The study will examine the effect of using Negative Pressure Wound Therapy (NPWT) compared with standard wound dressing among patients undergoing elective open surgery for incisional hernia. The study's main hypothesis is that NPWT will decrease the post-operative incidence of surgical site infections and also improve the patients' quality of life including less scar-related pain and higher cosmetic satisfaction.

In recent years, negative pressure wound therapy (NPWT) has been utilized for the treatment of complicated wounds within orthopedic and vascular surgery, whereas incisions after abdominal surgery have not been treated with prophylactic negative pressure wound treatment to the same extent. Patients undergoing incisional hernia repair per definition have elicited insufficient wound healing (i.e. the hernia), and often carry comorbidities such as diabetes, obesity and a history of smoking, leaving them at a high risk of developing wound complications. Despite efforts to reduce this risk, the incidence remains as high as 50% in some series. Wound complications are especially concerning in patients undergoing incisional hernia repair, as a foreign body (synthetic polypropylene mesh) is placed in the abdominal wall during the procedure. Wound complications are directly associated with an increased risk of hernia recurrence, which reduces the patients' quality of life and has severe socioeconomic costs including a higher risk of prolonged hospital admission, re-operation, re-admission and increased mortality (2). The aim of this trial is to examine the effects of prophylactic NPWT on postoperative wound complications after open incisional hernia repair compared with standard care, i.e. an operative dressing. It is our hypothesis that NPWT significantly reduces the incidence of surgical site infections (SSI) as defined by the Center for Disease Control.

Since Bispebjerg Hospital in Denmark is the regional center for complex hernias, this is one of the few sites where a randomized trial including 110 patients undergoing open incisional hernia repair is feasible. To date, only five randomized controlled trials of prophylactic NPWT for closed abdominal incisions have been published. In the most recent meta-analysis of these trials, there was no reduced risk of wound complications in patients treated with NPWT, however results indeed seemed subjective to type-II error (relative risk 0.56 (95% confidence interval 0.30-1.03, P = 0.064). Thus, adding another randomized trial expectedly will alter the conclusion of the next meta-analysis.

The study type is a randomized controlled trial (RCT) comprising two treatment groups, i.e. one of the following:

1. STANDARD CARE After skin closure, a standard operative dressing is applied in the entire length of the incision. This operative dressing is removed in the morning of postoperative day two. Only in the case of blood or serous fluid mandating changing of the dressing, will this be done prior to postoperative day 2.
2. INTERVENTION After skin closure, NPWT in the form of Prevena™ (KCI/Acelity, San Antonia, TX, USA) is applied using the following technique: The sterile foam dressing is removed from the package and placed on the incision in the entire length, on top of which the sterile dressing is placed, ensuring air tightness. An appropriate hole in the dressing is cut at the center of the dressing and the tube for the interface pad is connected and a negative pressure of 125mmHg is applied. The Prevena™ system is removed on the morning of postoperative day 3.

Patients are included in the study during the planning of surgery in the outpatient clinic or within a week before surgery at the planned visit in the department of surgery. Patients are randomized to intervention or standard treatment in a 1:1 allocation ratio, which will be performed using computer generated sequences with varying block sizes (http://www.sealedenvelope.com/). This randomization will generate randomization and code envelopes and is carried out by a physician not otherwise involved in the study. On the day of surgery, the patients are given a randomization number. Corresponding randomization envelopes contain information about the intervention the patient is to receive and are thus opened during surgery, i.e. immediately after closure of the linea alba, whereas the code envelopes will be opened at the time of data analysis after all included patients have completed 30-day follow up. Based on the average number of elective open incisional hernia repairs at the study's operating site, the patient recruitment is expected to take 1 to 2 years.

PARTICIPANTS

The following baseline data are registered for each participant:

• Age [nominal: number]
• Sex [categorical: Male, Female]
• Number of previous abdominal operations [nominal: number]
• Number of previous incisional hernia repairs [nominal: number]
• Smoking status [categorical: Active smoker, Non-smoker]
• BMI [kg/m2]
• Chronic obstructive pulmonary disease [categorical: Yes, No]
• Diabetes [categorical: Yes, No]
• American Society of Anesthesiology (ASA) class [categorical: 1, 2, 3, 4, 5]
• Site of incisional hernia [categorical: Midline, Upper left, Lower left, Upper right, Lower right, Other]
• Orientation of hernia incision [categorical: Horizontal, Vertical]
• Bleeding disorder + anticoagulative medication [categorical: Yes, No]
• Serum albumin level [numerical: g/L]
• Maximal horizontal fascial defect [numerical: centimeters]
• Maximal vertical fascial defect [numerical: centimeters]
• Botox [categorical: Yes, No]

Perioperative established variables

• Type of procedure/repair [categorical: Rives-Stoppa, RS+TAR, onlay, IPOM, RS+ECS, other]
• Operative time [numerical: minutes]
• Length of incision [numerical: centimeters]
• Contamination grade [categorical: clean, clean-contaminated, contaminated, dirty]
• Type of mesh
• Commentary option (e.g. perioperative complications)

ETHICAL CONSIDERATIONS This trial aim to improve the treatment of patients undergoing open abdominal surgery by reducing the incidence of wound complications. We hypothesize that the intervention will be an improvement compared with the standard treatment currently offered, without any severe side-effects. This includes both in terms of the expected reduction in wound complication incidence as well as an increase in patient quality of life. Thus, the expected benefits from participation in the current trials outweigh any potential drawbacks and is therefore considered ethical appropriate. Lastly, the trial conforms to the Helsinki Declaration.

Inclusion Criteria:

• patients undergoing elective open incisional hernia repair

Exclusion Criteria:

• active superficial or deep wound infection
• inability to provide informed consent