The Veterinary Guide to Negative Pressure Wound Therapy (Part 1)
Welcome to our two part series on negative pressure wound therapy (NPWT), also commonly known as “Vacuum Assisted Closure” or “VAC ®”. This novel way to treat difficult wounds is an emerging technology in veterinary and human medicine. It’s a terrific option for your patients big and small, and with a little background knowledge, quite simple to institute.
In Part 1, our esteemed guest author Dr. Sam Franklin will introduce us to the nuts and bolts of NPWT and in Part 2, he will teach us how you can institute this technology with your own patients.
What is NPWT Therapy? Negative pressure wound therapy is simply sealing a wound in a special bandage to create an airtight closure and applying a continuous vacuum to the wound for a certain period using a special machine that generates constant negative pressure.
One common commercially available system is distributed by Kinetic Concepts Incorporated (KCI; San Antonio, TX) and their proprietary system is called vacuum-assisted closure (V.A.C.) ®.
A note on semantics: Because the V.A.C. is one of the most commonly used systems many refer to NPWT as “VAC therapy” as though they are synonymous. This is technically incorrect if a system other than V.A.C. ® is being used.
A Review of Wound Healing and Bandaging Let’s go back to veterinary school for a moment. Recall that wound healing involves several overlapping stages including inflammation, repair, and maturation. The inflammatory phase also includes a debridement ‘sub stage’ and the repair phase includes granulation and epithelialization ‘sub stages’.
A practitioner’s role in wound management is to facilitate wound closure by one of four methods:
Primary closure – surgical closure of a fresh, clean wound with minimal soft tissue damage within several hours after wounding.
Delayed primary closure – surgical closure of a wound after debridement and wound management (typically 1-3 days) but PRIOR to the appearance of granulation tissue. This is the least commonly employed wound management practice because the risk of infection is higher if a wound is closed prior to abundant granulation tissue formation.
Secondary closure – surgical closure of a wound after debridement and wound management has been performed and the wound bed is covered with granulation tissue.
Healing by second intention – wound management without surgical closure.
Of these four methods, secondary closure or healing by second intention are most commonly used. With either of these methods, debridement is performed and bandaging is used to hasten the formation of granulation tissue.
Common bandaging techniques include the application of wet-to-dry bandages, dry-to-dry bandages, sugar or honey bandages and others.
Figure 1. Example of a dehisced surgical wound that was managed until granulation tissue was abundant.
These methodologies can be effective, but they can also be labor and time intensive, frequently requiring bandage changes 2-3 times daily depending upon the effusiveness and contamination of the wound. In some instances, bandaging may need to be performed for several days or weeks until granulation tissue is present and surgical closure can be performed.
Why Would You Choose NPWT? NPWT can be used for a variety of purposes (see below) but the most common application is to hasten the debridement and granulation stages of wound healing. In other words, NPWT is essentially used in lieu of the more traditional bandaging techniques mentioned above to hasten the appearance of granulation tissue.
What’s the main benefit of NPWT over traditional bandages? NPWT bandages can be changed as infrequently as once every 72 hours, making them less labor intensive.
Negative Pressure Wound Therapy Can Be Used in Several Clinical Situations:
To speed debridement and granulation of open wounds, including over exposed orthopedic implants
Over closed incisions to hasten how quickly they heal
Over full thickness free skin grafts to maximize viability of the graft
To manage septic peritonitis cases
Of these, the most common use for NPWT is open, soft tissue wounds that would otherwise be treated with bandages for debridement and granulation purposes (e.g. tie-over bandages, wet-to-dry, foam, and petrolatum impregnated gauze dressings). In my experience, excellent success can be achieved with these more traditional methodologies but they can also be very time and labor intensive.
Figure 2. Example of a dog that suffered severe wounds after being attacked by a larger dog.
Conversely, use of NPWT requires a greater up front cost: you need to charge for the NPWT unit and all the disposable materials mentioned above.
However, expense and time can be saved because NPWT does not require a bandage again for up to 72 hours. Further, granulation tissue is obtained in fewer days, decreasing the total number of days and number of times that the wound dressing needs to be changed.
I frequently apply NPWT, leave it on for 72 hours, and either have sufficient granulation tissue to warrant surgical closure at that time or I replace the NPWT dressing, leave it for an additional cycle (48-72 hours) and am usually able to perform closure at that time.
The use of NPWT decreases the amount of time that a patient needs to be treated with open wound management and the frequency of wound management sessions, thereby decreasing the total time investment in the treatment and hastening their recovery.
Figure 3. Same dog with the wound now filled with gauze (laparotomy sponges) and sealed with Ioban. Two Jackson-Pratt drains were tunneled subcutaneously and exited through healthy tissue cranially. A purse string of Fluorofil suture (pink) can be seen sealing the drain exit site.
In my opinion, and based on mounting evidence (see below), this approach speeds healing for our patients. I also hypothesize that NPWT can in some cases be more cost effective. Stay tuned for part 2 for some specific case examples!
What is the Evidence? NPWT has been used for many years in people, and numerous studies have been undertaken in an effort to clarify the mechanisms of action and potential benefits. A thorough review of such literature is beyond the scope of this summary.
As the application of NPWT to clinical veterinary patients has grown, a few publications regarding clinical use in veterinary medicine have surfaced. Most of these articles have been general descriptions of potential benefits, uses, and applications (similar to but more detailed than this article) including case reports and one case series. Readers are strongly encouraged to review these articles for further information.
In addition, there have been two rigorous experimental studies performed in dogs that specifically evaluate two different applications of NPWT in veterinary medicine (number 1 and 2 below). These are worth particular attention.
Ready for Part 2: Instituting NPWT in Your Practice?
REFERENCES TO CONSULT:
Effects of negative pressure wound therapy on healing of open wounds in dogs. Demaria M, Stanley BJ, Hauptman JG, Steficek BA, Fritz MC, Ryan JM, Lam NA, Moore TW, Hadley HS. Vet Surg. 2011 Aug;40(6):658-69. doi: 10.1111/j.1532-950X.2011.00849.x. Epub 2011 Jul 19.
Effects of negative pressure wound therapy on healing of free full-thickness skin grafts in dogs. Stanley BJ, Pitt KA, Weder CD, Fritz MC, Hauptman JG, Steficek BA. Vet Surg. 2013 Jun;42(5):511-22. doi: 10.1111/j.1532-950X.2013.12005.x. Epub 2013 Mar 29.
Vacuum-assisted wound closure: application and mechanism of action. Kirby K, Wheeler JL, Farese JP, Ellison GW, Bacon NJ, Sereda CW, Lewis DD. Compendium: continuing education for veterinarians, 2009 31(12): E1-E7.
Vacuum-assisted wound closure: clinical applications. Kirby K, Wheeler JL, Farese JP, Ellison GW, Bacon NJ, Sereda CW, Lewis DD. Compendium: continuing education for veterinarians, 2010 32(3): E1-7.
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.