Advances in Negative Pressure Wound Therapy for the Wound Clinic

Negative pressure wound therapy (NPWT) has evolved over the years to offer wound patients faster healing. These authors outline the current NPWT products available and discuss where the future might take negative pressure technology.

In the outpatient setting, treating chronic open wounds places a significant burden on the patient, usually requiring multiple clinic visits, costly topical dressings, specialized home care, and potential hospital stays. The benefits of negative pressure wound therapy (NPWT) facilitating earlier closure of wounds are well documented in the literature.

NPWT was first introduced in the 1990s for the management of large nonhealing infected wounds.¹ Since then, the advancements in this technology have resulted in a modality that can be utilized for a multitude of wounds, providing a tailored therapy for each patient’s specific needs. This evolution has also benefited the clinician by increasing the ease of dressing application and program settings.

How NPWT Works

NPWT uses negative pressure, usually in conjunction with a reticulated foam interface, that increases healing through macrostrain and microstrain at the wound surface, exudate/debris removal, and alteration in the wound bed.^2,3  

Macrostrain promotes healing in several ways: it stimulates myofibroblast differentiation to contribute to the healing process through myofibroblast involvement in the inflammatory response to injury, reduces edema by compressive force, and draws the wound edges together.^2,4 Microstrain occurs when the negative pressure is initiated and the wound surface is physically pulled into the foam, resulting in mechanical force at a cellular level. This stimulates transforming growth factor (TGF-β1) to be released from platelets. In turn, this allows for fibroblasts to form collagen, which supports the cellular matrix.² This mechanical force also alters the wound environment by creating perfusion changes at the wound surface, resulting in hyperperfusion on deeper vessels and hypoperfusion on superficial vessels.

Using NPWT decreases the bacterial load by removing harmful exudate, which likely contains elevated levels of proteases, cytokines, and neutrophils that interfere with wound healing.² As exudate and debris are removed, the intrinsic tension in the extracellular space is decreased, leading to the proliferation of cells and increased blood flow and perfusion to the tissue.⁵ Edema is thought to be decreased with negative pressure by reducing the burden on the lymphatic system in addition to promoting lymphatic drainage.³ These overall effects promote angiogenesis and wound contraction.²

A Closer Look at the NPWT Products Available for Today’s Clinician

Since the development of NPWT in the 1990s, the advancements in this technology have resulted in a treatment that can be used in the outpatient setting on a multitude of wounds ranging from postoperative incisions to wounds that are completely necrotic. Additionally, the outpatient clinician has the ability to adjust the settings on the machine, review the machine history, and choose the type of wound interface and drape that secures the dressing.

After a good seal is established on the wound in the clinic, there is always a risk of the patient experiencing a leak or loss of suction in between appointments; certain machines have the capability of sending out an alert to their manufacturer that will trigger a follow up call to try to troubleshoot the issue. This ensures that therapy is not interrupted for extended periods of time and can also help the patient avoid a needless trip to the emergency room. Adjusting the PSI and/or the duration of suction for intermittent settings affects the stimulation of the wound bed.

There is a variety of interfaces available to modify topical therapy for the patient’s specific needs, which includes an array of foams. Aside from the hydrophobic black polyurethane foam, there is a hydrophilic, dense white foam with a higher tensile strength. This is appropriate to use in tunnels and undermining and is safe to use on grafts to promote adherence. Some foams have a silver antimicrobial component so they can remain in place for longer if needed. Other foams have bigger reticulations that affect the amount of strain on the wound surface. Although not available in the outpatient setting yet, some foams have less hydrophobic properties, which allow for better absorption and an even distribution of instillation fluid, which is beneficial for clearing highly necrotic wounds. Foams are available in many different sizes and shapes; some are precut or spiraled, and others have premade track pads.

There are many choices of drapes available to protect the periwound and secure the dressing. A silicone acrylic adhesive drape takes into account sensitive skin and allows for a less traumatic removal. There is a drape available that has higher moisture vapor permeability to decrease skin moisture. Incisional dressings typically have an interface already built into the drape so it can be easily placed.

The outpatient clinician also has a variety of machines to choose from depending on the length of treatment or patient comfort. If a short duration is all that is needed, there are machines that are single use and completely disposable after 7 or 30 days of use. For the patient who will require longer therapy, a rechargeable battery-operated unit is more appropriate. Many companies are also developing machines that are smaller, quieter, and lighter for patient discretion and carrying comfort. User interface is also becoming easier with touch screens or one-button functionality.

Case Study

This is a 47-year-old patient status post-open heart transplant whose right groin was cannulated for the bypass then later for continuous renal replacement therapy (CRRT). Postoperative recovery was complicated by the development of a right groin seroma associated with mass effect and compression on femoral vessels, which led to isolated right lower extremity edema. The patient eventually required debridement of the right groin seroma, and a V.A.C. (KCI, an Acelity company) was placed on June 6 in the operating room. The wound at that time measured 4.4 cm x 3.5 cm x 2.2 cm = 33.88cm³.

Care was first established at the outpatient wound center on June 14. The wound at that time measured 3 cm x 4.4 cm x 3.7cm = 48.84 cm³. White foam was placed to the base of the wound due to the proximity of the femoral vein, the remainder of the wound was filled with black foam, and the seal was obtained at -125 mmHg continuous suction. The patient showed great improvement in granulation tissue at each appointment despite his immunosuppressed status. As the depth filled in, only black foam was used to fill the defect so as to continue to stimulate as much granulation as possible. By July 23, the wound had significantly contracted and was granulated close to skin level. The patient then transitioned to topical dressings.

This case is a great representation of how NPWT facilitates robust granulation in a patient where healing would be especially slow due to his immunosuppressed status.

Looking Forward

The future development of NPWT technology should include incorporation of the dwell and instill feature, which is only available during the inpatient setting at this time. The benefit to this therapy is that removal of harmful debris and exudate can be achieved on a patient who has a highly necrotic wound but is not a surgical candidate. Having this available as an outpatient treatment would potentially lessen the length of hospital stay because the therapy could follow patients into the home setting.

Surveillance of infection is always done at each visit but is sometimes difficult to discern with just the patient’s presentation. Therefore, a foam that could change colors if a higher bacterial load was present, like a litmus test, would be helpful for earlier detection.

Losing the therapy seal is a constant threat. Developing a spray that patients could use at home to plug any breaks would be an easy way of reestablishing the seal until they could come into the clinic. For skin folds where obtaining and keeping a seal is troublesome, a malleable silicone strip or something of the like could be used to fill in the gap and would be easier to remove than stoma paste.

Remote monitoring could be taken one step further to somehow measure the amount of contraction of the wound and send that report to the clinic for better tracking.

Conclusion

The benefits of healing patients faster with NPWT increase as this technology continues to evolve; this allows the clinician to develop a truly tailored care plan in the outpatient setting. The success of this modality will continue to spur the development of novel devices to meet the needs of each patient.

Stephanie Georgoudiou, MSN, APRN, AGPCNP-BC, CWCN, is a nurse practitioner in the Department of Physical Medicine and Rehabilitation at the University of Texas Southwestern Medical Center in Dallas.

Paul Kim, DPM, MS, is the Medical Director in the Department of Plastic Surgery, Department of Orthopedic Surgery at the University of Texas Southwestern in Dallas.

1. Sinha K, Chauhan VD, Maheshwari R, et al. Vacuum assisted closure therapy versus standard wound therapy for open musculoskeletal injuries. Adv Orthoped. 2013;245940.
2. Kim PJ, Applewhite A, Dardano AN, et al. Use of a novel foam dressing with negative pressure wound therapy and instillation: recommendations and clinical experience. Wounds. 2018;30(3 suppl):S1-S17.
3. Panayi AC, Leavitt T, Orgill DP. Evidence based review of negative pressure wound therapy. World J Dermatol. 2017;6(1):1-16.
4. Goss S, Schwartz J, Facchin F, et al. Negative pressure wound therapy with instillation (NPWTi) better reduces post-debridement bioburden in chronically infected lower extremity wounds than NPWT alone. J Am Coll Clin Wound Spec. 2012; 4(4):74-80.
5. Meloni M, Izzo V, Vainieri E, et al. Management of negative pressure wound therapy in the treatment of diabetic foot ulcers. World J Orthoped. 2018;6(4):387-393.