Topical Negative Pressure

Topical negative pressure therapy (TNP) distributes negative pressure (i.e., sub-atmospheric pressure) across an ulcer WSA via continuous or intermittent application of vacuum through a sealed dressing. This therapy to promote wound healing has been used to treat a variety of acute and chronic wounds including pressure injuries (Smith et al. 2007; Argenta & Morykwas 1997). An airtight system is created using special foam, sterile tubing and canister, and an adhesive film drape (Houghton & Campbell 2007). Vacuum is applied via a suction bottle or pump (Műllner et al.1997). The negative pressure in the wound bed removes local edema, increases blood flow, decreases local tissue edema, decreases bacterial colonization, and increases granulation tissue formation and mechanical wound closure (Smith et al. 2007; Houghton & Campbell 2007; Argenta & Morykwas 1997).

Summarized Level 5 Evidence Studies

Ho et al. (2010) conducted a retrospective analysis of negative pressure wound therapy versus traditional best practice standard care on stage III or IV pelvic pressure injuries in patients with SCI. No significant difference in WSA was found between groups. Treated patients registered as having significantly poor nutritional status as measured by lowered serum albumin concentrations (p<0.05) during the four-week study. This was not apparent in the control group and therefore suggests that the treatment may have partially contributed to the lower serum albumin concentrations in malnourished participants who are less able to compensate for wound-related protein loss. A case study (N=1) described increased TNP performance when used in combination with super-oxidised solution (SOS-Dermacyn) for infection control (Angelis et al. 2012). Another potential contraindication for TNP is described in Mhatre et al. (2013) where a case study of two individuals with SCI described TNP triggered episodes of autonomic dysreflexia. Since only three TNP studies for people with SCI were found, these two case studies are included only as additional information, but they do not impact the evidentiary conclusions.

Discussion

Sundby et al. (2018) randomized 9 participants in a lower-powered cross-over trial to explored the use of an intermittent negative pressure (INP) device for home use in addition to standard wound care (SWC) for SCI patients with chronic leg and foot ulcers. Seven of nine study participants adhered to a median of 90% of the prescribed 8-week INP-protocol and completed the study without side effects. PWAT improvement was observed in 4/4 patients for INP + SWC vs. 2/5 patients for SWC alone (P=0.13). Wound surfact area (WSA) improved in 3/4 patients allocated to INP + SWC vs. 3/5 patients in SWC alone (P=0.72). INP can be used as a home-based treatment for parients with SCI, and its efficiacy showed statistical significance compared to the control group, but should be tested in an adequately sized, preferably multicenter randomized trial.

Dwivedi et al. (2017) randomized 44 SCI patients to receive negative pressure wound therapy (NPWT) using a novel negative pressure device (n=22) or PI treated with a traditional wet to moist gauze (n=22). The authors investiaged the level of matrix metalloproteinase-8 (MMP-8) and wound-healing outcome measures (length, width, and depth, exudate amount, and tissue type) of PIs. At the end of 9 weeks, significantly lower levels of MMP-8 were observed and showed a positive correlation with reduction in the length, width, and depth of PIs in the NPWT group (P=0.04, P=0.001, P<0.05 respectively), while in the control group, negative correlation was observed in association with MMP-8 and the length, width, and depth of PIs. Exudate levels were significantly lower in the NPWT group compared with the conventional dressing group which lasted from week 3 through week 9. Red granulation tissue formation was significantly higher in the NPWT group after week 6 (P =0.001). Similarly, a prospective controlled trial by Srivastava et al. (2002) compared pressure injury wound healing with conventional dressing and by an innovative negative pressure device (NPD). 48 SCI patients with PIs of stages 3 and 4 were recruited. Patients were divided into two groups: group A (n=24) received NPWT using NPD, and group B (n=24) received conventional methods of dressing. At week 9, all patients on NPD showed a statistically significant improvement in PI healing in terms of slough clearance, granulation tissue formation, wound discharge, and culture. A significant reduction in wound size and ulcer depth was observed in NPD as compared with conventional methods at all follow-up time points (P=0.0001). NPWT by the innovative device heals PIs at a significantly higher rate than conventional treatment. These devices have been safe, easy to apply, and cost-effective.

De Laat et al. (2011) randomized 12 inpatients with SCI to TNP or conventional sodium hypochlorite dressing (control) and yielded an almost two-times faster TNP healing time to 50% wound volume reduction (p<0.001) with minimal adverse events. Similar results were achieved for a parallel group of 12 inpatients of mixed disease etiology who also suffered with difficult-to-heal wounds. Combined results including both groups of patients did not alter the efficacy or safety conclusions. Another advantage of TNP is the reduced workload required of caregivers. The TNP sealed sponges are changed every 48 hours in contrast to the thrice daily sodium hypochlorite-soaked dressing changes.

Coggrave et al. (2002) applied TNP continuously to pressure injuries of seven individuals with SCI to prepare the wound for surgical closure. Treatment time varied from 11 to 73 days with percent decrease in wound volume varying from 33% to 96%. Granulation tissue was seen to develop and bacterial colonization decreased in five cases. Given the small sample size and variable responses, this study provides limited evidence.

A case series by Dessy et al. (2015) invesitaged the complications of a closed-loop, non-invasive vacuum-assisted closure (VAC) therapy. The intended use of this intervention is to use localised negative pressure applied on porous polyurethane absorbent foams to promote healing of acute and chronic wounds. Study authors reported 11 cases of a rare complication of foam-fragment retention within the wound. Thus, this therapy did not promote healing but further hindered it.

Conclusion

There is level 1b evidence (from one RCT: Sundby et al. 2018) that intermittent negative pressure (INP) device plus standard wound care (SWC) is effective for wound healing compared to SWC alone in SCI patients home care.

There is level 1b and level 2 evidence (from one RCT and one prospective controlled study: Dwivedi et al. 2017; Srivastava et al. 2002) that negative pressure wound therapy (NPWT) has shown to reduce levels of MMP-8, increase the rate of healing, reduce exudate production and enhance the rate of formation of red granulation tissue when compared to conventional wet gauze alone.

There is level 1b evidence (from one RCT and one pre-post study: De Laat et al. 2011; Coggrove et al. 2012) that topical negative pressure facilitates wound healing for pressure injuries in people with SCI and other patient etiologies.

There is level 4 evidence (from one case series: Dessy et al. 2015) that vacuum-assisted closure (VAC) therapy does not promote wound healing and may cause rare complications including foam-fragment retention within the wound.