What are the factors affecting wound healing and how does Vacuum-Assisted Closure (VAC) therapy promote wound healing?

Wound Healing Process and Factors Affecting Healing with VAC Therapy

Phases of Wound Healing

Wound healing is a complex biological process that occurs through four overlapping phases:

• Hemostasis: Begins immediately after injury with blood clot formation and platelet degranulation, releasing growth factors like PDGF that stimulate chemotaxis and mitogenicity of neutrophils, monocytes, macrophages, and fibroblasts 1
• Inflammation: Characterized by increased vascular permeability and recruitment of inflammatory cells, with macrophages playing a key role in wound debridement and secreting growth factors (PDGF, TGF-β, EGF, FGF-2, VEGF) 1
• Proliferation: Involves extracellular matrix synthesis, angiogenesis, and epithelialization, with fibroblasts proliferating under the influence of PDGF, FGF-2, and TGF-β 1, 2
• Remodeling/Maturation: Final phase where matrix synthesis and tissue remodeling occur, with PDGF stimulating mesenchymal progenitor cell migration and TGF-β promoting fibroblast differentiation into myofibroblasts for wound contraction 1, 2

Factors Affecting Wound Healing

Local Factors

• Wound Infection: Prompt management of infection with antibiotics and debridement is critical, as infections can rapidly progress and impede healing 1
• Tissue Perfusion: Adequate blood supply is essential; revascularization may be necessary in cases of peripheral artery disease 1
• Wound Debridement: Removal of necrotic tissue and slough is crucial to enable wound healing and remove reservoirs of pathogens 1
• Pressure on Wound: Offloading pressure from wounds, particularly in diabetic foot ulcers, is crucial for healing 1
• Biofilm Formation: Biofilms can disrupt normal healing patterns by creating barriers to cell migration 3

Systemic Factors

• Diabetes: Impairs healing through multiple mechanisms including neuropathy, vascular disease, and impaired immune function 1, 4
• Nutritional Status: Poor nutrition can delay wound healing; adequate protein and micronutrients are essential 2, 4
• Smoking: Decreases tissue oxygenation and impairs healing 4
• Age: Advanced age is associated with delayed wound healing 4
• Medications: Certain drugs like corticosteroids and chemotherapeutic agents can impair healing 4
• Stress: Psychological stress can delay wound healing through neuroendocrine effects 4

Vacuum-Assisted Closure (VAC) Therapy

VAC therapy is highly effective for promoting wound healing by creating localized negative pressure over the wound bed, which enhances granulation tissue formation, improves circulation, and accelerates wound closure. 5, 6

Mechanism of Action of VAC Therapy

• Fluid Removal: Removes excess exudate and edema from the extravascular space 6
• Improved Circulation: Increases local blood flow and tissue perfusion 5, 6
• Enhanced Granulation: Promotes formation of granulation tissue through mechanical stretch 5, 6
• Bacterial Clearance: Reduces bacterial load in the wound 6
• Wound Contraction: Facilitates wound edge approximation 6

Clinical Evidence for VAC Therapy

• Randomized controlled trials have demonstrated that VAC therapy significantly decreases time to complete wound healing compared to conventional dressing (22.52 vs. 33.85 days) 7
• VAC therapy accelerates granulation tissue formation (2.91 cm²/day vs. 2.16 cm²/day with conventional dressing) 7
• Complete wound healing was achieved in 65.51% of patients with critical limb ischemia after surgical revascularization using VAC therapy, with an average healing period of 45.4 days 5

Application of VAC Therapy

• VAC therapy can be used after revascularization and minor amputation when primary or delayed secondary closure is not feasible 1
• It is particularly effective for patients with diabetes with nonhealing wounds 1, 7
• The therapy should be applied after proper debridement of nonviable tissue 1, 3

Contraindications and Precautions for VAC Therapy

• Not recommended for wounds with untreated osteomyelitis 1
• Should be used cautiously in patients with active bleeding or on anticoagulants 6
• Not suitable for wounds with exposed blood vessels, organs, or malignancy 6

Comprehensive Wound Management Approach

An effective wound management strategy should include:

• Adequate debridement of nonviable tissue 1
• Management of infection and inflammation 1
• Pressure offloading when appropriate 1
• Maintaining a conducive wound-healing environment with appropriate dressings 1
• Revascularization for adequate perfusion in ischemic wounds 1
• Medical optimization of host factors (e.g., glycemic control, smoking cessation) 1
• Control of edema 1
• Pain management 1

VAC therapy should be considered as an adjunctive treatment when wounds do not heal with standard care, particularly for diabetic foot ulcers and after surgical revascularization for critical limb ischemia 1, 5, 7.