Wound VAC method involves the application of a medical grade, reticulated polyurethane ether foam dressing that is attached to a non-collapsible flight tube which, in turn, is emotionally involved in a vacuum source. The side port in the tube is used and enhances the dressing process thereby encouraging communication between the tube and reticulated foam dressing process (Unger, 2008). The reticulated foam dressing process is minimized to closely be conventional to the geometry of the wound bed and thereafter is placed in the wound defect so as to allow wound defect to lie parallel to the skin. The reticulated foam dressing helps in the absorption of both wound exudates and to evenly dispense the negative pressure all over the entire wound. An adhesive drape is therefore placed over the foam dressing and the tube and is affixed to be intact to the skin, creating an airtight compartment over the wound bed.
Dealey (1998) asserts that the evacuation tube is extended to a collection vessel that is connected to an adjustable vacuum pump. Characteristically, the vacuum pump can be programmed to provide various amounts of negative pressure on an intermittent or continuous basis depending on the type of the wound being dressed. The general architecture, drapes, foam types, and the process of regulating of the vacuum pump can be modified according to the uniqueness of every wound. In presentation of definite guidelines for the use of negative pressure devices is beyond the compass of this review.
Altered blood flow: it was further suggested that in wounds where the edges are not opposed, healing generally is considered to take place through secondary intention; secondary intention is a process that needs a matrix of small blood vessels and connective tissue across the wound defect to be created. Once developed, this matrix creates a path through which the keratinocytes migration takes place and in this way the wound defect is covered. Vacuum-assisted closure in most instances can be applied in this process through increasing blood flow to the wound margins, which not only increases the delivery of oxygen and other nutrients, but also assists in minimizing waste products. Using a laser Doppler to scrutinize blood flow, some researcher observed that a vacuum system led to increased margins of flow of blood.
This increase in blood flow did not last for much time but indeed just around few minutes. Granulation tissue also appeared at a greater rate in wounds treated with the wound VAC, and as a result this led to the proposition that increased blood flow was responsible for the accelerated formation of granulation tissue and thereafter the consequent wound healing (Douglass, 2003). It was later observed that increase in blood flow to wounds experimentally created in the ears of white rabbits and subsequently treated with vacuum-assisted technology. Microscopic examination and image pattern psychoanalysis discovered that increased blood flow was brought about by increased vascular diameter, blood flow velocity, and blood volume, as well as increased angiogenesis and endothelial proliferation.
Later researchers came up with an idea and employed a swine model to further study the impact of the wound VAC on blood flow in the immediate and adjacent vicinity of a sensitive wound. The observation made was that the wound VAC decreased blood flow (hypo perfusion) in the immediate proximity of wounds created in anesthetized swine but increased blood flow (hyper perfusion) in areas 1.5 to 3.0 centimeters far from the wound. The changes in blood flow were directly linked to the amount of negative pressure obligatory on the wound. VAC compared with the traditional treatment modalities, the homogeneouspessimistic pressure applied to the wound as a result leads to what is referred to as arteriolar dilatationand increased microcirculation, and in this manner it optimizes the woundenvironment (Dowsett, 2005). Through a continuous suction, fluid excess and tissueedema are decreased which reduces bacterial colonization. Theseaffirmative effects on wound encourage granulation tissue proliferationand accelerated wound healing in the traditional methods applied. Additionally, through the air-tightseal additional wound contamination is effectively prevented in the traditional method of wound healing process. This makes this process more effective but the problem being that it takes much time to heal.
On an interesting note, blood flow in the area of hypo perfusion increased by roughly 50% over basal levels when the negative pressure was “off,” suggesting that a reactive hyperemia response occurred during the “off” part of the intermittent vacuum cycle. The authors further suggested that by removing the negative pressure, a period of hyper perfusion and resulting “hyper oxygenation” of the tissue is created; and therefore leading to stoppage of chronic ischemia. This is due to the fact that contrasting regional effects on blood flow, these investigators argue that the beneficial impact of negative pressure is related to its ability to reduce wound edema and to tapenade bleeding as an alternative of its ability to increase the flow of blood.