Emerging Concepts With VAC Therapy
Vacuum Assisted Closure (VAC, KCI) may be the most impressive device for the foot since AO fixation revolutionized elective foot surgery. For large or difficult wounds, VAC therapy can rapidly improve granulation tissue and speed up coverage of exposed tendon and bones. Indeed, this often occurs in days to weeks rather than months. Most clinicians are convinced at the bedside when they see dramatic changes in the characteristics of a wound such as size, depth and exposed structures.
There is a growing body of evidence that supports the clinical observations and animal research that have been the mainstay of evidence on VAC therapy since the Food And Drug Administration (FDA) approved the device in 1995. While the study on the use of VAC therapy for open amputations was a milestone, other randomized clinical studies, which should be published in the not too distant future, may help us understand more about VAC therapy applications and economic advantages of this type of advanced wound care technology.1
Animal studies have demonstrated that VAC therapy can significantly reduce the bacterial load in contaminated wounds, increase blood flow, improve granulation tissue and spur flap survival. Morykwas and colleagues compared wounds in a Chester pig model treated with and without VAC therapy.2,3 Negative pressure wound therapy increased granulation tissue threefold. Due to the dramatic increase in granulation tissue, structures such as bone, tendon and exposed hardware that are usually difficult to cover can be bridged with VAC therapy.1 The tissue coverage can be dramatic.
Armstrong’s study demonstrated a significant improvement in granulation tissue in the VAC therapy treatment group, faster healing rates and a higher proportion of healed wounds.1 Patients reached a level of 76 to 100 percent granulation tissue coverage of the wound bed twice as fast with VAC therapy. Additionally, 56 percent of open amputations treated with VAC therapy healed completely in 16 weeks compared to 39 percent in the control arm. The rate of complete healing in wounds that average 20 cm2 was as good as Dermagraft (Advanced BioHealing) and Apligraf’s (Organogenesis) healing in wounds that were 2 to 3 cm2.4 That represents about a tenfold difference in wound size with the same healing rate.
Can VAC Therapy Lead To Reduced Bioburden In The Wound?
Morykwas also identified a significant reduction in quantitative bacterial cultures with VAC therapy.2,3 By the fifth day, quantitative cultures decreased to less than 105 organisms per gram in the wounds treated with VAC therapy and during the same time period, quantitative cultures increased in control wounds.2
In the randomized clinical study by Armstrong in 2005, there was not a significant difference in wound infections in 163 patients with diabetes treated with VAC therapy for open foot amputations compared to standard therapy.1 It seems logical that an active drainage system under pressure would reduce edema and facilitate the removal of infectious materials from the wound bed. Infection was not a primary endpoint of the study and the study did not require routine qualitative or quantitative cultures.
Accordingly, it was difficult to evaluate if there was a measurable difference in bioburden or if different diagnostic criteria across study sites may have played a role. There may have been a bias to treat patients with antibiotics if they had periwound redness and maceration. One often sees these conditions with the use of VAC therapy.
When it comes to high-risk patients, the rule of thumb is to err on the side of more aggressive treatment. In clinical practice, this probably means using antibiotics to treat a wound that one suspects of being infected. In the Lancet randomized clinical trial, there was not a significant difference in serious adverse events in VAC therapy and standard therapy groups (including infection). However, there was a trend toward more patients requiring a second amputation in the standard therapy group.1