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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 ulcers (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).

Table: Topical Negative Pressure Therapy for Pressure Ulcer Healing Post SCI

Discussion

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.

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 ulcers in patients with SCI. No significant difference in WSA was found between groups. Despite the use of WSA software (versus manual measurement) for more objective WSA measurements, a key problem with the data is that depth measures were not included. This is particularly problematic given that lack of depth measurements may ignore the importance of healing of undermining and tunnelling in more severe wounds. Another key finding by Ho et al. (2010) was that treated patients registered has having significantly poor nutritional status as measured by lowered serum albumin concentrations (p<0.05) during the 4 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. The significance of this finding is likely reduced with the absence of prealbumin measurements that better reflect recent and common nutritional factors such as dehydration.

Coggrave et al. (2002) applied TNP continuously to pressure ulcers 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 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.

Conclusion

There is level 1a evidence (from one randomized controlled trial and one pre-post study; De Laat et al. 2011; Coggrove et al. 2012) that topical negative pressure facilitates wound healing for pressure ulcers in people with SCI and other patient etiologies. This conclusion is contradicted by level 5 evidence (from one observational study; Ho et al. 2010) but there are significant limitations in the latter study.

  • Pressure ulcer healing after a SCI is improved when topical negative pressure (TNP) therapy is administered as compared to traditional sodium hypochlorite dressing changes.