INVIPS trial highlights potential of negative pressure to reduce surgical wound infections

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Julien Hasselmann ESVS
Julien Hasselmann

Based on the results of the INVIPS trial, incisional negative pressure wound therapy (INPWT) has been shown to decrease the risk of surgical site infections (SSIs) following vascular surgery with inguinal incision. Conducted at Skane University Hospital (Malmӧ, Sweden), the trial focused on inguinal incisions as “one of the highest risk factors” for wound infection in the post-operative course.

Julien Hasselmann (Lund University Hospital, Lund, Sweden), who presented the results at the European Society for Vascular Surgery annual meeting (ESVS 2019; 24­–27 September 2019; Hamburg, Germany), said: “Despite all of our achievements with endovascular procedures, open vascular surgery still has an important place in good patient care. However, open surgery often comes at a price: surgical wound infections.”

Commenting on why inguinal incisions present such a high risk, Hasselmann explained that a high bacterial concentration, moisture, dense lymphatics and mobile, uneven wound surfaces are all responsible for this increased probability of complications. Furthermore, it was emphasised during the presentation that changes to antibiotic prophylaxis (with trimethoprim and sulfamethoxazole used instead of cloxacillin) failed to decrease the rate of infection, during a study conducted in 2015.

With these alterations having no impact, INPWT was considered as “an alternative preventative measure”. This therapy, as Hasselmann underlined, “uses dressings directly applied onto regularly sutured incisions at the end of the procedure”; once applied, the dressing is connected to a pump that produces -80mmHg constant suction.

Hasselmann added: “The dressing we used was the PICO dressing by Smith & Nephew, but there are similar versions of this from other manufacturers on the market. The unique feature of this PICO dressing was that 80% of the fluid was resorbed by evaporation. No fluid container is needed either, so the apparatus is very light and portable. The pump is programmed to last for seven days, at which point the entire dressing can be taken off.”

In order to assess the potential of INPWT to reduce surgical site infections—with benefits such as decreased drainage time when applied to orthopaedic wounds already demonstrated—a randomised controlled trial (INVIPS) took place between November 2013 and October 2018, comparing a standard dressing to the PICO negative pressure dressing on closed inguinal incisions.

Groins investigated in the trial were randomised to either INPWT or a control dressing, and in bilateral cases, the right side was always randomised to one of the dressings, with the left side receiving the opposite. According to Hasselmann, “this design decreased the number of incisions we needed to show a difference between the two treatments”.

Primary endpoints established for the study included SSIs, as defined by CDC classification and ASEPSIS score, as well as other wound complications that may develop within the 90 days following surgery. In terms of inclusion criteria, patients scheduled for elective vascular procedures, with inguinal incisions, were enrolled in the trial, while persons with ongoing infections in the inguinal area were excluded for participating. In addition, Hasselman outlined that “both groups (control and INPWT) were similar in terms of patient and perioperative features”.

Recently published in the Annals of Surgery, results of the investigation showed that of the 139 patients operated on and selected for the trial, there was a “significantly lower infection rate” in those treated with INPWT, according to both the ASEPSIS and CDC criteria for wound infections. Furthermore, patients in both groups were divided for statistical correctness into those who underwent unilateral procedures (120), and those who underwent bilateral procedures (19).

In the unilateral cohort, a wound infection rate of 11.9% was recorded in those who received INPWT, compared to 29.5% in the control group, while in the bilateral cohort, just 5.3% of those who underwent INPWT developed a wound infection compared to 26.3% of the control patients [combined p=0.02]. This represented a significant improvement, although there were no differences between the INWPT and control patients with regard to other surgical site complications.

Speaking to iWounds News, Hasselmann concluded: “The trial was performed on inguinal incisions alone, but it did show that we can actually reduce the incidence of SSIs significantly using negative pressure. Wound complications are not to be reckoned with, and there are data which demonstrate that even if patients do not die from direct complications resulting from surgical wounds, such as an SSI, you still have a higher mortality rate. By reducing the infection rate then, we are not only tackling a problem for all surgeons and a hassle for patients, but we might actually be able to save lives.”

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