.3%)	0.6001
COPD	9 (14.1%)	29 (21.2%)	0.2530
Diabetes mellitus	33 (51.6%)	86 (62.8%)	0.1655
Smoking			0.0154
Never	7 (10.9%)	39 (28.5%)
Former	23 (35.9%)	33 (24.1%)
Current	34 (53.1%)	65 (47.5%)
Previous wound complication	14 (21.9%)	44 (32.1%)	0.1810
Amputation—above knee	9 (14.1%)	20 (14.6%)	0.0371
Amputation—below knee	6 (9.4%)	13 (9.5%)
Amputation—foot/toes	2 (3.1%)	18 (13.1%)
Bypass—fem/pop	31 (48.4%)	43 (31.4%)
Bypass—fem/Tib	9 (14.1%)	12 (8.8%)
Bypass—other	3 (4.7%)	9 (6.6%)
Embolectomy/thrombectomy	3 (4.7%)	12 (8.7%)
Closure/debridement	1 (1.6%)	7 (5.0%)
Other	0 (0%)	3 (2.2%)

The bolded values were ones that demonstrated statistical significance with a p-value less than 0.05.

The factors associated with open wounds at the 2-week follow-up appointment are outlined in Table 2. There was a significant reduction in the number of open wounds in the Prevena group compared to the control group at the 2-week follow-up (10.9% Prevena vs 33.6% control; p = .0005). The rate of open wounds at 2 weeks also varied according to the type of procedure (Table 2).

Table 2.

Factors associated with wound open at two weeks.

Factor	Subgroup n	Wound open n (%)	p-Value
Control	137	46 (33.6%)	0.0005
Prevena	64	7 (10.9%)	0.0005
Never smoked	46	15 (32.6%)	0.5469
Former smoker	56	14 (25.0%)
Current smoker	99	24 (24.2%)
Previous wound complication	58	19 (32.8%)	0.0786
No previous complication	143	34 (23.8%)	0.0786
Amputation—above knee	29	6 (20.7%)	<0.0001
Amputation—other	39	21 (53.8%)
Bypass procedure	107	22 (12.8%)
Debridement	4	2 (50%)
Other	22	3 (4.2%)
CAD	103	26 (25.2%)	0.7504
No CAD	98	27 (27.6%)	0.7504
History of CABG	41	9 (22.0%)	0.5544
No history of CABG	160	44 (27.5%)	0.5544
Stent placement	50	15 (30.0%)	0.5789
No stent placement	151	38 (25.2%)	0.5789
COPD	38	10 (26.3%)	1.000
No COPD	163	43 (26.4%)	1.000
Diabetes mellitus	119	31 (26.1%)	1.000
No diabetes mellitus	82	22 (26.8%)	1.000

The bolded values were ones that demonstrated statistical significance with a p-value less than 0.05.

The Prevena group had fewer BKA procedures than the control group. To ensure this did not account for the decreased rate of open wounds at 2 weeks in the Prevena group, a logistic regression analysis was performed. The results from this analysis suggest that even after controlling for the differences in type of procedure between study groups, the Prevena group had a 70% decrease in the odds of an open wound at 2 weeks. For further examination, the rate of wound closure at 2 weeks was compared between the Prevena and control patients, stratified by BKA versus other procedures. For BKA procedures, the rate of wound closure for the experimental group was 6/8 (75%) versus 13/31 for the control group (42%, p = .1274). For non-BKA procedures, the experimental group’s rate was 51/56 (91%) compared to 78/102 in the control group (76%, p = .008). BMI was not an important contributor to the number of open wounds at 2 weeks postoperatively (p = .0717).

When evaluated in aggregate, the Prevena group had a statistically significant reduction in the number of patients who succumbed to the composite outcome (13 (20.3%) Prevena vs 72 (52.6%) control; p < .0001). There was also a statistically significant reduction in the total number of complications in each group (Table 3). When evaluated individually, the secondary endpoints revealed a trend toward decreased need for surgical revision, ED visits, and antibiotic use.

Table 3.

Number of complications by group.

Complication	Prevena n (%)	Control n (%)	p-Value
Composite (open wound at 2 weeks, antibiotic use, ED visit, and surgical revision)	13 (20.3%)	72 (52.6%)	<0.0001
# Complications			0.0005
0	51 (79.7%)	65 (47.5%)
1	3 (4.7%)	32 (23.4%)
2	3 (4.7%)	16 (11.7%)
3	4 (6.3%)	15 (11.0%)
4	3 (4.7%)	9 (6.6%)
Open at 2 weeks	7 (10.9%)	46 (33.6%)	0.0005
Surgical revision	8 (12.5%)	33 (24.1%)	0.0624
ED visit	9 (14.1%)	31 (22.6%)	0.1866
Antibiotic prescription	9 (14.1%)	35 (25.6%)	0.0703

The bolded values were ones that demonstrated statistical significance with a p-value less than 0.05.

Discussion

In our study, there was a significant reduction in open wounds for those managed with Prevena Wound VAC compared to conventional dressings at a 2-week follow-up appointment (10.9% Prevena vs 33.6% control; p = .0005). The control group and Prevena group were equivalent according to comorbidities (coronary artery disease, history of CABG, COPD, and diabetes) and procedure type. However, there was an increased rate of smoking among those in the Prevena group. Previous research has emphasized the detrimental effects of smoking on the wound healing process. This difference in patient selection only further supports the enhanced wound healing that a Prevena Wound VAC can provide for high-risk patients.

The original data set noted a larger proportion of BKA operations in the control arm. A regression analysis was performed to identify any potential for confounding bias, and upon further investigation, those patients undergoing a BKA continued to have improved results with Wound VAC therapy. The only attributable factor in the reduction of open wounds at 2 weeks was incisional wound management with NPWT. Although not reaching statistical significance, there was a tendency toward reduced complications for all types of procedures when assessing the rate of open wounds at 2 weeks, with the most notable decrease observed in arterial bypass procedures. There was a statistically significant reduction in morbidity in the NPWT group when looking at all complications together. The complications reviewed were wound dehiscence, drainage precluding the removal of staples or sutures, surgical site infection necessitating antibiotic prescription, postoperative emergency department visit, hospital readmission, and the need for surgical revision at the 2-week reevaluation. Together this translates toward a trend of decreased utilization of hospital resources.

NPWT has traditionally been used to facilitate healing of large open wounds. However, given the significant economic burden that surgical site wound complications incur, its use and study on the management of such wounds have increased. Surgical site infections in the United States alone cost over an estimated $3 billion USD per year.⁷ Given its potential benefit to reduce these complications and their resultant economic burden, it stands to reason that recent studies have focused heavily on those patients believed to be at highest risk. Thus, the currently proposed indications for its use include those patients with the greatest operation-related risk factors including BMI, smoking status, diabetes, and prolonged operation time.^8,9

A meta-analysis performed by Shiroky et al. examined the impact of NPWT for primarily closed surgical incisions in patients from various surgical fields including orthopedics, obstetrics, general, cardiothoracic, urology, neurosurgery, plastics, and vascular surgery. Their research demonstrated a 40% reduction in surgical site infections compared to those treated with conventional dressings, which is consistent with our secondary endpoint results.¹⁰ It is important to note, vascular surgery patients are known to be at an increased risk for poor wound healing and wound complications, making them a crucial population to study the effects of NPWT on incisional wound complications and healing. With an incidence of surgical site infections reported at 5–10% for arterial intervention, and upward of 10–20% for lower-limb bypass grafts, wound complication reduction has the potential to greatly decrease associated morbidity, mortality, antibiotic use, overall hospital resource utilization, and economic burden.¹

The 3M Prevena VAC system examined in this study utilizes a dressing-skin interface that is impregnated with 0.019% ionic silver to decrease bacterial colonization of the wound VAC fabric.¹¹ Silver-containing dressings have been associated with accelerated healing in vascular wounds such as venous leg ulcers.¹² Therefore, it is possible that the silver dressing had an additional effect in decreasing wound infections and accelerating healing as compared to a standard wound VAC alone as silver is a known antimicrobial. The Prevena VAC includes a portable battery pack that lasts approximately 7 days from the time it is turned on. The VAC device was left on for this 7-day period without being taken down or monitoring. Patients were allowed to discharge to home when medically able and did not have to remain in the hospital given the portable nature of the Prevena VAC device.

In recent years, NPWT dressings have shown promise in reducing wound complications in a variety of settings for vascular surgery patients, but the evidence has been unclear if they reduce groin wound complications in closed incisions after vascular surgery. In addition to this, no current consensus exists for the ideal dressing of arterial intervention procedures or amputations. Pesonen et al. analyzed the prophylactic use of vacuum-assisted therapy for primarily closed groin wounds in vascular surgery patients and found promising results. Although their sample size was small, their research suggests that prophylactic VAC placement for high-risk patients may decrease wound complications, readmission due to groin wound complications, and a potential cost benefit.¹³ The meta-analysis completed by Wee et. al. on closed incision NPWT in vascular surgery reports significant reductions in infections, need for antibiotics, and surgical re-intervention, but without difference in length of stay or mortality.¹⁴ And finally, the meta-analysis from Svensson-Bjork et al., which specifically evaluated NPWT of closed groin incisions in arterial surgery, reports a significant reduction in surgical site infections.¹⁵

It is therefore reasonable to conclude that our findings are in accordance with previous literature and add to the current body of evidence to support NPWT as a prophylactic measure in reducing the risk of wound complications in primarily closed incisions of patients at enhanced risk of infection, particularly patients at risk of poor wound healing due to poor vascularization from BMI, smoking, and diabetes. These patients should be highly considered for incisional site NPWT which may lead to decreased trends in antibiotic use, ED visits, readmissions, and surgical revisions; all of which translates to a trend of decreased hospital resource utilization and, ultimately, economic burden. Further studies of a large-scale, multicenter nature to evaluate optimal protocols for the application of NPWT would be needed before the widespread implementation of such devices.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Kody Kasten

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