INTRODUCTION:

There are a wide variety of dressing techniques and materials available for management of both acute wounds and chronic non-healing wounds. The primary objective in both the cases is to achieve a healed closed wound. However, in a chronic wound the dressing may be required for preparing the wound bed for further operative procedures such as skin grafting. An ideal dressing material should not only accelerate wound healing but also reduce loss of protein, electrolytes and fluid from the wound, and help to minimize pain and infection.

What is Negative pressure wound therapy (NPWT)?

Negative pressure wound therapy also called vacuum therapy, Vacuum assisted closure, vacuum sealing or topical negative pressure therapy is a sophisticated development of a standard surgical procedure, the use of vacuum assisted drainage to remove blood or serous fluid from a wound or operation site.

In essence the technique is very simple. A piece of foam with an open-cell structure is introduced into the wound and a wound drain with lateral perforations is laid on top of it. The entire area is then covered with a transparent adhesive membrane, which is firmly secured to the healthy skin around the wound margin. When the exposed end of the drain tube is connected to a vacuum source, fluid is drawn from the wound through the foam into a reservoir for subsequent disposal.¹

The plastic membrane prevents the entry of air and allows a partial vacuum to form within the wound, reducing its volume and facilitating the removal of fluid. The foam ensures that the entire surface area of the wound is uniformly exposed to this negative pressure effect, prevents occlusion of the perforations in the drain by contact with the base or edges of the wound, and eliminates the theoretical possibility of localised areas of high pressure and resultant tissue necrosis.²

Indications and contraindications

The principal indications for the use of NPWT: ³

· Acute and traumatic wounds

· Sub acute wounds (i.e. dehisced incisions)

· Pressure ulcers

· Chronic open wounds

(stasis ulcers and diabetic ulcers)

· Meshed grafts

· Flaps

· Venous stasis ulcers

· Lower extremity diabetic ulcers

· Pressure ulcers

· Lower extremity flaps

· Dehisced incisions

· Grafts

Contraindications include:

· Fistulas to organs or body cavities

· Necrotic tissue in eschar

· Osteomyelitis (untreated)

· Malignancy in the wound

Mechanism of action of negative pressure wound therapy

1. Mechanical stress on the wound bed:

In NPWT mechanical stimulation of cells leads to cell proliferation and levels of granulation tissue. Application of mechanical force to wounds induces tissue deformation at the level of individual cells, leading to cell stretch, therefore providing a powerful mechanism for inducing cell proliferation and angiogenesis.

2. Enhanced blood perfusion:

Optimal blood perfusion is necessary to deliver oxygen, nutrients, blood cells and growth factors to a wound and in order to remove waste products such as carbon dioxide. NPWT enhances blood perfusion to a wound.

3. Oedema and wound exudate is reduced

Wound oedema and exudate occur as a consequence of the inflammatory response, and are enhanced in the inflammation stage of healing of which chronic wounds are stuck in this stage. NPWT helps to reduce oedema and get the wound out of the inflammation stage of wound healing.

4. Wound fluid composition is altered

In chronic wounds proteolytic activity is elevated and this is central in the difference between acute and chronic wounds. NPWT treated wounds indicating that NPWT helps reduce proteolytic enzyme activity.

5. Reduced bacterial burden

Bacterial burden in chronic wounds has also been shown to be reduced by the suction action of NPWT.

6. Cost effectiveness and quality of life

Two areas where NPWT has been evaluated and explains why it is used in practice are its cost effectiveness and its effect on quality of life. NPWT is an expensive therapy, cost savings were made in terms of the accelerated healing times in patients treated with NPWT and in reduced frequency of dressing changes needed. Wounds treated with NPWT healed 2.5 times faster than conventional dressings.⁵

Patient assessment for NPWT⁵

Action	Rationale
Carry out an holistic assessment of the patient which will include:
a) Wound aetiology and position of the wound	a) NPWT is contraindicated in certain wound types. The underlying cause of the wound and any complications must be established to enable assessment of the appropriate application. The position of the wound may also prevent NPWT being applied effectively
b) Nutritional assessment	b) Adequate nutrition plays a fundamental role in the process of wound repair and contributes significantly to the formation of white blood cells, antibodies, fibroblasts and collagen. Haemoglobin and serum albumin levels should also have been checked to ensure nutritional support is adequate for wound healing.
c) Pain	c) NPWT can cause discomfort and pain. Analgesia may be required prior to dressing changes.
d) Level of pressure ulcer risk	d) If NPWT is applied to a wound, the patient may be required to be nursed in bed. Appropriate preventative measures will need to be taken such as a pressure ulcer risk assessment.
e) Peri-wound assessment	e) There needs to be at least a 2cm border of unbroken skin surrounding the wound. A complete seal with the film drape is required for the vacuum to be created.
f) Assessment of Quality of life and issues of diversity	f) Patients may become anxious about starting the therapy. Agreement and concordance with the therapy is essential for it to be therapeutically effective. The provision of information is known to reduce anxiety and will help patients to understand the therapy prior to giving consent. If a patient has a NPWT device attached to their wound and are having to carrying the pump around, this can affect the patient’s quality of life. Patients may not comply with the treatment if it affects their quality of life and this may have an impact on the effectiveness of the therapy. Such a situation should not be a reason for denying this treatment unless the situation is contributing to possible risks or harm.
g) Mobilisation	g) The ability of a patient to mobilise with a NPWT device should be assessed. Mobilising with such a device may increase the risk of a fall.

Procedure of NPWT⁴

Step 1

The foam dressing is cut to the approximate size of the wound with scissors (Figure1) and placed gently into position (Figure 2).

Figure 1 Figure 2

Step 2

The perforated drain tube is then located on top of the foam and a second piece of foam placed over the top (Figure3). For shallower wounds, a single piece of foam may be used and the drainage tube is inserted inside it.

Figure 3

Step 3

The foam, together with the first few inches of the drainage tube and the surrounding area of healthy skin, is then covered with the adhesive transparent membrane supplied (Figure 4). At this stage it is important to ensure that the membrane forms a good seal both with the skin and the drainage tube.

Figure 4

Step 4

The distal end of the drain is connected to the VAC unit, (Figure 5) which is programmed to produce the required level of pressure.

Figure 5

Step 5

Once the vacuum is switched on, the air is sucked out of the foam causing it to collapse inwards drawing the edges of the wound in with it (Figure 6).

Figure 6

Step 6

Fluid within the wound is taken up by the foam and transported into the disposable container within the main vacuum unit.

The removal of NPWT⁵

Actions	Rationale
1.The NPWT device should be switched off 15 – 30 minutes before removal of the foam	To reduce the risk of the dressing adhering to the wound bed and to minimise patient discomfort
2. Raise the tube connector above the level of the pump unit and drain exudate into the canister.	To ensure there is no fluid which could leak at the disconnection site.
3 Clamp off both sections of tubing	To prevent fluid from leaking out
4 Wash hands and apply apron and non-sterile gloves in accordance with Infection Control procedures.	To reduce the risk of cross infection
5 Disconnect the dressing tubing from the suction tubing.	To separate the dressing from the NPWT device.
6 If the suction bottle is either two thirds full or has been in use for seven days it will need to be changed. If the same suction is to continue being used, ensure the connector end is covered with sterile gauze or a sterile field whilst disconnected.	The suction is a sealed unit that contains a solidifying agent. It should be changed regularly to prevent infection or overfilling of the canister. Changes in the exudate colour and the amount of exudate should be recorded.
7 Gently stretch the occlusive film horizontally and slowly pull away from the skin. Do not peel back.	To break the film adhesive whilst minimising trauma to the patient
8 Gently remove the foam or gauze from the wound using saline to assist removal if necessary.	To minimise trauma to the wound tissue when removing the dressing.
9 Check the number of gauze and foam pieces removed from the wound is the same as the number that were originally placed in the wound.	To ensure all the dressing is removed as if retained will cause failure to heal and may require surgical removal.
10 All the NPWT consumables (tubing, suction and dressings) are all disposable items that when removed should be discarded in an orange infectious clinical waste bag	To reduce the risk of infection
11 Remove apron and gloves. Discard them. A clean apron and gloves should be applied and hands washed between removing the old dressing and applying a new one to the patient.	To reduce the risk of infection and to prevent contamination of the wound.

NPWT settings⁵

Type of Wound Target	Initial Cycle	Subsequent Cycle	Target Pressure Black Foam (PU)	Pressure White Foam (PVA)	Dressing Change Interval
Acute/ Traumatic Wounds	Continuous for first 48 hours	Intermittent 5 minutes on, 2 minutes off for rest of therapy	125 mmHg	125 – 175 mmHg Titrate pressure up 25 mmHg for wounds with high exudate	Every 48 hours Every 12-24 hours with infected wounds
Surgical Wound Dehiscence	Continuous for duration of therapy	-	125 mmHg	125 – 175 mmHg Titrate pressure up 25 mmHg for wounds with high exudate	Every 48 hours Every 12-24 hours with infected wounds
Pressure Ulcers Every 48 hours	Continuous for first 48 hours	Intermittent 5 minutes on, 2 minutes off for rest of therapy	125 mmHg	125 – 175 mmHg Titrate pressure up 25 mmHg for wounds with high exudate	Every 12-24 hours with infection
Meshed Grafts and Bioengineered Tissues	Continuous for duration of therapy 75 – 125 mmHg	Graft requires covering with wide meshed non-adherent dressing if black foam issued	125mmHg	Titrate pressure up 25 mmHg for wounds with high exudate	Remove dressing after 4-5 days when using either foam
Chronic Ulcers, i.e. Leg Ulcers	Continuous for first 48 hours	Intermittent 5 minutes on, 2 minutes off for rest of therapy	50 – 125 mmHg	125 – 175 mmHg Titrate up 25 mmHg for wounds with high exudate	Every 48 hours Every 12-24 hours with infected wounds
Flaps	Continuous for duration of therapy	-	125 – 150 mmHg	125 – 175 mmHg Titrate up 25 mmHg for wounds with high exudate	Fresh flaps = 72 hrs If there are complications every 48 hours. Every 12-24 hours with infection

Benefits of NPWT:

· earlier hospital discharge

· fewer wound dressing changes

· less need for surgery

· savings in nursing costs

· enable transfer from hospital to lower-cost health care setting

· improved quality of life

Disadvantages of NPWT:

· need to be hooked up to the unit for at least 22 hours a day

· initial pain, due to the application of negative pressure

· Negative-pressure wound therapy is not always effective and a non-healing wound may require other, potentially more invasive treatment.

Potential complications of NPWT:

Rarely, complications may occur which may require discontinuation of negative-pressure wound therapy.³These may include:

· pressure necrosis (tissue death) from the tubing

· injury to skin around the wound

· growth of granulation tissue into the foam dressing

· increased pain initially, due to reduced pressure as the foam collapses

· contact dermatitis due to the adhesive transparent tape

· fistula (tunnel) formation

· Development of skin cancer as a result of increased blood flow in the wound bed (very rare).

· Negative-pressure wound therapy may need to be stopped if the patient experiences:

· intolerance or non-adherence to the treatment

· lack of healing

· frank pus in the dressing or canister

· Uncontrolled bleeding or blood clot under the dressing.

CONCLUSION:

Dressings have advanced to such an extent that they now actively promote wound healing while maintaining a moist wound environment . One of the advances in wound care include negative pressure wound therapy (NPWT), which is clinically proven to promote active wound healing at the cellular level through negative pressure. Negative pressure wound care (NPWC) has been known to have the potential to promote wound healing, alleviate concerns such as increasing exudate and odor, and improve quality of life for patients.

REFERENCES:

1. Argenta, L.C., Morykwas, M.J. Vacuum assisted closure: a new method for wound control and treatment. Clinical experience. Annals of Plastic Surgery. 1997,38(6): 563-7

2. Hunter, J.E., Teot, L., Horch, R. and Banwell, P.E. Evidence-based medicine: vacuum-assisted closure in wound care management. International Wound Journal 2007,4(3): pp. 256-269.

3. Hunter, J.E., Teot, L., Horch, R. and Banwell, P.E. Evidence-based medicine: vacuum-assisted closure in wound care management. International Wound Journal 2007, 4(3): pp. 256-269.

4. Steve Thomas. An introduction to the use of vacuum assisted closure, Worldwide wounds:May 2001: Available from, http://www.worldwidewounds.com/2001/may/Thomas/Vacuum-Assisted-Closure.html

5. Guideline for Procedure for the use of Negative Pressure Wound Therapy (NPWT). Available from:file:///C:/Users/user/Downloads/Negative_Pressure_Wound_Therapy_(NPWT)%20(1).pdf

Received on 19.12.2017 Modified on 11.01.2018

Asian J. Nursing Education and Research. 2018; 8(3):447-450.

DOI: 10.5958/2349-2996.2018.00091.5