The Veterinary Guide to Negative Pressure Wound Therapy (Part 2)
We hope you enjoyed Dr. Franklin’s excellent introduction to negative pressure wound therapy (NPWT) in Part 1 of this Series. Now it’s time to learn how to institute this technology in your practice.
The Technology and Application NPWT is in its infancy in veterinary medicine. There are only two companies that I am aware of actively marketing to veterinarians: KCI Animal Health (San Antonio, Texas) and the Talley Group (Lansing, MI).
However, numerous systems are in use for wound management in human medicine and could be adapted to animals. For example, I have used a Smith & Nephew wound management system on several dogs with success.
Regardless of which system is used, all have several basic and essential components and the principles of application do not differ between systems.
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Here are the Working Parts of NPWT:
1. The Contact Layer: After appropriate debridement (sharp, mechanical, or autolytic) of the wound, a bandaging layer is applied to the wound bed. Contact layers are usually either a proprietary foam product (KCI) or gauze in the form of surgical sponges. (Hover over the photos below for details).
2. Wound Sealant Drape: After application of the contact layer the wound must be bandaged to create an airtight seal. Both the Talley Group and KCI provide and market their own product and both are clear, plastic-like adhesive draping material similars to incise drapes used in surgery (Figure 3). Other products such as Ioban (3M™) can suffice.
3. The Drain: A drain must be placed within the wound through which negative pressure is applied. There are a few methods for accomplishing this.
The first is placement of a drain into the wound prior to application of the adhesive drape.The drain then exits at the wound edge. Using this method, the airtight seal is occasionally lost at the exit location and negative pressure cannot be maintained. In my experience, this can be a challenging method because the drain tube creates an irregular surface at the wound edge that is difficult to successfully incorporate and seal with the incise drape (Figure 3).
Alternatively, you can apply the proprietary T.R.A.C. pad (KCI) to a hole made in the adhesive drape after adhesive drape application if using the V.A.C. ® system. This means that the wound edge retains a relatively flat contour for 360 degrees that is not affected by a drain tube exiting the wound edge. I find that it is easier to seal such a wound as the drape can more easily adhere (Figure 4).
Finally, you can tunnel a tube from within the wound, through the subcutaneous tissue, and exit healthy skin at a point a few centimeters from the wound edge and place a purse string suture around the drain exit point to maintain an airtight seal (Figure 5). This technique also avoids having a wound edge that is interrupted by the drain exit site, facilitating adhesion of your occlusive drape.
A disadvantage of this last technique is the potential for contamination of otherwise healthy subcutaneous tissue with passage of the drain, although I have not had this be a clinically relevant limitation in my patients. Note that numerous different multi-fenestrated drains can be used including Jackson Pratt drains or red rubber tubes with additional holes made in the tube.
4. The Receptacle Canister: The drain is then attached to a receptacle canister that collects the exudate that is suctioned from the wound. Canisters come in different shapes and sizes and can be rigidly attached to the vacuum unit or may stand alone. The most pertinent question regarding canisters, in my opinion, is the size relative to the fluid production from the wound. Some small canisters can fill in < 24 hours and need to be replaced more frequently than larger ones and it can be more time and cost effective to just use a larger container. Conversely, larger containers are more burdensome to carry outside with the animal.
5. The Connection to the Unit: The canister is connected to the unit either directly (KCI, Talley Group) or via a tube leading from the collection canister to the vacuum unit (e.g. Smith & Nephew). There should be a filter incorporated in this line (or within the machine) to prevent aspiration of contents from the receptacle canister and contamination of the machine.
6. The Vacuum Unit: The vacuum unit generates the negative pressure. Units differ in their features and bells and whistles but at the minimum, the unit should include an ability to adjust the time that pressure is applied to the wound, the amount of pressure that is to be applied, and whether the pressure is applied continuously or cyclically during the chosen treatment period.
Choosing a Vacuum Unit A few units are available (as mentioned above) and a review of them is beyond the scope of this article. However, in my opinion, it is unlikely that all units are of the same quality. When purchasing a unit I advise performing thorough research on the different units available. One of the important characteristics of a unit may be the degree of error or discrepancy that is tolerated between the chosen pressure to be applied to the wound (chosen by the user) and the actual pressure at the level of the wound.
At least some units (V.A.C.; KCI) actively measure and adjust the pressure continuously in an effort to tightly maintain the appropriate pressure. This is a feature termed “regulated pressure feedback”. Some units also measure and sound an alarm if the pressure cannot be maintained (KCI and Talley Group units).
It is also worth mentioning the use of alternative methods of negative pressure application. For example, there are reports (personal communication) of veterinarians using in-house suction lines to deliver negative pressure to wounds. Such use of negative pressure has not been published to my knowledge and this application is cautioned if you cannot verify that the appropriate level of pressure is being applied to the wound.
NPWT Application in Practice: Case Examples
Case Example 1: Courtesy of Dr. Matthew Silvius, Eagle Animal Hospital, Riverside, Missouri
A 2-year-old, 55 kg, male Great Pyrenees was attacked by other dogs about 7-10 days prior to presentation. The dog had a large, infected wound over the dorsum of the lower lumbar region with necrosis of the overlying skin. Once the necrotic skin was removed, the defect was measured as being approximately 40 cm x 40 cm in size.
Dr. Silvius performed surgical debridement and initiated wound management (see Figure 8A). As can be seen in the following images he obtained a healthy appearing wound bed. Note that he used a ‘tie-over’ bandage as one can see the loops of suture around the periphery of the wound. A referral for NPWT was discussed but declined by the owner and thus conservative wound management was continued.
Dr. Silvius eventually placed a meshed, free skin graft to fill a small to moderate portion of the remaining wound. The graft remained viable and with wound contraction and neo-epithelialization the wound closed with an excellent result (Figure 8B-D). I congratulate Dr. Silvius on an excellent job and an excellent result!
This case illuminates the substantial amount of time and energy necessary in caring for a dog with severe wounds, as it took approximately two months to achieve resolution of this wound. This time and energy investment is one reason why I recommend negative pressure wound therapy for similar patients.
Case Example 2:
A middle-aged spayed female American Staffordshire Terrier who was hit by a car and subsequently presented to an emergency clinic. She suffered a large degloving wound over the left elbow that involved greater than 300˚ of the circumference of the limb. Initial debridement was performed and bandaging was applied for two consecutive days at which time, she was subsequently referred to me. I removed the bandaging and performed additional wound debridement (Figure 9).
At that point, I was highly confident that I could use conservative bandage management and would be able to obtain a healthy bed of granulation tissue throughout the wound. I expected that once such a wound bed was obtained, I would be able to close the wound using an axillary skin fold flap or axial pattern flap. However, I suspected that it would take one to two weeks of such management before granulation filled the wound. Further, the dog was uncomfortable and required sedation in order to change the bandaging.
As a result, I thought that it would be more time and potentially cost effective to treat this patient with NPWT. I believed that possibly after one cycle of 72 hours, and certainly by the end of a second cycle (48-72 additional hours) of NPWT, this wound would be ready for surgical closure. Unfortunately, I did not have a NPWT unit available to me at that time due to logistical reasons. Therefore, as much as I would have enjoyed keeping this case, treating him, and ultimately doing surgery, I applied a tie-over bandage and referred him to another hospital for NPWT.
Case Example 3:
A spayed female Yorkshire terrier was attacked by a larger dog. She had two notable
wounds on her ventral thorax: one on midline and the other on her left ventrolateral thorax.
The skin defects were not enormous but the subcutaneous and muscular layers were notably traumatized as often occurs with dog bites. Contamination was presumed and therefore I did not want to perform primary closure. I elected instead to perform wound management and subsequently secondary closure.
I elected to place a single NPWT dressing that would treat both wounds simultaneously. I tunneled the drain from one wound to the other, used gauze as a contact layer in both wounds, and sealed the wound. After a few days, a healthy bed of granulation tissue was obtained and I was able to perform surgical closure. The wounds healed uneventfully and the dog made a full recovery.
More links to published case reports are provided below.
It should also be noted that negative pressure wound therapy has applications beyond small animal medicine. KCI hosts a website (www.kcianimalhealth.com) that provides case examples for large and small animals, including exotic species. They also have other useful resources such as user manuals and quick references.
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Additional case reports of NPWT in veterinary medicine:
Vacuum-assisted wound closure following urine-induced skin and thigh muscle necrosis in a cat. Owen L, Hotston-Moore A, Holt P. Vet Comp Orthop Traumatol. 2009;22(5):417-21. doi: 10.3415/VCOT-08-12-0123. Epub 2009 Aug 28.
Use of a nanocrystalline silver dressing and vacuum-assisted closure in a severely burned dog. Mullally C, Carey K, Seshadri R. JVECCS 2010 20(4): 456-463.
Successful wound healing over exposed metal implants using vacuum-assisted wound closure in a dog. Bertran J, Farrell M, Fitzpatrick N. J Small Anim Pract. 2013 Jul;54(7):381-5. doi: 10.1111/jsap.12055. Epub 2013 Apr 8.
About the Author
Dr. Sam Franklin earned his DVM from Colorado State University and then completed a rotating internship at the University of Pennsylvania. At the University of Missouri, he completed his surgical residency and a PhD investigating the use of stem cells and absorbable scaffolds to resurface osteoarthritic hips. He passed the certifying examinations and became a Diplomate in the American College of Veterinary Surgeons and the American College of Veterinary Sports Medicine and Rehabilitation in 2012 and 2013 respectively. He now practices at the University of Georgia and his clinical practice and research is focused on orthopedics, sports medicine, and rehabilitation. He has particular interest in minimally invasive surgical techniques such as arthroscopy and minimally invasive fracture repair as well as regenerative therapies such as platelet rich plasma injections and stem cell therapy. Outside of the hospital, Dr. Franklin likes to spend time with his wife, Ashley, and running with their two dogs.