April 12, 2013
A vacuum treatment designed for humans is now being used in horse health care.
A chance meeting between a large animal veterinarian and a plastic surgeon has added a new tool to the equine veterinarian’s nearly empty wound therapy toolbox.
In 2000, Dr. Kim Gemeinhardt of Latitude 36 Mobile Veterinary Services in Germanton, North Carolina, was visiting her father at Wake Forest Baptist Hospital, where Dr. Joseph Molnar from the department of plastic and reconstructive surgery of the Wake Forest University School of Medicine in Winston-Salem, North Carolina, was treating him for a large bed sore.
Dr. Molnar was using a vacuum-assisted closure technique that had reduced the healing times for all kinds of wounds in people for a decade. Dr. Gemeinhardt immediately saw potential for the therapy in the large animals she cared for.
Until recently, a horse with a wound lacking enough tissue to close and stitch had a single option for treatment: what vets call “benign neglect” – essentially leaving the wound to heal itself. Such wounds must heal from the inside out, filling themselves with new tissue, and eventually leveling out and scabbing over, a process called “granulating” or “second intention” healing. The only therapy for such cases traditionally had been to hose out the wound, keep it clean and administer antibiotics.
When Dr. Gemeinhardt approached Dr. Molnar about trying the VAC system on large animals, she was met with surprising enthusiasm. In fact, the plastic surgeon offered to work with her in the field to help get the VAC working for veterinary applications.
“I could tell Kim was very practical,” Dr. Molnar says of their first encounters. “We both saw the opportunity this could have for animals and seized it. I told her if she had a suitable patient, we could try this thing out.”
Dr. Molnar’s experience with the VAC in humans began in 1994. The system was developed by his colleagues at Wake Forest University, Dr. Louis Argenta and Michael Morykwas, Ph.D., initially as a way to manage chronic wounds. The company Kinetic Concepts worked with the creators and produces the pumps used in the therapy. The results have been so impressive in humans that the VAC system is now a regular sight at nearly every hospital.
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Even though the treatment was straight forward, relatively inexpensive and widely accepted in humans, its animal applications were limited to some initial testing on swine. When Drs. Gemeinhardt and Molnar connected, the right personalities clicked in place to change that. As Dr. Molnar jokes, “We’d used it on enough people to make sure it’s safe for horses.”
It wasn’t long before a horse provided the opportunity to see just how effective it might be in this application, running into a gate latch and tearing a gaping hole in its neck. Dr. Molnar not only generously shared the VAC knowledge gleaned from his human patients in the hospital to help in this trial, but he also worked hands-on with the equine project in the barn
“Dr. Molnar is amazing,” Dr. Gemeinhardt says. “He came out, and I even remember him on a ladder in the middle of the stall at midnight working (on the VAC).”
The VAC uses a small electrical vacuum to keep a continual suction on a healing wound. A tube runs from the pump and enters the wound area through a plastic drape (a plastic sheeting bandage) covering the wound and sealing around its edges so a continuous vacuum is created underneath. A sponge-like open-cell material is cut to fit the wound, placed in it, and that provides air space between the drape and the healing tissue. The tubing from the pump is embedded in this spongy area, where it sucks out the dead cells and serum produced by the healing process.
The first attempt to use VAC on a horse provided many challenges.
“We put our heads together,” Dr. Molnar says, “and that, with a little duct tape, got us going.”
In truth, duct tape did help overcome some of the setbacks the doctors encountered in that first equine VAC application. For instance, they discovered that shaving the skin around the edge of the wound did not work in horses because rapid hair regrowth broke the VAC seal, so they switched to a depilatory cream for hair removal.
Straight static tubing used for humans tended to kink with the horse’s movements, so coil tubing was improvised. The horse’s neck movements caused bandages to slip, so duct tape was added around the edges of the drape, a Sleazy
neck cover was put over the area, and a neck cradle was put on the horse to minimize this problem. And so on.
“That first case was a success in that we learned how to keep the VAC in place,” Dr. Gemeinhardt says. “We were unsuccessful at keeping the VAC on the wound for more than a couple of hours at a time.”
Because of the learning curve in adapting the VAC to horses, the healing time of that first horse did not show substantial improvements over the horse’s natural healing ability. However, on that one case, the team worked out all the major problems for applying the VAC system to horses.
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The Next Patient
As gaping wounds go, Impression’s was as impressive as it gets.
“The guy who called in was a real cowboy,” Dr. Gemeinhardt says. “Nothing bothers him … his voice was shaking on the phone. ‘Kim, can you come right now? This horse has a hole in his neck big enough to put my fist in!’ That was the smaller wound. I could put my head in the big one!”
The 9-year-old American Quarter Horse gelding was found in a wooded pasture by his owner, Tracey Clayton.
“I went down where he was standing … with his head down,” she says. “I saw the small wound first. When I saw the other side of that horse, I was not prepared – I don’t see how he was still standing.”
Impression had suffered two enormous wounds to the neck; the larger was more than 8 inches by 7 inches and more than 3 inches deep, and the smaller one was just more than half that size.
Even early on, the wounds could not be closed; the deficit of tissue was just too great. This problem coupled with the size, shape and location of the injuries made clean healing from stitching all or some of the affected areas unlikely and could actually increase the risk of infection by providing better conditions for bacteria to thrive.
A course of medications was begun, and saline-soaked gauze was rolled over the wounds and attached with a self-adhesive bandage to serve as a wet-to-dry dressing. Impression was put up in a stall with food and water at chest height and left alone.
The following day, the dressings were removed. To being preparation for the VAC treatment, depilatory cream was applied around the edge of the wounds to create a hairless strip. This zone provides the smooth surface necessary for a good seal with the adhesive barrier drape. The first case helped the experimenting doctors realize that a 24-hour period is required between application of the hair remover and set-up of the VAC due to an inflammatory response cause by the cream that produces a serious discharge from the skin for hours.
The second day, Dr. Gemeinhardt uncovered the wounds and removed all dead or compromised tissue. With the information gleaned from the first case, getting the VAC going on Impression was straightforward. First, a dressing made from medical-grade open-cell polyurethane ether foam was trimmed to fill the wounds’ cavities. Into this spongy hollow, the evacuation tube was set. A single tube ran embedded through the foam in both wounds in series because they were so close.
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With the foam and tube in place, a tissue adhesive was applied to the depilated skin around the injuries and the wounds were covered with a single adhesive drape, pressed firmly against the skin to create an airtight seal around the perimeters of both wounds. The entire border of the dressing was then duct-taped to the surrounding hair for added security.
The evacuation with a liter flask in-line ran up and was attached to the pump mounted in the rafters to create the vacuum. An electrical cord was run well overhead, providing power for the pump. For further system security, the tube was anchored to Impression’s mane, and a stretch fabric neck covering provided extra strain relief. Finally, a wooden cradle modified with gauze and duct tape for cushioning was put around the entire area to limit flexing of the neck.
Every three to four days, Dr. Gemeinhardt replaced the dressings and measured the wounds. The wound quickly decreased in size from the time the VAC was installed on Day 2 until Day 12. The rate of reduction slowed after that until the removal of the VAC system on Day 29.
The wounds decreased in depth as granulation tissue filled the cavities. As the wounds leveled out toward the end of therapy, the foam dressings were reduced in size and the aspiration fluid likewise steadily decreased. In the onset of treatment the flask required emptying every 10 to 12 hours, and by the completion of treatment, the flask did not fill even after 48 hours.
Impression was kept in a stall during the 29-day recovery period. Beginning on Day 8, Impression was allowed some light physical therapy in the form of hand-grazing. From Day 14 on, Tracey began
When the VAC was removed on Day 29, Impression could be ridden.
Follow-up care only required wet-to-dry dressings, with the wounds flushed with saline solution at each dressing change. The stretch fabric hood was also kept over the neck until skin growth over the affected areas was complete and strong. Within a week after the VAC was removed, the wound areas became level with the surrounding neck muscle.
The final results proved fantastic, with the gelding retaining full mobility of his neck. Cosmetically, he didn’t look bad either. The VAC treatment did not seem to adversely affect the jugular vein, esophagus or trachea, even though they had been exposed to the interior of the wounds and therefore pressure from the vacuum pump during the early phases of treatment.
The results of Impression’s case are particularly impressive due to the massive nature of the wounds he suffered. Even if the method of “benign neglect” had ultimately produced the same healing results and infection had not set in, his recovery would have been counted in months and certainly would not have been so far along in as few as 29 days.
Dr. Gemeinhardt cites the main reason for this success as the system’s ability to provide overall cleanliness. The VAC system tightly seals out any contaminants, and everything but healthy tissue and blood supply are wicked away, creating the ultimate healing environment for a wound.
Dr. Gemeinhardt said that she feels certain that the VAC allows for more regular movement of the horse in the stall environment during recovery than those without it.
“Because we can keep the horse moving around more,” she says, “it is more likely a horse will retain full range of motion after recovery.”
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Horses that Dr. Gemeinhardt have treated have tolerated the VAC system very well – both the dressing and suction in the wounds on their bodies as well as the tubes and sound coming from the pump.
When asked if this was the result of these horses being particularly easygoing, Dr. Gemeinhardt says, “This is a nonpainful bandaging system.”
It is known from human applications that there is no itching or discomfort caused by the vacuum in the wound area, so the horses haven’t been inclined to rub or bite at the dressings. Other than gentle nosing of the coil tubing from simple curiosity and some flexing of it from a horse’s regular stall movements, the coil tubing was easily kept out of the way by taking it from the horse up and into the rafters above the stall.
Portable vacuum pump units are being developed. Placing these onto the horse or its blanket in some manner would make the VAC system self-contained aboard the horse and allow a more normal horse lifestyle during recovery periods, including a quicker return to exercise, than the present pump models.
The VAC is also cost effective: The procedure is straightforward; the pumps are reusable; the tubing is cheap. The dressings can get expensive, particularly for larger wounds, however any costs created by the VAC therapy may be offset at least in part by the rapid healing times being seen in these cases which require overall far fewer days of care and can get a working horse back to work much sooner.
“As far as where we go next,” Dr. Gemeinhardt says, “I think it is a method that can be adapted to so many cases that its use should be considered by anyone dealing with wounds
or difficult surgical sites.”