NPWT Tools - an overview
Although NPWT treatment was developed in the 60s, it wasn't until the turn of the century that it was widely commercially available. When we started using NPWT, only a few pump models were available, and the choice of products was very clear. A lot has happened since then. If we look at all the products available for NPWT treatment today, the options are downright confusing. Several "pirate-copy" products have also appeared on the Asian market in the past years.
All these pump models have in common that their job is to achieve suction. The pumps are built into fancy-looking exteriors, and the better models have gotten touch screens with comprehensive menus. However, no matter how fancy the pump looks- its primary function is to supply a suction of around 100 mmHg. The only pumps that really stick out from the crowd are the ones that can provide irrigation of the wound simultaneously as providing suction. Currently, only a few pumps have this capability.
This chapter will look at the pump models from some of the biggest manufacturers globally. You can choose between tiny pumps for more minor wounds, medium-sized pumps for larger wounds, and very big pumps for complicated cases. Most pumps have integrated batteries that can be charged, and the average battery time for most models is around 6 hours before a recharge is needed. Some simple pumps achieve suction with a spring- or bellow operated system- these are far cheaper.
Figure 1 An overview of some of the medium-sized pumps available today. Some of the models are not produced anymore but may be available at sites like ebay. Most producers continue selling dressings for their pumps even though some pump models no longer are produced.
Figure 2 An overview of small NPWT pumps available. The tiniest pumps do not have a container to collect the wound exudate - here, the dressing itself absorbs the exudate. Accordingly, if there is a lot of exudate, this type of NPWT may not be suitable. While small NPWT pumps are very user friendly for the caregiver and the patient, this does not necessarily mean that they are easy to use in all situations. The small pumps are often less forgiving in terms of tolerating some leakage.
Figure 3: Several NPWT pumps are available that do not need electricity or batteries. The models shown in the first row, rely on a spring mechanism to achieve suction. The model in the bottm-left is a large bellow. When the air is pressed out of it, it will generate an adequate suction for NPWT. Although these pumps are usually a lot cheaper than battery driven models, they are still quite expensive and not readily available in Africa. However, the bellow model has been designed for low-resource healthcare systems and is quite affordable. We have written a sepearte chapter on work-around solutions when you do not have access to commercially made pumps.
Which pump should you use?
If the acquisition of commercial NPWT pumps is entirely out of your reach, take a look at our chapter on DIY solutions for NPWT.
In many Western countries' public health care systems, the acquisition of such products goes via tender. Manufacturers present their products and the consumer ( healthcare facility) decides which one to buy according to product properties and price. This is the procedure at our workplace as well. Every 4 years ( when a new tender takes place) we may have a new supplier of pumps. In other words, sometimes you cannot choose which models you would like to use because this is decided for you by someone else.
Your choice of pump depends on a long list of factors:
Price: for many caregivers, the cost of the pumps is the most important factor. That is understandable because these pumps are costly. There are quite considerable price differences between models. Do some thorough research before you buy one or several pumps. Can you buy a used pump from, for example, eBay? If the patient has to pay for the entire treatment- what can the patient afford?
Do not only look at the price of the pump. The price of the dressing kits is usually much more relevant. Be aware that many producers lease out their pumps ( sometimes at no cost) but charge a little extra for the dressing kits.
If you can lease medium-sized pumps " for free," this may be the most economical choice. We wrote "for free" with apostrophes because, in reality, nothing is for free. When you lease pumps without paying for the pumps themselves, you will pay for them by buying the dressing kits from the same supplier. Many caregivers buy the small pumps, assuming they are cheaper alternatives. That is not necessarily the case. If you lease the larger pumps and can buy dressing kits at a sensible price, this is usually the more economical alternative. Having medium-sized pumps also means that you can handle more challenging wounds. The bigger pumps are also more forgiving in terms of handling small leaks.
What are you going to use the pump for? Which type of wounds are you going to treat? Do you usually treat smaller wounds, or do you work at a trauma facility where you see large and complicated wounds that will benefit from NPWT with irrigation?
Are you looking for a pump you can send home with the patient? Or will the pump remain in the clinic to treat patients admitted to the ward?
2. The versatility of the pump system. Be aware that most manufacturers have designed their pumps such that only their canisters ( for exudate collection) and only their tubes will fit the pumps. In other words, in most cases, you will have to buy single-use dressings, tubes, and canisters from the same manufacturer. These single-use kits are usually quite expensive. Some pump models can be more easily adapted so you can improvise with " home-made" dressing kits and exudate collectors.
3. Service: If you have the financial resources to purchase a pump from a supplier in Africa, this is the preferred choice. If you buy or lease a pump from one of the leading producers ( KCI/Acelity, Smith & Nephew, Mölnlycke, or Convatec), they will ensure that you get some training they will provide follow-up and service of the pumps. The pumps have internal filters that need to be serviced at regular intervals. Ideally, it would be best if you used the supplier that is closest to you.
5. How many pumps will you need? This depends, of course, on how intensively you are planning on using NPWT. As a reference- our wound care clinic serves a population of about 50.000 people. We have five medium/large pumps available, and we always have at least ten mini-pumps in storage.
In the following section, we will briefly look at the leading suppliers of NPWT in Europe.
Smith & Nephew
KCI Acelity / 3M
KCI Acelity is the manufacturer that has the longest experience with NPWT. KCI was the first company globally to commercialize negative pressure wound treatment under the patented name V.A.C.®. KCI. Acelity has the widest choice of NPWT products available. Their latest generation of pumps is highly advanced and the flagship models can irrigate the wound during the vacuum therapy, thus keeping bacterial numbers low. This technology is called V.A.C. Veraflo ( previously called VAC Instill).
KCI. Acelity has a wide assortment of foams available; they come with and without silver coatings. They also have a preformed foam designed for complex hand wounds.
In 2016 KCI Acelity bought the rights to two types of mini pumps that do not require electricity or batteries. The company thus has a portfolio of NPWT equipment that ranges from the most advanced to more simple models.
In 2019 3M acquired Acelity and its KCI subsidiaries for approximately 6,7 billion US Dollars, showing the importance of these wound care products on the market today.
It is still possible to buy dressing kits, and canisters for the early models sold almost 20 years ago. This is a very positive aspect showing that these pumps were made to last.
Figure 4 KCI Acelity ( now 3M) has the most extensive portfolio of NPWT-related products. They now have eight different pumps in their portfolio including the mechanical pumps which do not require electricity to be operated. They provide a wide range of foams, adapters and tubes and are a good choice if you can afford these products. The biggest pump- the VAC Veraflo has the ability to irrigate the wound during vacuum therapy.
Smith & Nephew
Following the success of KCI's introduction of the VAC system, Smith & Nephew took up the competition and developed their own NPWT pumps. Their portfolio is more straightforward and consists of the Renasys models and the small PICO models. The image below also includes two older models ( renasys EZ Plus and Renasys Go), which are no longer sold in Europe. However, we mention them since many of these pumps are still functional, and some have been taken into use in Africa. On Smith & Nephews website, they are still shown, and it is still possible to buy canisters and dressing kits for these.
Smith & Nephew now offers the Renasys Touch pump in their newest assortment. This is a medium-sized pump, and as the name implies, it has a touch screen.
While KCI exclusively recommends foam as a contact medium in the wound, Smith & Nephew offers two types of dressings. One is a gauze impregnated with PHMB ( an antibacterial agent), and the other is foam. There are situations, for example, in a very irregular wound bed, where a gauze medium is a more suitable dressing for NPWT.
Smith & Nephew has had enormous success with the tiny pump sold under the name PICO. The first model was the PICO 1.6 and was sold from 2011 onwards. In 2019 this was upgraded, and the PICO pump was sold in three variations: PICO 7, PICO 14, and PICO 7Y. The latter model allows two wounds from the same patient to connect using a Y-adapter. PICO7 and PICO14 refer to that the pump lasts either 7 or 14 days. These pumps are programmed to expire after that period and cannot be used further. These are "single-use negative pressure wound therapy" devices, also termed -sNPWT. It is debatable whether these single-use NPWT devices are optimal from an environmental view. We generate quite a lot of electronic waste from such products at our clinic.
The PICO pumps do not have a canister to collect wound exudate. The dressings themselves are designed such that all the exudate collects in them. The dressings are very easy to apply and they come in many sizes and shapes.
Figure 5 The current NPWT pump assortment from Smith & Nephew are the Renasys Touch, PICO7, PICO14, and PICO7Y. The latter model allows two wounds from the same patient to connect to one pump using a Y-adapter. The earlier models were Renasys EZ+ (the largest pump on the image above)), Renasys GO (medium sized pump) and the PICO 1.6 ® (mini pump). Smith & Nephew has both foam- and gauze-based dressings. In addition, Smith & Nephew has an interesting assortment of different drain tubes that can be used in wounds with channels or fistulas.
Figure 6 Smith & Nephew has a wide assortment of dressings for their PICO pumps. In addition, they provide so-called multi-site dressings which have a special shape making them easy to place in anatomical areas like front of the neck, shoulder, knee and armpits. The shape of the mulit-site dressings also allows for a better range of motion.
In recent years Mölnlycke has joined the NPWT market. They have only two choices of pumps, taking some of the confusion out of the wide choice some other companies offer. Their medium pump is called Avance, and the smaller version is named Avance Solo. Their NPWT dressings are foam-based. The foam Mölnlycke uses is green in color but is the same type of foam compared to the other producers.
These pumps are simple to use, and with a very clear portfolio, it may seem less daunting to start with NPWT Mölnlycke has an interesting sealing agent - Mepiseal. This is a silcone-based sealing paste that can be used around the dressing in areas with skin folds, to achieve a better seal.
Figure 7 Mölnlycke`s NPWT system consists of the Avance ( medium-sized pump) and the Avance Solo ( smaller version). Mölnlycke uses a green foam as dressing, but despite the characteristic color, it is a regular polyurethane foam like those of other producers. Below: Mepiseal is a silicone-based paste that is useful to fill skin folds to achieve a good seal, especially in difficult areas like perianal, inguinal, between toes, or under armpits.
Convatec only has one pump on the market, sold under the name Avelle. It is a tiny pump that is quite similar in size to Smith & Nephew`s PICO pumps. There are two major differences however. Firstly, the dressing technology differs from all the other NPWT dressings. Convatec uses their patented hydrofiber technology in these dressings. These hydrofiber dressings have excellent absorption properties ( vertical absorption) keeping the peri-wound areas nice and dry. The other difference is that the pump lasts for 30 days. These two differences makes this small pump a worthy competitor to other smaller pumps.
Figure 8 Convatec`s mini-pump Avelle can be used for 30 days. Like other mini-pumps, it has no canister for exudate collection and instead relies on the exudate to be collected in the dressing. Convatec`s dressings rely on their patented Hydrofiber technology, performing well under NPWT.
Which type of dressing medium should you use? Gauze or foam? Black foam or white foam?
The negative pressure principle will only work in wounds when the wound surface is in contact with a gauze, foam, or other dressing. We call this material the medium. You cannot simply place a sheet of plastic over a wound and connect this to a suction pump- this will lead to a disaster.
If you use a mini NPWT pump like the PICO or Avelle pump, the kit includes a dressing with a tube already connected to this, which leads directly to the pump. If the wound is not too deep ( < 1cm), this is all you will need, and you do not have to worry about choices like gauze or foam. However, even with the smaller pumps- if the wound is deeper ( > 1 cm), you will need some type of filler to fill the cavity. In that case, you will be faced with the choice between gauze and foam, after all.
When using larger pumps, we always have to choose which type of medium we will fill the wound with. Some producers only have one kind of medium - for example, only foam available. However, it is essential to know that you cannot use regular foam in all situations. If you have exposed tendon or bone, you will have to use gauze or white foam or protect these tissues with a contact layer like a perforated silicone netting.
You can use regular cotton gauze as a medium for NPWT. This will work very well as long as you monitor the treatment closely and make sure that the pump is functioning well at all times during the treatment. If the pump stops working for some hours, there is a danger of bacteria thriving too well under the warm, moist, and occlusive NPWT dressing, and this can cause severe infection. For that reason, gauze with antibacterial properties is advisable. Kerlix AMD is a gauze impregnated with PHMB and is commonly used worldwide as a medium with NPWT. However, antibacterial gauze is not a guarantee against infection if a pump malfunctions or a tube is blocked! And you can certainly not use it in infected wounds!
While gauze works well as an NPWT medium, foam seems to lead to slightly faster granulation in most cases. There are three types of foams available. White foam is a more gentle medium. It has finer pores and is pre-moistened with sterile saline. White foam is used when applying NPWT over sensitive structures like exposed tendons or exposed bone to prevent the drying out of these structures. You should never apply black foam directly over these sensitive tissues. If you do not have white foam available, you can protect tendons and bone with barrier netting- for example, a perforated silicone netting. White foam is also much stronger than black foam- it does not tear easily. We had several accidents with black foam when we placed this in tunnels or deeper cavities. Black foam sometimes adheres firmly to the wound bed over a few days. We have had trouble retrieving bits of torn black foam from such wound areas. Consequently, we only use white foam in tunnels and deeper cavities.
Black foam ( or green foam) is the most used medium worldwide. When used correctly, it provides superior granulation tissue formation. It is available with and without antibacterial properties. As with gauze, you cannot use regular or antibacterial black foam in infected wounds! We sometimes choose a silver impregnated black foam if we have a clean wound but want to extend the dressing change intervals. Maybe the patient lives far away and cannot come to our clinic several times a week. With a silver impregnated foam, we can often extend the dressing changes to 7 days.
A special variant of the black foam is a new type of foam by KCI/3M ( Veraflo Cleanse foam). This is used in conjunction with the pump that can irrigate the wound regularly during the treatment. The foam has large perforations making it easier for superficial necrosis and fibrine to loosen from the wound bed.
Table 1 Characteristics and indications for the use of foams and gauze in NPWT
Figure 8 Commonly used mediums in NPWT.
Left: Kerlix from Kendall (Covidien) is the most common gauze used in NPWT. It is impregnated with PHMB and therefore has antibacterial properties.
Middle: White Foam has finer pores and comes pre-moistened with sterile saline water. It is commonly used over sensitive structures like exposed tendon or bone. It is made of very strong material and does not tear easily. Therefore, we prefer to use white foam in tunnels or cavities. This ensures that the foam does not tear when we retrieve it during dressing changes.
Right: Upper: KCI/3M V.A.C. Granufoam
Middle: Mölnlykke Foam
Below: V.A.C. Granufoam Silver (foam impregnated with silver to provide antibacterial properties)
Figure 9 The ultimate NPWT pump available today is the KCI/3M VAC Ulta pump. It can irrigate the wound with saline ( or an antibacterial rinse solution) at regular intervals. Commonly the rinsing solution is left in the wound for a few minutes to "dwell" in the wound bed. This type of NPWT technology is named NPWTi-d, where i stands for irrigation and d for dwell. You can use regular foam with this pump. However, the manufacturers have designed a new type of foam ( Verflo Cleanse foam) with large perforations. The perforated foam is placed at the bottom of the wound bed. The large perforations make it easier for superficial necrosis and fibrine to loosen from the wound bed.
Using tubes in channels or fistulas
It is essential to understand that wound exudate will accumulate in all areas of the wound bed which are not in contact with the NPWT medium, be it gauze or foam. This is a phenomenon we have called pooling. Pus can form in these areas with exudate collection, leading to infection.
When we have a long but narrow channel, we can often not place foam or gauze into this as it will not fit. In these situations, it can be helpful to use a perforated tube. This has to be perforated along the entire course of the tube. Smith & Nephew offers a variety of tubes for this purpose. It is also possible to treat fistulas by this method. However, it is vital to know where the fistula leads. It is contraindicated to use NPWT in fistulas where the origin of the fistula is unknown!
Figure 10 All cavities and channels have to be in contact with a medium ( foam or gauze) to prevent exudate pooling. If the wound has a deeper tract or tunnel, it is possible to place a perforated tube into the channel. The tube then leads to the foam or gauze, placed in the rest of the wound bed. Some manufacturers like Smith & Nephew provide different types of perforated tubes. It is possible to treat fistulas in this manner, but it is essential to know the origin of the fistula. It is contraindicated to use NPWT in fistulas where the source is unknown.
When do you need a contact layer netting?
A contact layer is usually a thin perforated material placed in the wound bed as a protective layer. Most modern contact layers are made of silicone to prevent them from adhering to the wound bed. Others are made of rayon ( a type of nylon) or vaseline-impregnated gauze.
When we place NPWT on a wound that contains areas of exposed tendon or bone, we have to protect these from drying out. Especially when we place foam directly on these structures, we may irreversibly damage them. In these situations, we may use the white foam as a barrier. If we do not have this available, we can use contact netting as protection.
Some contact layers have antibacterial properties. Some contain silver or are impregnated with iodine. This may be useful in situations where we extend the dressing change intervals.
Figure 11 Contact layer nettings can protect sensitive tissues like exposed tendons or bone when using NPWT. Most contact layer nettings are made of perforated silicone (left). Some contain silver ( middle) or iodine ( right) to provide antibacterial properties.