What is NPWT?
Terminology
Negative Pressure Wound Therapy (NPWT) has several names, including sub-atmospheric pressure device (SPD), topical negative pressure (TNP), vacuum-assisted closure (VAC), vacuum sealing technique (VST), and sealed surface wound suction (SSS). Note that the term VAC is a registered trademark for products from KCI Medical and should, strictly speaking, be reserved for those products. If we want to appear super knowledgeable, you should actually write it like this: VAC™.
In recent years, there has been a consensus on using the term NPWT, and it is this term that is primarily used in the literature. Throughout our website, we also use the term Negative Pressure Wound Therapy (NPWT).
You may occasionally encounter unfamiliar abbreviations, such as MPNPWT, which stands for mechanically powered negative pressure. That is when we use mechanically powered pumps (for example, by a spring mechanism) rather than an electric pump. Other common abbreviations include tNPWT (traditional NPWT, meaning regular pumps) instead of sNPWT (single-use disposable pumps). Are you slightly confused by these abbreviations? Don't worry; you're not alone.
As technology matured, new methods of using Negative Pressure Wound Therapy (NPWT) were developed. Sometimes NPWT is used on closed surgical wounds, specifically incisional NPWT, abbreviated as iNPWT. At other times, we use pumps that can irrigate the wound with saline or an antibacterial solution and allow the fluid to dwell there for several minutes - a combination of irrigation and dwell NPWT, abbreviated as NPWTid.
What is NPWT?
NPWT involves placing a medium, either gauze or foam, into a wound. This is then covered with a self-adhesive, occlusive plastic drape to create an airtight atmosphere. A tube is connected to this, which leads to a suction pump, thus creating a vacuum in the wound area.
Most pumps are designed to deliver a negative pressure of about minus 80-120 mmHg. This is quite an intense vacuum pressure. If you apply a blood pressure cuff to your arm and pump it up to 120 mmHg, you will appreciate the strength of this pressure, although with negative pressure wound therapy (NPWT), it is applied in the opposite direction.
The pump must be connected to the wound continuously. It is quite common to change dressings every third day; however, longer shift intervals may be acceptable in some cases. NPWT treatment often lasts for 2-3 weeks. ære koblet til hele tiden. Ofte skifter en bandasjen hver 3. dag. Behandlingen varer ofte i 2-3 uker.
Negative pressure wound therapy (NPWT) is generally used to promote granulation tissue formation in wounds. It is essential to understand that NPWT does not promote the migration of skin cells over the wound. Once a wound has filled nicely with granulation tissue, the NPWT is discontinued, and other treatment modalities are then used.
Despite the advent of numerous new techniques and technologies, negative pressure wound therapy (NPWT) remains a cornerstone of managing complex wounds. In our experience, no other modality in wound care treatment has the same potency to steer a wound in the right direction.

Figure 1 Once a wound has granulated as nicely as shown in the image above; there is no need to continue the NPWT treatment.
Wounds with little necrosis that show some signs of granulation tissue here and there often respond well to NPWT treatment. If there is exposed bone or exposed tendon in the wound bed, you will need some experience to use NPWT in these wounds. Tendons and bones do not respond well to NPWT treatment, and you can actually harm these structures if you are not careful. We will discuss these scenarios later on in the chapter.
When used incorrectly, NPWT can cause harm to the patient. One of the biggest dangers is turning off or disconnecting the suction pump for several hours. The airtight dressing, which an NPWT dressing is, will create a greenhouse-like environment for bacteria. Within a few hours, high concentrations of pathogenic bacteria can develop under the plastic film, and in some cases, this can cause severe infections and septicemia.
There are several contraindications associated with the use of Negative Pressure Wound Therapy (NPWT), and it is essential to be aware of these before initiating NPWT. We will discuss the indications and contraindications later in the chapter.
How does NPWT work?
When cells in the wound bed are subjected to a vacuum effect, they undergo mechanical deformation. The suction effect pulls on the cells, thus stimulating cell division. Under ideal conditions (i.e., a young patient and a clean wound), we sometimes see granulation tissue developing at 5-10 times the speed of natural tissue formation.
Studies show that negative pressure wound therapy (NPWT) stimulates the growth of new blood vessels in the wound bed, a process known as angiogenesis. The suction also removes exudate, keeping the wound cleaner in the process. Many strains of bacteria do not thrive well in a subatmospheric environment, and the bacterial burden is often lower when using NPWT.
Paradoxically, NPWT does not aid the epithelialization process. In the early years of NPWT, caregivers were not aware of this, and some patients used an NPWT pump for several months without achieving healing. Once the wound bed has filled with granulation tissue, you will actually delay healing if you continue with NPWT treatment. So the key to success is using NPWT in the right type of wound for the correct amount of time.
When the wound has filled with healthy granulation tissue, it is time to discontinue the negative pressure wound therapy (NPWT) and use an alternative treatment modality to encourage skin cells to migrate onto the granulation tissue. The exception to this rule is when a split-thickness skin graft is placed onto the granulated wound. Using NPWT for about 5-7 days over the skin graft will help the graft attach to the wound bed.
Video 1. This film by KCI/3M illustrates how the wound bed responds to the negative pressure. Copyright: 3M/KCI https://www.youtube.com/watch?v=4yPnWIrLKhg
Video 2: An interactive case-based discussion by HMP Education about different aspects of NPWT. This video is over an hour long, but it is worth watching, as it contains several valuable insights. Copyright: HMP Education https://www.youtube.com/watch?v=lPtU-rMg34w
Key principles of NPWT
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Before starting NPWT, you need a plan. What do you hope to achieve with the Negative Pressure Wound Therapy (NPWT) treatment? Do you want to " kick-start" a wound that seems to have stalled? Do you want to form granulation tissue as quickly as possible? Do you want NPWT to control the amount of exudate that comes from a wound?
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Before you embark on the NPWT, you will also need a solid plan for the logistics. How often do you plan to change the NPWT dressings, and who will perform the dressing changes? What should the patient do when a blockage or leakage alarm sounds while they are at home? Who will check the pump several times daily to ensure it is working correctly and that the pump's batteries are charged? Does the patient have access to electricity to charge the pump? If the dressing changes are to occur at your clinic, who will perform the NPWT treatments if you have a few days off work and are the only one with knowledge about NPWT?
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NPWT will only help to promote granulation tissue. It will not help skin cells to migrate over the wound!
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NPWT should not be used in wounds with much necrotic tissue, have a high bacterial burden, or are infected, smelly wounds, in cases with untreated osteomyelitis, close to major blood vessels, wounds with fistulas to internal organs, or malignant wounds.
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To make NPWT work, you have to place a medium into the wound; this can be a gauze material or a foam. You cannot simply put a plastic film over a wound and attach a tube to it, then apply suction. If you try that, it will likely end in disaster, most likely a severe infection.
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It is essential to understand that the medium (gauze or foam) is in direct contact with the entire wound cavity. If there are pockets where the medium is not in contact, exudate will not be sucked out of these pockets. This can lead to bacteria thriving in these areas and cause infection. This is a fundamental principle of NPWT. This is, for example, particularly important in deep ulcerations, such as extensive pressure ulcers. You need to be vigilant and ensure that the medium is in contact with the entire wound cavity to prevent infection.
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It is essential that the NPWT dressing is as airtight as possible. Some caregivers believe that a small leakage is insignificant, which is incorrect. When the dressing is 100% airtight, we see the best results, and there is usually less smell coming from the wound. We hypothesize that leakages give rise to a higher bacterial burden developing under the NPWT dressing. We also see more peri-wound skin maceration when the dressing is not entirely airtight.
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If an NPWT pump is switched off for several hours or is malfunctioning, this can lead to a severe infection, including septicemia. An NPWT dressing without active suction attached to it behaves like a greenhouse for bacteria. We have witnessed life-threatening septicemia in patients where a pump had been switched off for a whole day. Most producers, therefore, advise changing the entire dressing if the pump has been switched off for more than two to three hours.
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As technology advances, some negative pressure wound therapy (NPWT) pumps have become compact and user-friendly. However, be aware that the small pumps have limitations regarding the types of wounds for which they can be used. They are less forgiving regarding leaks and may be more challenging to apply to difficult anatomical areas, such as the groin area, for example.
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We consistently achieve the best results when using NPWT with simultaneous irrigation. This type of NPWT involves rinsing the wound bed with saline or antibacterial solutions at regular intervals. NPWT with irrigation enables us to use NPWT in wounds that are less clean or in wounds where we are concerned about infection. Pumps with this capability are significantly more expensive than standard NPWT pumps. We will discuss this technology later on in the chapter.
Video 3: HMP Education has provided us with several excellent webinars on NPWT. This video discusses some of the scientific evidence behind NPWT technology. This presentation is 60 minutes long. Copyright: HMP Education https://www.youtube.com/watch?v=eifwxbOZiZ8
Video 4: HMP Education has provided us with several excellent webinars on NPWT. While this video may be more useful for experienced NPWT users, it also contains some valuable insights for beginners. This presentation is about 58 minutes long. Copyright: HMP Education https://www.youtube.com/watch?v=ZpcECExJFGM