Negative Pressure Wound Therapy (NPWT): How It Works and What Supplies You Need

What is Negative Pressure Wound Therapy?

Negative Pressure Wound Therapy (NPWT), also known as vacuum-assisted closure (VAC), is a treatment that applies controlled sub-atmospheric pressure to a wound bed through a sealed dressing system. The pressure is typically set between -50 and -200 mmHg, depending on the wound type and patient tolerance.

How NPWT Promotes Healing

NPWT works through multiple mechanisms:

• Exudate management - actively removes excess wound fluid, reducing peri-wound maceration and bacterial load
• Perfusion enhancement - intermittent negative pressure increases blood flow to the wound bed
• Oedema reduction - removes interstitial fluid, improving oxygen and nutrient delivery
• Granulation tissue stimulation - mechanical stretch and micro-deformation promote cell proliferation
• Wound contraction - draws wound edges together

Indications for NPWT

NPWT is indicated for:

• Chronic wounds (diabetic foot ulcers, pressure injuries, venous leg ulcers)
• Post-surgical wounds that have dehisced or are healing by secondary intention
• Traumatic wounds
• Burns (split-thickness graft donor sites and recipient sites)
• Flaps and grafts (to improve take and reduce seroma/haematoma)
• Meshed grafts (to secure the graft and remove exudate)

Contraindications and Cautions

NPWT should not be used in the following situations without specialist assessment:

• Neglected or inadequately debrided wounds with necrotic tissue
• Wounds with untreated osteomyelitis
• Wounds with fistulas to organs or body cavities
• Wounds with exposed blood vessels, nerves, or anastomotic sites
• Malignant wounds (unless for palliative symptom management)
• Patients on anticoagulant therapy (increased bleeding risk)

NPWT Dressing Components

A standard NPWT dressing consists of:

1. Wound filler - open-cell polyurethane foam (black foam) for most wounds, or polyvinyl alcohol foam (white foam) for wounds where ingrowth is a concern
2. Non-adherent contact layer - optional, to prevent foam ingrowth into fragile granulation tissue
3. Transparent film drape - creates the airtight seal over the foam and peri-wound skin
4. Suction tubing and canister - connects the dressing to the NPWT pump and collects exudate
5. NPWT pump unit - delivers controlled negative pressure (continuous or intermittent)

NPWT Dressing Change Procedure

1. Wash hands and apply clean gloves
2. Turn off the NPWT pump and disconnect tubing
3. Gently remove the transparent film and foam. If the foam is adherent, irrigate with saline to loosen
4. Cleanse the wound with normal saline or a wound cleanser such as Prontosan or Granudacyn
5. Assess the wound bed for tissue type, exudate, signs of infection, and dimensions
6. Cut foam to fit the wound cavity (do not pack tightly; foam expands under pressure)
7. Apply foam, cover with transparent drape (extend 3-5cm beyond wound margins), and create a seal
8. Connect tubing, turn on pump, and verify seal integrity (no hissing, foam collapses under pressure)
9. Document dressing change, wound assessment, and pressure setting

Adjunctive Wound Cleansing for NPWT Patients

Before applying NPWT dressings, thorough wound cleansing is essential. EMIS+ carries:

• Prontosan Wound Irrigation Solution - contains polyhexanide and betaine for antimicrobial cleansing and biofilm disruption
• Prontosan Wound Gel - for debridement and sustained antimicrobial action in dry or necrotic areas
• Granudacyn Wound Irrigation Solution - hypochlorous acid-based cleanser, safe for frequent use

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NPWT in Singapore Home Care

NPWT is increasingly used in the home setting in Singapore, particularly for patients discharged from hospital with complex wounds. EMIS+ provides NPWT supplies and can arrange WOCN nurse home visits for dressing changes and wound assessment. Home NPWT requires patient/caregiver training on pump operation, seal maintenance, and alarm troubleshooting.

Frequently Asked Questions

How often should NPWT dressings be changed?

NPWT dressings are typically changed every 48-72 hours for infected wounds, and every 3-5 days for clean, non-infected wounds. The canister should be changed when full or every 7 days, whichever comes first.

Is NPWT painful?

Some patients experience discomfort during dressing removal, especially if foam has adhered to granulation tissue. Using a non-adherent contact layer or saline irrigation before removal can reduce pain. The negative pressure itself is usually described as a pulling or tugging sensation rather than pain.

Can NPWT be used on infected wounds?

Yes, NPWT can be used on infected wounds, but the infection must be managed concurrently with appropriate systemic antibiotics and antimicrobial dressings. Dressing changes should be more frequent (every 24-48 hours) for infected wounds. Instillation NPWT (with antimicrobial solution) is available for heavily colonised or infected wounds.

Where can I buy NPWT supplies in Singapore?

EMIS+ stocks NPWT foam dressings, transparent film drapes, tubing, and canisters compatible with major NPWT systems. We also carry Prontosan and Granudacyn wound cleansers for pre-NPWT wound preparation. WhatsApp +65 8139 8668 for product compatibility advice.