Negative pressure wound therapy: mechanisms of action and clinical uses

Published on October 7, 2014   32 min
0:00
Hello, I'm Doctor Dennis Orgill, and today I'd like to talk about negative pressure wound therapy, mechanism of action, and clinical uses.
0:11
For financial disclosures, I've had passed research funding and have been a consultant and an expert witness for KCI.
0:20
Today we'll begin by discussing the history and technology transfer of negative pressure wound therapy devices, we'll review the biology of skin stretching, and we'll talk about the four primary mechanisms of negative pressure wound therapy, which include macrodeformation, microdeformation, fluid removal, and a moist wound environment. We'll then discuss secondary mechanisms which include, angiogenesis, inflammation, regulation of matrix metalloproteinases, and their effect on peripheral nerves. Finally, we'll go over some case examples including sternal wounds, open abdomens, groin wounds, and skin grafts following a brief discussion.
1:05
When clinicians started using negative pressure wound therapy devices, they had some amazing results. On the left you see a patient of ours who came into the hospital with necrotizing faciitis. She had peripheral vascular disease and diabetes, and this required a hip disarticulation. We placed the vac device on and changed it over 30 days. Normally we would have put a large flap on this, but she was too sick in the ICU. This could eventually be covered with a skin graft to close the wound. On the right, we commonly use a vac device to cover skin grafts, and this shows how this is applied to a lower leg wound.
1:46
Suction has a long history in the use of medicine and surgery. At the top left is a commonly used chest tube system in our hospital which carefully regulates suction, usually between 20 and 40 millimeters of mercury. Below that is a suction drain which also provides a low suction pressure to evacuate fluid from surgical wounds. On the right is a gomco devise which has the capacity to provide intermittent suction, particularly for the gastrointestinal tract.
2:26
Prior to using negative pressure wound therapy devices, many wound care products were based on the work of George Winters in 1962 when he described how wounds would heal faster if they were kept moist and allowed to dry out. Today in the U.S., there are over 1,500 products available for use. This makes for the average clinician difficult decisions on what to use in each specific patient.
2:53
In 1997, Louis Argenta and Michael Morykwas published two very important articles in the annals of plastic surgery where they introduced vacuum-assisted closure, both in the clinical setting and in the experimental work which they had done leading to their clinical interventions.
3:16
In 1997 a commercial device became available for clinical use. We began using it in our institution, and you can see how this ramped up over the next several years. We now use about 1,000 of these devices per year in our institution.
3:34
In order to understand the biology of stretching skin, it's important to understand the concepts of basic mechanics. The first is stress, which is defined as the force divided by the cross sectional area over which the force is applied. Strain is how much an object stretches and is defined as the stretch length over the original length. A ratio of stress over strain produces the modulus of elasticity, often referred to as the Young's Modulus. The Poisson's Ratio talks about how much an object deforms in the opposite dimension to which the primary deformation occurs. And this is the ratio between the strain in the x divided by the strain in the y dimension.
4:24
There's been a well-described relationship between the function of a cell and the cell shape. This is best described by Doland Engber in his FASEB article of 1999. For all non-maligneant cells when they're small and become spherical, they tend to undergo apoptosis or programmed cell death. When stretched a bit, they tend to differentiate. When stretched more, they tend to divide and proliferate.
4:51
These theoretical concepts have been applied clinically in a very important paper by Daya from South Africa. He showed that he could tape the scalps of burn victims who had heavy scars, and over time the scalp would stretch out and the scarred skin could be resected, and this could be closed in a straight line. This is obviously a much simpler procedures than tissue expansion, which requires the use of a more complicated medical device.
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Negative pressure wound therapy: mechanisms of action and clinical uses

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