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Skin Integrity and Pressure Injuries

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).

Author Year
Country
PEDro Score
Research Design
Sample Size
Methods
Outcome
Sundby et al. 2018
Norway
RCT Crossover
PEDro=6
Ninitial=9
Nfinal=7
Population: Mean age=57.3yr; Gender: males=8, females=1; ASIA Class: A=8, C=1; Mean time with pressure injuries: 52wk; Pressure injury stage: III=6, IV=3.
Intervention: Patients were randomized to receive either at-home intermittent negative pressure (INP) plus standard wound care (SWC) versus SWC alone. INP protocol was used 120min/day. A crossover design was used, with the first 8 wks using INP to avoid potential carryover, and then crossed over.
Outcome Measures: Ulcer healing (Photographic Wound Assessment Tool (PWAT)), wound surface area (WSA).
1. There was greater improvement in the treatment group for WSA compared to control, but it was not statistically significant (p=0.72).
2. Improvements in PWAT were seen in all four INP+SWC patients, compared to 2/5 SWC alone, however, it was not statistically significant (p=0.13).

Dwivedi et al. 2017
India
RCT
PEDro=6
N=44

Population: NPWT Group (n=22): Mean age=53.5yr; Gender: males=17, females=5; Pressure injury stage: III=8, IV=14; Control Group (n=22): Mean age=54.3yr; Gender: males=16, females=6; Pressure injury stage: III=9, IV=13.
Intervention:
Participants were randomized to receive either a novel negative pressure wound therapy (NPWT) device, or to conventional wound care with wet to moist gauze dressings. Measurements were taken at weeks 0, 3, 6 and 9.
Outcome Measures:
Matrix Metalloproteinase-8 (MMP-8) level, Wound healing parameters (PU length, PU width, PU depth, exudate amount, tissue type).

1. Length of PU reduced significantly in the NPWT group compared to controls in weeks 6 and 9 (p=0.04, p=0.001 respectively).
2. Width of PU reduced significantly in the NPWT group compared to controls in week 9 (p=0.006).
3. Depth of PU reduced significantly in the NPWT group compared to controls in week 9 (p=0.01).
4. The NPWT had significantly less exudate compared to controls in weeks 3,6, and 9 (p=0.001 for all time points).
5. Tissue parameters improved (less sloughing, improved formation of red granulation tissue) in the NPWT group when compared to controls at weeks 6 and 9 (p=0.001).
6. Between-group comparison showed a significantly significant MMP-8 level decrease in the NPWT device group compared to controls at weeks 6 and 9 (p=0.006, p<0.0001 respectively).

Effect Sizes: Forest plot of standardized mean differences (SMD ± 95%C.I.) as calculated from pre- and post-intervention data

De Laat et al. 2011
Netherlands
RCT
PEDro=7
N=24
Population: Patients 18 yr who were admitted to the study hospital with difficultto-heal surgical wounds, or paraplegic and tetraplegia patients with pressure injuries grade IV according to the European Pressure injury Advisory Panel grading system 19.
Intervention: Topical negative pressure therapy or treatment with conventional dressing therapy with sodium hypochlorite
Outcome Measures: 50% wound volume reduction, with a maximum follow-up time of 6 wk, measuring the difference between the weekly measured wound volume and the initial wound volume before treatment.
1. Topical negative pressure resulted in almost 2 times faster wound healing than treatment with sodium hypochlorite and is safe to use in patients with difficult-to-heal wounds.
Srivastava et al. 2016
India
Prospective Controlled
Trial
N=48
Population: Negative Pressure Wound Therapy (NPWT group): Mean age=53.5 yr; Gender: males=19, females=5; Level of injury: paraplegia; Pressure injury stage: III=9, IV=15. Standard care (Control group): Mean age=54.34 yr; Gender: males=18, females=6; Level of injury: paraplegia; Pressure injury stage: III=10, IV=14.
Intervention: NPWT group (n=24): Negative pressure wound therapy using sterilized foam and negative pressure in addition to standard care. Control group (n=24): Standard care, where the pressure injury (PU) was cleaned with normal saline and packed with sterilized gauze, changed once or twice daily depending on dressing soakage.
Outcome Measures: Wound surface area; Depth of wound; Discharge; Conversion of slough into red granulating tissue.
1. At 3 wk, 6 wk, and 9 wk, NPWT group had a significantly smaller wound surface area (p=0.0001) and wound depth (p=0.0001) compared to control group. The wound surface area and wound depth decreases at each time point were significant in NPWT group (p=0.0001) but not in the control group.
2. In NPWT group, wound discharge became minimal at 3-6 wk and negligible at 9 wk, but in control
group, wound discharge continued until 9 wk.
3. At 3 wk, wound bed slough converted to granulation tissue in 33.3% of NPWT participants and 0% of control participants. At 9 wk, conversion was at 100% for NPWT group and 41.7% for control group.
Coggrave et al. 2002
United Kingdom
Pre-post
N=7
Population: Mean age=44.4 yr; Gender: males=5, females=2; Level of injury: paraplegia=4, tetraplegia=3; Location of pressure injury: trochanter=3, sacrum=4; Stage of ulcer: IV=6.
Intervention: Topical negative pressure (TNP) applied continuously (125 mmHg), dressing changed every 4-7 days. All patients seen and assessed by dietitian; nursed on a pressure redistribution surface; turned frequently; wound debrided as necessary pre-treatment.
Outcome Measures: Picture and wound swabs (every dressing change); Pressure injury volume (beginning and end of treatment).
1. Within 1-2 days of treatment initiation, granulation tissue developed in all wounds.
2. Wound volume and grade decreased (33-96%) in all subjects, but rate and extent varied. Bacterial colonization was also reduced in each wound.
3. Limited dressing problems were described, although rashes and pain were reported in some.
4. Seal preservation in certain areas, overlapping foam on healthy skin, and pressure application on bony protrusions, were reported as practical problems.
Dessy et al. 2015
Italy
Case Series
N=11
Population: Mean age=30 yr; Gender: males=10, females=1; Level of injury: paraplegia; Pressure injury stage: III or IV.
Intervention: Vacuum-assisted closure (VAC), consisting of polyurethane foams and negative pressure.
Outcome Measures: Presence of foram fragments.
1. 11 cases of foam fragment retention within the wound were described, resulting in progressive wound worsening that consisted of symptomatic bad-smelling, discharge with positive germ culture, and progressive wound enlargement.

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.

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