Negative Pressure Wound Therapy: What Is It And How It Works

Negative pressure wound therapy (NPWT) is a tool that helps to heal different types of wounds, including infected, chronic, open, or closed surgical wounds, and many others that are discussed in this article, by creating negative pressure on the wound site. NPWT with the instillation of medications works better than traditional NPWT.

NPWT application on the wound

Before the NPWT apparatus is applied, the wound is covered with open-cell foam or gauze dressing. Then it is sealed with an occlusive drape. The suction tube is fixed to the wound dressing, and the vacuum pump sucks all liquids and bacteria into the liquid waste collector.

The pressure can range from -50 mm Hg to -125 mm Hg; the pressure used depends on the individual situation. Most commonly, -125 mm Hg of pressure is used, and the dressing is left for 48 to 72 hours. If the wound is infected, the dressing period is shorter, ranging from 12 to 24 hours. The pressure helps to close the edges of the wound and eliminates the excess wound liquids.

The therapy can be used until the wound is closed, or in some cases when surgical closure will be performed to prepare the wound for closure.

Types of NPWT

There are a few types of NPWT:

• NPWT. This is a traditional method when only pressure is applied to the wound intermittently or constantly.
• NPWT with instillation and dwell time. This type of therapy is advanced because there is an opportunity to instill antibiotics, saline, or antiseptics and prevent the growth of bacteria. During this therapy, there is a time when a topical solution can dwell and after that time it is removed by NPWT technology.

NPWT with instillation has many advantages when compared with traditional NPWT.

• Effectiveness. More effective management for trunk and extremity wounds.
• Complicated wounds. Better treatment options for complex wounds, for example, invasive osteomyelitis of the proximal femur and complex spine wounds.
• Infection. Superior treatment for open-infected wounds or chronic wounds.

How does NPWT work?

The processes and stages that are responsible for wound healing are a natural process without any disturbances. However, if the wound cannot heal in the proper way or it takes a long time, then NPWT can help. So, how NPWT can help?

A systematic review of the application of NPWT showed that it is not fully understood how NPWT helps to heal wounds. Here I will explain a few possible ways how the intervention of NPWT works from the scientific point of view.

The first suggestion for wound healing, when NPWT is applied, is that therapy increases local blood flow and the production of granulation tissue. As we know, when the wound is not properly surrounded by oxygen because of many valid reasons (diabetes, obesity, stress, and other factors) the wound cannot heal and the chronic wound processes start. NPWT can help in this situation because the pressure increases blood flow, which brings oxygen to the wound.

Moreover, tightly covered wounds have less opportunity for bacteria multiplication, exudation, and edema.

Another possible mechanism that was found during research with animal models, is that NPWT increases fibrocytes, which contribute to tissue fibrosis by producing collagen and increasing vascular endothelial growth.

The science does not fully understand the healing mechanism when the NPWT is applied but with one thing it agrees is that NPWT therapy helps.

However, it is important to mention that there are several reports that NPWT caused negative and severe events, such as pain, bleeding, secondary wound formation, anxiety, and necrotizing fasciitis.

What kind of wounds NPWT can help?

There is a wide range of wounds that negative pressure wound therapy is recommended, for example:

NPWT is recommended to prevent complications in the surgical area or to heal chronic or infected wounds. The studies show very good outcomes in wound healing when there are pressure ulcers, chronic diabetes, or arterial and venous ulcers.

Contraindications for NPWT

As with all treatments, this therapy also has contraindications for some wounds or medical conditions:

Furthermore, there are some cautions and medical doctors must evaluate such conditions, exposed nerve or vascular structure (heart or large blood vessels), this can cause massive blood loss because of the erosion.

In addition to medical contraindications, there are also others that are more associated with the patient and their senses. When NPWT is applied, the skin can be irritated, the patient can feel pain, and a bad smell can appear. The pain can be reduced by reducing pressure and skin irritation can be mitigated by topical creams or ointments.

To sum up, negative pressure wound therapy is a way for difficult and chronic wounds that can help to heal faster, especially when NPWT with instillation can be applied. NPWT can be applied for many wounds because of the adaptive pressure and period of storage on the wound that depends on the wound's degree of complexity.