Going with the Flow: Negative Pressure Wound Therapy Dressings

Introduction and Purpose:Historically when using Negative Pressure Wound Therapy (NPWT), gauze wound contact layers (WCLs) have been used with lower negative pressures than foam. Most of the time, the negative pressure prescribed for foam has been over -40mmHg higher than that prescribed for gauze, e.g. -125mmHg for foam and -80mmHg for gauze. However, since NPWT treatments with foam WCL dressings and higher negative pressures can cause ingrowth, which can cause bleeding and patient pain, more research is needed to ascertain whether this difference in negative pressure is necessary.

Methodology:A flow rate test apparatus was created by connecting Fetal Bovine Serum (FBS), which was used to emulate exudate, with tubing to the typical dressings, typical NPWT drain, and NPWT pump located on a platform. The fluid flow rate was calculated by measuring the time it took the FBS to reach designated end points marked on the tubing. For both types of WCLs, the NPWT pump was set at -80mmHg.  This process was repeated 3 times each for both gauze and foam.

Findings:The average flow rate for gauze was 2.3 mL/s, with a confidence of +/- 0.4. The foam had a lower average flow rate of 1.4 mL/s and a lower deviation confidence of +/- 0.1. While the gauze had a higher overall flow rate for each of the tests, the foam had a lower deviation and much more consistent overall results.

Conclusion: Due to their similar flow rates at the same lower pressure, the results suggest that using a foam dressing at a lower negative pressure setting may be as efficacious as using a higher negative pressure setting. This in turn implies that lower settings may be used to help reduce pain and bleeding related to dressing changes; however, more clinical studies and data are needed.