Negative Pressure Wound Therapy (Wound VAC)

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Introduction   

Negative pressure wound therapy (NPWT), also known as a wound vac, can be a powerful tool in combatting acute and chronic wounds. It relies on generating a negative pressure on the surface of a difficult wound to promote wound healing.

The goal of this course is to develop an understanding of mechanism of action of NPWT, discuss appropriate nursing assessment of these wounds, evaluate adjunct treatment options and troubleshooting support tips.

We will review basic concepts of the integumentary system and the normal wound healing process to support the rationale of NPWT.

Definition

Negative pressure wound therapy (NPWT) is the application of sub-atmospheric pressure to help reduce inflammatory exudate and promote granulation tissue in an effort to enhance wound healing (4). The idea of applying negative pressure therapy is that once the pressure is lower around the wound, the gentle vacuum suction can lift fluid and debris away and give the wound a fighting chance to heal naturally.

NPWT has a long and interesting history. The idea of suctioning fluid from wounds as therapy is not a new concept. The process was first called “cupping” and was described in Ebers Papyrus around 500 BC; historians tell us that a form of wound suction was used around 1000 BC in China, 600 BC in Babylon and Assyria, and in 400 BC by Greeks who heated copper bowls over wounds to remove blood and fluids (5).

Modern medicine has built upon a very old concept. Thankfully, nurses have a slightly easier tool in NPWT devices than heating copper bowls.

Indications for Use 

Negative pressure wound therapy is widely used for the management of both acute and chronic wounds. This therapy is helpful for a broad range of wounds, from pressure ulcers to closed surgical incisions.  

The system is now implemented routinely for open wounds, such as open fractures, fasciotomies, diabetic foot ulcers, and infected wounds. Delayed wound healing and difficult wounds are seen more commonly in elderly patients and those with comorbidities (1).  

It’s important to review the basic anatomy of our integumentary system, types of wounds, and barriers to healing to understand the usefulness of NPWT. 

Basic Anatomy of Integumentary System 

Our integumentary system is considered the body’s largest organ. Our skin acts as a shield against heat, light, bacteria, infection, and injury. Other functions include body temperature regulation, storage of water and fat, sensory function, prevention of water loss, and a basic storage compartment for the organs (6).  

The skin is made up of 3 layers. Each layer has unique functions: 

1. Epidermis 

1. Dermis 

1. Subcutaneous fat layer (hypodermis) 

The epidermis is the thin outer layer of our skin, it contains squamous cells, basal cells, and melanocytes (gives skin its color). The dermis is the middle layer of skin, it contains blood vessels, hair follicles, sweat glands, nerves, lymph vessels, fibroblasts, and sebaceous glands (6). It is important to remember that the dermis contains nerves and nerve receptors. 

The subcutaneous fat layer is the deepest layer of skin and is made up of a network of collagen and fat cells; this layer conserves the body's heat and protects the body from injury by acting as a shock absorber (6).

This design was created on Canva.com on September 28, 2023. It is copyrighted by Abbie Schmitt, RN, MSN and may not be reproduced without permission from Nursing CE Central. 

Types of Wounds 

Negative pressure wound therapy is primarily used to treat complex wounds that are non-healing or at risk of non-healing. It is also indicated for acute wounds when the wound cannot be closed due to the risk of infection, active infection, skin tension, or swelling (7).  

Closure or skin grafting of acute wounds, such as open fractures or burns, are at high risk for infection due to microorganisms becoming trapped in the soft tissue leading to abscess development.  

Examples of possible wounds to apply NPWT (1):  

• Diabetic foot ulcers 
• Bed sores 
• Skin graft fixation  
• Burns 
• Crush injuries 
• Sternal/abdominal wound dehiscence  
• Fasciotomy wounds 
• Animal bites 

• Frostbite 

Barriers to Healing 

Age 

• Increased risk of tearing and shearing due to thinning of epidermis and decrease in elastin 
• Phases of healing are prolonged 
• Increased risk of dehiscence as the dermis has slower contractility 
• Skin more susceptible to bacterial growth and infections as pH becomes more neutral with age  

Co-morbidities 

• Cardiopulmonary Disease 

• Oxygen-transport pathways are affected 
• O2 necessary for wound healing 

• Diabetes Mellitus 

• High glycemic levels predispose patients to infection 
• Microvasculature and neuropathic components of DM increase the risk for impaired healing  
• Poor glycemic control can increase the risk of ulceration and delayed healing 

• Immune-suppressing conditions (Cancer, HIV, immunosuppressive therapy, immunosuppression syndrome) 

• Inflammatory phase (immunology) is impaired 
• Increased risk for infection 

Impaired Perfusion and Oxygenation 

• Peripheral Vascular Impairment 

• Proper perfusion is required for growth of new tissue and immunological responses of the tissue. 
• Arterial insufficiency (blood flow to extremities) leads to necrosis or lack of response to edema. 

Neurological Impairment  

• Peripheral neuropathy 

• Complication related to DM, alcoholism, chemotherapy 
• Loss of neuronal signaling and transmission 
• Loss of the sensory ability to recognize and react to sensations of touch, pressure, temperature, pain. Example: patient leaving foot on hot surface because there was no pain sensation, leading to burn wound. 

• Spinal cord injury 

Mechanism of Action 

The mechanism of action is dependent on applying negative pressure, which is below atmospheric pressure, to the wound. This pressure allows the gentle vacuum suction to lift fluid and exudate away from the wound to enhance healing (3).  

The vacuum is gentle because powerful suction would remove newly formed tissue as well. The mechanism of action is not only in removing fluid and debris from the tissue, but the pressure causes stimulation of the growth of granulation tissue at a macroscopic and microscopic level.  

The porous foam shrinks in size with the application of negative pressure and exerts strain on the wound bed, which leads to macro- and micro-deformation of the wound (3). Microdeformation is simply a term used to describe microscopic tissue cell reactions. This reaction can be compared to a battery jump-start of a car; the stimulation causes the battery to engage. 

NPWT systems consist of a sterile foam sponge, a semi-occlusive adhesive cover, a fluid collection system or canister, and a suction pump (1). The foam sponge is applied to the wound and covered. A fenestrated tube is embedded in the foam and the wound is sealed with adhesive tape to make it airtight, and the machine delivers continuous or intermittent suction, ranging from 50 to 125 mmHg (1). 

This design was created on Canva.com on October 1, 2023. It is copyrighted by Abbie Schmitt, RN, MSN and may not be reproduced without permission from Nursing CE Central. 

Proper application of the NPWT is important for the mechanism of action to be effective. Research supports that NPWT is effective at creating a stable wound environment, reduces inflammation and bacterial load, improves tissue perfusion, and stimulates granulation tissue and angiogenesis (1).  

Imagine you want to plant a garden in a swampy location, you would first need to divert the water and algae from the land, cover it with a greenhouse with consistent heat and pressure, and cultivate the soil for optimal growth. Similarly, NPWT creates the most ideal conditions possible for tissue regeneration.  

Contraindications 

NPWT would be contraindicated for the following: 

• Wounds involving untreated osteomyelitis. 
• Wounds that have exposed blood vessel 
• Wounds with exposed nerves, anastomotic sites, or organs 
• Wounds including open joint capsules 
• Malignant wounds 
• Wounds with necrotic tissue; it is recommended to excise first 

The following wounds could benefit from NPWT, but caution should be given (5): 

• Wounds with visible fistula 
• Wounds with exposed bone or tendon 

• The bone or tendon should be isolated from direct pressure  

• Patient with clotting disorders or that are taking anticoagulants, due to an increased risk of bleeding. 
• Compromised microvascular blood flow to the wound bed. 

Assessment 

A focused assessment should be done for patients with NPWT devices in place, both on the machine settings, the dressing, and the wound itself. Thorough documentation of the wound is essential to see the progression of wound healing. 

Suction Device Settings: 

• Continuous or intermittent 
• Pressure Setting: Range of pressure settings from -40mmHg to -200mmHg, which can be tailored for different types of wounds (7). This is set by the medical provider. 

Laboratory assessment is meaningful in wound care. Labs can be used to assess oxygenation or indicators of infection (6). 

Dressing Assessment 

The appearance of the NPWT and dressing should be clean, dry, intact, and sealed. The tubing should not be twisted or kinked, and the clear adhesive dressing should not be wrinkled or overlapping. Please see below an example of the appropriate appearance of a dressing. 

Wound Assessment: 

• Anatomic location 
• Type of wound  
• Degree of tissue damage 
• Description of wound bed 
• Wound size 
• Wound edges and surrounding skin 
• Signs of infection 
• Pain 

Anatomical Location  

Anatomical terms and numbering should be used to make sure the location of each wound is documented. Patients often have more than one wound, so the treatment needs to be specified for each wound.  

Wound Base 

Assess the color of the wound base. Healthy granulation tissue appears pink and moist due to the new capillary formation. The appearance of slough (yellow) or eschar (black) in the wound base should be documented and communicated to the health care provider (1).  

This tissue may need to be removed to optimize healing. If any discoloration or duskiness of the wound bed or wound edges are identified, the suction should initially be reduced or switched off (7).  

Type and Amount of Exudate 

Assess the color, thickness, and amount of exudate (drainage) The amount of drainage from wounds is categorized as scant, small/minimal, moderate, or large/copious.  

Terms are used when describing exudate: sanguineous, serous, serosanguinous, and purulent (6).  

• Sanguineous: fresh bleeding  
• Serous: Clear, thin, watery plasma 
• Serosanguinous: Serous drainage with small amounts of blood noted 
• Purulent: Thick and opaque. The color can be tan, yellow, green, or brown. This is an abnormal finding and should be reported to a physician or wound care provider. 

Wound Size  

Wounds should be measured on admission, wound vac dressing changes, or as needed for abnormal events. Many healthcare facilities use disposable, clear plastic measurement tools to measure the area of a wound.  

Consistent measurement is vital to the assessment of wound healing. 

• Measure the greatest length, width, and depth of the wound in centimeters 
• Examples of wound classification tools: 

• NPUAP staging system for pressure injuries 
• Payne-Martin classification system for skin tears 
• CEAP (clinical, etiologic, anatomic, and pathophysiology) system for venous ulcers 

Tunneling or Undermining 

Tunneling is when a wound has moved underneath the skin, making a “tunnel.” The depth of tunneling can be measured by gently inserting a sterile, cotton-tipped applicator into the tunnel and noting the length from the wound base to the end of the tract (7). Undermining occurs when the tissue under the wound edges becomes eroded, resulting in a pocket beneath the skin at the wound’s edge.  

Healing Process 

It is important to recognize the entire process of normal wound healing. There are four phases of wound healing: hemostasis, inflammatory, proliferative, and maturation (6).  

Hemostasis begins immediately after injury, involving platelet aggregation and activation of clotting factor (6). A platelet “plug” is formed as fibrinogen converts to fibrin and binds to itself. Vasoconstriction occurs at this time, decreasing blood loss and allowing clot formation.  

The inflammatory phase begins right after the injury and the injured blood vessels leak and cause localized swelling. The swelling, warmth, pain, and redness present during this stage of wound healing are related to the release of white blood cells, growth factors, nutrients, and enzymes to help control bleeding and prevent infection (6).  

The proliferative phase of wound healing involves “rebuilding” with new tissue made up of collagen and extracellular matrix; granulation tissue is built stronger with proper oxygen and nutrients.  

Key nursing knowledge: Dark granulation tissue can indicate infection, ischemia, or poor perfusion. The maturation phase of wound healing is when collagen is remodeled, aligns along tension lines, water is reabsorbed so the collagen fibers can lie closer together and cross-link, and the wound fully closes (1). 

There are three types of wound healing: primary intention, secondary intention, and tertiary intention.  

Primary intention means that the wound healing is supported by sutures, staples, glue, or otherwise closed so the wound heals beneath the closure (6).  

Secondary intention must happen when the edges of a wound cannot be approximated, or “brought together,” so the wound heals with the production of granulation tissue from the bottom up (6).  

Wounds that heal by secondary intention are at higher risk for infection, so contamination prevention is essential. Pressure ulcers are an example of wounds that heal by secondary intention.  

Tertiary intention refers to a wound that needs to remain open, often due to severe infection. Wounds with secondary and tertiary intention have longer healing times (2). 

Alternatives when NPWT fails 

• Hyperbaric Oxygen Therapy (HBOT): 

• HBOT is a treatment in which the wound is exposed to pure oxygen in a pressurized chamber to enhance wound healing (3). 

• Bioengineered Tissue:  

• Skin grafting or bioengineered tissue to promote tissue growth and healing.  
• Skin grafts are considered as a treatment option if a wound is so large that it can’t close on its own. In this procedure, skin is taken from another part of your body – usually your thigh – and transplanted onto the wound (2). 
• Some grafts are made from human cell products and synthetic materials. Studies have shown that these increase the chances of poorly healing venous leg ulcers closing faster. (2) 

• Electrical Stimulation Therapy:  

• Electrical stimulation therapy applies electrical currents to stimulate wound healing and tissue generation (4). It may be used to treat chronic wounds or pressure ulcers. 

Adjunct Treatment Options 

When selecting an adjunctive therapy for wound management, the patient's medical history, overall health, co-morbidities, ambulation status, psychosocial aspects, environmental factors, and the specific needs of the wound should all be considered. Each patient is unique, and an individualized care plan is the goal.  

Treatment of the underlying contributing disorder will be essential. For example, a patient with uncontrolled diabetes that has led to poor circulation can benefit from glycemic control.  

Take a look at the larger, holistic picture. It can be helpful for the healthcare team to create a concept map of problems that contribute to the wound. 

Topical Agents and Dressings 

Various creams, ointments, or dressings can promote wound healing and prevent infection. One example is silver-based products, which are commonly used in reducing bacterial burden and treating wound infection (4). 

Nutrition Therapy for Wound Healing 

Patients with wounds would benefit from nutrition consultation and ongoing support.  

Nutrients from foods help the body build and repair tissue and fight infection. An increase in calories and protein is important, as well as blood sugar control for diabetics.  

Vitamins C, D, B-6, B-12, folate, and others aid in repairing tissues (6). Minerals such as iron, magnesium, calcium, zinc, and others support the cardiovascular system making sure cells have enough oxygen, the nervous system, and immunological function (6). 

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Compression Therapy 

Compression therapy uses pressure to reduce swelling and improve blood flow to the wound. There are common compression devices or stockings available. It is frequently used to treat venous leg ulcers (6). 

Hyperbaric Oxygen Therapy (HBOT) 

HBOT can also be used as an adjunct treatment in which the patient breathes pure oxygen in a pressurized chamber to increase the amount of oxygen in the blood, which enhances wound healing (3). 

Troubleshooting Tips 

You may encounter complications with the wound dressing or the wound vac equipment. The most common complications associated with NPWT are pain, bleeding, and infection (7).  

The wound therapy relies on an adequate seal similar to a regular vacuum, so a loss of suction can result in ineffective treatment. If loss of seal occurs, the nurse should assess the seal around the wound dressing and note if the transparent adhesive sealant tape has either been misapplied or has come off due to poor contact with the underlying skin.  

A loss of suction could also result from incorrect placement of the suction drain tube, loss of battery power, blockage of the suction drain tube, or if the suction device is full of output (7). Sometimes the location of the wound leads to difficulty in keeping the dressing seal in place; for example, the abdomen or near joints, so movement can misplace the dressing and break the seal. Patient education is key to maintaining proper suction. 

Troubleshooting Tips: 

• Confirm the machine is on and set to the appropriate negative pressure. 
• Make sure the foam is collapsed and the NPWT device is maintaining the prescribed therapy and pressure. 
• Assess the negative pressure seal and check for leaks. 
• Check for kinks in the tubing and make sure all clamps are open. 
• Avoid getting the machine wet. 

• Assess the drainage chamber to make sure it is filling correctly and does not need changing. 
• Address alarm issues: 

• Canister may be full 
• Leak in the system  
• Low/dead Battery 

• The device should not be turned off for more than two hours without ordered discontinuation. 

• If the device is off, apply a moist dressing and notify the provider immediately. 

Case Study 

Mr. Smith is a 59-year-old male presented to his primary care provider and referred to general surgery; diagnosed with lymphedema and multiple, copiously draining ulcerations on the left lower extremity.  

The patient presented with lymphedema and multiple ulcerations on the left lower extremity with copious amounts of drainage. This is an ongoing, worsening issue for over 8 months and has failed to respond to compression, foam dressings, or hydrocolloid dressing.  

The hospitalist has ordered surgical consultation, who scheduled debridement of the wounds and application of a wound vac following the procedure; Negative pressure wound therapy (NPWT) orders in place.  

CHIEF COMPLAINT: "The sores on my feet are draining more and I can no longer go to work because my boots do not fit on my foot.” He also reports a loss of appetite, chills, and loss of sensation to his left lower extremity.  

HISTORY OF PRESENT ILLNESS: Patient is a 59-year-old truck driver who has previous medical history of DM Type II, hypertension requiring use of anti-hypertensive medication, and hyperlipidemia (non-compliant with medication regimen). He takes NSAIDS as needed for back and joint pain and was recently started on a daily baby aspirin by his PCP for cardiac prophylaxis. He denies alcohol intake. He reports smoking a pack of cigarettes per day. 

PHYSICAL EXAMINATION: Examination reveals an alert and oriented 59-YO male. He appears anxious and irritated. Vital sips are as follows. Blood Pressure 155/90 mmHg, Heart Rate 120/min - HR Thready - Respiratory Rate - 20 /minute; Temperature 98.0  

ENT/SKIN: Facial pallor and cool, moist skin are noted. No telangiectasia of the lips or oral cavity is noted. Wound: 3 cm x 2 cm x 1 cm wound to lateral LLE. Wound base is dark red with yellow-green drainage present. Removed 4 x 4 dressing has a 5 cm diameter ring of drainage present. The surrounding skin is red, warm, tender to palpation, and with a dusky appearance to the entire LLE.  

CHEST: Lungs are clear to auscultation and percussion. The cardiac exam reveals a regular rhythm with an S4. No murmur is appreciated. Peripheral pulses are present but are rapid and weak. A positive Stemmer sign was noted and palpable pedal pulses with mild symptoms of venous insufficiency were noted. 

ABDOMEN/RECTUM: The abdomen reveals a rounded abdomen. Bowel sounds are present.

Conclusion

Hopefully, upon completion of this course, you feel empowered and curious about the use of negative pressure wound therapy (NPWT). Wound vacs can be a powerful tool in combatting acute and chronic wounds, it is a well-documented concept throughout history.

The nurse should be knowledgeable on the integumentary system makeup and types of wounds this therapy is indicated for. The mechanism of action of NPWT is critical knowledge when assessing the healing of a wound. Adjunct treatment options and troubleshooting support tips are also meaningful in the care of patients with NPWT.

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