Engelhardt 2016.

Methods	Study design: randomised controlled trial Study grouping: parallel Ethics and informed consent: ethics approved and consent obtained Follow‐up period: primary endpoint of the study was the occurrence of SSIs Sample size calculation: not stated ITT analysis: no number randomised: 141 number analysed: 132 Funding: not stated Pre‐registration: not stated
Participants	Location: Germany Intervention group (high risk): n = 64control group (high risk): n = 68 Mean age (range): intervention group = 72 (64 to 75)control group = 70 (60 to 78) Inclusion criteria: all consecutive patients scheduled for vascular surgery with a femoral cutdown; age > 18 years and the need for an open, non‐emergency surgical procedure for peripheral arterial disease or aneurysm involving the femoral artery using a longitudinal femoral cutdown in the groin Exclusion criteria: dementia (not capable of informed consent) and declining to participate
Interventions	Aim/s: to determine whether closed‐incision negative pressure therapy is able to reduce SSI rate in the groin after vascular surgery Group 1 (NPWT) intervention: NPWT was applied on the closed skin intraoperatively. The system is comprised of a therapy unit containing a pump with a 45‐millilitre canister delivering a continuous negative pressure of 125 mmHg and a self adhesive dressing with a foam bolster that manifolds the negative pressure to the incision area. A special polyester interface layer protects the skin from direct contact with the foam bolster, while at the same time allowing delivery of negative pressure and fluid removal. Group 2 (control) intervention: absorbent adhesive dressing Study date/s: January 2012 and October 2014
Outcomes	infection Validity of measure/s: all wounds were documented with photos and classified according to the Szilagyi classification. Grade I infections only involved the skin (dermal infection); grade II extended to the subcutaneous tissue without reaching the vessels; and grade III finally involved the artery or bypass. Time points: 5th postoperative day and 6 weeks after surgery
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Random assignment of the participants to the 2 treatment groups was performed according to an external randomisation sequence.
Allocation concealment (selection bias)	Low risk	Sealed randomisation envelopes were provided by an external institution. On eligibility confirmation, the sequential randomisation envelope was opened, and the assignment was allocated.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Evidence for participants: not possible Comment: unlikely to affect outcomes Evidence for personnel: not possible Comment: unlikely to affect outcomes
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Quote: "all wounds were documented by photography and classified according to the Szilagyi classification" Comment: unclear whether outcome assessment was blinded
Incomplete outcome data (attrition bias) All outcomes	High risk	ITT not used; 141 participants were randomised, and 132 completed the study; 9 participants (6%) did not complete follow‐up due to urgent reoperation or death during follow‐up.
Selective reporting (reporting bias)	Low risk	Planned outcomes reported.
Other bias	Low risk	None detected.