Wound Vac

 Q: In the initial phase of Negative Pressure Wound Therapy (NPWT) - Wound Vac - the perfusion is increased? 

A) True

B) False

Answer: B

It is beyond the scope of this website to describe in detail the working of Wound-Vac. The negative pressure system of wound-vac generates a pressure gradient between the wound and suction canister. This negative pressure transports the fluid from wound bed and interstitial space and reduces wound edema. It also causes cell/tissue modulation. The pressure applied in wound-vac is 5-10 mmHg. Also, the foam in wound-vac system contracts and draws the edges of the wound together. 

Wound-Vac has also many indirect effects of wound healing. The major indirect effects are 

• Alterations in blood flow 
•  Diminished inflammatory response 
• Altered bacterial burden
• Changes in wound biochemistry

It was thought that negative pressure increases the blood flow/perfusion. In reality, this pressure leads to a paradoxical decrease in perfusion and causes local ischemia in the early phases. This ischemia stimulates the release of growth factors and vasoactive agents, leading to increase granulation and healing.

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References:

1. Venturi ML, Attinger CE, Mesbahi AN, et al. Mechanisms and clinical applications of the vacuum-assisted closure (VAC) Device: a review. Am J Clin Dermatol 2005; 6:185. 

2. Kairinos N, Solomons M, Hudson DA. The paradox of negative pressure wound therapy--in vitro studies. J Plast Reconstr Aesthet Surg 2010; 63:174.